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Archive for July, 2011

New research from last week 29/2011

Posted by Ari Jokimäki on July 25, 2011

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Systematic depth errors found in XBTs

Direct Evidence of a Changing Fall-rate Bias in XBTs Manufactured During 1986–2008 – DiNezio & Goni (2011) “We present direct evidence of systematic depth errors consistent with a fall-rate bias in 52 temperature profiles collected using eXpendable BathyThermographs (XBTs). The profiles were collected using the same recording system and under the same ocean conditions, but with XBTs manufactured during years 1986, 1990, 1991, 1995, and 2008. The depth errors are estimated by comparing each XBT profile with a co-located profile obtained from Conductivity Temperature Depth (CTD) casts using a methodology that unambiguously separates depth errors from temperature errors. According to the manufacture date of the probes, the XBT fall-rate error has changed from (−3.77 ± 0.57) % of depth in 1986 to (−1.05 ± 1.34) % of depth in 2008. The year dependence of the fall-rate bias can be identified with statistical significance (1σ) below 500 m, where the effect of the fall-rate bias is larger. This result is the first direct evidence of changes in the XBT fall-rate characteristics. Therefore, for the 1986–2008 period, the hypothesis that the XBT errors are due to a time-varying fall-rate bias, as hypothesized by Wijffels et al. (2008), cannot be rejected. Additional implications for current efforts to correct the historical temperature profile database are discussed.” Pedro N. DiNezio and Gustavo J. Goni, Journal of Atmospheric and Oceanic Technology 2011 ; e-View, doi: 10.1175/JTECH-D-11-00017.1. [Full text]

Model study on black carbon global situation

Black carbon in the atmosphere and snow, from pre-industrial times until present – Skeie et al. (2011) “The distribution of black carbon (BC) in the atmosphere and the deposition of BC on snow surfaces since pre-industrial time until present are modelled with the Oslo CTM2 model. The model results are compared with observations including recent measurements of BC in snow in the Arctic. The global mean burden of BC from fossil fuel and biofuel sources increased during two periods. The first period, until 1920, is related to increases in emissions in North America and Europe, and the last period after 1970 are related mainly to increasing emissions in East Asia. Although the global burden of BC from fossil fuel and biofuel increases, in the Arctic the maximum atmospheric BC burden as well as in the snow was reached in 1960s, with a slight reduction thereafter. The global mean burden of BC from open biomass burning sources has not changed significantly since 1900. With current inventories of emissions from open biomass sources, the modelled burden of BC in snow and in the atmosphere north of 65° N is small compared to the BC burden of fossil fuel and biofuel origin. From the concentration changes radiative forcing time series due to the direct aerosol effect as well as the snow-albedo effect is calculated for BC from fossil fuel and biofuel. The calculated radiative forcing in 2000 for the direct aerosol effect is 0.35 W m−2 and for the snow-albedo effect 0.016 W m−2 in this study. Due to a southward shift in the emissions there is an increase in the lifetime of BC as well as an increase in normalized radiative forcing, giving a change in forcing per unit of emissions of 26 % since 1950.” Skeie, R. B., Berntsen, T., Myhre, G., Pedersen, C. A., Ström, J., Gerland, S., and Ogren, J. A., Atmos. Chem. Phys., 11, 6809-6836, doi:10.5194/acp-11-6809-2011, 2011. [Full text]

Spatially and seasonally complex medieval climate anomaly in Europe

The medieval climate anomaly in Europe: comparison of the summer and annual mean signals in two reconstructions and in simulations with data assimilation – Goosse et al. (2011) “The spatial pattern and potential dynamical origin of the Medieval Climate Anomaly (MCA, around 1000 AD) in Europe are assessed with two recent reconstructions and simulations constrained to follow those reconstructions by means of paleoclimate data assimilation. The simulations employ a climate model of intermediate complexity (LOVECLIM). The data assimilation technique is based on a particle filter using an ensemble of 96 simulations. The peak winter (and annual mean) warming during the MCA, in our analyses, is found to be strongest at high latitudes, associated with strengthened mid-latitude westerlies. Summer warmth, by contrast, is found to be greatest in southern Europe and the Mediterranean Sea, associated with reduced westerlies and strengthened southerly winds off North Africa. The results of our analysis thus underscore the complexity of the spatial and seasonal structure of the MCA in Europe.” Hugues Goosse, Joel Guiot, Michael E. Mann, Svetlana Dubinkina and Yoann Sallaz-Damaz, Global and Planetary Change, doi:10.1016/j.gloplacha.2011.07.002.

Red Sea is warming rapidly

Abrupt warming of the Red Sea – Raitsos et al. (2011) “Coral reef ecosystems, often referred to as “marine rainforests,” concentrate the most diverse life in the oceans. Red Sea reef dwellers are adapted in a very warm environment, fact that makes them vulnerable to further and rapid warming. The detection and understanding of abrupt temperature changes is an important task, as ecosystems have more chances to adapt in a slowly rather than in a rapid changing environment. Using satellite derived sea surface and ground based air temperatures, it is shown that the Red Sea is going through an intense warming initiated in the mid-90s, with evidence for an abrupt increase after 1994 (0.7°C difference pre and post the shift). The air temperature is found to be a key parameter that influences the Red Sea marine temperature. The comparisons with Northern Hemisphere temperatures revealed that the observed warming is part of global climate change trends. The hitherto results also raise additional questions regarding other broader climatic impacts over the area.” Raitsos, D. E., I. Hoteit, P. K. Prihartato, T. Chronis, G. Triantafyllou, and Y. Abualnaja (2011), Geophys. Res. Lett., 38, L14601, doi:10.1029/2011GL047984.

Atmospheric methane changes over western Pacific

Interannual variability and trends in atmospheric methane over the western Pacific from 1994 to 2010 – Terao et al. (2011) “We present an analysis of interannual variability (IAV) and trends in atmospheric methane (CH4) mixing ratios over the western Pacific between 55°N and 35°S from 1994 to 2010. Observations were made by the Center for Global Environmental Research (CGER) of the National Institute for Environmental Studies (NIES), using voluntary observation ships sailing between Japan and Australia/New Zealand and between Japan and North America, sampling background maritime air quasi-monthly (∼10 times per year) with high latitudinal resolution. In addition, simulations of CH4 were performed using NIES atmospheric transport model. A large CH4 increase was observed in the tropics (10°N–5°S) during 1997 (between 15 ± 3 and 19 ± 3 ppb yr−1) and during 1998 for other regions (40°N–50°N: 10 ± 2–16 ± 1 ppb yr−1; 10°S–25°S: 12 ± 2–22 ± 4 ppb yr−1). The CH4 increase leveled off from 1999 to 2006 at all latitudes. The CH4 growth rate was enhanced in 2007 (25°N–50°N: 10 ± 1–12 ± 3 ppb yr−1; 15°S–35°S: 7 ± 1–8 ± 1 ppb yr−1) but diminished thereafter; however, a large CH4 growth (10 ± 1–17 ± 1 ppb yr−1) was observed in 2009 over the northern tropics (0°–15°N). These observations, combined with the simulation results, suggest that to explain the CH4 increase in 2007 would require an increase in surface emissions of ∼20 ± 3 Tg-CH4 yr−1 globally and an increase in the Northern Hemisphere (NH) of 4–7 ± 3 Tg-CH4 yr−1 more than that in the Southern Hemisphere (SH), assuming no change in OH concentrations; alternatively, a decrease in OH concentrations of 4.5 ± 0.6%–5.5 ± 0.5% yr−1 globally would be required if we assume no change in surface emissions. Over the western Pacific, the IAV in CH4 within the northern tropics was characterized by a high growth rate in mid-1997 and a reduced growth in 2007. The present data indicate that these events were strongly influenced by the IAV in atmospheric circulation associated with El Niño and La Niña events. Our observations captured the CH4 anomaly in 1997 associated with forest fires in Indonesia. The IAV and trends in CH4 as seen by our data sets capture the global features of background CH4 levels in the northern midlatitudes and the SH, and regional features of CH4 variations in the western tropical Pacific.” Terao, Y., H. Mukai, Y. Nojiri, T. Machida, Y. Tohjima, T. Saeki, and S. Maksyutov (2011), J. Geophys. Res., 116, D14303, doi:10.1029/2010JD015467.

In-situ SST measurement biases and uncertainties, paper 1

Reassessing biases and other uncertainties in sea surface temperature observations measured in situ since 1850: 1. Measurement and sampling uncertainties – Kennedy et al. (2011) “New estimates of measurement and sampling uncertainties of gridded in situ sea surface temperature anomalies are calculated for 1850 to 2006. The measurement uncertainties account for correlations between errors in observations made by the same ship or buoy due, for example, to miscalibration of the thermometer. Correlations between the errors increase the estimated uncertainties on grid box averages. In grid boxes where there are many observations from only a few ships or drifting buoys, this increase can be large. The correlations also increase uncertainties of regional, hemispheric, and global averages above and beyond the increase arising solely from the inflation of the grid box uncertainties. This is due to correlations in the errors between grid boxes visited by the same ship or drifting buoy. At times when reliable estimates can be made, the uncertainties in global average, Southern Hemisphere, and tropical sea surface temperature anomalies are between 2 and 3 times as large as when calculated assuming the errors are uncorrelated. Uncertainties of Northern Hemisphere averages are approximately double. A new estimate is also made of sampling uncertainties. They are largest in regions of high sea surface temperature variability such as the western boundary currents and along the northern boundary of the Southern Ocean. The sampling uncertainties are generally smaller in the tropics and in the ocean gyres.” Kennedy, J. J., N. A. Rayner, R. O. Smith, D. E. Parker, and M. Saunby (2011), J. Geophys. Res., 116, D14103, doi:10.1029/2010JD015218. [Full text]

In-situ SST measurement biases and uncertainties, paper 2

Reassessing biases and other uncertainties in sea surface temperature observations measured in situ since 1850: 2. Biases and homogenization – Kennedy et al. (2011) “Changes in instrumentation and data availability have caused time-varying biases in estimates of global and regional average sea surface temperature. The size of the biases arising from these changes are estimated and their uncertainties evaluated. The estimated biases and their associated uncertainties are largest during the period immediately following the Second World War, reflecting the rapid and incompletely documented changes in shipping and data availability at the time. Adjustments have been applied to reduce these effects in gridded data sets of sea surface temperature and the results are presented as a set of interchangeable realizations. Uncertainties of estimated trends in global and regional average sea surface temperature due to bias adjustments since the Second World War are found to be larger than uncertainties arising from the choice of analysis technique, indicating that this is an important source of uncertainty in analyses of historical sea surface temperatures. Despite this, trends over the twentieth century remain qualitatively consistent.” Kennedy, J. J., N. A. Rayner, R. O. Smith, D. E. Parker, and M. Saunby (2011), J. Geophys. Res., 116, D14104, doi:10.1029/2010JD015220. [Full text]

Methane feedbacks in atmosphere might double methane warming effect

Large methane releases lead to strong aerosol forcing and reduced cloudiness – Kurtén et al. (2011) “The release of vast quantities of methane into the atmosphere as a result of clathrate destabilization is a potential mechanism for rapid amplification of global warming. Previous studies have calculated the enhanced warming based mainly on the radiative effect of the methane itself, with smaller contributions from the associated carbon dioxide or ozone increases. Here, we study the effect of strongly elevated methane (CH4) levels on oxidant and aerosol particle concentrations using a combination of chemistry-transport and general circulation models. A 10-fold increase in methane concentrations is predicted to significantly decrease hydroxyl radical (OH) concentrations, while moderately increasing ozone (O3). These changes lead to a 70 % increase in the atmospheric lifetime of methane, and an 18 % decrease in global mean cloud droplet number concentrations (CDNC). The CDNC change causes a radiative forcing that is comparable in magnitude to the longwave radiative forcing (“enhanced greenhouse effect”) of the added methane. Together, the indirect CH4-O3 and CH4-OH-aerosol forcings could more than double the warming effect of large methane increases. Our findings may help explain the anomalously large temperature changes associated with historic methane releases.” Kurtén, T., Zhou, L., Makkonen, R., Merikanto, J., Räisänen, P., Boy, M., Richards, N., Rap, A., Smolander, S., Sogachev, A., Guenther, A., Mann, G. W., Carslaw, K., and Kulmala, M., Atmos. Chem. Phys., 11, 6961-6969, doi:10.5194/acp-11-6961-2011, 2011. [Full text]

Feedbacks causing polar amplification during Mid-Holocene

Polar amplification in the mid-Holocene derived from dynamical vegetation change with a GCM – O’ishi & Abe-Ouchi (2011) “AOGCM simulations of the mid-Holocene tend to largely underestimate annual mean temperature over land in northern hemisphere compared to that of paleodata reconstruction. While the vegetation feedback has not been yet quantitatively reported, its neglect is suggested to be one of the cause of this underestimation. Here, we perform several experiments using an atmosphere-ocean-vegetation coupled model and quantify a vegetation-induced feedback in the mid-Holocene climate using MIROC GCM. Our result indicates an annual warming of +1.3K over land north of 40°N in the mid-Holocene, much larger than the previous GCM results. This warming is due to direct amplification of warming over high latitude land through increases in vegetation and reduced albedo during the summer and indirect amplification through sea-ice feedback in autumn and winter and snow albedo feedback in spring. These feedback were not properly represented in previous GCM analysis.” O’ishi, R., and A. Abe-Ouchi (2011), Geophys. Res. Lett., 38, L14702, doi:10.1029/2011GL048001.

Contributors to last interglacial sea level rise

The role of ocean thermal expansion in Last Interglacial sea level rise – McKay et al. (2011) “A compilation of paleoceanographic data and a coupled atmosphere-ocean climate model were used to examine global ocean surface temperatures of the Last Interglacial (LIG) period, and to produce the first quantitative estimate of the role that ocean thermal expansion likely played in driving sea level rise above present day during the LIG. Our analysis of the paleoclimatic data suggests a peak LIG global sea surface temperature (SST) warming of 0.7 ± 0.6°C compared to the late Holocene. Our LIG climate model simulation suggests a slight cooling of global average SST relative to preindustrial conditions (ΔSST = −0.4°C), with a reduction in atmospheric water vapor in the Southern Hemisphere driven by a northward shift of the Intertropical Convergence Zone, and substantially reduced seasonality in the Southern Hemisphere. Taken together, the model and paleoceanographic data imply a minimal contribution of ocean thermal expansion to LIG sea level rise above present day. Uncertainty remains, but it seems unlikely that thermosteric sea level rise exceeded 0.4 ± 0.3 m during the LIG. This constraint, along with estimates of the sea level contributions from the Greenland Ice Sheet, glaciers and ice caps, implies that 4.1 to 5.8 m of sea level rise during the Last Interglacial period was derived from the Antarctic Ice Sheet. These results reemphasize the concern that both the Antarctic and Greenland Ice Sheets may be more sensitive to temperature than widely thought.” McKay, N. P., J. T. Overpeck, and B. L. Otto-Bliesner (2011), Geophys. Res. Lett., 38, L14605, doi:10.1029/2011GL048280.

Reducing uncertainty in Holocene carbon dioxide estimates

Observational constraints on the causes of Holocene CO2 change – Goodwin et al. (2011) “The mechanisms that controlled past atmospheric CO2 levels are not directly measurable, hence many proxy data sources are combined when reconstructing past carbon cycling. The accuracy of Holocene modeling reconstructions is checked by seeking consistency between data-based observables and their numerically simulated counterparts. A new framework is presented to evaluate which combinations of observables can best constrain carbon cycle mechanisms with the minimum of uncertainty. We show that when previous studies have combined ocean temperatures, ocean [CO32−], and the δ13C of atmospheric CO2 as observables, uncertainties in the data sources are amplified by over 2 orders of magnitude when reconstructing the mechanisms responsible for CO2 increase. However, incorporating mean δ13C of ocean DIC since 8000 years ago as an additional data source reduces the uncertainties by more than a factor of 5, making this observable a priority for future research. Our analysis indicates that the 20 ppm increase in CO2 between 8000 years BP and preindustrial was caused by significant CaCO3 precipitation and a reduction in the ocean soft tissue pump. Meanwhile, an increase in terrestrial carbon storage opposed the CO2 increase. The methods presented here are useful for investigating a range of paleoclimate events.” Goodwin, P., K. I. C. Oliver, and T. M. Lenton (2011), Global Biogeochem. Cycles, 25, GB3011, doi:10.1029/2010GB003888.

Early Eocene perhaps was not super-hot

Warm, not super-hot, temperatures in the early Eocene subtropics – Keating-Bitonti et al. (2011) “The early Eocene (ca. 55–48 Ma) encompasses one of the warmest intervals of the past 65 m.y. and is characterized by an unusually low equator-to-pole thermal gradient. Recent proxy studies suggest temperatures well in excess of 30 °C even at high latitudes, but conflicting interpretations derived from different types of data leave considerable uncertainty about actual early Eocene temperatures. A robust comparison among new paleotemperature proxies may provide insight into possible biases in their temperature estimates, and additional detail on the spatial distribution of temperatures will further resolve the early Eocene meridional temperature gradient. We use a suite of paleotemperature proxies based on the chemistry of bivalve shell carbonate and associated sedimentary organic matter from the United States Gulf Coastal Plain to constrain climate at a subtropical site during this key interval of Earth history. Oxygen isotope and clumped isotope analyses of shell carbonate and two tetraether lipid analyses of sedimentary organic carbon all yield temperatures of ∼27 °C. High-resolution, intraannual oxygen isotope data reveal a consistent, large range of seasonal variation, but clumped isotope data suggest that seasonality is due primarily to precipitation, not to temperature. These paleotemperature estimates are 2–3 °C warmer than the northern Gulf of Mexico today, and generally consistent with early Eocene temperature estimates from other low and mid-latitude locations, but are significantly cooler than contemporaneous estimates from high southern latitudes.” Caitlin R. Keating-Bitonti, Linda C. Ivany, Hagit P. Affek, Peter Douglas and Scott D. Samson, Geology, v. 39 no. 8 p. 771-774, doi: 10.1130/G32054.1.

Climate change increases fish species richness of Baltic Sea by increasing salinity

What is the effect of climate change on marine fish biodiversity in an area of low connectivity, the Baltic Sea? – Hiddink & Coleby (2011) “Aim: Climate change could result in an increase in species richness because large-scale biogeography suggests that more species could be gained from equatorial regions than may be lost pole-ward. However, the colonization of newly available habitat may lag behind the rate dictated by climatic warming if there exists of a lack of connectivity between ‘donor’ and receiving areas. The objective of this study was to compare how regional warming affected the biodiversity of marine fish in areas that differed in their connectivity in the Baltic Sea. Location: North-east Atlantic, Kattegat and Baltic Sea. Methods: The total species richness and the mean species richness from scientific surveys were related to changes in temperature and salinity. Changes in the extent of the distribution of individual fish species were related to the latitudinal distribution, salinity tolerance, maximum body size and exploitation status to assess to what extent climate change and fishing impacts could explain changes in species richness in the Baltic. Results: Rising temperatures in the well-connected Kattegat correlated to an increase in the species richness of fish, due to an increase in low-latitude species. Unexpectedly, species richness in the poorly connected Baltic Sea also increased. However, the increase seems to be related to higher salinity rather than temperature and there was no influx of low-latitude species. Main conclusions: These results do not support the hypothesis that low-connectivity areas are less likely to see increases in species richness in response to warming. This indicates that the effect of climate change on biodiversity may be more difficult to predict in areas of low connectivity than in well-connected areas.” Jan Geert Hiddink, Chris Coleby, Global Ecology and Biogeography, DOI: 10.1111/j.1466-8238.2011.00696.x.

Anthropogenic soils define the Anthropocene

Anthropogenic soils are the golden spikes for the Anthropocene – Certini & Scalenghe (2011) “We propose that the Anthropocene be defined as the last c. 2000 years of the late Holocene and characterized on the basis of anthropogenic soils. This contrasts with the original definition of the Anthropocene as the last c. 250 years (since the Industrial Revolution) and more recent proposals that the Anthropocene began some 5000 to 8000 years ago in the early to mid Holocene (the early-Anthropocene hypothesis). Anthropogenic soil horizons, of which several types are recognized, provide extensive terrestrial stratigraphic markers for defining the start of the Anthropocene. The pedosphere is regarded as the best indicator of the rise to dominance of human impacts on the total environment because it reflects strongly the growing impact of early civilisations over much of the Earth’s surface. Hence, the composition of anthropogenic soils is deemed more appropriate than atmospheric composition in providing ‘golden spikes’ for the Anthropocene.” Giacomo Certini, Riccardo Scalenghe, Anthropogenic soils are the golden spikes for the Anthropocene, The Holocene July 19, 2011 0959683611408454, doi: 10.1177/0959683611408454.

Greenhouse gas emissions from cereals

An agronomic assessment of greenhouse gas emissions from major cereal crops – Linquist et al. (2011) “Agricultural greenhouse gas (GHG) emissions contribute approximately 12% to total global anthropogenic GHG emissions. Cereals (rice, wheat and maize) are the largest source of human calories, and it is estimated that world cereal production must increase 1.3% annually to 2025 in order to meet growing demand. Sustainable intensification of cereal production systems requires maintaining high yields while reducing environmental costs. We conducted a meta-analysis (57 published studies consisting of 62 study sites and 328 observations) to test the hypothesis that the Global Warming Potential (GWP) of CH4 and N2O emissions from rice, wheat, and maize, when expressed per ton of grain (yield-scaled GWP), is similar, and that lowest value for each cereal is achieved at near optimal yields. Results show that the GWP of CH4 and N2O emissions from rice (3757 kg CO2 eq ha−1 season−1) was higher than wheat (662 kg CO2 eq ha−1 season−1) and maize (1399 kg CO2 eq ha−1 season−1). The yield-scaled GWP of rice was about four times higher (657 kg CO2 eq Mg−1) than wheat (166 kg CO2 eq Mg−1) and maize (185 kg CO2 eq Mg−1). Across cereals, the lowest yield-scaled GWP values were achieved at 92% of maximal yield and was about twice as high for rice (279 kg CO2 eq Mg−1) than wheat (102 kg CO2 eq Mg−1) or maize (140 kg CO2 eq Mg−1), suggesting greater mitigation opportunities for rice systems. In rice, wheat and maize, 0.68%, 1.21% and 1.06% of N applied was emitted as N2O, respectively. In rice systems, there was no correlation between CH4 emissions and N rate. Finally, when evaluating issues related to food security and environmental sustainability other factors including cultural significance, the provisioning of ecosystem services, food security, and human health and well-being must also be considered.” Bruce Linquist, Kees Jan van Groenigen, Maria Arlene Adviento-Borbe, Cameron Pittelkow, Chris van Kessel, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02502.x.

Norwegian peat cores tell the climate of the past 7500 years

Climate changes during the last c. 7500 years as recorded by the degree of peat humification in the Lofoten region, Norway – Vorren et al. (2011) “Two peat cores from two neighbouring bogs in Lofoten, northern Norway were densely AMS dated and analysed for humification. The two cores have been influenced by human agricultural impact, especially c. 1600 cal. a BP, which may have affected the local hydrology of the bogs. From 7400 cal. a BP onwards, 19 distinct wet-shifts are recorded in the two cores. Eight or nine of these correspond chronologically to periods of low solar activity. This correlation is most convincing during the last 2000 years. Some wet-shifts are connected with a solar low-activity period during the Subboreal/Subatlantic transition, which in central Europe is dated at 2750–2565 cal. a BP. For Lofoten, the corresponding Subboreal/Subatlantic transition – or the wet-shift marking this transition – is dated at c. 2600 cal. a BP. Some wet-shifts occur just before or just after solar low-activity periods, but only four of the nineteen wet-shifts are clearly not temporally connected with periods of low solar activity. Compared with the wet-shifts in NW European (mainly British Isles) bogs, there are more frequent wet-shifts in northern Norway. Compared with other peat cores in northern Norway, especially for the interval 6500–5000 cal. a BP, Lofoten deviates by its lack of wet-shifts. As in England, Scotland and Ireland, there is regional variability in the temporal formation of wet-shifts in northern Norway.” Karl-Dag Vorren, Christin Eldegard Jensen, Eilif Nilssen, Boreas, DOI: 10.1111/j.1502-3885.2011.00220.x.

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New research from last week 28/2011

Posted by Ari Jokimäki on July 18, 2011

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Medici Network temperature record from 1654-1670 recovered

The earliest temperature observations in the world: the Medici Network (1654–1670) – Camuffo & Bertolin (2011) “This paper presents the earliest temperature observations, scheduled every 3–4 h in the 1654–1670 period, which have been recovered and analysed for the first time. The observations belong to the Medici Network, the first international network of meteorological observations, based on eleven stations, the two main ones being Florence and Vallombrosa, Italy. All observations were made with identical thermometers and operational methodology, including outdoor exposure in the shade and in the sunshine to evaluate solar heating, state of the sky, wind direction and precipitation frequency. This paper will consider only the regular temperature series taken in the shade. The observations were made with the newly invented spirit-in-glass thermometer, also known as Little Florentine Thermometer (LFT). The readings have been transformed into modern units of temperature (°C) and time (TMEC). The LFT has been analysed in detail: how it was made, its linearity, calibration and performances. Since the middle of the LIA, the climate in Florence has shown less than 0.18°C warming. However, although the yearly average showed little change, the seasonal departures are greater, i.e. warmer summers, colder winters and unstable mid seasons. The temperature in the Vallombrosa mountain station, 1,000 m a.m.s.l, apparently rose more, i.e. 1.41°C. A discussion is made on the interpretation of this finding: how much it is affected by climate change or bias. A continuous swinging of the temperature was observed in the Mediterranean area, as documented by the long instrumental observations over the 1654–2009 period. However, changes in vegetation, or exposure bias might have contributed to reduce the homogeneity of the series over the centuries.” Dario Camuffo and Chiara Bertolin, Climatic Change, DOI: 10.1007/s10584-011-0142-5.

Why is northern Tibetan Plateau warming up so rapidly?

The significant climate warming in the northern Tibetan Plateau and its possible causes – Guo & Wang (2011) “We have identified the northern Tibetan Plateau as having experienced the most significant warming of any region in the entire plateau domain since 1961. Warming in the northern plateau violates the previously suggested elevation dependency of warming trends. Further analysis shows that the increase in surface air temperature in summer has played a primary role in the rapid increase of the annual mean air temperature in the northern Tibetan Plateau since the mid-1980s. In addition, the summer air temperature is correlated with ozone in the region, a result which is statistically significant. This correlation seems to have a relationship with solar radiation and ozone depletion ratios. Further discussion shows that the most significant warming in the northern plateau may be related to radiative and dynamical heating that are results of pronounced stratospheric ozone depletion.” Donglin Guo and Huijun Wang, International Journal of Climatology, DOI: 10.1002/joc.2388. [Full text]

Determining forcings over the last 2009 years

Response of Earth’s surface temperature to radiative forcing over A.D. 1–2009 – Friend (2011) “An energy balance model (EBM) of the annual global mean surface temperature is described and calibrated to the sensitivity and temporal dynamics of the Goddard Institute for Space Studies modelE global climate model (GCM). The effective radiative forcings of 10 agents are estimated over the past 2009 years and used as inputs to the model. Temperatures are relatively stable from around A.D. 300 until a “Medieval Climate Anomaly” starting around A.D. 1050. This is ended by a massive volcanic eruption in A.D. 1258, which initiates a multicentury era of low and relatively variable global mean temperatures, including a “Little Ice Age” A.D. 1588–1720. This era only ends at the beginning of the 20th century. The model estimate of forced centennial variability is smaller than the observed variability in reconstructions over the past two millennia. Also, the default parameterization results in less warming than observed over A.D. 1910–1944. Prediction uncertainty in the pre-industrial era is dominated by solar forcing, with the climate feedback factor and volcanic aerosols also playing important roles. In contrast, prediction uncertainty post–A.D. 1750 is much higher and dominated by uncertainties in direct and indirect aerosol and land use forcings. Improving estimates of these will greatly increase our ability to attribute observed temperature variability to contemporary forcings.” Friend, A. D. (2011), J. Geophys. Res., 116, D13112, doi:10.1029/2010JD015143.

AMO might be a statistical artifact

Is the Atlantic Multidecadal Oscillation (AMO) a statistical phantom? – Vincze & Jánosi (2011) “In this work we critically compare the consequences of two assumptions on the physical nature of the AMO index signal. First, we show that the widely used approach based on red noise statistics cannot fully reproduce the empirical correlation properties of the record. Second, we consider a process of long range power-law correlations and demonstrate its better fit to the AMO signal. We show that in the latter case, the multidecadal oscillatory mode of the smoothed AMO index with an assigned period length of 50–70 years can be a simple statistical artifact, a consequence of limited record length. In this respect, a better term to describe the observed fluctuations of a smooth power-law spectrum is Atlantic Multidecadal Variability (AMV).” Vincze, M. and Jánosi, I. M., Nonlin. Processes Geophys., 18, 469-475, doi:10.5194/npg-18-469-2011, 2011. [Full text]

Deep ocean is important for Earth’s radiation balance

Importance of the deep ocean for estimating decadal changes in Earth’s radiation balance – Palmer et al. (2011) “We use control run data from three Met Office Hadley Centre climate models to investigate the relationship between: net top-of-atmosphere radiation balance (TOA), globally averaged sea surface temperature (SST); and globally averaged ocean heat content (OHC) on decadal timescales. All three models show substantial decadal variability in SST, which could easily mask the long-term warming associated with anthropogenic climate change over a decade. Regression analyses are used to estimate the uncertainty of TOA, given the trend in SST or OHC over the same period. We show that decadal trends in SST are only weakly indicative of changes in TOA. Trends in total OHC strongly constrain TOA, since the ocean is the primary heat store in the Earth System. Integrating OHC over increasing model levels, provides an increasingly good indication of TOA changes. To achieve a given accuracy in TOA estimated from OHC we find that there is a trade-off between measuring for longer or deeper. Our model results suggest that there is potential for substantial improvement in our ability to monitor Earth’s radiation balance by more comprehensive observation of the global ocean.” Palmer, M. D., D. J. McNeall, and N. J. Dunstone (2011), Geophys. Res. Lett., 38, L13707, doi:10.1029/2011GL047835.

Melting of Greenland and Antarctica shows in Earth’s oblateness

Recent changes in the Earth’s oblateness driven by Greenland and Antarctic ice mass loss – Nerem & Wahr (2011) “We use temporal gravity variations from GRACE to investigate changes in a 34-year time series of Earth’s oblateness (J2) observed by satellite laser ranging (SLR). We use 2002–2010 GRACE data to compute the effects of Greenland and Antarctic ice mass variations on J2 (2.0 and 1.7 × 10−11/year respectively). Their combined effect on the J2 trend during the GRACE mission is 3.7 × 10−11/year, which agrees well with the GIA-corrected SLR J2 trend over the same time period. The results suggest that at least since 2002, ice loss from Greenland and Antarctica has been the dominant contributor to the current GIA-corrected J2 trend, which apparently began sometime in the 1990s.” Nerem, R. S., and J. Wahr (2011), Geophys. Res. Lett., 38, L13501, doi:10.1029/2011GL047879.

Up to 1/3 of late 20th century warming could have been natural variability

On the time-varying trend in global-mean surface temperature – Wu et al. (2011) “The Earth has warmed at an unprecedented pace in the decades of the 1980s and 1990s (IPCC in Climate change 2007: the scientific basis, Cambridge University Press, Cambridge, 2007). In Wu et al. (Proc Natl Acad Sci USA 104:14889–14894, 2007) we showed that the rapidity of the warming in the late twentieth century was a result of concurrence of a secular warming trend and the warming phase of a multidecadal (~65-year period) oscillatory variation and we estimated the contribution of the former to be about 0.08°C per decade since ~1980. Here we demonstrate the robustness of those results and discuss their physical links, considering in particular the shape of the secular trend and the spatial patterns associated with the secular trend and the multidecadal variability. The shape of the secular trend and rather globally-uniform spatial pattern associated with it are both suggestive of a response to the buildup of well-mixed greenhouse gases. In contrast, the multidecadal variability tends to be concentrated over the extratropical Northern Hemisphere and particularly over the North Atlantic, suggestive of a possible link to low frequency variations in the strength of the thermohaline circulation. Depending upon the assumed importance of the contributions of ocean dynamics and the time-varying aerosol emissions to the observed trends in global-mean surface temperature, we estimate that up to one third of the late twentieth century warming could have been a consequence of natural variability.” Zhaohua Wu, Norden E. Huang, John M. Wallace, Brian V. Smoliak and Xianyao Chen, Climate Dynamics, DOI: 10.1007/s00382-011-1128-8.

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Papers on land use effect on climate

Posted by Ari Jokimäki on July 14, 2011

This is a list of papers on land use effect on climate. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Modelling the effects of land-use/land-cover changes on the near-surface atmosphere in southern South America – Beltrán-Przekurat et al. (2011) “A fully coupled atmospheric-biospheric regional climate model, GEMRAMS, was used to evaluate potential effects of land-use/land-cover changes (LULCC) on near-surface atmosphere over a southern South American domain at seasonal time scales. In GEMRAMS, leaf area index and canopy conductance are computed based on modelled temperature, solar radiation, and the water status of the soil and air, allowing a two-way interaction between canopy and atmosphere. Several austral spring-early summer simulations were conducted using land cover representing current (i.e. agricultural landscape), natural (i.e. before European settlement), and afforestation scenarios for three periods associated with El Niño-Southern Oscillation (ENSO) conditions. The shift to agriculture resulted in a generalized decrease in albedo, reducing the available energy at the near-surface. The energy partitioning between latent and sensible heat fluxes changed, leading to distinct temperature responses. A shift from grass to agriculture led to cooler and wetter near-surface atmospheric conditions. Warmer temperatures resulted from the conversion of wooded grasslands or forest to agriculture. The LULCC-induced signal was spatially heterogeneous and with a seasonal component associated with vegetation phenology. A significant decrease in maximum temperatures in the southern and central Pampas led to a decrease in the diurnal temperature range. Basing on some observational studies in this region our results suggest a potential strong influence of LULCC on the maximum temperatures in central Argentina in summer. Afforestation resulted overall in cooler temperatures. For both LULCC scenarios the direction of the energy fluxes and temperature changes remained in general the same in two extreme ENSO years, although for some vegetation conversions the signal reversed direction. Overall, the impacts were enhanced during a dry year, but the response also depended on the vegetation types involved in the conversion. The effects on precipitation were insignificant in the agriculture-conversion scenario and a general increase was found in the afforested scenario.” Adriana Beltrán-Przekurat, Roger A. Pielke Sr, Joseph L. Eastman, Michael B. Coughenour, International Journal of Climatology, DOI: 10.1002/joc.2346.

A dampened land use change climate response towards the tropics – van der Molen et al. (2011) “In climate simulations we find a pronounced meridional (equator to pole) gradient of climate response to land cover change. Climate response approaches zero in the tropics, and increases towards the poles. The meridional gradient in climate response to land cover change results from damping feedbacks in the tropics, rather than from polar amplification. The main cause for the damping in the tropics is the decrease in cloud cover after deforestation, resulting in increased incoming radiation at the surface and a lower planetary albedo, both counteracting the increase in surface albedo with deforestation. In our simulations, deforestation was also associated with a decrease in sensible heat flux but not a clear signal in evaporation. Meridional differences in climate response have implications for attribution of observed climate change, as well as for climate change mitigation strategies.” M. K. van der Molen, B. J. J. M. van den Hurk and W. Hazeleger, Climate Dynamics, DOI: 10.1007/s00382-011-1018-0. [Full text]

Effect of including land-use driven radiative forcing of the surface albedo of land on climate response in the 16th–21st centuries – Eliseev & Mokhov (2011) “A change in ecosystem types, such as through natural-vegetation-agriculture conversion, alters the surface albedo and triggers attendant shortwave radiative forcing (RF). This paper describes numerical experiments performed using the climate model (CM) of the Institute of Atmospheric Physics (IAP), Russian Academy of Sciences, for the 16th–21st centuries; this model simulated the response to a change in the contents of greenhouse gases (tropospheric and stratospheric), sulfate aerosols, solar constant, as well as the response to change in surface albedo of land due to natural-vegetation-agriculture conversion. These forcing estimates relied on actual data until the late 20th century. In the 21st century, the agricultural area was specified according to scenarios of the Land Use Harmonization project and other anthropogenic impacts were specified using SRES scenarios. The change in the surface vegetation during conversion from natural vegetation to agriculture triggers a cooling RF in most regions except for those of natural semiarid vegetation. The global and annual average RF derived from the IAP RAS CM in late 20th century is −0.11 W m−2. Including the land-use driven RF in IAP RAS CM appreciably reconciled the model calculations to observations in this historical period. For instance, in addition to the net climate warming, IAP RAS CM predicted an annually average cooling and reduction in precipitation in the subtropics of Eurasia and North America and in Amazonia and central Africa, as well as a local maximum in annually average and summertime warming in East China. The land-use driven RF alters the sign in the dependence that the amplitude of the annual cycle of the near-surface atmospheric temperature has on the annually averaged temperature. One reason for the decrease in precipitation as a result of a change in albedo due to land use may be the suppression of the convective activity in the atmosphere in the warm period (throughout the year in the tropics) and the corresponding decrease in convective precipitation. In the 21st century, the effect that the land-use driven RF has on the climate response for scenarios of anthropogenic impact is generally small.” A. V. Eliseev and I. I. Mokhov, Izvestiya Atmospheric and Oceanic Physics, Volume 47, Number 1, 15-30, DOI: 10.1134/S0001433811010075.

The HYDE 3.1 spatially explicit database of human-induced global land-use change over the past 12,000 years – Goldewijk et al. (2011) “Aim: This paper presents a tool for long-term global change studies; it is an update of the History Database of the Global Environment (HYDE) with estimates of some of the underlying demographic and agricultural driving factors. Methods: Historical population, cropland and pasture statistics are combined with satellite information and specific allocation algorithms (which change over time) to create spatially explicit maps, which are fully consistent on a 5′ longitude/latitude grid resolution, and cover the period 10,000 bc to ad 2000. Results: Cropland occupied roughly less than 1% of the global ice-free land area for a long time until ad 1000, similar to the area used for pasture. In the centuries that followed, the share of global cropland increased to 2% in ad 1700 (c. 3 million km2) and 11% in ad 2000 (15 million km2), while the share of pasture area grew from 2% in ad 1700 to 24% in ad 2000 (34 million km2) These profound land-use changes have had, and will continue to have, quite considerable consequences for global biogeochemical cycles, and subsequently global climate change. Main conclusions: Some researchers suggest that humans have shifted from living in the Holocene (emergence of agriculture) into the Anthropocene (humans capable of changing the Earth’s atmosphere) since the start of the Industrial Revolution. But in the light of the sheer size and magnitude of some historical land-use changes (e.g. as result of the depopulation of Europe due to the Black Death in the 14th century and the aftermath of the colonization of the Americas in the 16th century) we believe that this point might have occurred earlier in time. While there are still many uncertainties and gaps in our knowledge about the importance of land use (change) in the global biogeochemical cycle, we hope that this database can help global (climate) change modellers to close parts of this gap.” Kees Klein Goldewijk, Arthur Beusen, Gerard van Drecht, Martine de Vos, Global Ecology and Biogeography, Volume 20, Issue 1, pages 73–86, January 2011, DOI: 10.1111/j.1466-8238.2010.00587.x. [Full text]

Investigating the climate impacts of global land cover change in the community climate system model – Lawrence & Chase (2010) “Recently, (Pitman et al., 2009) found a wide range of bio-geophysical climate impacts from historical land cover change when modelled in a suite of current global climate models (GCMs). The bio-geophysical climate impacts of human land cover change, however, have been investigated by a wide range of general circulation modelling, regional climate modelling, and observational studies. In this regard the IPCC 4th assessment report specifies radiative cooling of 0.2 W/m 2 as the dominant global impact of human land cover change since 1750, but states this has a low to medium level of scientific understanding. To further contribute to the understanding of the possible climatic impacts of anthropogenic land cover change, we have performed a series of land cover change experiments with the community land model (CLM) within the community climate system model (CCSM). To do this we have developed a new set of potential vegetation land surface parameters to represent land cover change in CLM. The new parameters are consistent with the potential vegetation biome mapping of (Ramankutty and Foley, 1999), with the plant functional types (PFTs) and plant phenology consistent with the current day Moderate Resolution Imaging Spectroradiometer (MODIS) land surface parameters of (Lawrence and Chase, 2007). We found that land cover change in CCSM resulted in widespread regional warming of the near surface atmosphere, but with limited global impact on near surface temperatures. The experiments also found changes in precipitation, with drier conditions regionally, but with limited impact on average global precipitation. Analysis of the surface fluxes in the CCSM experiments found the current day warming was predominantly driven by changes in surface hydrology through reduced evapo-transpiration and latent heat flux, with the radiative forcing playing a secondary role. We show that these finding are supported by a wide range of observational field studies, satellite studies and regional and global climate modelling studies.” Peter J. Lawrence, Thomas N. Chase, Journal of Climatology, Volume 30, Issue 13, pages 2066–2087, 15 November 2010, DOI: 10.1002/joc.2061. [Full text]

Anthropogenic land cover changes in a GCM with surface albedo changes based on MODIS data – Kvalevåg et al. (2010) “This study uses a global climate model (GCM) to investigate the climate response at the surface and in the atmosphere caused by land use change. The climate simulations are performed with the National Center for Atmospheric Research Community Land Model 3.5 (CLM3.5) coupled to the Community Atmosphere Model 3 (CAM3) and a slab ocean model. We use the Moderate Resolution Imaging Spectroradiometer (MODIS) surface albedo product to represent surface albedo in the CLM3.5 for both present day and to reconstruct the surface albedo for natural pre-agriculture conditions. We compare simulations including vegetation changes and surface albedo changes to simulations including only surface albedo changes. We find that the surface albedo change is most dominant in temperate regions while the change in evapotranspiration drives the climate response in the tropics. Our results show that land cover changes contribute to an annual global warming of 0.04 K, but there are large regional differences. In North America and Europe, the surface temperatures decrease by − 0.11 and − 0.09 K, respectively, while in India the surface temperatures increase by 0.09 K. When we fix the vegetation cover in the simulations and let the climate changes be driven only by the differences in surface albedo, the annual global mean surface warming is reduced, and all three regions are now associated with surface cooling. We also show that the surface albedo value for cropland is of major importance in climate simulations of land cover change. The surface albedo effect is the main driving mechanism when the change in surface albedo between agricultural and natural vegetation is substantial. Finally, we argue that differences in the surface albedo value of cropland implemented in earlier land use change studies explain the diversity in the sign and magnitude of the climate response.” Maria Malene Kvalevåg, Gunnar Myhre, Gordon Bonan, Samuel Levis, International Journal of Climatology, Volume 30, Issue 13, pages 2105–2117, 15 November 2010, DOI: 10.1002/joc.2012. [Full text]

Impacts of land use land cover on temperature trends over the continental United States: assessment using the North American Regional Reanalysis – Fall et al. (2010) “We investigate the sensitivity of surface temperature trends to land use land cover change (LULC) over the conterminous United States (CONUS) using the observation minus reanalysis (OMR) approach. We estimated the OMR trends for the 1979–2003 period from the US Historical Climate Network (USHCN), and the NCEP-NCAR North American Regional Reanalysis (NARR). We used a new mean square differences (MSDs)-based assessment for the comparisons between temperature anomalies from observations and interpolated reanalysis data. Trends of monthly mean temperature anomalies show a strong agreement, especially between adjusted USHCN and NARR (r = 0.9 on average) and demonstrate that NARR captures the climate variability at different time scales. OMR trend results suggest that, unlike findings from studies based on the global reanalysis (NCEP/NCAR reanalysis), NARR often has a larger warming trend than adjusted observations (on average, 0.28 and 0.27 °C/decade respectively). OMR trends were found to be sensitive to land cover types. We analysed decadal OMR trends as a function of land types using the Advanced Very High Resolution Radiometer (AVHRR) and new National Land Cover Database (NLCD) 1992–2001 Retrofit Land Cover Change. The magnitude of OMR trends obtained from the NLDC is larger than the one derived from the ‘static’ AVHRR. Moreover, land use conversion often results in more warming than cooling. Overall, our results confirm the robustness of the OMR method for detecting non-climatic changes at the station level, evaluating the impacts of adjustments performed on raw observations, and most importantly, providing a quantitative estimate of additional warming trends associated with LULC changes at local and regional scales. As most of the warming trends that we identify can be explained on the basis of LULC changes, we suggest that in addition to considering the greenhouse gases–driven radiative forcings, multi-decadal and longer climate models simulations must further include LULC changes.” Souleymane Fall, Dev Niyogi, Alexander Gluhovsky, Roger A. Pielke Sr, Eugenia Kalnay, Gilbert Rochon, International Journal of Climatology, Volume 30, Issue 13, pages 1980–1993, 15 November 2010, DOI: 10.1002/joc.1996. [Full text]

How well do we know the flux of CO2 from land-use change? – Houghton (2010) “Five new estimates of global net annual emissions of carbon from land use and land-use change collectively describe a gradually increasing trend in emissions, from ∼0.6 PgC yr−1 in 1850 to ∼1.3 PgC yr−1 in the period 1950–2005, with an annual range that varies between ±0.2 and ±0.4 PgC yr−1 of the mean. All estimates agree in the upward trend from 1850 to ∼1950 but not thereafter. In recent decades, when rates of land-use change and biomass density should be better known than in the past, the estimates are more variable. Most analyses have used three quasi-independent estimates of land-use change that are based on national and international agricultural and forestry data of limited accuracy in many countries. Further, the estimates of biomass used in the analyses have a common but limited literature base, which fails to address the spatial variability of biomass density within ecosystems. In contrast to the sources of information that have been used to date, a combination of existing ground and remote sensing data are available to determine with far higher accuracy rates of land-use change, aboveground biomass density, and, hence, the net flux of carbon from land use and land-use change.” R. A. Houghton, Tellus B, Volume 62, Issue 5, pages 337–351, November 2010, DOI: 10.1111/j.1600-0889.2010.00473.x. [Full text]

Forestation of boreal peatlands: Impacts of changing albedo and greenhouse gas fluxes on radiative forcing – Lohila et al. (2010) “We estimated the magnitude of the radiative forcing (RF) due to changes in albedo following the forestation of peatlands, and calculated the net RF by taking into account the changes in both the albedo and the greenhouse gas (GHG) fluxes during one forest rotation. Data on radiation, tree biomass, and soil GHG fluxes were combined with models for canopy cover, tree carbon accumulation, and the RF due to increased atmospheric GHG concentrations for four typical site cases in Finland covering two soil nutrient levels in the south and north of the country. We also studied the observed long-term surface temperatures to detect any indications of drainage-induced effects. The magnitude of the albedo-induced RF was similar to that caused by the carbon sequestration of the growing trees. At three site cases out of four the drainage induced a cooling or negative RF, the tendency for cooling being higher at sites with a higher nutrient level. The differences in albedo-induced RF mainly arose from the spring season due to (1) the different snow cover duration in the south versus the north, and (2) the different albedos of drained and undrained snow covered peatlands. An increase in the maximum daily temperatures was observed in April in southern Finland, where the most intensive drainage practices have taken place, suggesting that forestry drainage has potentially affected the local climate. Our results show that the decreasing albedo resulting from peatland forestation contributes significantly to the RF, balancing out or even exceeding the cooling effect due to the changing GHG fluxes.” Lohila, A., K. Minkkinen, J. Laine, I. Savolainen, J.-P. Tuovinen, L. Korhonen, T. Laurila, H. Tietäväinen, and A. Laaksonen (2010), J. Geophys. Res., 115, G04011, doi:10.1029/2010JG001327.

Uncertainties in climate responses to past land cover change: First results from the LUCID intercomparison study – Pitman et al. (2009) “Seven climate models were used to explore the biogeophysical impacts of human-induced land cover change (LCC) at regional and global scales. The imposed LCC led to statistically significant decreases in the northern hemisphere summer latent heat flux in three models, and increases in three models. Five models simulated statistically significant cooling in summer in near-surface temperature over regions of LCC and one simulated warming. There were few significant changes in precipitation. Our results show no common remote impacts of LCC. The lack of consistency among the seven models was due to: 1) the implementation of LCC despite agreed maps of agricultural land, 2) the representation of crop phenology, 3) the parameterisation of albedo, and 4) the representation of evapotranspiration for different land cover types. This study highlights a dilemma: LCC is regionally significant, but it is not feasible to impose a common LCC across multiple models for the next IPCC assessment.” Pitman, A. J., et al. (2009), Geophys. Res. Lett., 36, L14814, doi:10.1029/2009GL039076. [Full text]

Carbon cycling under 300 years of land use change: Importance of the secondary vegetation sink – Shevliakova et al. (2009) “We have developed a dynamic land model (LM3V) able to simulate ecosystem dynamics and exchanges of water, energy, and CO2 between land and atmosphere. LM3V is specifically designed to address the consequences of land use and land management changes including cropland and pasture dynamics, shifting cultivation, logging, fire, and resulting patterns of secondary regrowth. Here we analyze the behavior of LM3V, forced with the output from the Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric model AM2, observed precipitation data, and four historic scenarios of land use change for 1700–2000. Our analysis suggests a net terrestrial carbon source due to land use activities from 1.1 to 1.3 GtC/a during the 1990s, where the range is due to the difference in the historic cropland distribution. This magnitude is substantially smaller than previous estimates from other models, largely due to our estimates of a secondary vegetation sink of 0.35 to 0.6 GtC/a in the 1990s and decelerating agricultural land clearing since the 1960s. For the 1990s, our estimates for the pastures’ carbon flux vary from a source of 0.37 to a sink of 0.15 GtC/a, and for the croplands our model shows a carbon source of 0.6 to 0.9 GtC/a. Our process-based model suggests a smaller net deforestation source than earlier bookkeeping models because it accounts for decelerated net conversion of primary forest to agriculture and for stronger secondary vegetation regrowth in tropical regions. The overall uncertainty is likely to be higher than the range reported here because of uncertainty in the biomass recovery under changing ambient conditions, including atmospheric CO2 concentration, nutrients availability, and climate.” Shevliakova, E., S. W. Pacala, S. Malyshev, G. C. Hurtt, P. C. D. Milly, J. P. Caspersen, L. T. Sentman, J. P. Fisk, C. Wirth, and C. Crevoisier (2009), Global Biogeochem. Cycles, 23, GB2022, doi:10.1029/2007GB003176. [Full text]

Influence of modern land cover on the climate of the United States – Diffenbaugh (2009) “I have used a high-resolution nested climate modeling system to test the sensitivity of regional and local climate to the modern non-urban land cover distribution of the continental United States. The dominant climate response is cooling of surface air temperatures, particularly during the warm-season. Areas of statistically significant cooling include areas of the Great Plains where crop/mixed farming has replaced short grass, areas of the Midwest and southern Texas where crop/mixed farming has replaced interrupted forest, and areas of the western United States containing irrigated crops. This statistically significant warm-season cooling is driven by changes in both surface moisture balance and surface albedo, with changes in surface moisture balance dominating in the Great Plains and western United States, changes in surface albedo dominating in the Midwest, and both effects contributing to warm-season cooling over southern Texas. The simulated changes in surface moisture and energy fluxes also influence the warm-season atmospheric dynamics, creating greater moisture availability in the lower atmosphere and enhanced uplift aloft, consistent with the enhanced warm-season precipitation seen in the simulation with modern land cover. The local and regional climate response is of a similar magnitude to that projected for future greenhouse gas concentrations, suggesting that the climatic effects of land cover change should be carefully considered when crafting policies for regulating land use and for managing anthropogenic forcing of the climate system.” Noah S. Diffenbaugh, Climate Dynamics, Volume 33, Numbers 7-8, 945-958, DOI: 10.1007/s00382-009-0566-z. [Full text]

Surface temperature cooling trends and negative radiative forcing due to land use change toward greenhouse farming in southeastern Spain – Campra et al. (2008) “Greenhouse horticulture has experienced in recent decades a dramatic spatial expansion in the semiarid province of Almeria, in southeastern (SE) Spain, reaching a continuous area of 26,000 ha in 2007, the widest greenhouse area in the world. A significant surface air temperature trend of −0.3°C decade−1 in this area during the period 1983–2006 is first time reported here. This local cooling trend shows no correlation with Spanish regional and global warming trends. Radiative forcing (RF) is widely used to assess and compare the climate change mechanisms. Surface shortwave RF (SWRF) caused through clearing of pasture land for greenhouse farming development in this area is estimated here. We present the first empirical evidences to support the working hypothesis of the development of a localized forcing created by surface albedo change to explain the differences in temperature trends among stations either inside or far from this agricultural land. SWRF was estimated from satellite-retrieved surface albedo data and calculated shortwave outgoing fluxes associated with either uses of land under typical incoming solar radiation. Outgoing fluxes were calculated from Moderate Resolution Imaging Spectroradiometer (MODIS) surface reflectance data. A difference in mean annual surface albedo of +0.09 was measured comparing greenhouses surface to a typical pasture land. Strong negative forcing associated with land use change was estimated all year round, ranging from −5.0 W m−2 to −34.8 W m−2, with a mean annual value of −19.8 W m−2. According to our data of SWRF and local temperatures trends, recent development of greenhouse horticulture in this area may have masked local warming signals associated to greenhouse gases increase.” Campra, P., M. Garcia, Y. Canton, and A. Palacios-Orueta (2008), J. Geophys. Res., 113, D18109, doi:10.1029/2008JD009912. [Full text]

Radiative forcing over the conterminous United – Barnes & Roy (2008) “Recently available satellite land cover land use (LCLU) and albedo data are used to study the impact of LCLU change from 1973 to 2000 on surface albedo and radiative forcing for 36 ecoregions covering 43% of the conterminous United States (CONUS). Moderate Resolution Imaging Spectroradiometer (MODIS) snow-free broadband albedo values are derived from Landsat LCLU classification maps located using a stratified random sampling methodology to estimate ecoregion estimates of LCLU induced albedo change and surface radiative forcing. The results illustrate that radiative forcing due to LCLU change may be disguised when spatially and temporally explicit data sets are not used. The radiative forcing due to contemporary LCLU albedo change varies geographically in sign and magnitude, with the most positive forcings (up to 0.284 Wm−2) due to conversion of agriculture to other LCLU types, and the most negative forcings (as low as −0.247 Wm−2) due to forest loss. For the 36 ecoregions considered a small net positive forcing (i.e., warming) of 0.012 Wm−2 is estimated.” Barnes, C. A., and D. P. Roy (2008), Geophys. Res. Lett., 35, L09706, doi:10.1029/2008GL033567. [Full text]

Modeled Impact of Anthropogenic Land Cover Change on Climate – Findell et al. (2007) “Equilibrium experiments with the Geophysical Fluid Dynamics Laboratory’s climate model are used to investigate the impact of anthropogenic land cover change on climate. Regions of altered land cover include large portions of Europe, India, eastern China, and the eastern United States. Smaller areas of change are present in various tropical regions. This study focuses on the impacts of biophysical changes associated with the land cover change (albedo, root and stomatal properties, roughness length), which is almost exclusively a conversion from forest to grassland in the model; the effects of irrigation or other water management practices and the effects of atmospheric carbon dioxide changes associated with land cover conversion are not included in these experiments. The model suggests that observed land cover changes have little or no impact on globally averaged climatic variables (e.g., 2-m air temperature is 0.008 K warmer in a simulation with 1990 land cover compared to a simulation with potential natural vegetation cover). Differences in the annual mean climatic fields analyzed did not exhibit global field significance. Within some of the regions of land cover change, however, there are relatively large changes of many surface climatic variables. These changes are highly significant locally in the annual mean and in most months of the year in eastern Europe and northern India. They can be explained mainly as direct and indirect consequences of model-prescribed increases in surface albedo, decreases in rooting depth, and changes of stomatal control that accompany deforestation.” Findell, Kirsten L., Elena Shevliakova, P. C. D. Milly, Ronald J. Stouffer, 2007, J. Climate, 20, 3621–3634, doi: 10.1175/JCLI4185.1. [Full text]

Radiative forcing due to anthropogenic vegetation change based on MODIS surface albedo data – Myhre et al. (2005) “In this study we use the capabilities of the MODerate Resolution Imaging Spectroradiometer (MODIS) land surface product to estimate the radiative forcing due to surface albedo changes caused by anthropogenic vegetation changes. We improve the representation of the present surface albedo by using data retrieved from MODIS. The change in surface albedo is based on the current vegetation land cover from MODIS, the MODIS surface albedos for those vegetation types, and a data set for potential natural vegetation. We arrive at a radiative forcing due to anthropogenic vegetation changes of −0.09 Wm−2 since pre-agriculture times to present, weaker than most earlier published results for this climate forcing mechanism. This is mainly due to a lower surface albedo associated with cropland and further with the use of MODIS data to allow us to constrain the surface albedo change.” Myhre, G., M. M. Kvalevåg, and C. B. Schaaf (2005), Geophys. Res. Lett., 32, L21410, doi:10.1029/2005GL024004. [Full text]

Impacts of future land cover changes on atmospheric CO2 and climate – Sitch et al. (2005) “Climate-carbon cycle model CLIMBER2-LPJ is run with consistent fields of future fossil fuel CO2 emissions and geographically explicit land cover changes for four Special Report on Emissions Scenarios (SRES) scenarios, A1B, A2, B1, and B2. By 2100, increases in global mean temperatures range between 1.7°C (B1) and 2.7°C (A2) relative to the present day. Biogeochemical warming associated with future tropical land conversion is larger than its corresponding biogeophysical cooling effect in A2, and amplifies biogeophysical warming associated with Northern Hemisphere land abandonment in B1. In 2100, simulated atmospheric CO2 ranged from 592 ppm (B1) to 957 ppm (A2). Future CO2 concentrations simulated with the model are higher than previously reported for the same SRES emission scenarios, indicating the effect of future CO2 emission scenarios and land cover changes may hitherto be underestimated. The maximum contribution of land cover changes to future atmospheric CO2 among the four SRES scenarios represents a modest 127 ppm, or 22% in relative terms, with the remainder attributed to fossil fuel CO2 emissions.” Sitch, S., V. Brovkin, W. von Bloh, D. van Vuuren, B. Eickhout, and A. Ganopolski (2005), Global Biogeochem. Cycles, 19, GB2013, doi:10.1029/2004GB002311. [Full text]

Natural and anthropogenic climate change: incorporating historical land cover change, vegetation dynamics and the global carbon cycle – Matthews et al. (2004) “This study explores natural and anthropogenic influences on the climate system, with an emphasis on the biogeophysical and biogeochemical effects of historical land cover change. The biogeophysical effect of land cover change is first subjected to a detailed sensitivity analysis in the context of the UVic Earth System Climate Model, a global climate model of intermediate complexity. Results show a global cooling in the range of –0.06 to –0.22 °C, though this effect is not found to be detectable in observed temperature trends. We then include the effects of natural forcings (volcanic aerosols, solar insolation variability and orbital changes) and other anthropogenic forcings (greenhouse gases and sulfate aerosols). Transient model runs from the year 1700 to 2000 are presented for each forcing individually as well as for combinations of forcings. We find that the UVic Model reproduces well the global temperature data when all forcings are included. These transient experiments are repeated using a dynamic vegetation model coupled interactively to the UVic Model. We find that dynamic vegetation acts as a positive feedback in the climate system for both the all-forcings and land cover change only model runs. Finally, the biogeochemical effect of land cover change is explored using a dynamically coupled inorganic ocean and terrestrial carbon cycle model. The carbon emissions from land cover change are found to enhance global temperatures by an amount that exceeds the biogeophysical cooling. The net effect of historical land cover change over this period is to increase global temperature by 0.15 °C.” H.D. Matthews, A.J. Weaver, K.J. Meissner, N.P. Gillett and M. Eby, Climate Dynamics, Volume 22, Number 5, 461-479, DOI: 10.1007/s00382-004-0392-2. [Full text]

Role of land cover changes for atmospheric CO2 increase and climate change during the last 150 years – Brovkin et al. (2004) “We assess the role of changing natural (volcanic, aerosol, insolation) and anthropogenic (CO2 emissions, land cover) forcings on the global climate system over the last 150 years using an earth system model of intermediate complexity, CLIMBER-2. We apply several datasets of historical land-use reconstructions: the cropland dataset by Ramankutty & Foley (1999) (R&F), the HYDE land cover dataset of Klein Goldewijk (2001), and the land-use emissions data from Houghton & Hackler (2002). Comparison between the simulated and observed temporal evolution of atmospheric CO2 and δ13CO2 are used to evaluate these datasets. To check model uncertainty, CLIMBER-2 was coupled to the more complex Lund–Potsdam–Jena (LPJ) dynamic global vegetation model. In simulation with R&F dataset, biogeophysical mechanisms due to land cover changes tend to decrease global air temperature by 0.26°C, while biogeochemical mechanisms act to warm the climate by 0.18°C. The net effect on climate is negligible on a global scale, but pronounced over the land in the temperate and high northern latitudes where a cooling due to an increase in land surface albedo offsets the warming due to land-use CO2 emissions. Land cover changes led to estimated increases in atmospheric CO2 of between 22 and 43 ppmv. Over the entire period 1800–2000, simulated δ13CO2 with HYDE compares most favourably with ice core during 1850–1950 and Cape Grim data, indicating preference of earlier land clearance in HYDE over R&F. In relative terms, land cover forcing corresponds to 25–49% of the observed growth in atmospheric CO2. This contribution declined from 36–60% during 1850–1960 to 4–35% during 1960–2000. CLIMBER-2-LPJ simulates the land cover contribution to atmospheric CO2 growth to decrease from 68% during 1900–1960 to 12% in the 1980s. Overall, our simulations show a decline in the relative role of land cover changes for atmospheric CO2 increase during the last 150 years.” Victor Brovkin, Stephen Sitch, Werner Von Bloh, Martin Claussen, Eva Bauer, Wolfgang Cramer, Global Change Biology, Volume 10, Issue 8, pages 1253–1266, August 2004, DOI: 10.1111/j.1365-2486.2004.00812.x. [Full text]

Assessing climate forcings of the Earth system for the past millennium – Bauer et al. (2003) “The effects of natural and anthropogenic forcings (solar activity, volcanism, atmospheric CO2 concentration, deforestation) on climate changes are estimated with the Earth system model of intermediate complexity, CLIMBER-2, for the past millennium. Simulated surface air temperatures for the Northern Hemisphere from the combined forcing correlate reasonably well with paleoclimatic data (r = 0.70). The largest negative anomalies occur when insolation minima coincide with volcanic eruptions. Anthropogenic forcings impose additional climate changes after 1850. The increasing warming from increasing CO2 concentrations is attenuated by the cooling effect from deforestation. Results from differently combined forcings suggest that the relatively cool climate in the second half of 19th century is largely attributable to cooling from deforestation.” Bauer, E., M. Claussen, V. Brovkin, and A. Huenerbein (2003), Geophys. Res. Lett., 30(6), 1276, doi:10.1029/2002GL016639. [Full text]

Radiative forcing of climate by historical land cover change – Matthews et al. (2003) “The radiative effect of changing human land-use patterns on the climate of the past 300 years is discussed through analysis of a series of equilibrium and transient climate simulations using the UVic Earth System Climate Model. Land-surface changes are prescribed through varying land cover type, representing the replacement of natural vegetation by human agricultural systems from 1700 to 1992. All land cover simulations show a cooling in the range of 0.09 to 0.22°C with larger regional changes caused by local positive feedbacks.” Matthews, H. D., A. J. Weaver, M. Eby, and K. J. Meissner (2003), Geophys. Res. Lett., 30(2), 1055, doi:10.1029/2002GL016098. [Full text]

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New research from last week 27/2011

Posted by Ari Jokimäki on July 11, 2011

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

YD event might have been global and affected mankind

Evidence for Younger Dryas Global Climate Oscillation and Human Response in the American Southwest – Ballenger et al. (2011) “Whether or not abrupt YD climate change affected regional paleoenvironments and late Pleistocene hunter-gatherer populations is an important topic in the archaeology of the American Southwest. This paper reviews multiple, age-resolved proxy evidence to gauge the magnitude and direction of Younger Dryas Chronozone(YDC) environmental changes in different settings and systems. There is no record of YDC pluvial lake highstands in Arizona or New Mexico, but there are impressive records of vegetation, faunal,stable isotope, and geomorphological change coincident with the YDC. These correlate with important adaptive changes in human hunting and land use, as revealed in the analysis of the spatiotemporal distribution of late Pleistocene hunting technologies. Clovis and Folsom projectile point distributions do not support extant models ofpaleoenvironmental conditions in these interpretations. Significant cultural changes that coincide with the YDC include the Clovis-to-Folsom transition, the demise of mammoth hunting and the development of a highly successful emphasis on bison, increased regionalization, and the abandonment of the northwestern Chihuahuan and the Sonoran deserts by mobile, big-game hunters.” Jesse A.M. Ballenger, Vance T. Holliday, Andrew L. Kowler, William T. Reitze, Mary M. Prasciunas, D. Shane Miller and Jason D. Windingstad, Quaternary International, doi:10.1016/j.quaint.2011.06.040.

World War II bombing raids help to study contrail effect on climate

World War II contrails: a case study of aviation-induced cloudiness – Ryan et al. (2011) “Dense and persistent condensation trails or contrails were produced by daytime US Army Air Force (USAAF) bombing raids, flown from England to Europe during World War II (WW2). These raids occurred in years when civilian air travel was rare, giving a predominantly contrail-free background sky, in a period when there were more meteorological observations taken across England than at any time before or since. The aircraft involved in the raids entered formation at contrail-forming altitudes (generally over 16 000 ft, approximately 5 km) over a relatively small part of southeast England before flying on to their target. This formation strategy provides us a unique opportunity to carry out multiple observation-based comparisons of adjacent, same day, well-defined overflown and non-over-flown regions. We compile evidence from archived meteorological data, such as Met Office daily weather reports and individual station meteorological registers, together with historical aviation information from USAAF and Royal Air Force (RAF) tactical mission reports. We highlight a number of potential dates for study and demonstrate, for one of these days, a marked difference in the amount of high cloud cover, and a statistically significant (0.8 °C) difference in the 07:00–13:00 UTC temperature range when comparing data from highly overflown stations to those upwind of the flight path on the same day. Although one event cannot provide firm conclusions regarding the effect of contrails on climate, this study demonstrates that the wealth of observational data associated with WW2 bombing missions allows detailed investigation of meteorological perturbations because of aviation-induced cloudiness.” A. C. Ryan, A. R. MacKenzie, S. Watkins and R. Timmis, International Journal of Climatology, DOI: 10.1002/joc.2392. [Full text]

Not only CO2 but also man-made SOx, NOx and NH3 cause ocean acidification

Impacts of anthropogenic SOx, NOx and NH3 on acidification of coastal waters and shipping lanes – Hunter et al. (2011) “The acidification of the ocean by anthropogenic CO2 absorbed from the atmosphere is now well-recognized and is considered to have lowered surface ocean pH by 0.1 since the mid-18th century. Future acidification may lead to undersaturation of CaCO3 making growth of calcifying organisms difficult. However, other anthropogenic gases also have the potential to alter ocean pH and CO2 chemistry, specifically SOx and NOx and NH3. We demonstrate using a simple chemical model that in coastal water regions with high atmospheric inputs of these gases, their pH reduction is almost completely canceled out by buffering reactions involving seawater HCO3 and CO32− ions. However, a consequence of this buffering is a significant decrease in the uptake of anthropogenic CO2 by the atmosphere in these areas.” Hunter, K. A., et al. (2011), Geophys. Res. Lett., 38, L13602, doi:10.1029/2011GL047720.

King George Island ice cap retreating

Observed glacial changes on the King George Island ice cap, Antarctica, in the last decade – Rückamp et al. (2011) “The Antarctic Peninsula has been identified as a region of rapid on-going climate change with impacts on the cryosphere. The knowledge of glacial changes and freshwater budgets resulting from intensified glacier melt is an important boundary condition for many biological and integrated earth system science approaches. We provide a case study on glacier and mass balance changes for the ice cap of King George Island. The area loss between 2000 and 2008 amounted to about 20 km2 (about 1.6% of the island area) and compares to glacier retreat rates observed in previous years. Measured net accumulation rates for two years (2007 and 2008) show a strong interannual variability with maximum net accumulation rates of 4950mmw.e. a− 1 and 3184mmw.e. a− 1, respectively. These net accumulation rates are at least 4 times higher than reported mean values (1926–95) from an ice core. An elevation dependent precipitation rate of 343mmw.e. a− 1 (2007) and 432mmw.e. a− 1 (2008) per 100m elevation increase was observed. Despite these rather high net accumulation rates on the main ice cap, consistent surface lowering was observed at elevations below 270m above ellipsoid over an 11-year period. These DGPS records reveal a linear dependence of surface lowering with altitude with a maximum annual surface lowering rate of 1.44ma− 1 at 40m and − 0.20ma− 1 at 270m above ellipsoid. These results fit well to observations by other authors and surface lowering rates derived from the ICESat laser altimetry. Assuming that climate conditions of the past 11 years continue, the small ice cap of Bellingshausen Dome will disappear in about 285 years.” M. Rückamp, M. Braun, S. Suckro and N. Blindow, Global and Planetary Change, doi:10.1016/j.gloplacha.2011.06.009.

Cold fronts due to 2010 extreme arctic oscillation caused coral mortality in Florida

Catastrophic mortality on inshore coral reefs of the Florida keys due to severe low-temperature stress – Kemp et al. (2011) “Coral reefs of the Florida Keys typically experience seasonal temperatures of 20–31 °C. Deviation outside of this range causes physiological impairment of reef-building corals, potentially leading to coral colony death. In January and February 2010, two closely spaced cold fronts, apparently driven by an unusually extreme arctic oscillation, caused sudden and severe seawater temperature declines in the Florida Keys. Inshore coral reefs (e.g., Admiral Reef) experienced lower sustained temperatures (i.e., <12 °C) than those further offshore (e.g., Little Grecian Reef, minimum temperature = 17.2 °C). During February and March 2010, we surveyed Admiral Reef and observed a mass die-off of reef-building corals, whereas 12 km away Little Grecian Reef did not exhibit coral mortality. We subsequently measured the physiological effects of low temperature stress on three common reef-building corals (i.e., Montastraea faveolata, Porites astreoides, and Siderastrea siderea) surviving offshore over a range of temperatures that replicated the inshore cold-water anomaly (i.e., from 20 °C to 16 °C to 12 °C and back to 20 °C). Throughout the temperature modulations, coral respiration as well as endosymbiont gross photosynthesis and maximum PSII photosynthetic efficiency were measured. In addition, Symbiodinium genotypic identity, cell densities, and chlorophyll a content were determined at the beginning and conclusion of the experiment. All corals were significantly affected at 12 °C, but species-specific physiological responses were found indicating different coral and/or Symbiodinium cold tolerances. Montastraea faveolata and P. astreoides appeared to be most negatively impacted because, upon return to 20 °C, significant reductions in gross photosynthesis and dark respiration persisted. S. siderea, however readily recovered to pre-treatment rates of dark respiration and gross photosynthesis. Visual surveys of inshore reefs corroborated these results, with S. siderea being minimally affected by the cold-water anomaly whereas M. faveolata and P. astreoides exhibited nearly 100% mortality. This study highlights the importance of understanding the physiological attributes of genotypically distinct coral-Symbiodinium symbioses that contribute to tolerance, recovery and consequences to an environmental perturbation. These data also document effects of a rarely studied environmental stressor, possibly initiated by remote global climate events, on coral-Symbiodinium symbioses and coral reef communities." Dustin W. Kemp, Clinton A. Oakley, Daniel J. Thornhill, Laura A. Newcomb, Gregory W. Schmidt, William K. Fitt, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02487.x.

In warmer climate there will be more cyanobacteria in lakes

Warmer climates boost cyanobacterial dominance in shallow lakes – Kosten et al. (2011) “Dominance by cyanobacteria hampers human use of lakes and reservoirs worldwide. Previous studies indicate that excessive nutrient loading and warmer conditions promote dominance by cyanobacteria, but evidence from global scale field data has so far been scarce. Our analysis, based on a study of 143 lakes along a latitudinal transect ranging from subarctic Europe to southern South America, shows that while warmer climates do not result in higher overall phytoplankton biomass, the percentage of the total phytoplankton biovolume attributable to cyanobacteria increases steeply with temperature. Our results also reveal that the percent cyanobacteria is greater in lakes with high rates of light absorption. This points to a positive feedback because restriction of light availability is often a consequence of high phytoplankton biovolume, which in turn may be driven by nutrient loading. Our results indicate a synergistic effect of nutrients and climate. The implications are that in a future warmer climate, nutrient concentrations may have to be reduced substantially from present values in many lakes if cyanobacterial dominance is to be controlled.” Sarian Kosten, Vera L. M. Huszar, Eloy Bécares, Luciana S. Costa, Ellen van Donk, Lars-Anders Hansson, Erik Jeppesen, Carla Kruk, Gissell Lacerot, Néstor Mazzeo, Luc De Meester, Brian Moss, Miquel Lürling, Tiina Nõges, Susana Romo, Marten Scheffer, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02488.x.

Permafrost warms in Antarctic

A permafrost warming in a cooling Antarctica? – Guglielmin & Cannone (2011) “The magnitude and even direction of recent Antarctic climate change is still debated because the paucity of long and complete instrumental data records. While along Antarctic Peninsula a strong warming coupled with large retreat of glaciers occurred, in continental Antarctica a cooling was recently detected. Here, the first existing permafrost data set longer than 10 years recorded in continental Antarctica is presented. Since 1997 summer ground surface temperature showed a strong warming trend (0.31°C per year) although the air temperature was almost stable. The summer ground surface temperature increase seemed to be influenced mainly by the increase of the total summer radiation as confirmed also by the increase of the summer thawing degree days. In the same period the active layer exhibited a thickening trend (1 cm per year) comparable with the thickening rates observed in several Arctic locations where air warming occurred. At all the investigated depths permafrost exhibited an increase of mean annual temperature of approximately 0.1°C per year. The dichotomy between active layer thickness and air temperature trends can produce large unexepected and unmodelled impacts on ecosystems and CO2 balance.” Mauro Guglielmin and Nicoletta Cannone, Climatic Change, DOI: 10.1007/s10584-011-0137-2.

Extreme emission scenario model projects 2K more warming than IPCC’s highest

The response of the climate system to very high greenhouse gas emission scenarios – Sanderson et al. (2011) “Well informed decisions on climate policy necessitate simulation of the climate system for a sufficiently wide range of emissions scenarios. While recent literature has been devoted to low emissions futures, the potential for very high emissions has not been thoroughly explored. We specify two illustrative emissions scenarios that are significantly higher than the A1FI scenario, the highest scenario considered in past IPCC reports, and simulate them in a global climate model to investigate their climate change implications. Relative to the A1FI scenario, our highest scenario results in an additional 2 K of global mean warming above A1FI levels by 2100, a complete loss of arctic summer sea-ice by 2070 and an additional 43% sea level rise due to thermal expansion above A1FI levels by 2100. Regional maximum temperature increases from late 20th century values are 50–100% greater than A1FI increases, with some regions such as the Central US, the Tibetan plateau and Alaska showing a 300–400% increase above A1FI levels.” Benjamin M Sanderson, Brian C O’Neill, Jeffrey T Kiehl, Gerald A Meehl, Reto Knutti and Warren M Washington, 2011 Environ. Res. Lett. 6 034005, doi: 10.1088/1748-9326/6/3/034005. [Full text]

Waters around Greenland and Antarctica expected to warm at different pace

Different magnitudes of projected subsurface ocean warming around Greenland and Antarctica – Yin et al. (2011) “The observed acceleration of outlet glaciers and ice flows in Greenland and Antarctica is closely linked to ocean warming, especially in the subsurface layer. Accurate projections of ice-sheet dynamics and global sea-level rise therefore require information of future ocean warming in the vicinity of the large ice sheets. Here we use a set of 19 state-of-the-art climate models to quantify this ocean warming in the next two centuries. We find that in response to a mid-range increase in atmospheric greenhouse-gas concentrations, the subsurface oceans surrounding the two polar ice sheets at depths of 200–500 m warm substantially compared with the observed changes thus far. Model projections suggest that over the course of the twenty-first century, the maximum ocean warming around Greenland will be almost double the global mean, with a magnitude of 1.7–2.0 °C. By contrast, ocean warming around Antarctica will be only about half as large as global mean warming, with a magnitude of 0.5–0.6 °C. A more detailed evaluation indicates that ocean warming is controlled by different mechanisms around Greenland and Antarctica. We conclude that projected subsurface ocean warming could drive significant increases in ice-mass loss, and heighten the risk of future large sea-level rise.” Jianjun Yin, Jonathan T. Overpeck, Stephen M. Griffies, Aixue Hu, Joellen L. Russell & Ronald J. Stouffer, Nature Geoscience(2011), doi:10.1038/ngeo1189.

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Papers on atmospheric CO2 from proxies

Posted by Ari Jokimäki on July 6, 2011

This is a list of papers on atmospheric carbon dioxide contents determined from proxies. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (June 3, 2012): Hönisch et al. (2009) added. Thank to Nick for pointing it out.
UPDATE (April 18, 2012): Breecker et al. (2010) added. Thanks to Barry for pointing it out.

Atmospheric paleo-CO2 estimates based on Taxodium distichum (Cupressaceae) fossils from the Miocene and Pliocene of Eastern North America – Stults et al. (2011) “Neogene atmospheric paleo-CO2 estimates based on fossils of the extant cupressaceous conifer species Taxodium distichum from the Brandywine Formation of Maryland and the Citronelle Formation of southern Alabama are presented. These are important as the first such estimates from eastern North American paleofloras, and provide new evidence from a time for which the role of CO2 in climate change is controversial. Comparisons of the stomatal density (SD) of the fossil leaf cuticles to a calibration curve constructed from modern leaves of the same species collected over the last century of anthropogenic CO2 increase produces Miocene and Pliocene atmospheric paleo-CO2 mean estimates of 360 and 351 ppmv, respectively. Although the temporal resolution of the fossil sites is low, these results are in agreement with multiple independent proxies that indicate near modern CO2 levels during this interval, and demonstrate the utility of T. distichum leaves as instruments for stomatal frequency analysis.” Debra Z. Stults, Friederike Wagner-Cremer and Brian J. Axsmith, Palaeogeography, Palaeoclimatology, Palaeoecology, doi:10.1016/j.palaeo.2011.06.017.

Transient Middle Eocene Atmospheric CO2 and Temperature Variations – Bijl et al. (2010) “The long-term warmth of the Eocene (~56 to 34 million years ago) is commonly associated with elevated partial pressure of atmospheric carbon dioxide (pCO2). However, a direct relationship between the two has not been established for short-term climate perturbations. We reconstructed changes in both pCO2 and temperature over an episode of transient global warming called the Middle Eocene Climatic Optimum (MECO; ~40 million years ago). Organic molecular paleothermometry indicates a warming of southwest Pacific sea surface temperatures (SSTs) by 3° to 6°C. Reconstructions of pCO2 indicate a concomitant increase by a factor of 2 to 3. The marked consistency between SST and pCO2 trends during the MECO suggests that elevated pCO2 played a major role in global warming during the MECO.” Peter K. Bijl, Alexander J. P. Houben, Stefan Schouten, Steven M. Bohaty, Appy Sluijs, Gert-Jan Reichart, Jaap S. Sinninghe Damsté and Henk Brinkhuis, Science 5 November 2010: Vol. 330 no. 6005 pp. 819-821, DOI: 10.1126/science.1193654. [Full text]

Alkenone and boron-based Pliocene pCO2 records – Seki et al. (2010) “The Pliocene period is the most recent time when the Earth was globally significantly ( 3 °C) warmer than today. However, the existing pCO2 data for the Pliocene are sparse and there is little agreement between the various techniques used to reconstruct palaeo-pCO2. This disagreement, coupled with the general low temporal resolution of the published records, does not allow a robust assessment of the role of declining pCO2 in the intensification of the Northern Hemisphere Glaciation (INHG) and a direct comparison to other proxy records are lacking. For the first time, we use a combination of foraminiferal (δ11B) and organic biomarker (alkenone-derived carbon isotopes) proxies to determine the concentration of atmospheric CO2 over the past 5 Ma. Both proxy records show that during the warm Pliocene pCO2 was between 330 and 400 ppm, i.e. similar to today. The decrease to values similar to pre-industrial times (275–285 ppm) occurred between 3.2 Ma and 2.8 Ma — coincident with the INHG and affirming the link between global climate, the cryosphere and pCO2.” Osamu Seki, Gavin L. Foster, Daniela N. Schmidt, Andreas Mackensen, Kimitaka Kawamura and Richard D. Pancost, Earth and Planetary Science Letters, Volume 292, Issues 1-2, 15 March 2010, Pages 201-211, doi:10.1016/j.epsl.2010.01.037. [Full text]

A benthic δ13C-based proxy for atmospheric pCO2 over the last 1.5 Myr – Lisiecki (2010) “A high-resolution marine proxy for atmospheric pCO2 is needed to clarify the phase lag between pCO2 and marine climate proxies and to provide a record of orbital-scale pCO2 variations before the oldest ice core measurement at 800 ka. Benthic δ13C data should record deep ocean carbon storage and, thus, atmospheric pCO2. This study finds that a modified δ13C gradient between the deep Pacific and intermediate North Atlantic (Δδ13CP-NA/2) correlates well with pCO2. Δδ13CP-NA/2 reproduces characteristic differences between pCO2 and ice volume during Late Pleistocene glaciations and indicates that pCO2 usually leads terminations by 0.2–3.7 kyr but lags by 3–10 kyr during two “failed” terminations at 535 and 745 ka. Δδ13CP-NA/2 gradually transitions from 41- to 100-kyr cyclicity from 1.3–0.7 Ma but has no secular trend in mean or amplitude since 1.5 Ma. The minimum pCO2 of the last 1.5 Myr is estimated to be 155 ppm at ∼920 ka.” Lisiecki, L. E. (2010), Geophys. Res. Lett., 37, L21708, doi:10.1029/2010GL045109. [Full text]

Atmospheric CO2 concentrations during ancient greenhouse climates were similar to those predicted for A.D. 2100 – Breecker et al. (2010) “Quantifying atmospheric CO2 concentrations ([CO2]atm) during Earth’s ancient greenhouse episodes is essential for accurately predicting the response of future climate to elevated CO2 levels. Empirical estimates of [CO2]atm during Paleozoic and Mesozoic greenhouse climates are based primarily on the carbon isotope composition of calcium carbonate in fossil soils. We report that greenhouse [CO2]atm have been significantly overestimated because previously assumed soil CO2 concentrations during carbonate formation are too high. More accurate [CO2]atm, resulting from better constraints on soil CO2, indicate that large (1,000s of ppmV) fluctuations in [CO2]atm did not characterize ancient climates and that past greenhouse climates were accompanied by concentrations similar to those projected for A.D. 2100..” D. O. Breecker, Z. D. Sharp, and L. D. McFadden, PNAS January 12, 2010 vol. 107 no. 2 576-580, doi: 10.1073/pnas.0902323106. [Full text]

Coupling of CO2 and Ice Sheet Stability Over Major Climate Transitions of the Last 20 Million Years – Tripati et al. (2009) “The carbon dioxide (CO2) content of the atmosphere has varied cyclically between ~180 and ~280 parts per million by volume over the past 800,000 years, closely coupled with temperature and sea level. For earlier periods in Earth’s history, the partial pressure of CO2 (pCO2) is much less certain, and the relation between pCO2 and climate remains poorly constrained. We use boron/calcium ratios in foraminifera to estimate pCO2 during major climate transitions of the past 20 million years. During the Middle Miocene, when temperatures were ~3° to 6°C warmer and sea level was 25 to 40 meters higher than at present, pCO2 appears to have been similar to modern levels. Decreases in pCO2 were apparently synchronous with major episodes of glacial expansion during the Middle Miocene (~14 to 10 million years ago) and Late Pliocene (~3.3 to 2.4 million years ago).” Aradhna K. Tripati, Christopher D. Roberts and Robert A. Eagle, Science 4 December 2009: Vol. 326 no. 5958 pp. 1394-1397, DOI: 10.1126/science.1178296. [Full text]

Atmospheric Carbon Dioxide Concentration Across the Mid-Pleistocene Transition – Hönisch et al. (2009) “The dominant period of Pleistocene glacial cycles changed during the mid-Pleistocene from 40,000 years to 100,000 years, for as yet unknown reasons. Here we present a 2.1-million-year record of sea surface partial pressure of CO2 (Pco2), based on boron isotopes in planktic foraminifer shells, which suggests that the atmospheric partial pressure of CO2 (pco2) was relatively stable before the mid-Pleistocene climate transition. Glacial Pco2 was ~31 microatmospheres higher before the transition (more than 1 million years ago), but interglacial Pco2 was similar to that of late Pleistocene interglacial cycles (<450,000 years ago). These estimates are consistent with a close linkage between atmospheric CO2 concentration and global climate, but the lack of a gradual decrease in interglacial Pco2 does not support the suggestion that a long-term drawdown of atmospheric CO2 was the main cause of the climate transition.” Bärbel Hönisch, N. Gary Hemming, David Archer, Mark Siddall and Jerry F. McManus, Science 19 June 2009: Vol. 324 no. 5934 pp. 1551-1554, DOI: 10.1126/science.1171477.

CO2-forced climate thresholds during the Phanerozoic – Royer (2006) “The correspondence between atmospheric CO2 concentrations and globally averaged surface temperatures in the recent past suggests that this coupling may be of great antiquity. Here, I compare 490 published proxy records of CO2 spanning the Ordovician to Neogene with records of global cool events to evaluate the strength of CO2-temperature coupling over the Phanerozoic (last 542 my). For periods with sufficient CO2 coverage, all cool events are associated with CO2 levels below 1000 ppm. A CO2 threshold of below 500 ppm is suggested for the initiation of widespread, continental glaciations, although this threshold was likely higher during the Paleozoic due to a lower solar luminosity at that time. Also, based on data from the Jurassic and Cretaceous, a CO2 threshold of below 1000 ppm is proposed for the initiation of cool non-glacial conditions. A pervasive, tight correlation between CO2 and temperature is found both at coarse (10 my timescales) and fine resolutions up to the temporal limits of the data set (million-year timescales), indicating that CO2, operating in combination with many other factors such as solar luminosity and paleogeography, has imparted strong control over global temperatures for much of the Phanerozoic.” Dana L. Royer, Geochimica et Cosmochimica Acta, Volume 70, Issue 23, 1 December 2006, Pages 5665-5675, doi:10.1016/j.gca.2005.11.031. [Full text]

Changes in carbon dioxide during an oceanic anoxic event linked to intrusion into Gondwana coals – McElwain et al. (2005) “The marine sedimentary record exhibits evidence for episodes of enhanced organic carbon burial known as ‘oceanic anoxic events’ (OAEs). They are characterized by carbon-isotope excursions in marine and terrestrial reservoirs and mass extinction of marine faunas. Causal mechanisms for the enhancement of organic carbon burial during OAEs are still debated, but it is thought that such events should draw down significant quantities of atmospheric carbon dioxide. In the case of the Toarcian OAE (183 million years ago), a short-lived negative carbon-isotope excursion in oceanic and terrestrial reservoirs has been interpreted to indicate raised atmospheric carbon dioxide caused by oxidation of methane catastrophically released from either marine gas hydrates or magma-intruded organic-rich rocks. Here we test these two leading hypotheses for a negative carbon isotopic excursion marking the initiation of the Toarcian OAE using a high-resolution atmospheric carbon dioxide record obtained from fossil leaf stomatal frequency. We find that coincident with the negative carbon-isotope excursion carbon dioxide is first drawn down by 350 +/- 100 p.p.m.v. and then abruptly elevated by 1,200 +/- 400 p.p.m.v, and infer a global cooling and greenhouse warming of 2.5 +/- 0.1 °C and 6.5 +/- 1 °C, respectively. The pattern and magnitude of carbon dioxide change are difficult to reconcile with catastrophic input of isotopically light methane from hydrates5 as the cause of the negative isotopic signal. Our carbon dioxide record better supports a magma-intrusion hypothesis, and suggests that injection of isotopically light carbon from the release of thermogenic methane occurred owing to the intrusion of Gondwana coals by Toarcian-aged Karoo-Ferrar dolerites.” Jennifer C. McElwain, Jessica Wade-Murphy & Stephen P. Hesselbo, Nature 435, 479-482 (26 May 2005), doi:10.1038/nature03618

Mid-Cretaceous pCO2 based on stomata of the extinct conifer Pseudofrenelopsis (Cheirolepidiaceae) – Haworth et al. (2005) “Stomatal characteristics of an extinct Cretaceous conifer, Pseudofrenelopsis parceramosa (Fontaine) Watson, are used to reconstruct atmospheric carbon dioxide (pCO2) over a time previously inferred to exhibit major fluctuations in this greenhouse gas. Samples are from nonmarine to marine strata of the Wealden and Lower Greensand Groups of England and the Potomac Group of the eastern United States, of Hauterivian to Albian age (136–100 Ma). Atmospheric pCO2 is estimated from the ratios between stomatal indices of fossil cuticles and those from four modern analogs (nearest living equivalent plants). Using this approach, and two calibration methods to explore ranges, results show relatively low and only slightly varying pCO2 over the Hauterivian–Albian interval: a low of ∼560–960 ppm in the early Barremian and a high of ∼620–1200 ppm in the Albian. Data from the Barremian Wealden Group yield pCO2 values indistinguishable from a soil-carbonate–based estimate from the same beds. The new pCO2 estimates are compatible with sedimentological and oxygen-isotope evidence for relatively cool mid-Cretaceous climates.” Matthew Haworth, Stephen P. Hesselbo, Jennifer C. McElwain, Stuart A. Robinson and James W. Brunt, Geology, v. 33 no. 9 p. 749-752, doi: 10.1130/G21736.1.

Marked Decline in Atmospheric Carbon Dioxide Concentrations During the Paleogene – Pagani et al. (2005) “The relation between the partial pressure of atmospheric carbon dioxide (pCO2) and Paleogene climate is poorly resolved. We used stable carbon isotopic values of di-unsaturated alkenones extracted from deep sea cores to reconstruct pCO2 fromthe middle Eocene to the late Oligocene (∼45 to 25 million years ago). Our results demonstrate that pCO2 ranged between 1000 to 1500 parts per million by volume in the middle to late Eocene, then decreased in several steps during the Oligocene, and reached modern levels by the latest Oligocene. The fall in pCO2 likely allowed for a critical expansion of ice sheets on Antarctica and promoted conditions that forced the onset of terrestrial C4 photosynthesis.” Mark Pagani, James C. Zachos, Katherine H. Freeman, Brett Tipple and Stephen Bohaty, Science 22 July 2005: Vol. 309 no. 5734 pp. 600-603, DOI: 10.1126/science.1110063. [Full text]

Atmospheric CO2 During the Late Paleozoic and Mesozoic: Estimates from Indian Soils – Ghosh et al. (2005) No abstract. Prosenjit Ghosh, S.K. Bhattacharya and Parthasarathi Ghosh, A History of Atmospheric CO2 and Its Effects on Plants, Animals, and Ecosystems, Ecological Studies, 2005, Volume 177, Part 1., 8-34, DOI: 10.1007/0-387-27048-5_2. [Full text]

Fossil bryophytes as recorders of ancient CO2 levels: Experimental evidence and a Cretaceous case study – Fletcher et al. (2005) “Biological and geochemical CO2 proxies provide critical constraints on understanding the role of atmospheric CO2 in driving climate change during Earth history. As no single existing CO2 proxy is without its limitations, there is a clear need for new approaches to reconstructing past CO2 concentrations. Here we develop a new pre-Quaternary CO2 proxy based on the stable carbon isotope composition (δ13C) of astomatous land plants. In a series of CO2-controlled laboratory experiments, we show that the carbon isotope discrimination (Δ13C) of a range of bryophyte (liverwort and moss) species increases with atmospheric CO2 across the range 375 to 6000 ppm. Separate experiments establish that variations in growth temperature, water content and substrate type have minor impacts on the Δ13C of liverworts but not mosses, indicating the greater potential of liverworts to faithfully record past variations in CO2. A mechanistic model for calculating past CO2 concentrations from bryophyte Δ13C (White et al., 1994) is extended and calibrated using our experimental results. The potential for fossil liverworts to record past CO2 changes is investigated by analyzing the δ13C of specimens collected from Alexander Island, Antarctica dating to the “greenhouse” world of the mid-Cretaceous. Our analysis and isotopic model yield mid-Cretaceous CO2 concentrations of 1000–1400 ppm, in general agreement with independent proxy data and long-term carbon cycle models. The exceptionally long evolutionary history of bryophytes offers the possibility of reconstructing CO2 concentrations back to the mid-Ordovician, pre-dating all currently used quantitative CO2 proxies.” Fletcher, B. J., D. J. Beerling, S. J. Brentnall, and D. L. Royer (2005), Global Biogeochem. Cycles, 19, GB3012, doi:10.1029/2005GB002495. [Full text]

Fe(CO3)OH in goethite from a mid-latitude North American Oxisol: estimate of atmospheric CO2 concentration in the Early Eocene “climatic optimum” – Yapp (2004) “Measured mole fractions (X) and δ13C values of the Fe(CO3)OH component in pedogenic goethite from a mid-latitude Oxisol of Early Eocene age (≈52 Ma B.P.) range from 0.0014 to 0.0064 and −20.1 to −15.4‰, respectively. These values of X imply that concentrations of CO2 gas in the paleosol were ≈7400 to ≈34,000 ppm. δ13C and 1/X are correlated and define a linear, soil-CO2 diffusive mixing line with a positive slope. Such positive slopes are characteristic of mixing of two isotopically distinct CO2 endmembers (atmospheric CO2 and CO2 from oxidation of soil organic matter). From the intercept of the mixing line, it is calculated that the δ 13C value of organic matter in the ancient soil was ≈−28.0‰. The magnitude of the slope implies an Early Eocene atmospheric CO2 concentration of ≈2700 ppm. A simple model for forest soils suggests that a “canopy effect” may cause atmospheric CO2 concentrations deduced from pedogenic minerals to underestimate the actual concentrations of atmospheric CO2. If a significant forest canopy were present at the time of formation of pedogenic goethite in the Ione Fm, the concentration of 2700 ppm calculated for atmospheric CO2 could be slightly low, but the underestimate is expected to be < ≈300 ppm (i.e., less than the analytical uncertainty). The relatively high concentration of 2700 ppm inferred for atmospheric CO2 at ≈52 Ma B.P. would have been coincident with the Early Eocene climatic optimum. This result seems to support the case for an important role for variations of atmospheric CO2 in the modification of global paleoclimate.” Crayton J. Yapp, Geochimica et Cosmochimica Acta, Volume 68, Issue 5, 1 March 2004, Pages 935-947, doi:10.1016/j.gca.2003.09.002.

Goethite, calcite, and organic matter from Permian and Triassic soils: carbon isotopes and CO2 concentrations – Tabor et al. (2004) “Pedogenic goethites in each of two Early Permian paleosols appear to record mixing of two isotopically distinct CO2 components—atmospheric CO2 and CO2 from in situ oxidation of organic matter. The δ13C values measured for the Fe(CO3)OH component in solid solution in these Permian goethites are −13.5‰ for the Lower Leonardian (283 Ma BP) paleosol (MCGoeth) and −13.9‰ for the Upper Leonardian (270 Ma BP) paleosol (SAP). These goethites contain the most 13C-rich Fe(CO3)OH measured to date for pedogenic goethites crystallized in soils exhibiting mixing of the two aforementioned CO2 components. δ13C measured for 43 organic matter samples in the Lower Leonardian (Waggoner Ranch Fm.) has an average value of −20.3 ± 1.1‰ (1s). The average value yields a calculated Early Permian atmospheric Pco2 value of about 1 × PAL, but the scatter in the measured δ13C values of organic matter permits a calculated maximum Pco2 of 11 × PAL (PAL = present atmospheric level). Measured values of the mole fraction of Fe(CO3)OH in MCGoeth and SAP correspond to soil CO2 concentrations in the Early Permian paleosol profiles of 54,000 and 50,000 ppmV, respectively. Such high soil CO2 concentrations are similar to modern soils in warm, wet environments. The average δ13C values of pedogenic calcite from 9 paleosol profiles stratigraphically associated with MCGoeth (Waggoner Ranch Fm.) range from −6.5‰ to −4.4‰, with a mean δ13C value for all profiles of −5.4‰. Thus, the value of Δ13C between the pedogenic calcite data set and MCGoeth is 8.1 (±0.9)‰, which is in reasonable accord with the value of 7.7‰ expected if atmospheric Pco2 and organic matter δ13C values were the same for both paleosol types. Furthermore, the atmospheric Pco2 calculated for the Early Permian from the average measured carbon isotopic compositions of the paleosol calcite and organic matter is also analytically indistinguishable from 1 × PAL, with a maximum calculated atmospheric Pco2 (permitted by one standard deviation of the organic matter δ13C value) of 5 × PAL. If, however, measured average δ13C values of the plant organic matter are more positive than the original soil organic matter as a result of diagenetic loss of 13C-depleted, labile organic compounds, calculated Permian atmospheric Pco2 using these 13C-enriched organic values would underestimate the actual atmospheric Pco2 using either goethite or calcite. This is the first stratigraphically constrained, intrabasinal study to compare ancient atmospheric CO2 concentrations calculated from pedogenic goethite and calcite. These results demonstrate that the two different proxies record the same information about atmospheric CO2. The Fe(CO3)OH component in pedogenic goethite from a Triassic paleosol in Utah is significantly enriched in 13C relative to Fe(CO3)OH in goethites from soils in which there are mixtures of two isotopic CO2 components. Field-relationships and the δ13C value (−1.9‰) of the Triassic goethite indicate that this ancient paleosol profile experienced mixing of three isotopically distinct CO2 components at the time of goethite crystallization. The three components were probably atmospheric CO2, CO2 from in situ oxidation of organic matter and CO2 from in situ dissolution of preexisting calcite. Although mixing of three isotopically distinct CO2 components, as recorded by Fe(CO3)OH in goethite, has been described in modern soil, this is the first example from a documented paleosol. Its preservation affirms the need for careful, case-by-case assessment of ancient paleosols to establish that goethite in any particular soil is likely to be a valid proxy of atmospheric Pco2.” Neil J. Tabor, Crayton J. Yapp and Isabel P. Montañez, Geochimica et Cosmochimica Acta, Volume 68, Issue 7, 1 April 2004, Pages 1503-1517, doi:10.1016/S0016-7037(03)00497-6.

Terrestrial Evidence for Two Greenhouse Events in the Latest Cretaceous – Nordt (2003) “We present a terrestrial record of stable carbon and oxygen isotopes from paleosol carbonate for climate interpretations between ca. 71.0 and 63.6 Ma. Isotopic ratios point to covarying and elevated atmospheric CO2 pressures and temperatures between ca. 70.0 and 69.0 Ma and ca. 65.5 and 65.0 Ma. These two greenhouse episodes were characterized by atmospheric CO2 levels between 1000 and 1400 ppmV (V = volume) and by mean annual temperatures in west Texas between 21 and 23 {degrees}C (~35{degrees}N paleo-latitude). Atmospheric CO2 and temperature relations indicate that a doubling of pCO2 was accompanied by an ~0.6 {degrees}C increase in temperature. A temperature gradient of ~0.4 {degrees}C per degree of latitude is proposed for North America across the Cretaceous-Tertiary boundary when comparing temperature proxies from west Texas with paleobotanical work in North Dakota. Our data demonstrate strong coupling between terrestrial climates and ocean temperatures that were possibly forced by Deccan trap volcanic degassing, leading to dramatic global climate changes.” Lee Nordt, Stacy Atchley, and Steve Dworkin, GSA Today, v. 13(12), p. 4-9. [Full text]

Leaf stomatal frequency in the Australian tropical rainforest tree Neolitsea dealbata (Lauraceae) as a proxy measure of atmospheric pCO2 – Greenwood et al. (2003) “A putative relationship has been demonstrated for European and North American woody dicots and gymnosperms between leaf stomatal frequency and historical levels of atmospheric CO2. However, hitherto no such study has been presented for Australian tropical broadleaved evergreen trees. In this study, variation of stomatal index (SI) along environmental gradients is examined for the broadleaved evergreen tropical rainforest tree Neolitsea dealbata (Lauraceae). Historical herbarium samples from natural populations in northeastern and southeastern Queensland were analysed. Leaf SI for Neolitsea dealbata is shown to be insensitive to mean annual rainfall or seasonal totals, or to temperature variables, indicating the climatic factors that influence the water budget of the plants were not a factor controlling SI. Contrary to the pattern most commonly observed in temperate areas, SI decreased with elevation for collections within a single year for 3 out of 4 years surveyed, a pattern consistent with environmental factors other than pCO2 acting as the control over SI. However, an overall decrease in SI was recorded for samples collected in Queensland (30°–17°S) over the period 1899–1988, corresponding to a Southern Hemisphere increase in pCO2 from 295 to 350 ppm. Restricting the analysis to sites within an altitudinal band of 640–1120 m demonstrated a significant relationship between SI and pCO2 (r2=0.8942, F11=84.5, P<0.001). This data set was used to estimate atmospheric pCO2 from fossil leaf cuticle for the closely related genus Litsea, giving pCO2 values comparable to those estimated using Ginkgo from Northern Hemisphere fossil sites.” David R. Greenwood, Mark J. Scarr and David C. Christophel, Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 196, Issues 3-4, 1 August 2003, Pages 375-393, doi:10.1016/S0031-0182(03)00465-6. [Full text]

Atmospheric pCO2 since 60 Ma from records of seawater pH, calcium, and primary carbonate mineralogy – Demicco et al. (2003) “A 60 m.y. record of atmospheric pCO2 has been refined from knowledge of (1) secular changes in the major ion composition of seawater (particularly Ca and Mg) and (2) oscillations in the mineralogy of primary oceanic carbonate sediments. Both factors have had a significant impact on the chemistry of the ocean carbonate buffer system. Calculated atmospheric pCO2 oscillated between values of 100–300 ppm and to maxima of 1200–2500 ppm from 60 to 40 Ma and varied between 100 and 300 ppm from 25 Ma to the present. The refined pCO2 values are significantly lower than previous estimates made from seawater pH data where total dissolved inorganic carbon was assumed constant and more in line with modeling and stomatal index estimations of atmospheric pCO2 for the Tertiary.” Robert V. Demicco, Tim K. Lowenstein and Lawrence A. Hardie, Geology, v. 31 no. 9 p. 793-796, doi: 10.1130/G19727.1. [Full text]

Atmospheric pCO2 and depositional environment from stable-isotope geochemistry of calcrete nodules (Barremian, Lower Cretaceous, Wealden Beds, England) – Robinson et al. (2002) “Nodular soil carbonates (calcretes) are present in overbank facies of Lower Cretaceous, non-marine Wealden Beds (Wessex Formation) of southern England. Field evidence suggests that these calcretes formed mostly under semi-arid Mediterranean-type climatic conditions. Typical calcrete fabrics, identified petrographically, include floating detrital grains, corroded grain margins and circumgranular cracks defining peds. Localized alteration of primary micrites is mainly associated with large cracks where early non-ferroan diagenetic cementation and neomorphism was focused. Diagenetic ferroan calcites occur as void fills and yield relatively light carbon-isotope and oxygen-isotope compositions (δ13C= –15.0‰; δ18O= –6.3‰) compared to well-preserved micrite (δ13C= –10.2‰; δ18O= –4.0‰). Precise definition of δ13C values for well-preserved micrites allow estimation of partial pressure of atmospheric CO2 (pCO2) for the early Barremian of 560 ppmV using a published diffusion-reaction model. The data suggest that atmospheric CO2 was low during the mid-Early Cretaceous before rising to a previously defined mid-Cretaceous high. Data from calcretes in the Weald Clay highlight the need for selection of appropriate material and careful evaluation before pCO2 calculations are attempted. The Weald Clay samples come from marshy palaeoenvironments where ingress of atmospheric CO2 into the soil-zone was either reduced or prevented.” Stuart A. Robinson, Julian E. Andrews, Stephen P. Hesselbo, Jonathan D. Radley, Paul F. Dennis, Ian C. Harding & Perce Allen, Journal of the Geological Society; 2002; v. 159; issue.2; p. 215-224; DOI: 10.1144/0016-764901-015. [Full text]

Paleosol barometer indicates extreme fluctuations in atmospheric CO2 across the Cretaceous-Tertiary boundary – Nordt et al. (2002) “We present an atmospheric pCO2 (p is partial pressure) curve showing extreme fluctuations for the interval between ca. 77 and 63 Ma in southern Alberta, Canada, using a paleosol barometer. Paleosol carbonate nodules (micrite) were collected from 40 Bk horizons among 6 stratigraphic sections for stable carbon isotope analysis. Based on results from the study area, declining atmospheric pCO2 from 1200 ppmV (V is volume) in the Campanian to 780 ppmV in the Maastrichtian correlates with Late Cretaceous climate cooling and falling sea level as documented in global records. The remarkable rise in atmospheric pCO2 near 65.5 Ma (1440 ppmV) correlates with volcanic activity associated with the Deccan Traps, rising sea level, and warmer global climates. The decline in atmospheric pCO2 (760 ppmV) at the Cretaceous-Tertiary boundary and subsequent sharp rise into the Danian (1000 ppmV) occurred during static terrestrial temperatures and sea level. This work provides compelling evidence that atmospheric pCO2 curves modeled for the Phanerozoic do not offer the resolution needed to understand environmental conditions during catastrophic events in Earth’s history.” Lee Nordt, Stacy Atchley and S.I. Dworkin, Geology, v. 30 no. 8 p. 703-706, doi: 10.1130/0091-7613(2002).

Fossil plants as indicators of the Phanerozoic global carbon cycle – Beerling & Royer (2002) “Developments in plant physiology since the 1980s have led to the realization that fossil plants archive both the isotopic composition of atmospheric CO2 and its concentration, both critical integrators of carbon cycle processes through geologic time. These two carbon cycle signals can be read by analyzing the stable carbon isotope composition (δ13C) of fossilized terrestrial organic matter and by determining the stomatal characters of well-preserved fossil leaves, respectively. We critically evaluate the use of fossil plants in this way at abrupt climatic boundaries associated with mass extinctions and during times of extreme global warmth. Particular emphasis is placed on evaluating the potential to extract a quantitative estimate of the δ13C of atmospheric CO2 because of the key role it plays in understanding the carbon cycle. We critically discuss the use of stomatal index and stomatal ratios for reconstructing atmospheric CO2 levels, especially the need for adequate replication, and present a newly derived CO2 record for the Mesozoic that supports levels calculated from geochemical modeling of the long-term carbon cycle. Several suggestions for future research using stable carbon isotope analyses of fossil terrestrial organic matter and stomatal measurements are highlighted.” D.J. Beerling and D.L. Royer, Annual Review of Earth and Planetary Sciences, Vol. 30: 527-556 (Volume publication date May 2002), DOI: 10.1146/annurev.earth.30.091201.141413. [Full text]

An atmospheric pCO2 reconstruction across the Cretaceous-Tertiary boundary from leaf megafossils – Beerling et al. (2002) “The end-Cretaceous mass extinctions, 65 million years ago, profoundly influenced the course of biotic evolution. These extinctions coincided with a major extraterrestrial impact event and massive volcanism in India. Determining the relative importance of each event as a driver of environmental and biotic change across the Cretaceous-Tertiary boundary (KTB) crucially depends on constraining the mass of CO2 injected into the atmospheric carbon reservoir. Using the inverse relationship between atmospheric CO2 and the stomatal index of land plant leaves, we reconstruct Late Cretaceous-Early Tertiary atmospheric CO2 concentration (pCO2) levels with special emphasis on providing a pCO2 estimate directly above the KTB. Our record shows stable Late Cretaceous/Early Tertiary background pCO2 levels of 350–500 ppm by volume, but with a marked increase to at least 2,300 ppm by volume within 10,000 years of the KTB. Numerical simulations with a global biogeochemical carbon cycle model indicate that CO2 outgassing during the eruption of the Deccan Trap basalts fails to fully account for the inferred pCO2 increase. Instead, we calculate that the postboundary pCO2 rise is most consistent with the instantaneous transfer of ≈4,600 Gt C from the lithic to the atmospheric reservoir by a large extraterrestrial bolide impact. A resultant climatic forcing of +12 W m−2 would have been sufficient to warm the Earth’s surface by ≈7.5°C, in the absence of counter forcing by sulfate aerosols. This finding reinforces previous evidence for major climatic warming after the KTB impact and implies that severe and abrupt global warming during the earliest Paleocene was an important factor in biotic extinction at the KTB.” D. J. Beerling, B. H. Lomax, D. L. Royer, G. R. Upchurch, Jr., and L. R. Kump, PNAS June 11, 2002 vol. 99 no. 12 7836-7840, doi: 10.1073/pnas.122573099. [Full text]

Low atmospheric CO2 levels during the Permo- Carboniferous glaciation inferred from fossil lycopsids – Beerling (2002) “Earth history was punctuated during the Permo-Carboniferous [300–250 million years (Myr) ago] by the longest and most severe glaciation of the entire Phanerozoic Eon. But significant uncertainty surrounds the concentration of CO2 in the atmosphere through this time interval and therefore its role in the evolution of this major prePleistocene glaciation. Here, I derive 24 Late Paleozoic CO2 estimates from the fossil cuticle record of arborsecent lycopsids of the equatorial Carboniferous and Permian swamp communities. Quantitative calibration of Late Carboniferous (330–300 Myr ago) and Permian (270–260 Myr ago) lycopsid stomatal indices yield average atmospheric CO2 concentrations of 344 ppm and 313 ppm, respectively. The reconstructions show a high degree of self-consistency and a degree of precision an order of magnitude greater than other approaches. Low CO2 levels during the Permo-Carboniferous glaciation are in agreement with glaciological evidence for the presence of continental ice and coupled models of climate and ice-sheet growth on Pangea. Moreover, the Permian data indicate atmospheric CO2 levels were low 260 Myr ago, by which time continental deglaciation was already underway. Positive biotic feedbacks on climate, and geotectonic events, therefore are implicated as mechanisms underlying deglaciation.” D. J. Beerling, PNAS October 1, 2002 vol. 99 no. 20 12567-12571, doi: 10.1073/pnas.202304999 . [Full text]

Stability of atmospheric CO2 levels across the Triassic/Jurassic boundary – Tanner et al. (2001) “The Triassic/Jurassic boundary, 208 million years ago, is associated with widespread extinctions in both the marine and terrestrial biota. The cause of these extinctions has been widely attributed to the eruption of flood basalts of the Central Atlantic Magmatic Province. This volcanic event is thought to have released significant amounts of CO2 into the atmosphere, which could have led to catastrophic greenhouse warming, but the evidence for CO2-induced extinction remains equivocal. Here we present the carbon isotope compositions of pedogenic calcite from palaeosol formations, spanning a 20-Myr period across the Triassic/Jurassic boundary. Using a standard diffusion model, we interpret these isotopic data to represent a rise in atmospheric CO2 concentrations of about 250 p.p.m. across the boundary, as compared with previous estimates of a 2,000–4,000 p.p.m. increase. The relative stability of atmospheric CO2 across this boundary suggests that environmental degradation and extinctions during the Early Jurassic were not caused by volcanic outgassing of CO2. Other volcanic effects—such as the release of atmospheric aerosols or tectonically driven sea-level change—may have been responsible for this event.” Lawrence H. Tanner, John F. Hubert, Brian P. Coffey & Dennis P. McInerney, Nature 411, 675-677 (7 June 2001) | doi:10.1038/35079548.

A 300-million-year record of atmospheric carbon dioxide from fossil plant cuticles – Retallack (2001) “To understand better the link between atmospheric CO2 concentrations and climate over geological time, records of past CO2 are reconstructed from geochemical proxies. Although these records have provided us with a broad picture of CO2 variation throughout the Phanerozoic eon (the past 544 Myr), inconsistencies and gaps remain that still need to be resolved. Here I present a continuous 300-Myr record of stomatal abundance from fossil leaves of four genera of plants that are closely related to the present-day Ginkgo tree. Using the known relationship between leaf stomatal abundance and growing season CO2 concentrations I reconstruct past atmospheric CO2 concentrations. For the past 300 Myr, only two intervals of low CO2 (<1,000 p.p.m.v.) are inferred, both of which coincide with known ice ages in Neogene (1–8 Myr) and early Permian (275–290 Myr) times. But for most of the Mesozoic era (65–250 Myr), CO2 levels were high (1,000–2,000 p.p.m.v.), with transient excursions to even higher CO2 (>2,000 p.p.m.v.) concentrations. These results are consistent with some reconstructions of past CO2 (refs 1, 2) and palaeotemperature records, but suggest that CO2 reconstructions based on carbon isotope proxies may be compromised by episodic outbursts of isotopically light methane. These results support the role of water vapour, methane and CO2 in greenhouse climate warming over the past 300 Myr.” Gregory J. Retallack, Nature 411, 287-290 (17 May 2001) | doi:10.1038/35077041. [Full text]

CO2 levels in the Late Palaeozoic and Mesozoic atmosphere from soil carbonate and organic matter, Satpura basin, Central India – Ghosh et al. (2001) “A number of calcic palaeosols have been identified within the fluvial deposits of the Motur (Permian), the Denwa (Triassic), the Bagra (Jurassic) and the Lameta (Cretaceous) Formations of the Satpura sedimentary succession, Central India. These palaeosols show accumulation of pedogenic carbonates in rhizocretions and glaebules. The carbon isotopic compositions of these carbonates and the coexisting soil organic matters are used to determine the isotopic composition and the partial pressure of atmospheric CO2 using the CO2 palaeobarometer developed by Cerling [Am. J. Sci., 291 (1991) 377]. It is seen that the atmospheric CO2 level increased by a factor of 8 from the Permian to the Jurassic and declined again during the Cretaceous. The nature of the changes agrees with the result of the CO2 evolution model of Berner (GEOCARB II) but the magnitude of the CO2 increase in the Middle Jurassic and the Late Cretaceous was higher than the predicted value. Degassing of Earth’s interior due to rapid break-up of the Gondwana landmass during the Triassic and Jurassic period could have caused the rapid CO2 increase.” Prosenjit Ghosh, P Ghosh and S.K Bhattacharya, Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 170, Issues 3-4, 15 June 2001, Pages 219-236, doi:10.1016/S0031-0182(01)00237-1. [Full text]

Paleobotanical Evidence for Near Present-Day Levels of Atmospheric CO2 During Part of the Tertiary – Royer et al. (2001) “Understanding the link between the greenhouse gas carbon dioxide (CO2) and Earth’s temperature underpins much of paleoclimatology and our predictions of future global warming. Here, we use the inverse relationship between leaf stomatal indices and the partial pressure of CO2 in modern Ginkgo bilobaand Metasequoia glyptostroboides to develop a CO2 reconstruction based on fossil Ginkgo andMetasequoia cuticles for the middle Paleocene to early Eocene and middle Miocene. Our reconstruction indicates that CO2 remained between 300 and 450 parts per million by volume for these intervals with the exception of a single high estimate near the Paleocene/Eocene boundary. These results suggest that factors in addition to CO2 are required to explain these past intervals of global warmth.” Dana L. Royer, Scott L. Wing, David J. Beerling, David W. Jolley, Paul L. Koch, Leo J. Hickey and Robert A. Berner, Science 22 June 2001: Vol. 292 no. 5525 pp. 2310-2313, DOI: 10.1126/science.292.5525.2310. [Full text]

Atmospheric carbon dioxide concentrations over the past 60 million years – Pearson & Palmer (2000) “Knowledge of the evolution of atmospheric carbon dioxide concentrations throughout the Earth’s history is important for a reconstruction of the links between climate and radiative forcing of the Earth’s surface temperatures. Although atmospheric carbon dioxide concentrations in the early Cenozoic era (about 60 Myr ago) are widely believed to have been higher than at present, there is disagreement regarding the exact carbon dioxide levels, the timing of the decline and the mechanisms that are most important for the control of CO2 concentrations over geological timescales. Here we use the boron-isotope ratios of ancient planktonic foraminifer shells to estimate the pH of surface-layer sea water throughout the past 60 million years, which can be used to reconstruct atmospheric CO2 concentrations. We estimate CO2 concentrations of more than 2,000 p.p.m. for the late Palaeocene and earliest Eocene periods (from about 60 to 52 Myr ago), and find an erratic decline between 55 and 40 Myr ago that may have been caused by reduced CO2 outgassing from ocean ridges, volcanoes and metamorphic belts and increased carbon burial. Since the early Miocene (about 24 Myr ago), atmospheric CO2 concentrations appear to have remained below 500 p.p.m. and were more stable than before, although transient intervals of CO2 reduction may have occurred during periods of rapid cooling approximately 15 and 3 Myr ago.” Paul N. Pearson & Martin R. Palmer, Nature 406, 695-699 (17 August 2000), doi:10.1038/35021000. [Full text]

Fossil Plants and Global Warming at the Triassic-Jurassic Boundary – McElwain et al. (1999) “The Triassic-Jurassic boundary marks a major faunal mass extinction, but records of accompanying environmental changes are limited. Paleobotanical evidence indicates a fourfold increase in atmospheric carbon dioxide concentration and suggests an associated 3° to 4°C “greenhouse” warming across the boundary. These environmental conditions are calculated to have raised leaf temperatures above a highly conserved lethal limit, perhaps contributing to the >95 percent species-level turnover of Triassic-Jurassic megaflora.” J. C. McElwain, D. J. Beerling and F. I. Woodward, Science 27 August 1999: Vol. 285 no. 5432 pp. 1386-1390, DOI: 10.1126/science.285.5432.1386.

Stable isotopic composition of pedogenic carbonates of the Early Cretaceous Shimonoseki Subgroup, western Honshu, Japan – Lee & Hisada (1999) “Abundant pedogenic carbonate nodules are present in the Shimonoseki Subgroup in the Kanmon Basin of Kyushu and Honshu, Japan. The oxygen isotope compositions of these pedogenic carbonates range from −20.1 to −22.8‰ (PDB), which is 7‰ lower than those of the septarian crystallaria in the carbonate nodules. The meteoric water composition estimated from the oxygen isotope composition of the soil water in equilibrium with the carbonates is much depleted compared with the estimate from other sources. This suggests that the oxygen isotope compositions of the Shimonoseki pedogenic carbonates were modified during diagenesis. The carbon isotopic compositions of the Shimonoseki carbonates range from −5.4 to −7.0‰ (PDB), with an average of −6.7‰ (PDB), suggesting carbonate formation in soils dominated by C3 type of vegetation. An analysis of these values using Cerling’s model (Cerling, T.E., Wright, V.P., Vanstone, S.D., 1992. Further comments on using carbon isotopes in paleosols to estimate the CO2 content of the palaeo-atmosphere. J. Geol. Soc. London 148 (1991), 945–947; 149, 673–676) indicates that the partial pressure of CO2 in the Early Cretaceous Shimonoseki atmosphere was about 1700–3200 ppmV.” Yong Il Lee and Ken-ichiro Hisada, Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 153, Issues 1-4, 15 September 1999, Pages 127-138, doi:10.1016/S0031-0182(99)00069-3.

Late Miocene Atmospheric CO2 Concentrations and the Expansion of C4 Grasses – Pagani et al. (1999) “The global expansion of C4 grasslands in the late Miocene has been attributed to a large-scale decrease in atmospheric carbon dioxide (CO2) concentrations. This triggering mechanism is controversial, in part because of a lack of direct evidence for change in the partial pressure of CO2(pCO2) and because other factors are also important determinants in controlling plant-type distributions. Alkenone-based pCO2 estimates for the late Miocene indicate that pCO2 increased from 14 to 9 million years ago and stabilized at preindustrial values by 9 million years ago. The estimates presented here provide no evidence for major changes in pCO2 during the late Miocene. Thus, C4 plant expansion was likely driven by additional factors, possibly a tectonically related episode of enhanced low-latitude aridity or changes in seasonal precipitation patterns on a global scale (or both).” Mark Pagani, Katherine H. Freeman and Michael A. Arthur, Science 6 August 1999: Vol. 285 no. 5429 pp. 876-879, DOI: 10.1126/science.285.5429.876.

Miocene evolution of atmospheric carbon dioxide – Pagani et al. (1999) “Changes in pCO2 or ocean circulation are generally invoked to explain warm early Miocene climates and a rapid East Antarctic ice sheet (EAIS) expansion in the middle Miocene. This study reconstructs late Oligocene to late Miocene pCO2 from εp values based on carbon isotopic analyses of diunsaturated alkenones and planktonic foraminifera from Deep Sea Drilling Project sites 588 and 608 and Ocean Drilling Program site 730. Our results indicate that highest pCO2 occurred during the latest Oligocene (∼350 ppmv) but decreased rapidly at ∼25 Ma. The early and middle Miocene was characterized by low pCO2 (260–190 ppmv). Lower intervals of pCO2 correspond to inferred organic carbon burial events and glacial episodes with the lowest concentrations occurring during the middle Miocene. There is no evidence for either high pCO2 during the late early Miocene climatic optimum or a sharp pCO2 decrease associated with EAIS growth. Paradoxically, pCO2 increased following EAIS growth and obtained preindustrial levels by ∼10 Ma. Although we emphasize an oceanographic control on Miocene climate, low pCO2 could have primed the climate system to respond sensitively to changes in heat and vapor transport” Pagani, M., M. A. Arthur, and K. H. Freeman (1999), Paleoceanography, 14(3), 273–292, doi:10.1029/1999PA900006. [Full text]

Stable isotopic composition of calcic paleosols of the Early Cretaceous Hasandong Formation, southeastern Korea – Lee (1999) “Abundant pedogenic carbonate nodules are present in the Cretaceous non-marine Hasandong Formation, southeastern Korea. The oxygen isotope compositions of these pedogenic carbonates range from −14.2 to −18.0‰ (PDB). The meteoric water composition estimated from the oxygen isotope composition of the soil-water in equilibrium with the carbonates is much depleted compared with the previous estimate. This suggests that the oxygen isotope compositions of the Hasandong pedogenic carbonates were modified during diagenesis. The carbon isotopic compositions of the Hasandong carbonates range from −2.4 to −9.3‰ (PDB) with an average of −5.6‰ (PDB) suggesting carbonate formation in soils dominated by C3 type of vegetation. The estimated average composition of the vegetation is about 6‰ (PDB) enriched compared with the present-day C3 vegetation. This is probably due to atmospheric influence contributing about 35% of the total CO2 in the soil. An analysis of this contribution using the model of Cerling (1991) indicates that the partial pressure of CO2 in the Early Cretaceous Hasandong atmosphere was about 2300 ppmV.” Yong Il Lee, Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 150, Issues 1-2, 15 June 1999, Pages 123-133, doi:10.1016/S0031-0182(99)00010-3. [Full text]

Do fossil plants signal palaeoatmospheric carbon dioxide concentration in the geological past? – McElwain (1998) “Fossil, subfossil, and herbarium leaves have been shown to provide a morphological signal of the atmospheric carbon dioxide environment in which they developed by means of their stomatal density and index. An inverse relationship between stomatal density/index and atmospheric carbon dioxide concentration has been documented for all the studies to date concerning fossil and subfossil material. Furthermore, this relationship has been demonstrated experimentally by growing plants under elevated and reducedcarbon dioxide concentrations. To date, the mechanism that controls the stomatal density response to atmospheric carbon dioxide concentration remains unknown. However, stomatal parameters of fossil plants have been successfully used as a proxy indicator of palaeo–carbon dioxide levels. This paper presents new estimates of palaeo–atmospheric carbon dioxide concentrations for the Middle Eocene (Lutetian), based on the stomatal ratios of fossil Lauraceae species from Bournemouth in England. Estimates of atmospheric carbon dioxide concentrations derived from stomatal data from plants of the Early Devonian, Late Carboniferous, Early Permian and Middle Jurassic ages are reviewed in the light of new data. Semi–quantitative palaeo–carbon dioxide estimates based on the stomatal ratio (a ratio of the stomatal index of a fossil plant to that of a selected nearest living equivalent) have in the past relied on the use of a Carboniferous standard. The application of a new standard based on the present–day carbon dioxide level is reported here for comparison. The resultant ranges of palaeo–carbon dioxide estimates made from standardized fossil stomatal ratio data are in good agreement with both carbon isotopic data from terrestrial and marine sources and long–term carbon cycle modelling estimates for all the time periods studied. These data indicate elevated atmospheric carbon dioxide concentrations during the Early Devonian, Middle Jurassic and Middle Eocene, and reduced concentrations during the Late Carboniferous and Early Permian. Such data are important in demonstrating the long–term responses of plants to changing carbon dioxide concentrations and in contributing to the database needed for general circulation model climatic analogues.” Phil. Trans. R. Soc. Lond. B 29 January 1998 vol. 353 no. 1365 83-96, doi: 10.1098/rstb.1998.0193. [Full text]

Carbon isotopes in continental weathering environments and variations in ancient atmospheric CO2 pressure – Yapp & Poths (1996) “Abundance and carbon isotope data from an Fe(CO3)OH component in apparent solid solution in oolitic goethites have been used to infer ancient atmospheric CO2 pressures. A test of the validity of these estimates might be comparisons of the carbon isotope compositions of Fe(CO3)OH in oolitic goethites with time-equivalent pedogenic calcites. Temporal trends of the oolitic goethite and pedogenic calcite δ13C values are generally similar, but time-equivalent samples from each of these two groups are not common in the existing data. To facilitate discussion of the concept, comparisons were made of available goethite and calcite samples even though ages of the compared samples in each pair were not identical. In four out of the five comparisons, Fe(CO3)OH abundance and δ13C data were combined with pedogenic calcite δ13C data to calculate physically reasonable soil CO2 concentrations for the ancient calcitic soids. This suggests that the compared oolitic goethite and pedogenic calcite systems were responding to the same global scale phenomenon (i.e., atmospheric CO2). Atmospheric PCO2 as determined from the goethites in these four “well-behaved” cases ranged from values indistinguishable from modern (within analytical uncertainty) to values up to approximately 16 time modern (modern atmospheric PCO2 was taken to be 10−3.5 atm). One interpretation of the fifth, “anomalous”, comparison is that atmospheric CO2 levels increased from about 3 times modern to about 18 times modern from the Triassic into the Early Jurassic. This inferred value for the PCO2 of the Early Jurassic atmosphere is not uniquely constrained by the existing data and needs to be substantiated. However, even considerably lower Early Jurassic atmospheric PCO2 values of 6 to 9 times modern (i.e., 1/3 to 1/2 of the estimated value of 18 times modern) would still indicate significant differences between the global carbon cycles then and now. These results highlight the need for more research on the behavior of the atmosphere during and after the Triassic-Jurassic transition.” Crayton J. Yapp and Harald Poths, Earth and Planetary Science Letters, Volume 137, Issues 1-4, January 1996, Pages 71-82, doi:10.1016/0012-821X(95)00213-V.

Middle to Late Paleozoic Atmospheric CO2 Levels from Soil Carbonate and Organic Matter – Mora et al. (1996) “The stable carbon isotope compositions of ancient soil carbonate and coexisting soil organic matter indicate that atmospheric CO2 levels decreased by a factor of 10 during the middle to late Paleozoic era. Proxy measurements of CO2 were made by application of a soil carbonate CO2 paleobarometer to a suite of paleosols that share key physical and chemical characteristics. The estimates agree with theoretical models that imply that a decrease in Paleozoic atmospheric CO2 levels was associated with afforestation of the land surface by terrestrial plants and with global climate change leading to the extensive Permo-Carboniferous glaciation.” Claudia I. Mora, Steven G. Driese and Lee Ann Colarusso, Science 23 February 1996: Vol. 271 no. 5252 pp. 1105-1107, DOI: 10.1126/science.271.5252.1105.

A 400 million year carbon isotope record of pedogenic carbonate; implications for paleoatomospheric carbon dioxide – Ekart et al. (1995) “A 400 record of atmospheric carbon dioxide levels has been estimated by applying a CO2 paleobarometer to a database of 758 analyses of paleosol (fossil soil) carbonates. This database is a compilation of new data and previously published values from the literature. Many new analyses of Mesozoic paleosols are reported, an era poorly represented in the literature. Results indicate that large fluctuations in atmospheric carbon dioxide levels have occurred over the study interval, ranging from the current level up to ten times the current level. Declining pCO2 levels through the middle Paleozoic culminate in low levels in the Early Permian. An abrupt increase in pCO{sub 2} in the Early Permian is followed by a decrease prior to the Permo-Triassic boundary. Carbon dioxide levels increase through the Triassic to approx. 3,000 ppmV, a level maintained through the Jurassic period. Levels lowered through the Cretaceous, dropping to less than 1,000 ppmV prior to the Cretaceous-Tertiary boundary. Relatively low levels persisted throughout the Cenozoic, with some evidence of higher levels in the Eocene and Oligocene.” Douglas D. Ekart, Thure E. Cerling, Isabel P. Montanez, and Neil J. Tabor, American Journal of Science, Vol. 299, December 1999, P.805-827; doi:10.2475/ajs.299.10.805. [Full text]

Concentration of carbon dioxide in the Late Cretaceous atmosphere – Andrews et al. (1995) “Stable carbon isotope data from Late Cretaceous (Maastrichtian) palaeosols in India are used to estimate the concentration of carbon dioxide in the Late Cretaceous atmosphere. We show that the Maastrichtian atmosphere is unlikely to have contained more than about 1300 ppm by volume of CO2.This value agrees with an independently modeled value of CO2 in the Late Cretaceous atmosphere. A low concentration of the greenhouse gas carbon dioxide in the Maastrichtian atmosphere (relative to concentrations in the earlier Cretaceous) is consistent with palaeotemperature information from terrestrial plant and marine fossils, which suggest that the global climate cooled toward the end of the Cretaceous Period.” Andrews, J.E., Tandon, S.K., and Dennis, P.F. 1995, Journal of the Geological Society, London, v. 152, p. 1-3, DOI: 10.1144/gsjgs.152.1.0001.

Stomatal Density and Index of Fossil Plants Track Atmospheric Carbon Dioxide in the Palaeozoic – McElwain & Chaloner (1995) “It has been demonstrated that the leaves of a range of forest tree species have responded to the rising concentration of atmospheric CO2 over the last 200 years by a decrease in both stomatal density and stomatal index. This response has also been demonstrated experimentally by growing plants under elevated CO2 concentrations. Investigation of Quaternary fossil leaves has shown a corresponding stomatal response to changing CO2 concentrations through a glacial-interglacial cycle, as revealed by ice core data. Tertiary leaves show a similar pattern of stomatal density change, using palynological evidence of palaeo-temperature as a proxy measure of CO2 concentration. The present work extends this approach into the Palaeozoic fossil plant record. The stomatal density and index of Early Devonian, Carboniferous and Early Permian plants has been investigated, to test for any relationship that they may show with the changes in atmospheric CO2 concentration, derived from physical evidence, over that period. Observed changes in the stomatal data give support to the suggestion from physical evidence, that atmospheric CO2 concentrations fell from an Early Devonian high of 10-12 times its present value, to one comparable to that of the present day by the end of the Carboniferous. These results suggest that stomatal density of fossil leaves has potential value for assessing changes in atmospheric CO2 concentration through geological time.” Jennifer C. McElwain and William G. Chaloner, Ann Bot (1995) 76 (4): 389-395, doi: 10.1006/anbo.1995.1112. [Full text]

Palaeoclimate and palaeovegetation in central India during the Upper Cretaceous based on stable isotope composition of the palaeosol carbonates – Ghosh et al. (1995) “The oxygen isotope compositions of the pedogenic carbonates formed on the sediments of the Lameta Formation of Central India during the Upper Cretaceous range from −6.7 to −8.9‰. Estimates of the oxygen isotope composition of the soil-water in equilibrium with the carbonates suggest average meteoric water composition of −8‰. This value is considerably lighter compared to the modern precipitation in Central India (−3‰). The lighter oxygen isotope composition can be explained in terms of cumulative effects of highly seasonal (monsoon-like) climatic regime in a rain shadow zone and a more pronounced “continental effect” due to a bigger size of Cretaceous India. The carbon isotopic compositions of the Lameta carbonates range from −7.1 to −10.7 with an average of −9.1‰ suggesting pedogenesis in soils dominated by C3 type of vegetation. The estimated average composition of the vegetation is about 3‰ enriched compared to the modern day C3 vegetation. This is probably due to atmospheric influence contributing about 15% of the total CO2 in the soil. An analysis of this contribution using the model of Cerling (1991) indicates that the partial pressure of CO2 in the Late Cretaceous atmosphere was 800 – 12,000 ppmV” P. Ghosh, S.K.Bhattacharya and R.A. Jani, Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 114, Issues 2-4, April 1995, Pages 285-296, doi:10.1016/0031-0182(94)00082-J.

New atmospheric pCO2 estimates from palesols during the late Paleocene/early Eocene global warming interval – Sinha & Stott (1994) “The late Paleocene to early Eocene was one of the warmest intervals in Earth’s history. Superimposed on this long-term warming was an abrupt short-term extreme warm event at or near the Paleocene/Eocene boundary and centered in the higher latitudes. This short-term climate warming was associated with a major benthic foraminiferal extinction and a dramatic 3–4% drop in the ocean’s carbon isotopic composition. It has been suggested that the late paleocene/early Eocene global warming was caused by an enhanced greenhouse effect associated with higher levels of atmospheric CO2 relative to present levels. We present carbon isotopic data from the co-existing paleosols organic matter and carbonates from a terrestrial sequence in the Paris Basin, France that contradict the notion that an increase in atmospheric CO2 level was the cause of extreme warming for this time interval. Atmospheric pCO2 estimates for the Late Paleocene/early Eocene estimated from the terrestrial carbon isotopic record spanning the Paleocene/Eocene transition, are indistinguishable from each other and were generally between 300 and 700 ppm.” Ashish Sinha and Lowell D. Stott, Global and Planetary Change, Volume 9, Issues 3-4, December 1994, Pages 297-307, doi:10.1016/0921-8181(94)00010-7.

Paleoatmospheric Signatures in Neogene Fossil Leaves – Van Der Burgh et al. (1993) “An increase in the atmospheric carbon dioxide (CO2) concentration results in a decrease in the number of leaf stomata. This relation is known both from historical observations of vegetation over the past 200 years and from experimental manipulations of microenvironments. Evidence from stomatal frequencies of fossil Quercus petraea leaves indicates that this relation can be applied as a bioindicator for changes in paleoatmospheric CO2 concentrations during the last 10 million years. The data suggest that late Neogene CO2 concentrations fluctuated between about 280 and 370 parts per million by volume.” Johan Van Der Burgh, Henk Visscher, David L. Dilcher and Wolfram M. Kürschner, Science 18 June 1993: Vol. 260 no. 5115 pp. 1788-1790, DOI: 10.1126/science.260.5115.1788.

Fractionation of carbon isotopes by phytoplankton and estimates of ancient CO2 levels – Freeman & Hayes (1992) “Reports of the 13C content of marine particulate organic carbon are compiled and on the basis of GEOSECS data and temperatures, concentrations, and isotopic compositions of dissolved CO2 in the waters in which the related phytoplankton grew are estimated. In this way, the fractionation of carbon isotopes during photosynthetic fixation of CO2 is found to be significantly correlated with concentrations of dissolved CO2. Because ancient carbon isotopic fractionations have been determined from analyses of sedimentary porphyrins [Popp et al., 1989], the relationship between isotopic fractionation and concentrations of dissolved CO2 developed here can be employed to estimate concentrations of CO2 dissolved in ancient oceans and, in turn, partial pressures of CO2 in ancient atmospheres. The calculations take into account the temperature dependence of chemical and isotopic equilibria in the dissolved-inorganic-carbon system and of air-sea equilibria. Paleoenvironmental temperatures for each sample are estimated from re-constructions of paleogeography, latitudinal temper- ature gradients, and secular changes in low-latitude sea surface temperature. It is estimated that atmospheric partial pressures of CO2 were over 1000 μatm 160–100 Ma ago, then declined to values near 300 μatm during the next 100 Ma. Analysis of a high-resolution record of carbon isotopic fractionation at the Cenomanian-Turonian boundary suggests that the partial pressure of CO2 in the atmosphere was drawn down from values near 840 μatm to values near 700 μatm during the anoxic event.” Freeman, K. H., and J. M. Hayes (1992), Global Biogeochem. Cycles, 6(2), 185–198, doi:10.1029/92GB00190.

Correlation between isotope records in marine and continental carbon reservoirs near the Palaeocene/Eocene boundary – Koch et al. (1992) “CHANGES in the isotope content of the large marine carbon reservoir can force shifts in that of the smaller carbon pools in the atmosphere and on land. The carbon isotope compositions of marine carbonate sediments from the late Palaeocene vary considerably, exhibiting a sudden decrease close to the Palaeocene/Eocene boundary which coincides with deep-sea benthic extinctions1 and with changes in ocean circulation. Here we report that these fluctuations in the marine carbon isotope record are closely tracked by the terrestrial records provided by palaeosol carbonates and mammalian tooth enamel. In using palaeosol carbonates to reconstruct the CO2 content of the ancient atmosphere2, isotope shifts of this sort will have to be taken into account. The sharp decrease in 13C/12C ratios in the late Palaeocene provides a datum for precise correlation of marine and continental records, and suggests that abrupt climate warming at this time may have played an important role in the evolution of land mammals.” Paul L. Koch, James C. Zachos & Philip D. Gingerich, Nature 358, 319 – 322 (23 July 1992); doi:10.1038/358319a0. [Full text]

Higher temperatures and lower oceanic pCO2: A climate enigma at the end of the Paleocene Epoch – Stott (1992) “One of the largest and most abrupt climatic warming events documented in the geologic record occurred at the end of the Paleocene epoch. Oceanic deep waters warmed to 10°C, and high-latitude surface waters warmed from ∼10°C to ∼20°C within several thousand years. This coincided with weakened atmospheric circulation and the extinction of ∼50% of deep-sea benthic foraminiferal species. It has been suggested that this warm excursion was forced by higher atmospheric pCO2 and greenhouse effects caused by a pulse of hydrothermal activity and/or volcanism. Stable isotopic evidence is presented from two widely separated locations that suggest this warming was associated with a drop in oceanic pCO2 rather than an increase. Oceanic pCO2 change across this event was estimated using a model of 13C fractionation in photosynthate organic carbon versus [CO2aq], with solubility constants for CO2 and stable isotopic paleotemperature estimates. To derive a well-preserved record for surface ocean δ13C change the organic carbon bound within the calcite lattice of well-preserved planktonic foraminifera was extracted for isotopic analysis. With allowance for uncertainty in the isotopic differences between phytoplankton and foraminiferal organic matter, the initial results indicate a drop in surface ocean pCO2 at high and low latitudes from 600–700 parts per million (ppm) to ∼200 ppm. Lower pCO2 persisted for at least 10,000 years. The duration of the pCO2 excursion was long enough for the ocean and atmosphere to have reached a new steady state condition. There is no evidence of increased organic carbon burial in the deep sea during this period. Two alternative explanations are presented to account for such a rapid drop in oceanic pCO2. One involves reduced upwelling induced by diminished wind stress as atmospheric circulation weakened in response to climate warming. This would have reduced the rate of metabolic CO2 recycling into the surface ocean. It will be necessary to obtain data from regions outside potential upwelling zones in order to evaluate this. The second involves a readjustment of carbonate equilibria in the ocean to higher [CO3=] in the surface ocean, particularly at high latitudes where surface waters warmed to approximately 20°C. Such a shift in carbonate equilibria would have lowered the ocean’s capacity to take in CO2. If the initial results presented here do accurately reflect a change in the global ocean [CO2aq], the Paleocene/Eocene boundary event may provide clues about the ocean’s physical and biological response to rapid, large-scale perturbations in atmospheric pCO2 and to global warming.” Stott, L. D. (1992), Paleoceanography, 7(4), 395–404, doi:10.1029/92PA01183.

Use of carbon isotopes in paleosols as an indicator of the P(CO2) of the paleoatmosphere – Cerling (1992) “Measurements of carbon isotopic composition of coexisting paleosol organic matter and carbonate results in improved estimates of the paleo-P(CO2) content of the paleoatmosphere. Measurements from Tertiary paleosols indicate that the levels of CO2 in the early Eocene, middle and late Miocene, and Pliocene were less than 1000 ppmV. Early Cretaceous levels of P(CO2) were significantly higher, of the order of 1500 to 3000 ppmV.” Cerling, T. E. (1992), Global Biogeochem. Cycles, 6(3), 307–314, doi:10.1029/92GB01102.

Carbon dioxide in the atmosphere; evidence from Cenozoic and Mesozoic Paleosols – Cerling (1991) “A diffusion-reaction model for the isotopic composition of soil CO2 and soil carbonate is evaluated. It shows which variables are important under different conditions and shows that under certain circumstances the carbon isotopic composition of soil carbonate can be used to estimate P(CO2) of the atmosphere from late Paleozoic to the present. The isotopic composition of soil carbonate produced under uniform conditions is essentially constant below about 20 cm in most soils. Today, the isotopic composition of soil organic matter, which is mostly determined by the fraction of C4 biomass present, is the most important factor in determining the carbon isotopic composition of soil carbonate. However, prior to the advent of C4 plants making up a significant fraction of the biomass, probably in the Tertiary, the concentration of CO2 in the atmosphere can be estimated because of mixing of atmospheric CO2 with CO2 produced in the soil. The diffusion-reaction model also suggests that before the advent of higher land plants most soil carbonate should have {delta}13C values between {minus}6.5 and {minus}8.5 permil suggesting that P(CO2) was significantly higher than today, probably on the order of 1,500 to 3,000 ppmV.” Thure E. Cerling, American Journal of Science, Vol. 291, April 1991, P.377-400; doi:10.2475/ajs.291.4.377. [Full text]

Lacustrine carbonates and pedogenesis: sedimentology and origin of palustrine deposits from the Early Cretaceous Rupelo Formation, W Cameros Basin, N Spain – Platt (1989) “The Berriasian Rupelo Formation of the W Cameros Basin consists of a 2–200 m thickness of marginal and open lacustrine carbonate and associated deposits. Open lacustrine facies contain a non-marine biota with abundant charophytes (both stems and gyrogonites), ostracods, gastropods and rare vertebrates. Carbonate production was mainly biogenic. The associated marginal lacustrine (‘palustrine’) facies show strong indications of subaerial exposure and exhibit a wide variety of pedogenic fabrics. Silicified evaporites found near to the top of the sequence reflect a short hypersaline phase in the lake history. The succession was laid down in a low gradient, shallow lake complex characterized by wide fluctuations of the shoreline. Carbon and oxygen stable isotope analyses from the carbonates show non-marine values with ranges of δ13 from − 7 to − 11‰and δ18 from − 3 to − 7.5‰. Differences in the isotopic composition of open lacustrine carbonates are consistent with sedimentary evidence of variation in organic productivity within the lake. Analyses from the entire sample suite plot on a linear trend; isotopic compositions become lighter with increasing evidence of pedogenic modification. This suggests progressive vadose zone diagenesis and influence of meteoric waters rich in soil-derived CO2. The stable isotope data thus support evidence from petrography and facies relations that ‘palustrine’limestones form through pedogenic modification of lake carbonates.” Nigel H. Platt, Sedimentology, Volume 36, Issue 4, pages 665–684, August 1989.

Isotopic imprint of climate and hydrogeochemistry on terrestrial strata of the Triassic-Jurassic Hartford and Fundy rift basins – Suchecki et al. (1988) “Late Triassic to Early Jurassic terrestrial sequences in the Hartford and Fundy rift basins have distinctive carbon and oxygen isotopic compositions of calcite and dolomite. The isotopic data mostly reflect paleoclimatic fluctuations and hydrogeochemistry of the lacustrine, playa, and fluvial environments. Dolomites from laminae in three sequences of playa red mudstones and lacustrine gray to black mudstones in the Hartford basin have variable isotopic compositions (delta 13 C = -5.8 to + 1.8 per thousand PDB; delta 18 O = -7.2 to +0.7 per thousand PDB). Within any single symmetrical cycle of playa red mudstone–lacustrine gray, black, gray mudstone–playa red mudstone, there is a systematic change to relatively enriched 13 C compositions in dolomite in the grayish black and black mudstones in the center of the cycle. These carbon isotopic data suggest that the lacustrine sequences formed as the lakes changed from well mixed with anoxic bottom waters to stratified with anoxic bottom waters where 13 C-depleted carbon was concentrated in organic matter that was then buried. Calcites from lacustrine, micritic, and biomicritic limestones of the Scots Bay Formation of the Fundy basin have stable isotopic compositions (delta 13 C = -4.6 to -2.2 per thousand PDB; delta 18 O = -6.1 to -3.0 per thousand PDB) that become more enriched in 18 O and 13 C upward in shallowing depositional sequences. These isotopic data reflect initial calcite precipitation when a high inflow of fresh water produced high lake levels, followed by progressively lower inflow, resulting in lower lake stands and higher salinity due to continuing evaporative loss of surface water. The lake waters were well oxygenated at all times. In the Hartford basin, caliche calcites in fluvial mudstones and sandstones have isotopic compositions (delta 13 C = -7.3 to -3.8 per thousand PDB; delta 18 O = -8.0 to – 5.6 per thousand PDB) that reflect paleosol processes during climatic conditions that varied from warm and dry in Late Triassic time to relatively cooler and probably wetter in the Early Jurassic. Isotopic compositions of caliche calcites in redbeds in the Fundy basin indicate a parallel climate change from Late Triassic to Early Jurassic time, but also that the climate was relatively hotter and probably drier over the entire interval, as compared to the Hartford basin.” Robert K. Suchecki, John F. Hubert, and Carol C. Birney de Wet, Journal of Sedimentary Research; September 1988; v. 58; no. 5; p. 801-811; DOI: 10.1306/212F8E6D-2B24-11D7-8648000102C1865D.

CLOSELY RELATED

Molecular proxies for paleoclimatology – Eglinton & Eglinton (2008) “We summarize the applications of molecular proxies in paleoclimatology. Marine molecular records especially are proving to be of value but certain environmentally persistent compounds can also be measured in lake sediments, loess deposits and ice cores. The fundamentals of this approach are the molecular parameters, the compound abundances and carbon, hydrogen, nitrogen and oxygen isotopic contents which can be derived by the analysis of sediment extracts. These afford proxy measures which can be interpreted in terms of the conditions which control climate and also reflect its operation. We discuss two types of proxy; those of terrigenous and those of aquatic origin, and exemplify their application in the study of marine sediments through the medium of ten case studies based in the Atlantic, Mediterranean and Pacific Oceans, and in Antarctica. The studies are mainly for periods in the present, the Holocene and particularly the last glacial/interglacial, but they also include one study from the Cretaceous. The terrigenous proxies, which are measures of continental vegetation, are based on higher plant leaf wax compounds, i.e. long-chain (circa C30) hydrocarbons, alcohols and acids. They register the relative contributions of C3 vs. C4 type plants to the vegetation in the source areas. The two marine proxies are measures of sea surface temperatures (SST). The longer established one, (U37K′) is based on the relative abundances of C37 alkenones photosynthesized by unicellular algae, members of the Haptophyta. The newest proxy (TEX86) is based on C86 glycerol tetraethers (GDGTs) synthesized in the water column by some of the archaeal microbiota, the Crenarchaeota.” Timothy I. Eglinton and Geoffrey Eglinton, Earth and Planetary Science Letters, Volume 275, Issues 1-2, 30 October 2008, Pages 1-16, doi:10.1016/j.epsl.2008.07.012. [Full text]

Geocarb III: A Revised Model of Atmospheric CO2 over Phanerozoic Time – Berner & Kothavala (2001) “Revision of the GEOCARB model (Berner, 1991, 1994) for paleolevels of atmospheric CO2, has been made with emphasis on factors affecting CO2 uptake by continental weathering. This includes: (1) new GCM (general circulation model) results for the dependence of global mean surface temperature and runoff on CO2, for both glaciated and non-glaciated periods, coupled with new results for the temperature response to changes in solar radiation; (2) demonstration that values for the weathering-uplift factor fR(t) based on Sr isotopes as was done in GEOCARB II are in general agreement with independent values calculated from the abundance of terrigenous sediments as a measure of global physical erosion rate over Phanerozoic time; (3) more accurate estimates of the timing and the quantitative effects on Ca-Mg silicate weathering of the rise of large vascular plants on the continents during the Devonian; (4) inclusion of the effects of changes in paleogeography alone (constant CO2 and solar radiation) on global mean land surface temperature as it affects the rate of weathering; (5) consideration of the effects of volcanic weathering, both in subduction zones and on the seafloor; (6) use of new data on the 13C values for Phanerozoic limestones and organic matter; (7) consideration of the relative weather- ing enhancement by gymnosperms versus angiosperms; (8) revision of paleo land area based on more recent data and use of this data, along with GCM-based paleo-runoff results, to calculate global water discharge from the continents over time. Results show a similar overall pattern to those for GEOCARB II: very high CO2 values during the early Paleozoic, a large drop during the Devonian and Carbonifer- ous, high values during the early Mesozoic, and a gradual decrease from about 170 Ma to low values during the Cenozoic. However, the new results exhibit considerably higher CO2 values during the Mesozoic, and their downward trend with time agrees with the independent estimates of Ekart and others (1999). Sensitivity analysis shows that results for paleo-CO2 are especially sensitive to: the effects of CO2 fertilization and temperature on the acceleration of plant-mediated chemical weathering; the quantitative effects of plants on mineral dissolution rate for constant temperature and CO2; the relative roles of angiosperms and gymnosperms in accelerating rock weather- ing; and the response of paleo-temperature to the global climate model used. This emphasizes the need for further study of the role of plants in chemical weathering and the application of GCMs to study of paleo-CO2 and the long term carbon cycle.” Robert A. Berner and Zavareth Kothavala, American Journal of Science, Vol. 301, February 2001, P.182-204; doi:10.2475/ajs.301.2.182. [Full text]

Posted in AGW evidence, Climate science | 4 Comments »

New research from last week 26/2011

Posted by Ari Jokimäki on July 4, 2011

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as they are published. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. Here’s the archive for the news of previous weeks. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news. Planet 3.0 also reports new research.

Published last week:

Sun can’t explain temperature change since 1985

Solar activity – climate relations: A different approach – Stauning (2011) “The presentation of solar activity-climate relations is extended with the most recent sunspot and global temperature data series. The extension of data series shows clearly that the changes in terrestrial temperatures are related to sources different from solar activity after ~1985. Based on analyses of data series for the years 1850–1985 it is demonstrated that, apart from an interval of positive deviation followed by a similar negative excursion in Earth’s temperatures between ~1923 and 1965, there is a strong correlation between solar activity and terrestrial temperatures delayed by 3 years, which complies with basic causality principles. A regression analysis between solar activity represented by the cycle-average sunspot number, SSNA, and global temperature anomalies, ΔTA, averaged over the same interval lengths, but delayed by 3 years, provides the relation ΔTA=0.009 (±.002) SSNA. Since the largest ever observed SSNA is ~90 (in 1954–1965), the solar activity-related changes in global temperatures could amounts to no more than ±0.4 °C over the past ~400 years where the sunspots have been recorded. It is demonstrated that the small amplitudes of cyclic variations in the average global temperatures over the ~11 year solar cycle excludes many of the various driver processes suggested in published and frequently quoted solar activity-climate relations. It is suggested that the in-cycle variations and also the longer term variations in global temperatures over the examined 135 years are mainly caused by corresponding changes in the total solar irradiance level representing the energy output from the core, but further modulated by varying energy transmission properties in the active outer regions of the Sun.” P. Stauning, Journal of Atmospheric and Solar-Terrestrial Physics, doi:10.1016/j.jastp.2011.06.011.

Recent Antarctic sea ice increase might be measurement system artifact

Sudden increase in Antarctic sea ice: Fact or artifact? – Screen (2011) “Three sea ice data sets commonly used for climate research display a large and abrupt increase in Antarctic sea ice area (SIA) in recent years. This unprecedented change of SIA is diagnosed to be primarily caused by an apparent sudden increase in sea ice concentrations within the ice pack, especially in the area of the most-concentrated ice (greater than 95% concentration). A series of alternative satellite-derived records do not display any abnormal sudden SIA changes, but do reveal substantial discrepancies between different satellite sensors and sea ice algorithms. Sea ice concentrations in the central ice pack and SIA values derived from the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSRE) are consistently greater than those derived from the Special Sensor Microwave Imager (SSMI). A switch in source data from the SSMI to AMSRE in mid-2009 explains most of the SIA increase in all three affected data sets. If uncorrected for, the discontinuity artificially exaggerates the winter Antarctic SIA increase (1979–2010) by more than a factor of 2 and the spring trend by almost a factor of 4. The discontinuity has a weaker influence on the summer and autumn SIA trends, on calculations of Antarctic sea ice extent, and in the Arctic.” Screen, J. A. (2011), Geophys. Res. Lett., 38, L13702, doi:10.1029/2011GL047553.

Highest melt in 4200 years for Canadian Arctic ice caps

Recent melt rates of Canadian Arctic ice caps are the highest in four millennia – Fisher et al. (2011) “There has been a rapid acceleration in ice-cap melt rates over the last few decades across the entire Canadian Arctic. Present melt rates exceed the past rates for many millennia. New shallow cores at old sites bring their melt series up-to-date. The melt-percentage series from the Devon Island and Agassiz (Ellesmere Island) ice caps are well correlated with the Devon net mass balance and show a large increase in melt since the middle 1990s. Arctic ice core melt series (latitude range of 67 to 81 N) show the last quarter century has seen the highest melt in two millennia and The Holocene-long Agassiz melt record shows the last 25 years has the highest melt in 4200 years. The Agassiz melt rates since the middle 1990s resemble those of the early Holocene thermal maximum over 9000 years ago.” David Fisher, James Zheng, David Burgess, Christian Zdanowicz, Christophe Kinnard, Martin Sharp and Jocelyne Bourgeois, Global and Planetary Change, doi:10.1016/j.gloplacha.2011.06.005.

Cold surges are threatening wildlife in warmer climate

Different characteristics of cold day and cold surge frequency over East Asia in a global warming situation – Park et al. (2011) “This study investigates the changes in winter cold extreme events over East Asia in the present and future climates. Two distinct terms to indicate cold extreme events are analyzed: “cold day,” which describes a temperature below a certain threshold value (e.g., simply cold weather), and “cold surge,” which describes an abrupt temperature drop (e.g., relatively colder weather than a previous day). We analyze both observations and long-term climate simulations from 13 atmospheric and oceanic coupled global climate models (CGCMs). The geographical distribution of sea level pressure corresponding to a cold day (cold surge) is represented by a dipole (wave train) feature. Although cold day and cold surge show similar patterns of surface air temperature, they are induced by the out-of-phase sea level pressures. From the results of our analysis of a series of future projections for the mid and late twenty-first century using the 13 CGCMs, cold day occurrences clearly decrease with an increasing mean temperature (a correlation coefficient of −0.49), but the correlation between cold surge occurrences and the mean temperature is insignificant (a correlation coefficient of 0.08), which is supported by the same results in recent observation periods (1980–2006). Thus, it is anticipated that cold surge occurrences will remain frequent even in future warmer climate. This deduction is based on the future projections in which the change in the day-to-day temperature variability is insignificant, although the mean temperature shows significant increase. The present results suggest that living things in the future, having acclimatized to a warmer climate, would suffer the strong impact of cold surges, and hence the issue of vulnerability to cold surges should be treated seriously in the future.” Park, T.-W., C.-H. Ho, S.-J. Jeong, Y.-S. Choi, S. K. Park, and C.-K. Song (2011), J. Geophys. Res., 116, D12118, doi:10.1029/2010JD015369.

New radiosonde analysis shows troposphere warming

A quantification of uncertainties in historical tropical tropospheric temperature trends from radiosondes – Thorne et al. (2011) “The consistency of tropical tropospheric temperature trends with climate model expectations remains contentious. A key limitation is that the uncertainties in observations from radiosondes are both substantial and poorly constrained. We present a thorough uncertainty analysis of radiosonde-based temperature records. This uses an automated homogenization procedure and a previously developed set of complex error models where the answer is known a priori. We perform a number of homogenization experiments in which error models are used to provide uncertainty estimates of real-world trends. These estimates are relatively insensitive to a variety of processing choices. Over 1979–2003, the satellite-equivalent tropical lower tropospheric temperature trend has likely (5–95% confidence range) been between −0.01 K/decade and 0.19 K/decade (0.05–0.23 K/decade over 1958–2003) with a best estimate of 0.08 K/decade (0.14 K/decade). This range includes both available satellite data sets and estimates from models (based upon scaling their tropical amplification behavior by observed surface trends). On an individual pressure level basis, agreement between models, theory, and observations within the troposphere is uncertain over 1979 to 2003 and nonexistent above 300 hPa. Analysis of 1958–2003, however, shows consistent model-data agreement in tropical lapse rate trends at all levels up to the tropical tropopause, so the disagreement in the more recent period is not necessarily evidence of a general problem in simulating long-term global warming. Other possible reasons for the discrepancy since 1979 are: observational errors beyond those accounted for here, end-point effects, inadequate decadal variability in model lapse rates, or neglected climate forcings.” Thorne, P. W., et al. (2011), J. Geophys. Res., 116, D12116, doi:10.1029/2010JD015487.

World’s dry areas have increased and it’s going to get worse

Characteristics and trends in various forms of the Palmer Drought Severity Index during 1900–2008 – Dai (2011) “The Palmer Drought Severity Index (PDSI) has been widely used to study aridity changes in modern and past climates. Efforts to address its major problems have led to new variants of the PDSI, such as the self-calibrating PDSI (sc_PDSI) and PDSI using improved formulations for potential evapotranspiration (PE), such as the Penman-Monteith equation (PE_pm) instead of the Thornthwaite equation (PE_th). Here I compare and evaluate four forms of the PDSI, namely, the PDSI with PE_th (PDSI_th) and PE_pm (PDSI_pm) and the sc_PDSI with PE_th (sc_PDSI_th) and PE_pm (sc_PDSI_pm) calculated using available climate data from 1850 to 2008. Our results confirm previous findings that the choice of the PE only has small effects on both the PDSI and sc_PDSI for the 20th century climate, and the self-calibration reduces the value range slightly and makes the sc_PDSI more comparable spatially than the original PDSI. However, the histograms of the sc_PDSI are still non-Gaussian at many locations, and all four forms of the PDSI show similar correlations with observed monthly soil moisture (r = 0.4–0.8) in North America and Eurasia, with historical yearly streamflow data (r = 0.4–0.9) over most of the world’s largest river basins, and with GRACE (Gravity Recovery and Climate Experiment) satellite-observed water storage changes (r = 0.4–0.8) over most land areas. All the four forms of the PDSI show widespread drying over Africa, East and South Asia, and other areas from 1950 to 2008, and most of this drying is due to recent warming. The global percentage of dry areas has increased by about 1.74% (of global land area) per decade from 1950 to 2008. The use of the Penman-Monteith PE and self-calibrating PDSI only slightly reduces the drying trend seen in the original PDSI. The percentages of dry and wet areas over the global land area and six select regions are anticorrelated (r = −0.5 to −0.7), but their long-term trends during the 20th century do not cancel each other, with the trend for the dry area often predominating over that for the wet area, resulting in upward trends during the 20th century for the areas under extreme (i.e., dry or wet) conditions for the global land as a whole (∼1.27% per decade) and the United States, western Europe, Australia, Sahel, East Asia, and southern Africa. The recent drying trends are qualitatively consistent with other analyses and model predictions, which suggest more severe drying in the coming decades.” Dai, A. (2011), J. Geophys. Res., 116, D12115, doi:10.1029/2010JD015541.

Clouds don’t just cool

Cloud effect of persistent stratus nebulosus at the Payerne BSRN site – Wacker et al. (2011) “This analysis presents radiative transfer calculations of surface downwelling long-wave and short-wave radiation and the corresponding cloud radiative effect of single-layered, completely overcast stratus situations (stratus nebulosus) at the Baseline Surface Radiation Network (BSRN) site Payerne. We found an excellent agreement of 0.6 Wm–2 mean difference between modeled and observed downwelling long-wave radiation with a root mean squared error of 1.5 Wm–2 for 30 carefully selected cases. The discrepancies between modeled and observed diffuse downwelling short-wave radiation are with 2.8 ± 25.4 Wm–2 considerably higher. The net cloud radiative effect of the 30 cases shows a pronounced diurnal variation determined by the diurnal cycle of the short-wave cloud effect and the nearly constant positive long-wave cloud effect. Mean net cloud effect ranges from 80 ± 3 Wm–2 (min.: 75 Wm–2; max.: 85 Wm–2) during nighttime in the absence of solar radiation to − 197 ± 74 Wm–2 (min.: -373 Wm–2; max.: -91 Wm–2) around noon. Mean net cloud effect averaged over 24 hours is 18 ± 20 Wm–2 (min.: -28 Wm–2; max.: + 42 Wm–2) for the 30 casesassuming a persistent, completely overcast stratus cloud. This implies that stratus nebulosus can have a substantial positive radiative effect during the winter half year at this site.” S. Wacker, J. Gröbner, D. Nowak, L. Vuilleumier and N. Kämpfer, Atmospheric Research, doi:10.1016/j.atmosres.2011.06.007.

Measurements of ocean acidification in Japan

Ocean acidification off the south coast of Japan: A result from time series observations of CO2 parameters from 1994 to 2008 – Ishii et al. (2011) “Ocean acidification resulting from increases in present and future atmospheric CO2 levels could seriously affect diverse coastal and oceanic ecosystems. In this work, we determine that a significant trend in ocean acidification is superposed on the large seasonal and interannual variabilities of acidity in surface waters off the south coast of Honshu, Japan, based on our repeated observations of partial pressure of CO2 (pCO2), total inorganic carbon (TCO2), and pH. Multiple regression analysis of TCO2 as a function of temperature, salinity, and timing of observations shows that TCO2 increased at a rate of +1.23 ± 0.40 μmol kg−1 yr−1 for the period 1994–2008, while no long-term change has been determined for total alkalinity calculated from TCO2 and pCO2 in seawater. These results indicate that pH and the aragonite saturation state (Ωarag) are decreasing at a rate of −0.020 ± 0.007 decade−1 and −0.12 ± 0.05 decade−1, respectively. If future atmospheric CO2 levels keep increasing as predicted by the Intergovernmental Panel on Climate Change emission scenario A1FI, which postulates intensive fossil fuel use associated with very rapid economic growth, a further reduction of −0.8 to −1.0 in Ωarag is likely in the next 50 years. Such a rapid reduction of Ωarag could have negative impacts on a variety of calcareous organisms.” Ishii, M., N. Kosugi, D. Sasano, S. Saito, T. Midorikawa, and H. Y. Inoue (2011), J. Geophys. Res., 116, C06022, doi:10.1029/2010JC006831.

Vertical distribution of cloud feedback

The vertical distribution of cloud feedback in coupled ocean-atmosphere models – Soden & Vecchi (2011) “We assess the vertical distribution of cloud feedbacks in coupled climate models, taking care to distinguish between cloud feedbacks and a change in cloud forcing. We show that the effect of cloud changes on the longwave fluxes provides a strong positive feedback that is broadly consistent across models. In contrast, the effect of cloud changes on the shortwave fluxes ranges from a modest negative to a strong positive feedback, and is responsible for most of the intermodel spread in net cloud feedback. The feedback from high clouds is positive in all models, and is consistent with that anticipated by the Proportionately Higher Anvil Temperature hypothesis over the tropics. In contrast, low cloud cover is responsible for roughly three-quarters of the difference in global mean net cloud feedback among models, with the largest contributions from regions associated with low-level subtropical marine cloud systems.” Soden, B. J., and G. A. Vecchi (2011), Geophys. Res. Lett., 38, L12704, doi:10.1029/2011GL047632. [Full text]

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