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Archive for January, 2012

New research from last week 4/2012

Posted by Ari Jokimäki on January 30, 2012

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.

It’s hair-raising time for European hares. Forest soils are all wet and emitting methane. Some of those hares might think there’s nothing to worry because tree-rings prove that Medieval times were warmer in northern Scandinavia. Hares in United States have to deal with extreme warmth being more frequent. Southeast Asian bats are suffering from climate change so they won’t be bothering the hares so much anymore, but what will hares do with those damn squirrels that keep getting bigger?

Things in atmosphere are shifting polewards which means there will be less rain in subtropics. So perhaps hares in Europe get all wet if subtropic rains travel there. By the way, Antractic ozone recovery also might affect rain little bit but the hares don’t care.

Radiocarbon gradient between hemispheres is increasing but generally radiocarbon changes in the atmosphere suggest that some of that fossil carbon is being released to the atmosphere. Perhaps the hares are digging out so much fossils.

Photo: Tiina Oinas


Analysis of European parapatric hares and climate change

Parapatric species and the implications for climate change studies: a case study on hares in Europe – Acevedo et al. (2012)

Abstract: “Parapatry is a biogeographic term used to refer to organisms whose ranges do not overlap but are immediately adjacent to each other; they only co-occur – if at all – in a narrow contact zone. Often there are no environmental barriers in the contact zones, hence competitive interaction is usually advocated as the factor that modulates species distribution ranges. Even though the effects of climate change on species distribution have been widely studied, few studies have explored these effects on the biogeographical relationships between closely related, parapatric, species. We modelled environmental favourability for three parapatric hare species in Europe – Lepus granatensis, L. europaeus and L. timidus – using ecogeographical variables and projected the models into the future according to the IPCC A2 emissions scenario. Favourabilities for present and future scenarios were combined using fuzzy logic with the following aims: i) to determine the biogeographical relationships between hare species in parapatry, that is L. granatensis/L. europaeus and L. europaeus/L. timidus; and ii) to assess the effects of climate change on each species as well as on their interspecific interactions. In their contact area L. granatensis achieved higher favourability values than L. europaeus, suggesting that if both species have a similar population status, the former species may have some advantages over the latter if competitive relationships are established. Climate change had the most striking effect on the distribution of L. timidus, especially when interspecific interactions with L. europaeus were taken into account, which may compromise the co-existence of L. timidus. The results of this study are relevant not only for understanding the distribution patterns of the hares studied and the effects of climate change on these patterns, but also for improving the general application of species distribution models to the prediction of the effects of climate change on biodiversity.”

Citation: Pelayo Acevedo, Alberto Jiménez-Valverde, José Melo-Ferreira, Raimundo Real, Paulo Célio Alves, Global Change Biology, DOI: 10.1111/j.1365-2486.2012.02655.x.


Wet forest soils are important source for methane in Europe

Towards improved bottom-up inventories of methane from the European land surface – Grunwald et al. (2012)

Abstract: “Forests and wetlands are generally seen as opposites in the methane cycle of terrestrial ecosystems. Wetlands are sources for atmospheric methane and forest soils sinks. However, this greenhouse gas is also emitted by wet forest soils, which is commonly disregarded due to lacking information on their spatial distribution. Here, we estimated the potential bias made for the European methane budget of terrestrial ecosystems when neglecting wet forest ecosystems but including rice paddies and latest estimates for lakes. We appointed distinct annual methane rates for individual land use types based on a literature survey and weighted them according to their European area. This was performed separately for four major ecozones (cold, temperate, continental and Mediterranean). Three approaches were applied to test the bias of wet forest estimates: (1) the mean values for forests and wetlands were calculated in three different scenarios, (2) assuming that boreal needle-leaved evergreen forest with a low tree cover (< 40%) is predominately forested wetland (3) assuming different shares of wet forest ecosystems in individual forest areas. For the net balance 2.8 Tg CH4-C a−1 were calculated which includes emissions from rice paddies (0.2 Tg CH4-C a−1) and from lakes (2.5 Tg CH4-C a−1). The different approaches for the net balances that included wet forest ecosystems mainly ranged between 4.6 and 6.7 Tg CH4-C a−1. The results suggest that wet forest ecosystems are approximately as important as wetlands for the European methane balance. European bottom-up inventories are improved best by more accurate mapping of wetlands both within and outside forests and more flux data for lakes and continental wetlands.”

Citation: Dennis Grunwald, Ann-Catrin Fender, Stefan Erasmi, Hermann F. Jungkunst, Atmospheric Environment, http://dx.doi.org/10.1016/j.atmosenv.2012.01.025.


Extreme summer temperatures more common in United States due to greenhouse gases

Increasing prevalence of extreme summer temperatures in the U.S. – Duffy & Tebaldi (2012)

Abstract: “Human-caused climate change can affect weather and climate extremes, as well as mean climate properties. Analysis of observations and climate model results shows that previously rare (5th percentile) summertime average temperatures are presently occurring with greatly increased frequency in some regions of the 48 contiguous United States. Broad agreement between observations and a mean of results based upon 16 global climate models suggests that this result is more consistent with the consequences of increasing greenhouse gas concentrations than with the effects of natural climate variability. This conclusion is further supported by a statistical analysis based on resampling of observations and model output. The same climate models project that the prevalence of previously extreme summer temperatures will continue to increase, occurring in well over 50% of summers by mid-century.”

Citation: P. B. Duffy and C. Tebaldi, Climatic Change, DOI: 10.1007/s10584-012-0396-6.


Possible Antarctic ozone recovery is expected to cause changes in light precipitation

Impact of Antarctic ozone depletion and recovery on Southern Hemisphere precipitation, evaporation and extreme changes – Purich & Son (2012) [FULL TEXT]

Abstract: “The possible impact of Antarctic ozone depletion and recovery on Southern Hemisphere (SH) mean and extreme precipitation and evaporation is examined using multimodel output from the Climate Model Intercomparison Project 3 (CMIP3). By grouping models into four sets, those with and without ozone depletion in 20th century climate simulations and those with and without ozone recovery in 21st century climate simulations, and comparing their multimodel-mean trends, it is shown that Antarctic ozone forcings significantly modulate extratropical precipitation changes in austral summer. The impact on evaporation trends is however, minimal especially in 20th century climate simulations. In general, ozone depletion has increased precipitation in high-latitudes and decreased it in mid-latitudes, in agreement with the poleward displacement of the westerly jet and associated storm tracks by Antarctic ozone depletion. Although weaker, the opposite is also true for ozone recovery. These precipitation changes are primarily associated with changes in light precipitation (1–10 mm/day). Contributions by very-light precipitation (0.1-1 mm/day) and moderate-to-heavy precipitation (>10 mm/day) are minor. Likewise, no systematic changes are found in extreme precipitation events, although extreme surface wind events are highly sensitive to ozone forcings. This result indicates that, while extratropical mean precipitation trends are significantly modulated by ozone-induced large-scale circulation changes, extreme precipitation changes are likely more sensitive to thermodynamic processes near the surface than to dynamical processes in the free atmosphere.”

Citation: Ariaan Purich and Seok-Woo Son, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-11-00383.1.


Precipitation expected to decline in subtropics due to poleward shifts

21st-century multi-model subtropical precipitation declines are mostly mid-latitude shifts – Scheff & Frierson (2012) [FULL TEXT]

Abstract: “Declines in subtropical precipitation are a robust response to modeled 21st century global warming. Two suggested mechanisms are the “dry-get-drier” intensification of existing subtropical dry zones due to the thermodynamic increase in vapor transport, and the poleward expansion of these same dry zones due to poleward shifts in the modeled general circulation. Here, subtropical drying in the IPCC Fourth Assessment Report multi-model archive is compared to each of these two mechanisms. Each model’s particular, biased, seasonally and zonally varying mean state is considered relative to the location of that model’s predicted changes, and these relationships are recorded in a common framework that can be compared across models. The models have a strong tendency to reduce precipitation along the subtropical flanks of their existing mid-latitude cyclonic precipitation belts. This broad result agrees with the poleward-expansion mechanism, and with a poleward storm-track shift in particular. In contrast, the models have no clear tendency to reduce precipitation in the central nor equatorward portions of their subtropical dry zones, implying that the thermodynamic mechanism is broadly unimportant for the precipitation reductions. This is unlike the response of precipitation minus evaporation, which robustly declines in large portions of these regions, especially over the oceans. The models also tend to increase precipitation in their wet deep-tropical areas, but this is not as robust as the above reduction in the subtropical mid-latitudes. High-latitude precipitation increases are the most robust precipitation changes of all in this framework.”

Citation: Jack Scheff and Dargan Frierson, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-11-00393.1.


Tree ring reconstruction shows Roman and Medieval warm periods warmer than present in northern Scandinavia

Variability and extremes of northern Scandinavian summer temperatures over the past two millennia – Esper et al. (2012)

Abstract: “Palaeoclimatic evidence revealed synchronous temperature variations among Northern Hemisphere regions over the past millennium. The range of these variations (in degrees Celsius) is, however, largely unknown. We here present a 2000-year summer temperature reconstruction from northern Scandinavia and compare this timeseries with existing proxy records to assess the range of reconstructed temperatures at a regional scale. The new reconstruction is based on 578 maximum latewood density profiles from living and sub-fossil Pinus sylvestris samples from northern Sweden and Finland. The record provides evidence for substantial warmth during Roman and Medieval times, larger in extent and longer in duration than 20th century warmth. The first century AD was the warmest 100-year period (+ 0.60 °C on average relative to the 1951–1980 mean) of the Common Era, more than 1 °C warmer than the coldest 14th century AD (− 0.51 °C). The warmest and coldest reconstructed 30-year periods (AD 21–50 = + 1.05 °C, and AD 1451–80 = − 1.19 °C) differ by more than 2 °C, and the range between the five warmest and coldest reconstructed summers in the context of the past 2000 years is estimated to exceed 5 °C. Comparison of the new timeseries with five existing tree-ring based reconstructions from northern Scandinavia revealed synchronized climate fluctuations but substantially different absolute temperatures. Level offset among the various reconstructions in extremely cold and warm years (up to 3 °C) and cold and warm 30-year periods (up to 1.5 °C) are in the order of the total temperature variance of each individual reconstruction over the past 1500 to 2000 years. These findings demonstrate our poor understanding of the absolute temperature variance in a region where high-resolution proxy coverage is denser than in any other area of the world.”

Citation: Jan Esper, Ulf Büntgen, Mauri Timonen, David C. Frank, Global and Planetary Change, http://dx.doi.org/10.1016/j.gloplacha.2012.01.006.


Hemispheric shift in atmospheric radiocarbon

Observations of radiocarbon in CO2 at seven global sampling sites in the Scripps flask network: Analysis of spatial gradients and seasonal cycles – Graven et al. (2012)

Abstract: “High precision measurements of Δ14C were conducted for monthly samples of CO2 from seven global stations over 2- to 16-year periods ending in 2007. Mean Δ14C over 2005–07 in the Northern Hemisphere was 5 ‰ lower than Δ14C in the Southern Hemisphere, similar to recent observations from I. Levin. This is a significant shift from 1988–89 when Δ14C in the Northern Hemisphere was slightly higher than the South. The influence of fossil fuel CO2 emission and transport was simulated for each of the observation sites by the TM3 atmospheric transport model and compared to other models that participated in the Transcom 3 Experiment. The simulated interhemispheric gradient caused by fossil fuel CO2 emissions was nearly the same in both 1988–89 and 2005–07, due to compensating effects from rising emissions and decreasing sensitivity of Δ14C to fossil fuel CO2. The observed 5 ‰ shift must therefore have been caused by non-fossil influences, most likely due to changes in the air-sea 14C flux in the Southern Ocean. Seasonal cycles with higher Δ14C in summer or fall were evident at most stations, with largest amplitudes observed at Point Barrow (71°N) and La Jolla (32°N). Fossil fuel emissions do not account for the seasonal cycles of Δ14C in either hemisphere, indicating strong contributions from non-fossil influences, most likely from stratosphere-troposphere exchange.”

Citation: Graven, H. D., T. P. Guilderson, and R. F. Keeling (2012), Observations of radiocarbon in CO2 at seven global sampling sites in the Scripps flask network: Analysis of spatial gradients and seasonal cycles, J. Geophys. Res., 117, D02303, doi:10.1029/2011JD016535.


Fossil fuel emissions are the strongest contributor to atmospheric radiocarbon trends

Observations of radiocarbon in CO2 at La Jolla, California, USA 1992–2007: Analysis of the long-term trend – Graven et al. (2012)

Abstract: “High precision measurements of Δ14C were performed on CO2 sampled at La Jolla, California, USA over 1992–2007. A decreasing trend in Δ14C was observed, which averaged −5.5 ‰ yr−1 yet showed significant interannual variability. Contributions to the trend in global tropospheric Δ14C by exchanges with the ocean, terrestrial biosphere and stratosphere, by natural and anthropogenic 14C production and by 14C-free fossil fuel CO2 emissions were estimated using simple models. Dilution by fossil fuel emissions made the strongest contribution to the Δ14C trend while oceanic 14C uptake showed the most significant change between 1992 and 2007, weakening by 70%. Relatively steady positive influences from the stratosphere, terrestrial biosphere and 14C production moderated the decreasing trend. The most prominent excursion from the average trend occurred when Δ14C decreased rapidly in 2000. The rapid decline in Δ14C was concurrent with a rapid decline in atmospheric O2, suggesting a possible cause may be the anomalous ventilation of deep 14C-poor water in the North Pacific Ocean. We additionally find the presence of a 28-month period of oscillation in the Δ14C record at La Jolla.”

Citation: Graven, H. D., T. P. Guilderson, and R. F. Keeling (2012), Observations of radiocarbon in CO2 at La Jolla, California, USA 1992–2007: Analysis of the long-term trend, J. Geophys. Res., 117, D02302, doi:10.1029/2011JD016533.


Majority of South Asian bat species face range decreases and extinction risk with climate change

The projected effects of climatic and vegetation changes on the distribution and diversity of Southeast Asian bats – Hughes et al. (2012)

Abstract: “Southeast-Asia (SEA) constitutes a global biodiversity hotspot, but is exposed to extensive deforestation and faces numerous threats to its biodiversity. Climate change represents a major challenge to the survival and viability of species, and the potential consequences must be assessed to allow for mitigation. We project the effects of several climate change scenarios on bat diversity, and predict changes in range-size for 171 bat species throughout SEA. We predict decreases in species richness in all areas with high species richness (>80 species) at 2050-2080, using bioclimatic IPCC scenarios A2 (a severe scenario, continuously increasing human population size, regional changes in economic growth) and B1 (the ‘greenest’ scenario, global population peaking mid-century). We also predicted changes in species richness in scenarios that project vegetation changes in addition to climate change up to 2050. At 2050 and 2080, A2 and B1 scenarios incorporating changes in climatic factors predicted that 3-9% species would lose all currently suitable niche space. When considering total extents of species distribution in SEA (including possible range expansions), 2-6% of species may have no suitable niche space in 2050-2080. When potential vegetation and climate changes were combined only 1% of species showed no changes in their predicted ranges by 2050. Although some species are projected to expand ranges, this may be ecologically impossible due to potential barriers to dispersal, especially for species with poor dispersal ability. Only 1-13% of species showed no projected reductions in their current range under bioclimatic scenarios. An effective way to facilitate range shift for dispersal-limited species is to improve landscape connectivity. If current trends in environmental change continue and species cannot expand their ranges into new areas, then the majority of bat species in SEA may show decreases in range size and increased extinction risk within the next century.”

Citation: Alice C. Hughes, Chutamas Satasook, Paul J.J. Bates, Sara Bumrungsri, Gareth Jones, Global Change Biology, DOI: 10.1111/j.1365-2486.2012.02641.x.


Look out, squirrels are getting bigger!

Size Increase in High Elevation Ground Squirrels over the Last Century – Eastman et al. (2012)

Abstract: “There is increasing evidence for morphological change in response to 20th century environmental change, but how this relates to fluctuations in geographic range is unclear. We measured museum specimens from two time periods (1902-1950 and 2000-2008) that vary significantly in climate to assess if and how two high elevation contracting species of ground squirrels in the Sierra Nevada of California, Belding’s ground squirrel (Urocitellus beldingi) and the golden-mantled ground squirrel (Callospermophilus lateralis), and one lower elevation, stable species, the California ground squirrel (Otospermophilus beecheyi), have responded morphologically to changes in California over the last century. We measured skull length (condylobasal length), an ontogenetically more labile trait, and maxillary toothrow length (MTRL), a more developmentally constrained trait. C. lateralis and U. beldingi, both obligate hibernators, have increased in body size but have not changed in body shape. In contrast, O. beecheyi, which only hibernates in parts of its range, has shown no significant change in either morphometric trait. The increase in body size in the higher elevation species, presumably a plastic effect due to a longer growing season and thus prolonged food availability, opposes the expected direction of selection for decreased body size under chronic warming. We hypothesize that population contraction is related to physiological rather than nutritional constraints.”

Citation: Lindsey M. Eastman, Toni Lyn Morelli, Kevin C. Rowe, Chris J. Conroy, Craig Moritz, Global Change Biology, DOI: 10.1111/j.1365-2486.2012.02644.x.

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New research from last week 3/2012

Posted by Ari Jokimäki on January 23, 2012

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.

Q: Are Parisian air-conditioners making things all nice and cool or warming up the place? A: Warming up the place. Q: What is it that was travestically missing but has been found now? A: Energy. Q: What is the hypothesis that is constantly debunked by numerous peer-reviewed studies and gets yet another blow this week? A: Cosmic ray-climate connection. Q: As just about anything seems to affect North-Atlantic/Europe weather, does Indian summer monsoon do it too? A: Yes. Q: What is slowly increasing tropical Pacific east-west temperature gradient? A: Global warming. Q: What Alaskan treeline trees do when climate warms? A: Anything they feel like doing. Q: What lives longer if days get warmer but doesn’t if only nights get warmer? A: Root. Q: How do you explain carbon dioxide increase during last glacial termination? A: With salt, of course. Q: What keeps AMOC running? A: Mountains.

We also have studies on orbital control of carbon cycle, positive low-level cloud feedback, different kinds of cloud feedbacks, tropical glaciers, global sea level, electromagnetic imaging of permafrost, 1988 land uptake of carbon, temperature control over tropical tropopause water vapor and clouds, and Canadian lake plankton.


Past climate recording tropical glaciers are melting away

Tropical glaciers, recorders and indicators of climate change, are disappearing globally – Thompson et al. (2012) [FULL TEXT]

Abstract: “In this paper we review the interaction of El Niño Southern Oscillation (ENSO) variability and warming trends recorded in ice-core records from high-altitude tropical glaciers, discuss the implications of the warming trends for the glaciers and consider the societal implications of glacier retreat. ENSO has strong impacts on meteorological phenomena that directly or indirectly affect most regions on the planet and their populations. Many tropical ice fields have provided continuous annually resolved proxy records of climatic and environmental variability preserved in measurable parameters, especially oxygen and hydrogen isotopic ratios (δ18O, δD) and the net mass balance (accumulation). These records present an opportunity to examine the nature of tropical climate variability in greater detail and to extract new information on linkages between rising temperatures on tropical glaciers and equatorial Pacific sea surface temperatures in critical ENSO indicator regions. The long-term climate records from a collection of high-altitude tropical ice cores provide the longer-term context essential for assessing the significance of the magnitude and rate of current climate changes that are in large measure driving glacier retreat. The well-documented ice loss on Quelccaya in the Peruvian Andes, Naimona’nyi in the Himalaya, Kilimanjaro in eastern Africa and the ice fields near Puncak Jaya in Papua, Indonesia, presents a grim future for low-latitude glaciers. The ongoing melting of these ice fields (response) is consistent with model predictions for a vertical amplification of temperature in the tropics (driver) and has serious implications for the people who live in these areas.”

Citation: Thompson, Lonnie G.; Mosley-Thompson, Ellen; Davis, Mary E.; Brecher, Henry H., Annals of Glaciology, Volume 52, Number 59, December 2011 , pp. 23-34(12).


Global sea level budget since 1850

The historical global sea-level budget – Moore et al. (2012) [FULL TEXT]

Abstract: “We analyze the global sea-level budget since 1850. Good estimates of sea-level contributions from glaciers and small ice caps, the Greenland ice sheet and thermosteric sea level are available over this period, though considerable scope for controversy remains in all. Attempting to close the sea-level budget by adding the components results in a residual displaying a likely significant trend of 0.37 mm a-1 from 1955 to 2005, which can, however, be reasonably closed using estimated melting from unsurveyed high-latitude small glaciers and ice caps. The sea-level budget from 1850 is estimated using modeled thermosteric sea level and inferences from a small number of mountain glaciers. This longer-term budget has a residual component that displays a rising trend likely associated with the end of the Little Ice Age, with much decadal-scale variability that is probably associated with variability in the global water cycle, ENSO and long-term volcanic impacts.”

Citation: Moore, J.C.; Jevrejeva, S.; Grinsted, A., Annals of Glaciology, Volume 52, Number 59, December 2011 , pp. 8-14(7).


Explaining carbon dioxide increase during last glacial termination

Impact of oceanic processes on the carbon cycle during the last termination – Bouttes et al. (2012) [FULL TEXT]

Abstract: “During the last termination (from ~18 000 years ago to ~9000 years ago), the climate significantly warmed and the ice sheets melted. Simultaneously, atmospheric CO2 increased from ~190 ppm to ~260 ppm. Although this CO2 rise plays an important role in the deglacial warming, the reasons for its evolution are difficult to explain. Only box models have been used to run transient simulations of this carbon cycle transition, but by forcing the model with data constrained scenarios of the evolution of temperature, sea level, sea ice, NADW formation, Southern Ocean vertical mixing and biological carbon pump. More complex models (including GCMs) have investigated some of these mechanisms but they have only been used to try and explain LGM versus present day steady-state climates. In this study we use a coupled climate-carbon model of intermediate complexity to explore the role of three oceanic processes in transient simulations: the sinking of brines, stratification-dependent diffusion and iron fertilization. Carbonate compensation is accounted for in these simulations. We show that neither iron fertilization nor the sinking of brines alone can account for the evolution of CO2, and that only the combination of the sinking of brines and interactive diffusion can simultaneously simulate the increase in deep Southern Ocean δ13C. The scenario that agrees best with the data takes into account all mechanisms and favours a rapid cessation of the sinking of brines around 18 000 years ago, when the Antarctic ice sheet extent was at its maximum. In this scenario, we make the hypothesis that sea ice formation was then shifted to the open ocean where the salty water is quickly mixed with fresher water, which prevents deep sinking of salty water and therefore breaks down the deep stratification and releases carbon from the abyss. Based on this scenario, it is possible to simulate both the amplitude and timing of the long-term CO2increase during the last termination in agreement with ice core data. The atmospheric δ13C appears to be highly sensitive to changes in the terrestrial biosphere, underlining the need to better constrain the vegetation evolution during the termination.”

Citation: Bouttes, N., Paillard, D., Roche, D. M., Waelbroeck, C., Kageyama, M., Lourantou, A., Michel, E., and Bopp, L.: Impact of oceanic processes on the carbon cycle during the last termination, Clim. Past, 8, 149-170, doi:10.5194/cp-8-149-2012, 2012.


Possible link between orbital forcing and carbon cycle also under mid-Cretaceous greenhouse conditions

Orbital control on carbon cycle and oceanography in the mid-Cretaceous greenhouse – Giorgioni et al. (2012)

Abstract: “We established a new high-resolution carbonate carbon isotope record of the Albian interval of the Marne a Fucoidi Formation (Central Apennines, Italy), which was deposited on the southern margin of the western Tethys Ocean. Bulk carbonate sampled with 10–15 cm spacing was used for the construction of a continuous carbon isotope curve through the Albian stage. Spectral analyses reveal prominent 400 kyr cyclicity in the δ13C curve, which correlates with Milankovitch long eccentricity changes. Cycles occurring in our record resemble those observed in several Cenozoic δ13C records, suggesting that a link between orbital forcing and carbon cycling existed also under mid-Cretaceous greenhouse conditions. Based on comparisons with Cenozoic eccentricity-carbon cycle links we hypothesize that 400 kyr cycles in the mid-Cretaceous were related to a fluctuating monsoonal regime, coupled with an unstable oceanic structure, which made the oceanic carbon reservoir sensitive to orbital variations. In the Tethys these oceanographic conditions lasted until the Late Albian, and then were replaced by a more stable circulation mode, less sensitive to orbital forcing.”

Citation: Giorgioni, M., H. Weissert, S. M. Bernasconi, P. A. Hochuli, R. Coccioni, and C. E. Keller (2012), Orbital control on carbon cycle and oceanography in the mid-Cretaceous greenhouse, Paleoceanography, 27, PA1204, doi:10.1029/2011PA002163.


Mountain ranges have strong role in maintaining Atlantic Meridional Overturning Circulation

Mountain ranges favour vigorous Atlantic meridional overturning – Sinha et al. (2012)

Abstract: “We use a global Ocean-Atmosphere General Circulation Model (OAGCM) to show that the major mountain ranges of the world have a significant role in maintenance of the Atlantic Meridional Overturning Circulation (AMOC). A simulation with mountains has a maximum AMOC of 18 Sv (1 Sv = 106 m3 s-1) compared with ∼0 Sv for a simulation without mountains. Atlantic heat transport at 25°N is 1.1 PW with mountains compared to 0.2 PW without. The difference in AMOC is due to major changes in surface heat and freshwater (FW) fluxes over the Atlantic. In the Pacific changed surface fluxes lead to a meridional overturning circulation of 10 Sv. Our results suggest that the effects of mountains on the large-scale atmospheric circulation is to force the ocean towards a state with a vigorous AMOC and with no overturning in the Pacific.”

Citation: Sinha, B., A. T. Blaker, J. J.-M. Hirschi, S. Bonham, M. Brand, S. Josey, R. S. Smith, and J. Marotzke (2012), Mountain ranges favour vigorous Atlantic meridional overturning, Geophys. Res. Lett., 39, L02705, doi:10.1029/2011GL050485.


Why is there positive feedback from low level clouds in climate models?

Interpretation of the positive low-cloud feedback predicted by a climate model under global warming – Brient & Bony (2012) [FULL TEXT]

Abstract: “The response of low-level clouds to climate change has been identified as a major contributor to the uncertainty in climate sensitivity estimates among climate models. By analyzing the behaviour of low-level clouds in a hierarchy of models (coupled ocean-atmosphere model, atmospheric general circulation model, aqua-planet model, single-column model) using the same physical parameterizations, this study proposes an interpretation of the strong positive low-cloud feedback predicted by the IPSL-CM5A climate model under climate change. In a warmer climate, the model predicts an enhanced clear-sky radiative cooling, stronger surface turbulent fluxes, a deepening and a drying of the planetary boundary layer, and a decrease of tropical low-clouds in regimes of weak subsidence. We show that the decrease of low-level clouds critically depends on the change in the vertical advection of moist static energy from the free troposphere to the boundary-layer. This change is dominated by variations in the vertical gradient of moist static energy between the surface and the free troposphere just above the boundary-layer. In a warmer climate, the thermodynamical relationship of Clausius-Clapeyron increases this vertical gradient, and then the import by large-scale subsidence of low moist static energy and dry air into the boundary layer. This results in a decrease of the low-level cloudiness and in a weakening of the radiative cooling of the boundary layer by low-level clouds. The energetic framework proposed in this study might help to interpret inter-model differences in low-cloud feedbacks under climate change.”

Citation: Florent Brient and Sandrine Bony, Climate Dynamics, DOI: 10.1007/s00382-011-1279-7.


No link between cosmic rays/sun and MODIS cloud anomalies

A decade of the Moderate Resolution Imaging Spectroradiometer: is a solar – cloud link detectable? – Laken et al. (2012)

Abstract: “Based on the results of decadal correlation studies between International Satellite Cloud Climatology Project detected cloud anomalies and the galactic cosmic ray (GCR) flux it has been suggested that a relationship exists between solar activity and cloud cover. If valid, such a relationship could have important implications for our understanding of recent climate change. In this work, we present an analysis of the first decade of MODerate Resolution Imaging Spectroradiometer (MODIS) detected cloud anomalies, and compare the data at global and local geographical resolutions to Total Solar Irradiance (TSI), GCR variations and the Multivariate El Niño Southern Oscillation Index. We identify no statistically significant correlations between cloud anomalies and TSI/GCR variations, and conclude that solar related variability is not a primary driver of monthly to annual MODIS cloud variability. We observe a net increase in cloud detected by MODIS over the past decade of ~0.58 %, arising from a combination of a reduction in high – middle level cloud (−0.31 %) and an increase in low level cloud (of 0.89%); these long term changes may be largely attributed to ENSO induced cloud variability.”

Citation: Benjamin Laken, Enric Pallé, and Hiroko Miyahara, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-11-00306.1.


Electromagnetic imaging of permafrost down to 100m depths

Airborne electromagnetic imaging of discontinuous permafrost – Minsley et al. (2012)

Abstract: “The evolution of permafrost in cold regions is inextricably connected to hydrogeologic processes, climate, and ecosystems. Permafrost thawing has been linked to changes in wetland and lake areas, alteration of the groundwater contribution to streamflow, carbon release, and increased fire frequency. But detailed knowledge about the dynamic state of permafrost in relation to surface and groundwater systems remains an enigma. Here, we present the results of a pioneering ∼1,800 line-kilometer airborne electromagnetic survey that shows sediments deposited over the past ∼4 million years and the configuration of permafrost to depths of ∼100 meters in the Yukon Flats area near Fort Yukon, Alaska. The Yukon Flats is near the boundary between continuous permafrost to the north and discontinuous permafrost to the south, making it an important location for examining permafrost dynamics. Our results not only provide a detailed snapshot of the present-day configuration of permafrost, but they also expose previously unseen details about potential surface – groundwater connections and the thermal legacy of surface water features that has been recorded in the permafrost over the past ∼1,000 years. This work will be a critical baseline for future permafrost studies aimed at exploring the connections between hydrogeologic, climatic, and ecological processes, and has significant implications for the stewardship of Arctic environments.”

Citation: Minsley, B. J., et al. (2012), Airborne electromagnetic imaging of discontinuous permafrost, Geophys. Res. Lett., 39, L02503, doi:10.1029/2011GL050079.


New analysis of different kinds of cloud feedbacks

Computing and Partitioning Cloud Feedbacks using Cloud Property Histograms. Part I: Cloud Radiative Kernels – Zelinka et al. (2012) [FULL TEXT, PRESENTATION MATERIAL]

Abstract: “We propose a novel technique for computing cloud feedbacks using histograms of cloud fraction as a joint function of cloud top pressure (CTP) and optical depth (τ). These histograms were generated by the International Satellite Cloud Climatology Project (ISCCP) simulator that was incorporated into doubled CO2 simulations from eleven global climate models in the Cloud Feedback Model Intercomparison Project. We use a radiative transfer model to compute top of atmosphere flux sensitivities to cloud fraction perturbations in each bin of the histogram for each month and latitude. Multiplying these cloud radiative kernels with histograms of modeled cloud fraction changes at each grid point per unit of global warming produces an estimate of cloud feedback. Spatial structures and globally integrated cloud feedbacks computed in this manner agree remarkably well with the adjusted change in cloud radiative forcing. The global and annual mean model-simulated cloud feedback is dominated by contributions from medium thickness (3.6 ≤ τ < 23) cloud changes, but thick (τ ≥ 23) cloud changes cause the rapid transition of cloud feedback values from positive in midlatitudes to negative poleward of 50°S and 70°N. High (CTP < 440 hPa) cloud changes are the dominant contributor to LW cloud feedback, but because their LW and SW impacts are in opposition, they contribute less to the net cloud feedback than do the positive contributions from low (CTP ≥ 680 hPa) cloud changes. Mid-level (440 ≤ CTP < 680 hPa) cloud changes cause positive SW cloud feedbacks that are 80% as large as those due to low clouds. Finally, high cloud changes induce wider ranges of LW and SW cloud feedbacks across models than do low clouds.”

Part 2 of this paper was published earlier.

Citation: Mark D. Zelinka, Stephen A. Klein, Dennis L. Hartmann, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-11-00248.1.


Missing energy was not missing after all

Observed changes in top-of-the-atmosphere radiation and upper-ocean heating consistent within uncertainty – Loeb et al. (2012)

Abstract: “Global climate change results from a small yet persistent imbalance between the amount of sunlight absorbed by Earth and the thermal radiation emitted back to space. An apparent inconsistency has been diagnosed between interannual variations in the net radiation imbalance inferred from satellite measurements and upper-ocean heating rate from in situ measurements, and this inconsistency has been interpreted as ‘missing energy’ in the system. Here we present a revised analysis of net radiation at the top of the atmosphere from satellite data, and we estimate ocean heat content, based on three independent sources. We find that the difference between the heat balance at the top of the atmosphere and upper-ocean heat content change is not statistically significant when accounting for observational uncertainties in ocean measurements, given transitions in instrumentation and sampling. Furthermore, variability in Earth’s energy imbalance relating to El Niño-Southern Oscillation is found to be consistent within observational uncertainties among the satellite measurements, a reanalysis model simulation and one of the ocean heat content records. We combine satellite data with ocean measurements to depths of 1,800 m, and show that between January 2001 and December 2010, Earth has been steadily accumulating energy at a rate of 0.50±0.43 Wm−2 (uncertainties at the 90% confidence level). We conclude that energy storage is continuing to increase in the sub-surface ocean.”

Citation: Norman G. Loeb, John M. Lyman, Gregory C. Johnson, Richard P. Allan, David R. Doelling, Takmeng Wong, Brian J. Soden & Graeme L. Stephens, Nature Geoscience. doi:10.1038/ngeo1375.


Day warming increases root lifespan, night warming doesn’t

Day and night warming have different effect on root lifespan – Bai et al. (2012) [FULL TEXT]

Abstract: “Roots are key components of C cycling in terrestrial ecosystems and play an important role in the regulation of response of terrestrial ecosystems to global climate warming, which is predicted to occur with greater warming magnitudes at night than during daytime across different regions on the Earth. However, there has been no detailed study to investigate the effect of asymmetrical warming on root dynamics at the level of terrestrial ecosystems. To understand the effects of day and night warming on root lifespan in the semiarid temperate steppe in northern China, a field study with a full factorial design including control, day warming, night warming and continuous warming was conducted using modified rhizotron technique during three growing seasons in 2007–2009. Our results show that day, night and continuous warming had different effects on longevity of roots born in spring, summer and autumn, and that day warming significantly prolonged overall lifespan for the roots born in the three growing seasons, while night warning had no effect on overall lifespan. Day and night warming had different effects on root non-structural carbohydrate content, suggesting that allocation of photoassimilate may account for the differential responses of root lifespan to day and night warming. These results differ from other processes associated with ecosystems C cycle such as total ecosystem productivity, net ecosystem productivity and soil respiration. Our findings highlight that it is essential to incorporate the differential effects of day and night warming on root dynamics into simulating and predicting the responses and feedbacks of terrestrial ecosystems C cycling to global warming.”

Citation: Bai, W. M., Xia, J. Y., Wan, S. Q., Zhang, W. H., and Li, L. H.: Day and night warming have different effect on root lifespan, Biogeosciences, 9, 375-384, doi:10.5194/bg-9-375-2012, 2012.


Abrupt increase in the land uptake of carbon in 1988

Identification and characterization of abrupt changes in the land uptake of carbon – Beaulieu et al. (2012)

Abstract: “A recent study of the net land carbon sink estimated using the Mauna Loa, Hawaii atmospheric CO2 record, fossil fuel estimates, and a suite of ocean models suggests that the mean of the net land carbon uptake remained approximately constant for three decades and increased after 1988/1989. Due to the large variability in the net land uptake, it is not possible to determine the exact timing and nature of the increase robustly by visual inspection. Here, we develop a general methodology to objectively determine the nature and timing of the shift in the net land uptake based on the Schwarz Information Criterion. We confirm that it is likely that an abrupt shift in the mean net land carbon uptake occurred in 1988. After taking into account the variability in the net land uptake due to the influence of volcanic aerosols and the El Niño Southern Oscillation, we find that it is most likely that there is a remaining step increase at the same time (p-values of 0.01 and 0.04 for Mauna Loa and South Pole, respectively) of about 1 Pg C/yr. Thus, we conclude that neither the effect of volcanic eruptions nor the El Niño Southern Oscillation are the causes of the sudden increase of the land carbon sink. By also applying our methodology to the atmospheric growth rate of CO2, we demonstrate that it is likely that the atmospheric growth rate of CO2 exhibits a step decrease between two fitted lines in 1988–1989, which is most likely due to the shift in the net land uptake of carbon.”

Citation: Beaulieu, C., J. L. Sarmiento, S. E. Mikaloff Fletcher, J. Chen, and D. Medvigy (2012), Identification and characterization of abrupt changes in the land uptake of carbon, Global Biogeochem. Cycles, 26, GB1007, doi:10.1029/2010GB004024.


Complex response of Alaskan trees to warming

Do limiting factors at Alaskan treelines shift with climatic regimes? – Ohse et al. (2012) [FULL TEXT]

Abstract: “Trees at Alaskan treelines are assumed to be limited by temperature and to expand upslope and/or to higher latitudes with global warming. However, recent studies describe negative temperature responses and drought stress of Alaskan treeline trees in recent decades. In this study, we have analyzed the responses of treeline white spruce to temperature and precipitation according to different climatic regimes in Alaska, described as negative (cool) and positive (warm) phases of the Pacific Decadal Oscillation (PDO). We found that in three consecutive phases (positive from 1925–46, negative from 1947–76, and positive again from 1977–98), the growth responses to temperature and precipitation differed markedly. Before 1947, in a phase of warm winters and with summer temperatures being close to the century mean, the trees at most sites responded positively to summer temperature, as one would expect from treeline trees at northern high latitudes. Between 1947 and 1976, a phase of cold winters and average summers, the trees showed similar responses, but a new pattern of negative responses to the summer temperature of the year prior to growth coupled with positive responses to the precipitation in the same year emerged at some sites. As the precipitation was relatively low at those sites, we assume that drought stress might have played a role. However, the climate responses were not uniform but were modified by regional gradients (trees at northern sites responded more often to temperature than trees at southern sites) and local site conditions (forest trees responded more often to precipitation than treeline trees), possibly reflecting differences in energy and water balance across regions and sites, respectively. However, since the shift in the PDO in 1976 from a negative to a positive phase, the trees’ climate–growth responses are much less pronounced and climate seems to have lost its importance as a limiting factor for the growth of treeline white spruce. If predictions of continued warming and precipitation increase at northern high latitudes hold true, the growth of Alaskan treeline trees will likely depend on the ratio of temperature and precipitation increase more than on their absolute values, as well as on the interaction of periodic regime shifts with the global warming trend. Once a climatic limitation is lifted, other factors, such as insect outbreaks or interspecific competition, might become limiting to tree growth.”

Citation: B Ohse et al 2012 Environ. Res. Lett. 7 015505 doi:10.1088/1748-9326/7/1/015505.


Indian summer monsoon might have an effect to North Atlantic-Europe climate

Indian summer monsoon influence on the climate in the North Atlantic–European region – Lin & Wu (2012)

Abstract: “Previous studies have shown that climate anomalies over the North Atlantic–Europe (NAE) can influence the Indian summer monsoon (ISM) variability. It is, however, still an outstanding question whether the latter has a significant impact on the former. In this study, observational evidences indicate that the interannual variability of ISM is closely linked to the climate anomalies over NAE. A strong ISM is often associated with significant above normal precipitation over most of western Europe. Meanwhile, positive surface air temperature (SAT) anomalies are usually observed over the Mediterranean, accompanied by below normal SAT in Western Europe during a strong ISM summer. The situation is just opposite during a weak ISM summer. A global primitive equation model is utilized to assess the mechanism of the above observed connection.”

Citation: Hai Lin and Zhiwei Wu, Climate Dynamics, DOI: 10.1007/s00382-011-1286-8.


Possible regional detection of global warming in tropical Pacific

Is a global warming signature emerging in the tropical Pacific? – Ashok et al. (2012)

Abstract: “The tropical pacific experienced a hitherto-unseen anomalous basinwide warming from May 2009 through April 2010 with the maximum warming to the east of the dateline, but for a weak anomalous cooling west of 140°E after early boreal fall. Our observed analysis and model experiments isolate the potential teleconnections from TP during the summer of 2009. Further, we show through an empirical orthogonal function analysis of the tropical Pacific SSTA that the anomalous conditions in TP during this period could have manifested as a canonical El Niño, but for a slowly intensifying background west–east gradient. This zonal SST gradient is subject to an increasing trend associated with global warming. A possible implication is that any further increase in global warming may result in more basinwide warm events in place of canonical El Niños, along with the occurrence of more intense La Niñas and El Niño Modokis.”

Citation: Ashok, K., T. P. Sabin, P. Swapna, and R. G. Murtugudde (2012), Is a global warming signature emerging in the tropical Pacific?, Geophys. Res. Lett., 39, L02701, doi:10.1029/2011GL050232.


Quantification of the effect of air-conditioning on Paris temperatures

How much can air conditioning increase air temperatures for a city like Paris, France? – de Munck et al. (2012)

Abstract: “A consequence of urban heat islands in summer is an increase in the use of air conditioning in urbanized areas, which while cooling the insides of buildings, releases waste heat to the atmosphere. A coupled model consisting of a meso-scale meteorological model (MESO-NH) and an urban energy balance model (TEB) has been used to simulate and quantify the potential impacts on street temperature of four air conditioning scenarios at the scale of Paris. The first case consists of simulating the current types of systems in the city and was based on inventories of dry and evaporative cooling towers and free cooling systems with the river Seine. The other three scenarios were chosen to test the impacts of likely trends in air conditioning equipment in the city: one for which all evaporative and free cooling systems were replaced by dry systems, and the other two designed on a future doubling of the overall air conditioning power but with different technologies. The comparison between the scenarios with heat releases in the street and the baseline case without air conditioning showed a systematic increase in the street air temperature, and this increase was greater at nighttime than day time. It is counter-intuitive because the heat releases are higher during the day. This is due to the shallower atmospheric boundary layer during the night. The increase in temperature was 0.5 °C in the situation with current heat releases, 1 °C with current releases converted to only sensible heat, and 2 °C for the future doubling of air conditioning waste heat released to air. These results demonstrated to what extent the use of air conditioning could enhance street air temperatures at the scale of a city like Paris, and the importance of a spatialized approach for a reasoned planning for future deployment of air conditioning in the city.”

Citation: Cécile de Munck, Grégoire Pigeon, Valéry Masson, Francis Meunier, Pierre Bousquet, Brice Tréméac, Michèle Merchat, Pierre Poeuf, Colette Marchadier, International Journal of Climatology, DOI: 10.1002/joc.3415.


Measurements of temperature controlling water and cirrus clouds at tropical tropopause

Correlation among cirrus ice content, water vapor and temperature in the TTL as observed by CALIPSO and Aura/MLS – Flury et al. (2012) [FULL TEXT]

Abstract: “Water vapor in the tropical tropopause layer (TTL) has a local radiative cooling effect. As a source for ice in cirrus clouds, however, it can also indirectly produce infrared heating. Using NASA A-Train satellite measurements of CALIPSO and Aura/MLS we calculated the correlation of water vapor, ice water content and temperature in the TTL. We find that temperature strongly controls water vapor (correlation r=0.94) and cirrus clouds at 100 hPa (r=−0.9). Moreover we observe that the cirrus seasonal cycle is highly (r=−0.9) anticorrelated with the water vapor variation in the TTL, showing higher cloud occurrence during December-January-February. We further investigate the anticorrelation on a regional scale and find that the strong anticorrelation occurs generally in the ITCZ (Intertropical Convergence Zone). The seasonal cycle of the cirrus ice water content is also highly anticorrelated to water vapor (r=−0.91) and our results support the hypothesis that the total water at 100 hPa is roughly constant. Temperature acts as a main regulator for balancing the partition between water vapor and cirrus clouds. Thus, to a large extent, the depleting water vapor in the TTL during DJF is a manifestation of cirrus formation.”

Citation: Flury, T., Wu, D. L., and Read, W. G.: Correlation among cirrus ice content, water vapor and temperature in the TTL as observed by CALIPSO and Aura/MLS, Atmos. Chem. Phys., 12, 683-691, doi:10.5194/acp-12-683-2012, 2012.


Last century lake sediments in Canada show planktonic shift that is unique during Holocene

Using paleolimnology to track Holocene climate fluctuations and aquatic ontogeny in poorly buffered High Arctic lakes – Rouillard et al. (2012)

Abstract: “Fossil diatom assemblages, and spectrally-inferred dissolved organic carbon (DOC) and sedimentary chlorophyll-a (SedChla) were analysed on lake sediment cores from two poorly buffered lakes on Pim Island (High Arctic Canada) to assess their responses to Holocene climate changes and to document lake ontogeny. Following deglaciation, diatom assemblages were dominated by small benthic Fragilaria sensu lato taxa. During the mid-Holocene there was an abrupt shift to more circumneutral and slightly acidophilous taxa dominated by Achnanthes and Navicula taxa. The most recent sediments, we recorded an increase in the planktonic taxon Cyclotella radiosa. This shift of the last century is the most ecologically unique in the Holocene record and is indicative of longer ice-free summers consistent with modern climate warming. Inferred DOC and SedChla track some of the main Holocene climatic trends documented in the region, including the Holocene Thermal Maximum and Neoglacial period; however, changes in lakewater in DOC did not likely drive any of the recorded shifts in diatom assemblages. Compared to nearby well buffered sites, our poorly buffered lakes recorded a more dynamic diatom response to Holocene environmental change. The decreasing trend in diatom inferred pH is likely due to changes in the acid neutralizing capacity (ANC) driven by the release of alkalinizing base cations from the easily weathered glacial deposits in the early Holocene and later by climate-driven pH dynamics and within-lake dissolved inorganic carbon (DIC) dynamics. The diatom community composition in our study lakes is different and undergoes greater changes than in nearby well buffered lakes suggesting that softwater lakes in the high Arctic may respond most sensitively to climate and other environmental stressors.”

Citation: Alexandra Rouillard, Neal Michelutti, Peter Rosén, Marianne S.V. Douglas, John P. Smol, Palaeogeography, Palaeoclimatology, Palaeoecology, http://dx.doi.org/10.1016/j.palaeo.2012.01.011.


CLASSIC OF THE WEEK: Chamberlin (1906)

On a Possible Reversal of Deep-Sea Circulation and Its Influence on Geologic Climates – Chamberlin (1906) [FULL TEXT AVAILABLE IN ABSTRACT PAGE]

Abstract: No abstract.

Citation: T. C. Chamberlin, The Journal of Geology, Vol. 14, No. 5, Jul. – Aug.

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New research from last week 2/2012

Posted by Ari Jokimäki on January 16, 2012

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.

In this week’s papers global warming is cancelled. Couple of studies almost make it look like northern hemisphere hasn’t warmed at all. Antarctic snowmelt hasn’t increased either, and mass loss of Svalbard glaciers is at least slowing down. One study does see a GHG effect but there still might be less warming than usually is projected. On the other hand, only modest warming does some nasty things to tropical insects and arachnids, and even without warming, ocean acidification is going to cost us billions and billions of dollars (I’m glad that Euro is our currency here in Finland).

Looking at other papers this week, I bet you wouldn’t like to swim in Paleozoic tropical oceans. Scientists have done fancy tricks with Greenland ice core to reveal secrets of an old volcanic eruption. Lord Kelvin seems to be still doing science. Deforestation appears at least in some sense to be cool. We also have studies on sea level rise of southern Europe coast, North-Atlantic warming, Holocene abrupt climate changes, oceanic freshwater fluxes, and South Asia warming distribution.


Deforestation induces large increases in cold event frequency and intensity in South-America

Simulated links between deforestation and extreme cold events in South America – Medvigy et al. (2012)

Abstract: “Many modeling studies have indicated that deforestation will increase the average annual temperature in the Amazon. However, few studies have investigated the potential for deforestation to change the frequency and intensity of extreme events. This problem is addressed here using a variable-resolution GCM. The characteristic length scale (CLS) of the model’s grid mesh over South America is 25 km, comparable to that used by limited-area models. For computational efficiency, the CLS increases to 200 km over the rest of the world. It is found that deforestation induces large changes in the frequency of wintertime extreme cold events. Large increases in cold event frequency and intensity occur in the western Amazon and, surprisingly, in parts of southern South America, far from the actual deforested area. One possible mechanism for these remote effects involves changes in the position of the subtropical jet, caused by temperature changes in the Amazon. Increased understanding of these potential changes in extreme events will be important for local agriculture, natural ecosystems, and the human population.”

Citation: David Medvigy, Robert L. Walko, and Roni Avissar, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-11-00259.1.


Oceanic freshwater flux changes tend to amplify rather than suppress the global warming

Can oceanic freshwater flux amplify global warming? – Zhang & Wu (2012)

Abstract: “The roles of freshwater flux (defined as evaporation minus precipitation) changes in global warming are studied using simulations of a climate model in which the freshwater flux changes are suppressed in the presence of a doubling of CO2 concentration. The model simulations demonstrate that the warm climate leads to an acceleration of global water cycle which causes freshening in the high latitudes and salinification in the subtropics and midlatitudes. It is found that the freshwater flux changes tend to amplify rather than suppress the global warming. Over the global scale, this amplification is largely associated with high latitude freshening in a warm climate, which leads to a shoaling of the mixed layer depth, weakening of vertical mixing and thus a trapping of CO2-induced warming in the surface ocean. The latitudinal distribution of SST changes due to the effects of freshwater flux changes in a warm climate is complicated, which involves anomalous advection induced by both salinity and wind stress changes. In addition, atmospheric feedbacks associated with global warming also amplify the SST warming.”

Citation: Liping Zhang and Lixin Wu, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-11-00172.1.


Many causes of North Atlantic mid 1990′s rapid warming

Causes of the Rapid Warming of the North Atlantic ocean in the mid 1990s – Robson et al. (2012)

Abstract: “In the mid-1990s the subpolar gyre of the North Atlantic underwent a remarkable rapid warming, with sea surface temperatures increasing by around 1C in just 2 years. This rapid warming followed a prolonged positive phase of the North Atlantic Oscillation (NAO), but also coincided with an unusually negative NAO index in the winter of 1995/96. By comparing ocean analyses and carefully designed model experiments we show that this rapid warming can be understood as a delayed response to the prolonged positive phase of the NAO, and not simply an instantaneous response to the negative NAO index of 1995/96. Furthermore, we infer that the warming was partly caused by a surge, and subsequent decline, in the Meridional Overturning Circulation and northward heat transport of the Atlantic Ocean. Our results provide persuasive evidence of significant oceanic memory on multi-annual timescales, and are therefore encouraging for the prospects of developing skillful predictions.”

Citation: Jon Robson, Rowan Sutton, Katja Lohmann, Doug Smith and Matthew D. Palmer, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-11-00443.1.


Using Lord Kelvin’s measurements to determine smoke emissions in 1859

Smoke emissions from industrial western Scotland in 1859 inferred from Lord Kelvin’s atmospheric electricity measurements – Aplin (2012)

Abstract: “Lord Kelvin (William Thomson) made careful, calibrated measurements of the atmospheric Potential Gradient (PG) at three sites on the east side of Arran in 1859. The PG was always anomalously high in easterly and north-easterly winds. Positive space charge from sea spray may have contributed to the high PG at two coastal sites, but measurements made on Goatfell, inland and 100-175 m above sea level are unlikely to have been affected by spray. Instead, pollution from the Scottish mainland seems the more likely cause of the high PG at Goatfell, which varied from 300 to 1000 Vm−1 on 10th-11th October 1859, corresponding to smoke levels from 0.2 to 0.8 mgm−3. Gaussian plume calculations, based on the atmospheric conditions described by Lord Kelvin, and constrained by early Glaswegian pollution measurements, indicate a substantial source region located on the Scottish mainland, 20-40 km from Arran, emitting between 10-104 kgs−1.”

Citation: K.L. Aplin, Atmospheric Environment, http://dx.doi.org/10.1016/j.atmosenv.2011.12.053.


Tropical ectotherms are heading for catastrophe even with modest predicted warming

Degrees of disruption: projected temperature increase has catastrophic consequences for reproduction in a tropical ectotherm – Zeh et al. (2012)

Abstract: “Although climate change models predict relatively modest increases in temperature in the tropics by the end of the century, recent analyses identify tropical ectotherms as the organisms most at risk from climate warming. Because metabolic rate in ectotherms increases exponentially with temperature, even a small rise in temperature poses a physiological threat to tropical ectotherms inhabiting an already hot environment. If correct, the metabolic theory of climate warming has profound implications for global biodiversity, since tropical insects and arachnids constitute the vast majority of animal species. Predicting how climate change will translate into fitness consequences for tropical arthropods requires an understanding of the effects of temperature increase on the entire life history of the species. Here, in a comprehensive case study of the fitness consequences of the projected temperature increase for the tropics, we conducted a split-brood experiment on the neotropical pseudoscorpion, Cordylochernes scorpioides, in which 792 offspring from 33 females were randomly assigned at birth to control- and high-temperature treatments for rearing through the adult stage. The diurnally-varying, control-treatment temperature was determined from long-term, average daily temperature minima and maxima in the pseudoscorpion’s native habitat. In the high-temperature treatment, increasing temperature by the 3.5 °C predicted for the tropics significantly reduced survival and accelerated development at the cost of reduced adult size and a dramatic decrease in level of sexual dimorphism. The most striking effects, however, involved reproductive traits. Reared at high temperature, males produced 45% as many sperm as control males, and females failed to reproduce. Sequencing of the mitochondrial ND2 gene revealed two highly divergent haplogroups that differed substantially in developmental rate and survivorship but not in reproductive response to high temperature. Our findings suggest that reproduction may be the Achilles’ heel of tropical ectotherms, as climate warming subjects them to an increasingly adverse thermal environment.”

Citation: Jeanne A. Zeh, Melvin M. Bonilla, Eleanor J. Su, Michael V. Padua, Rachel V. Anderson, Dilpreet Kaur, Dou-Shuan Yang, David W. Zeh, Global Change Biology, DOI: 10.1111/j.1365-2486.2012.02640.x.


Global warming has increased Eurasian snow cover which cools boreal winters

Arctic warming, increasing snow cover and widespread boreal winter cooling – Cohen et al. (2012) [FULL TEXT]

Abstract: “The most up to date consensus from global climate models predicts warming in the Northern Hemisphere (NH) high latitudes to middle latitudes during boreal winter. However, recent trends in observed NH winter surface temperatures diverge from these projections. For the last two decades, large-scale cooling trends have existed instead across large stretches of eastern North America and northern Eurasia. We argue that this unforeseen trend is probably not due to internal variability alone. Instead, evidence suggests that summer and autumn warming trends are concurrent with increases in high-latitude moisture and an increase in Eurasian snow cover, which dynamically induces large-scale wintertime cooling. Understanding this counterintuitive response to radiative warming of the climate system has the potential for improving climate predictions at seasonal and longer timescales.”

Citation: Judah L Cohen et al 2012 Environ. Res. Lett. 7 014007 doi:10.1088/1748-9326/7/1/014007.


Increased cloud cover has slowed summer warming in Eurasia

Damped summer warming accompanied with cloud cover increase over Eurasia from 1982 to 2009 – Tang & Leng (2012) [FULL TEXT]

Abstract: “The relationship between summer temperature, total cloud cover and precipitation over Eurasia was investigated using observation-based products of temperature and precipitation, and satellite-derived cloud cover and radiation products. We used a partial least squares regression approach to separate the local influences of cloud cover and precipitation on temperature variations. Our results suggest that the variance of summer temperature is partly explained by changes in summer cloudiness. The summer temperature dependence on cloud cover is strong at the high latitudes and in the middle latitude semi-humid area, while the dependence on precipitation is strong in the Central Asia arid area and the southern Asia humid area. During the period 1982–2009, the damped warming in extended West Siberia was accompanied with increases in cloud cover, and the pronounced warming in Europe and Mongolia was associated with a decrease in cloud cover and precipitation. Our results suggest that cloud cover may be the important local factor influencing the summer temperature variation in Eurasia while precipitation plays an important role at the middle latitudes.”

Citation: Qiuhong Tang and Guoyong Leng 2012 Environ. Res. Lett. 7 014004 doi:10.1088/1748-9326/7/1/014004.


Study finds no statistically significant changes in Antarctic snowmelt since 1979

Insignificant change in Antarctic snowmelt volume since 1979 – Munneke et al. (2012) [FULL TEXT]

Abstract: “Surface snowmelt is widespread in coastal Antarctica. Satellite-based microwave sensors have been observing melt area and duration for over three decades. However, these observations do not reveal the total volume of meltwater produced on the ice sheet. Here we present an Antarctic melt volume climatology for the period 1979–2010, obtained using a regional climate model equipped with realistic snow physics. We find that mean continent-wide meltwater volume (1979–2010) amounts to 89 Gt y−1 with large interannual variability (σ = 41 Gt y−1). Of this amount, 57 Gt y−1 (64%) is produced on the floating ice shelves extending from the grounded ice sheet, and 71 Gt y−1 in West-Antarctica, including the Antarctic Peninsula. We find no statistically significant trend in either continent-wide or regional meltwater volume for the 31-year period 1979–2010.”

Citation: Kuipers Munneke, P., G. Picard, M. R. van den Broeke, J. T. M. Lenaerts, and E. van Meijgaard (2012), Insignificant change in Antarctic snowmelt volume since 1979, Geophys. Res. Lett., 39, L01501, doi:10.1029/2011GL050207.


Production loss of mollusks due to ocean acidification could be over 100 billion USD

Economic costs of ocean acidification: a look into the impacts on global shellfish production – Narita et al. (2012)

Abstract: “Ocean acidification is increasingly recognized as a major global problem. Yet economic assessments of its effects are currently almost absent. Unlike most other marine organisms, mollusks, which have significant commercial value worldwide, have relatively solid scientific evidence of biological impact of acidification and allow us to make such an economic evaluation. By performing a partial-equilibrium analysis, we estimate global and regional economic costs of production loss of mollusks due to ocean acidification. Our results show that the costs for the world as a whole could be over 100 billion USD with an assumption of increasing demand of mollusks with expected income growths combined with a business-as-usual emission trend towards the year 2100. The major determinants of cost levels are the impacts on the Chinese production, which is dominant in the world, and the expected demand increase of mollusks in today’s developing countries, which include China, in accordance with their future income rise. Our results have direct implications for climate policy. Because the ocean acidifies faster than the atmosphere warms, the acidification effects on mollusks would raise the social cost of carbon more strongly than the estimated damage adds to the damage costs of climate change.”

Citation: Daiju Narita, Katrin Rehdanz and Richard S. J. Tol, Climatic Change, DOI: 10.1007/s10584-011-0383-3.


Analysis of abrupt climate changes during Holocene

Patterns, processes, and impacts of abrupt climate change in a warm world: the past 11,700 years – Shuman (2012)

Abstract: “Abrupt environmental changes punctuated the warm Holocene epoch (the past ∼11,700 years), and studies of these episodes can provide insight into the dynamics that produce rapid climate changes, as well as their ecologic, hydrologic, and geomorphic impacts. This review considers the processes that generated warm world abrupt changes and their landscape and resource effects, including nonlinear climate system interactions, as well as the possibility that large climate variability can linearly produce apparent ‘state shifts.’ Representative examples of Holocene changes illustrate processes that could produce future changes, including (1) rapid changes in ice sheets, such as by ca 8200 years before AD 1950, (2) shifts in the behavior of the El Nino-Southern Oscillation (e.g., at ca 5600 years before AD 1950) and Atlantic Meridional Overturning Circulation (e.g., at ca 2700 years before AD 1950), and (3) land–atmosphere feedbacks, such as were possible in North Africa in the mid-Holocene. These case examples, drawn primarily from the Northern Hemisphere, also reveal the dynamics that generate the types of climate change impacts that would be particularly evident to individuals and societies, such as rapid tree species declines (observed to have taken place within as little time as 6–40 years) and persistent shifts in the regional availability of water. Holocene changes also demonstrate that even progressive climate change can produce important abrupt impacts; that increased rates of background climate forcing may increase the frequency of abrupt responses; and that impacts may well depend upon the particular sequence of changes.”

Citation: Bryan Shuman, Wiley Interdisciplinary Reviews: Climate Change, DOI: 10.1002/wcc.152.


Tropical oceans were colder sometimes during Paleozoic than during last glacial maximum

Low-latitude Ordovician to Triassic brachiopod habitat temperatures (BHTs) determined from δ18O[brachiopod calcite] : A cold hard look at ice-house tropical oceans – Giles (2012)

Abstract: “Some researchers have suggested that Phanerozoic land-based ice sheets extended occasionally into the tropical realm. If true, the tropical ocean at those times must have been distinctly colder than at the Last Glacial Maximum (LGM) when northern hemisphere ice sheets did not extend below 38° latitude. Low-latitude ocean temperatures derived from oxygen isotopes of brachiopod shells test this hypothesis by comparing the temperature regime for Paleozoic and early Mesozoic low-latitude settings to the tropical temperature regime of the modern interstadial ocean, and to mean temperatures estimated for the tropical ocean at LGM. A running mean of pH-adjusted brachiopod habitat temperatures (BHTs) shows that Paleozoic low-latitude oceans were, on average, cool to cold relative to the modern interstadial tropical ocean. At times during Pennsylvanian, Serpukhovian, Tournaisian and Ordovician-Silurian glaciations, these tropical seas were indeed significantly colder on average than at the LGM. Ice-sheets within tropical latitudes can be reasonably predicted at those times. Abundant and diverse Paleozoic brachiopod communities reflect these cool tropical oceans, consistent with modern brachiopod ecological preference for colder waters. Amplified Paleozoic temperature oscillations suggest recurring global warming events which episodically drove these cold tropical oceans to temperatures significantly higher than the warmest modern tropical ocean.”

Citation: Peter S. Giles, Palaeogeography, Palaeoclimatology, Palaeoecology, http://dx.doi.org/10.1016/j.palaeo.2012.01.002.


Ice free Arctic Ocean causes more precipitation which slows down glacier mass loss in Svalbard

The impact of a seasonally ice free Arctic Ocean on the temperature, precipitation and surface mass balance of Svalbard – Day et al. (2012) [FULL TEXT, CORRECTION]

Abstract: “The observed decline in summer sea ice extent since the 1970s is predicted to continue until the Arctic Ocean is seasonally ice free during the 21st Century. This will lead to a much perturbed Arctic climate with large changes in ocean surface energy flux. Svalbard, located on the present day sea ice edge, contains many low lying ice caps and glaciers and is expected to experience rapid warming over the 21st Century. The total sea level rise if all the land ice on Svalbard were to melt completely is 0.02 m. The purpose of this study is to quantify the impact of climate change on Svalbard’s surface mass balance (SMB) and to determine, in particular, what proportion of the projected changes in precipitation and SMB are a result of changes to the Arctic sea ice cover. To investigate this a regional climate model was forced with monthly mean climatologies of sea surface temperature (SST) and sea ice concentration for the periods 1961–1990 and 2061–2090 under two emission scenarios. In a novel forcing experiment, 20th Century SSTs and 21st Century sea ice were used to force one simulation to investigate the role of sea ice forcing. This experiment results in a 3.5 m water equivalent increase in Svalbard’s SMB compared to the present day. This is because over 50 % of the projected increase in winter precipitation over Svalbard under the A1B emissions scenario is due to an increase in lower atmosphere moisture content associated with evaporation from the ice free ocean. These results indicate that increases in precipitation due to sea ice decline may act to moderate mass loss from Svalbard’s glaciers due to future Arctic warming.”

Citation: Day, J. J., Bamber, J. L., Valdes, P. J., and Kohler, J.: The impact of a seasonally ice free Arctic Ocean on the temperature, precipitation and surface mass balance of Svalbard, The Cryosphere, 6, 35-50, doi:10.5194/tc-6-35-2012, 2012.


South Asia extreme temperature indices show general warming only in low altitudes and latitudes

Impact of altitude and latitude on changes in temperature extremes over South Asia during 1971–2000 – Revadekar et al. (2012)

Abstract: “South Asia covers more than 30° of latitude with weather observation stations situated from 6°N at Galle, Sri Lanka, to 36°N at Chitral in Pakistan. Moreover, the South Asian station network ranges in altitude from sea level to nearly 4000 m above sea level. This paper uses time series of 11 objectively defined indices of daily temperature extremes at 197 stations in Bangladesh, India, Nepal, Pakistan and Sri Lanka to examine the possible impacts of elevation and latitude on changes in temperature extremes over the period of 1971–2000. Trends in extreme indices are consistent with general warming only at low altitudes and latitudes. Stations at high altitudes and latitudes show both positive and negative trends in extreme temperature indices. As a notable example, the Diurnal Temperature Range (DTR), which has been known to decrease in most parts of the globe, has increasing trends over many high altitude stations in South Asia. Trends in extreme temperature indices at stations in South Asia higher than 2000 m above sea level are mostly in disagreement with those reported over the Tibetan Plateau. Observed trends at low altitude locations in South Asia suggest that these sites can generally expect future changes in temperature extremes that are consistent with broad-scale warming. High-elevation sites appear to be more influenced by local factors and, hence, future changes in temperature extremes may be less predictable for these locations.”

Citation: J. V. Revadekar, S. Hameed, D. Collins, M. Manton, M. Sheikh, H. P. Borgaonkar, D. R. Kothawale, M. Adnan, A. U. Ahmed, J. Ashraf, S. Baidya, N. Islam, D. Jayasinghearachchi, N. Manzoor, K. H. M. S. Premalal, M. L. Shreshta, International Journal of Climatology, DOI: 10.1002/joc.3418.


Greenland ice core shows that 1783 Laki volcanic plume did not reach stratosphere

Sulfur isotope evidence of little or no stratospheric impact by the 1783 Laki volcanic eruption – Lanciki et al. (2012)

Abstract: “Historic records and research have suggested that the 1783–1784 eruption of the Laki fissure volcano in Iceland impacted Northern Hemisphere climate significantly, probably as a result of the direct injection of volcanic materials into the stratosphere where the volcanic aerosols would linger for years to cause surface cooling across the Northern Hemisphere. However, recent modeling work indicates the Laki climatic impact was limited to the Northern Hemisphere and only in the second half of 1783. We measured sulfur-33 isotope excess (Δ33S) in volcanic sulfate of historical eruptions including Laki found in Summit, Greenland ice cores. No Δ33S excess is found in sulfate of apparently tropospheric eruptions, while sulfate of stratospheric eruptions is characterized by significant Δ33S excess and a positive-to-negative change in Δ33S during its gradual removal from the atmosphere. Because the same characteristics have been previously found in volcanic sulfate in Antarctica snow, the results from Greenland indicate similar global processes of stratospheric chemical conversion of SO2 to sulfate. The isotopic composition of Laki sulfate is essentially normal and shows no characteristics of sulfate produced by stratospheric photochemical reactions. This clearly indicates that the Laki plume did not reach altitudes of the stratospheric ozone layer. Further, the short aerosol residence time (<6 months) suggests that the bulk of the Laki plume and subsequent aerosols were probably confined to the middle and upper troposphere. These conclusions support the hypothesis of D’Arrigo and colleagues that the unusually cold winter of 1783–1784 was not caused by Laki.”

Citation: Lanciki, A., J. Cole-Dai, M. H. Thiemens, and J. Savarino (2012), Sulfur isotope evidence of little or no stratospheric impact by the 1783 Laki volcanic eruption, Geophys. Res. Lett., 39, L01806, doi:10.1029/2011GL050075.


Improved constraints lead to relatively low projections of 21st century warming

Improved constraints on 21st-century warming derived using 160 years of temperature observations – Gillett et al. (2012)

Abstract: “Projections of 21st century warming may be derived by using regression-based methods to scale a model’s projected warming up or down according to whether it under- or over-predicts the response to anthropogenic forcings over the historical period. Here we apply such a method using near surface air temperature observations over the 1851–2010 period, historical simulations of the response to changing greenhouse gases, aerosols and natural forcings, and simulations of future climate change under the Representative Concentration Pathways from the second generation Canadian Earth System Model (CanESM2). Consistent with previous studies, we detect the influence of greenhouse gases, aerosols and natural forcings in the observed temperature record. Our estimate of greenhouse-gas-attributable warming is lower than that derived using only 1900–1999 observations. Our analysis also leads to a relatively low and tightly-constrained estimate of Transient Climate Response of 1.3–1.8°C, and relatively low projections of 21st-century warming under the Representative Concentration Pathways. Repeating our attribution analysis with a second model (CNRM-CM5) gives consistent results, albeit with somewhat larger uncertainties.”

Citation: Gillett, N. P., V. K. Arora, G. M. Flato, J. F. Scinocca, and K. von Salzen (2012), Improved constraints on 21st-century warming derived using 160 years of temperature observations, Geophys. Res. Lett., 39, L01704, doi:10.1029/2011GL050226.


Sea level rise and vertical land motion in southern Europe coast

Coastal sea level rise in southern Europe and the nonclimate contribution of vertical land motion – Wöppelmann & Marcos (2012)

Abstract: “In this study, we extend the advanced approach of combining tide gauge and satellite altimetry data with supplemental equations from adjacent tide gauge records of at least 30 years of common data to investigate the relative importance of the nonclimate contribution of vertical land movement to the observed rates of sea level change along the coasts of southern Europe. The sensitivity tests proved that the advanced approach is robust and accurate at the submillimeter per year level of around 0.4 mm yr−1 in estimating rates of vertical land movements. It enabled identifying stations displaying large rates of vertical land movements that must be taken into account when predicting future sea level rise and appraising the exposure to its impacts on populations and assets. The average rate of coastal climate-related sea level rise in the Mediterranean Sea was consequently revisited to be of 1.7 mm yr−1 over the past century, whereas the Atlantic northern Iberian coast revealed a significant high rate of sea level rise in excess of 3.4 mm yr−1 for the past 70 years. Future work should consider applying this powerful approach to other geographic contexts as a useful source of supplementary data for geodynamic studies.”

Citation: Wöppelmann, G., and M. Marcos (2012), Coastal sea level rise in southern Europe and the nonclimate contribution of vertical land motion, J. Geophys. Res., 117, C01007, doi:10.1029/2011JC007469.


CLASSIC OF THE WEEK: Langley (1876)

Measurement of the Direct Effect of Sun-spots on Terrestrial Climates – Langley (1876) [FULL TEXT]

No abstract. In this paper, Samuel Langley (who made the measurements Arrhenius used in his legendary paper) calculates that the effect of sun-spots to the temperature of Earth is between 0.063 and 0.29 degrees Celsius.

Citation: Langley, S. P., 1876, Monthly Notices of the Royal Astronomical Society, Vol. 37, p.5.

Posted in Climate science | 1 Comment »

Papers on end-Permian mass extinction and climate

Posted by Ari Jokimäki on January 12, 2012

This is a list of papers that discuss the role of climate in end-Permian mass extinction. The list is not complete, and will most likely be updated in future in order to make it more thorough and more representative.

Calibrating the End-Permian Mass Extinction – Shen et al. (2011) “The end-Permian mass extinction was the most severe biodiversity crisis in Earth history. To better constrain the timing, and ultimately the causes of this event, we collected a suite of geochronologic, isotopic, and biostratigraphic data on several well-preserved sedimentary sections in South China. High-precision U-Pb dating reveals that the extinction peak occurred just before 252.28 ± 0.08 million years ago, after a decline of 2 per mil (‰) in δ13C over 90,000 years, and coincided with a δ13C excursion of −5‰ that is estimated to have lasted ≤20,000 years. The extinction interval was less than 200,000 years and synchronous in marine and terrestrial realms; associated charcoal-rich and soot-bearing layers indicate widespread wildfires on land. A massive release of thermogenic carbon dioxide and/or methane may have caused the catastrophic extinction.” Shu-zhong Shen, James L. Crowley, Yue Wang, Samuel A. Bowring, Douglas H. Erwin, Peter M. Sadler, Chang-qun Cao, Daniel H. Rothman, Charles M. Henderson, Jahandar Ramezani, Hua Zhang, Yanan Shen, Xiang-dong Wang, Wei Wang, Lin Mu, Wen-zhong Li, Yue-gang Tang, Xiao-lei Liu, Lu-jun Liu, Yong Zeng, Yao-fa Jiang, Yu-gan Jin, Science 9 December 2011: Vol. 334 no. 6061 pp. 1367-1372, DOI: 10.1126/science.1213454.

Carbon-isotope stratigraphy across the Permian–Triassic boundary: A review – Korte & Kozur (2010) “The Palaeozoic–Mesozoic transition is marked by distinct perturbations in the global carbon cycle resulting in a prominent negative carbon-isotope excursion at the Permian–Triassic (P–T) boundary, well known from a plethora of marine and continental sediments. Potential causes for this negative δ13C trend (and their links to the latest Permian mass extinction) have been intensively debated in the literature. In order to draw conclusions regarding causation, a general δ13C curve was defined after consideration of all available datasets and with due reference to the biostratigraphic background. The most important features of the P–T carbon-isotope trend are the following: the 4–7‰ δ13C decline (lasting ∼500,000 years) is gradual and began in the Changhsingian at the stratigraphic level of the C. bachmanni Zone. The decreasing trend is interrupted by a short-term positive event that starts at about the latest Permian low-latitude marine main extinction event horizon (=EH), indicating that the extinction itself cannot have caused the negative carbon-isotope excursion. After this short-term positive excursion, the δ13C decline continues to a first minimum at about the P–T boundary. A subsequent slight increase is followed by a second (occasionally two-peaked) minimum in the lower (and middle) I. isarcica Zone. The negative carbon-isotope excursion was most likely a consequence of a combination of different causes that may include: (1) direct and indirect effects of the Siberian Trap and contemporaneous volcanism and (2) anoxic deep waters occasionally reaching very shallow sea levels. A sudden release of isotopically light methane from oceanic sediment piles or permafrost soils as a source for the negative carbon-isotope trend is questionable at least for the time span a little below the EH and somewhat above the P–T boundary.” Christoph Korte, Heinz W. Kozur, Journal of Asian Earth Sciences, Volume 39, Issue 4, 9 September 2010, Pages 215-235, doi:10.1016/j.jseaes.2010.01.005.

Massive volcanism at the Permian–Triassic boundary and its impact on the isotopic composition of the ocean and atmosphere – Korte et al. (2010) “Bulk carbonate and conodonts from three Permian–Triassic (P–T) boundary sections at Guryul Ravine (Kashmir), Abadeh (central Iran) and Pufels/Bula/Bulla (Italy) were investigated for δ13C and δ18O. Carbon isotope data highlight environmental changes across the P–T boundary and show the following features: (1) a gradual decrease of ∼4‰ to more than 7‰ starting in the Late Permian (Changhsingian) C. bachmanni Zone, with two superimposed transient positive excursions in the C. meishanensis–H. praeparvus and the M. ultima–S. ? mostleri Zones; (2) two δ13C minima, the first at the P–T boundary and a higher, occasionally double-minimum in the lower I. isarcica Zone. It is unlikely that the short-lived phenomena, such as a breakdown in biological productivity due to catastrophic mass extinction, a sudden release of oceanic methane hydrates or meteorite impact(s), could have been the main control on the latest Permian carbon isotope curve because of its prolonged (0.5 Ma) duration, gradual decrease and the existence of a >1‰ positive shift at the main extinction horizon. The P–T boundary δ13C trend matches in time and magnitude the eruption of the Siberian Traps and other contemporaneous volcanism, suggesting that volcanogenic effects, such as outgassed CO2 from volcanism and, even more, thermal metamorphism of organic-rich sediments, as the likely cause of the negative trend.” Christoph Korte, Prabhas Pande, P. Kalia, Heinz W. Kozur, Michael M. Joachimski, Hedi Oberhänsli, Journal of Asian Earth Sciences, Volume 37, Issue 4, 1 March 2010, Pages 293-311, doi:10.1016/j.jseaes.2009.08.012.

Illawarra Reversal: The fingerprint of a superplume that triggered Pangean breakup and the end-Guadalupian (Permian) mass extinction – Isozaki (2009) “The Permian magnetostratigraphic record demonstrates that a remarkable change in geomagnetism occurred in the Late Guadalupian (Middle Permian; ca. 265 Ma) from the long-term stable Kiaman Reverse Superchron (throughout the Late Carboniferous and Early-Middle Permian) to the Permian–Triassic Mixed Superchron with frequent polarity changes (in the Late Permian and Triassic). This unique episode called the Illawarra Reversal probably reflects a significant change in the geodynamo in the outer core of the planet after a 50 million years of stable geomagnetism. The Illawarra Reversal was likely led by the appearance of a thermal instability at the 2900 km-deep core–mantle boundary in connection with mantle superplume activity. The Illawarra Reversal and the Guadalupian–Lopingian boundary event record the significant transition processes from the Paleozoic to Mesozoic–Modern world. One of the major global environmental changes in the Phanerozoic occurred almost simultaneously in the latest Guadalupian, as recorded in 1) mass extinction, 2) ocean redox change, 3) sharp isotopic excursions (C and Sr), 4) sea-level drop, and 5) plume-related volcanism. In addition to the claimed possible links between the above-listed environmental changes and mantle superplume activity, I propose here an extra explanation that a change in the core’s geodynamo may have played an important role in determining the course of the Earth’s surface climate and biotic extinction/evolution. When a superplume is launched from the core–mantle boundary, the resultant thermal instability makes the geodynamo’s dipole of the outer core unstable, and lowers the geomagnetic intensity. Being modulated by the geo- and heliomagnetism, the galactic cosmic ray flux into the Earth’s atmosphere changes with time. The more cosmic rays penetrate through the atmosphere, the more clouds develop to increase the albedo, thus enhancing cooling of the Earth’s surface. The Illawarra Reversal, the Kamura cooling event, and other unique geologic phenomena in the Late Guadalupian are all concordantly explained as consequences of the superplume activity that initially triggered the breakup of Pangea. The secular change in cosmic radiation may explain not only the extinction-related global climatic changes in the end-Guadalupian but also the long-term global warming/cooling trend in Earth’s history in terms of cloud coverage over the planet.” Yukio Isozaki, Gondwana Research, Volume 15, Issues 3-4, June 2009, Pages 421-432, Special Issue: Supercontinent Dynamics, doi:10.1016/j.gr.2008.12.007.

Elevated atmospheric CO2 and the delayed biotic recovery from the end-Permian mass extinction – Fraiser & Bottjer (2007) “Excessive CO2 in the Earth ocean–atmosphere system may have been a significant factor in causing the end-Permian mass extinction. CO2 injected into the atmosphere by the Siberian Traps has been postulated as a major factor leading to the end-Permian mass extinction by facilitating global warming, widespread ocean stratification, and development of anoxic, euxinic and CO2-rich deep waters. A broad incursion of this toxic deep water into the surface ocean may have caused this mass extinction. Although previous studies of the role of excessive CO2 have focused on these “bottom-up” effects emanating from the deep ocean, “top-down” effects of increasing atmosphere CO2 concentrations on ocean-surface waters and biota have not previously been explored. Passive diffusion of atmospheric CO2 into ocean-surface waters decreases the pH and CaCO3 saturation state of seawater, causing a physiological and biocalcification crisis for many marine invertebrates. While both “bottom-up” and “top-down” mechanisms may have contributed to the relatively short-term biotic devastation of the end-Permian mass extinction, such a “top-down” physiological and biocalcification crisis would have had long-term effects and might have contributed to the protracted 5- to 6-million-year-long delay in biotic recovery following this mass extinction. Earth’s Modern marine biota may experience similar “top-down” CO2 stresses if anthropogenic input of atmosphere/ocean CO2 continues to rise.” Margaret L. Fraiser, David J. Bottjer, Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 252, Issues 1-2, 20 August 2007, Pages 164-175, The Permian-Triassic Boundary Crisis and Early Triassic Biotic Recovery, doi:10.1016/j.palaeo.2006.11.041.

Paleophysiology and end-Permian mass extinction – Knoll et al. (2007) “Physiological research aimed at understanding current global change provides a basis for evaluating selective survivorship associated with Permo-Triassic mass extinction. Comparative physiology links paleontological and paleoenvironmental observations, supporting the hypothesis that an end-Permian trigger, most likely Siberian Trap volcanism, touched off a set of physically-linked perturbations that acted synergistically to disrupt the metabolisms of latest Permian organisms. Global warming, anoxia, and toxic sulfide probably all contributed to end-Permian mass mortality, but hypercapnia (physiological effects of elevated PCO2) best accounts for the selective survival of marine invertebrates. Paleophysiological perspectives further suggest that persistent or recurring hypercapnia/global warmth also played a principal role in delayed Triassic recovery. More generally, physiology provides an important way of paleobiological knowing in the age of Earth system science.” Andrew H. Knoll, Richard K. Bambach, Jonathan L. Payne, Sara Pruss, Woodward W. Fischer, Earth and Planetary Science Letters, Volume 256, Issues 3-4, 30 April 2007, Pages 295-313, doi:10.1016/j.epsl.2007.02.018. [Full text]

End-Permian mass extinction pattern in the northern peri-Gondwanan region – Shen et al. (2007) “The Permian-Triassic extinction pattern in the peri-Gondwanan region is documented biostratigraphically, geochemically and sedimentologically based on three marine sequences deposited in southern Tibet and comparisons with the sections in the Salt Range, Pakistan and Kashmir. Results of biostratigraphical ranges for the marine faunas reveal an end-Permian event comparable in timing with that known at the Meishan section in low palaeolatitude as well as Spitsbergen and East Greenland in northern Boreal settings although biotic patterns earlier in the Permian vary. The previously interpreted delayed extinction (Late Griesbachian) at the Selong Xishan section is not supported by our analysis. The end-Permian event exhibits an abrupt marine faunal shift slightly beneath the Permian-Triassic boundary (PTB) from benthic taxa- to nektic taxa-dominated communities. The climate along the continental margin of Neo-Tethys was cold before the extinction event. However, a rapid climatic warming event as indicated by the southward invasion of abundant warm-water conodonts, warm-water brachiopods, calcareous sponges, and gastropods was associated with the extinction event. Stable isotopic values of δ13Ccarb, δ13Corg and δ18O show a sharp negative drop slightly before and during the extinction interval. Sedimentological and microstratigraphical analysis reveals a Late Permian regression, as marked by a Caliche Bed at the Selong Xishan section and the micaceous siltstone in the topmost part of the Qubuerga Formation at the Qubu and Tulong sections. The regression was immediately followed by a rapid transgression beneath the PTB. The basal Triassic rocks fine upward, and are dominated by dolomitic packstone/wackestone containing pyritic cubes, bioturbation and numerous tiny foraminifers, suggesting that the studied sections were deposited during the initial stage of the transgression and hence may not have been deeply affected by the anoxic event that is widely believed to characterise the zenith of the transgression.” Shu Zhong Shen, Chang-Qun Cao, Charles M. Henderson, Xiang-Dong Wang, Guang R. Shi, Yue Wang, Wei Wang, Palaeoworld, Volume 15, Issue 1, January 2006, Pages 3-30, doi:10.1016/j.palwor.2006.03.005. [Full text]

Middle-Late Permian mass extinction on land – Retallack et al. (2006) “The end-Permian mass extinction has been envisaged as the nadir of biodiversity decline due to increasing volcanic gas emissions over some 9 million years. We propose a different tempo and mechanism of extinction because we recognize two separate but geologically abrupt mass extinctions on land, one terminating the Middle Permian (Guadalupian) at 260.4 Ma and a later one ending the Permian Period at 251 Ma. Our evidence comes from new paleobotanical, paleopedological, and carbon isotopic studies of Portal Mountain, Antarctica, and comparable studies in the Karoo Basin, South Africa. Extinctions have long been apparent among marine invertebrates at both the end of the Guadalupian and end of the Permian, which were also times of warm-wet greenhouse climatic transients, marked soil erosion, transition from high- to low-sinuosity and braided streams, soil stagnation in wetlands, and profound negative carbon isotope anomalies. Both mass extinctions may have resulted from catastrophic methane outbursts to the atmosphere from coal intruded by feeder dikes to flood basalts, such as the end-Guadalupian Emeishan Basalt and end-Permian Siberian Traps.” Gregory J. Retallack, Christine A. Metzger, Tara Greaver, A. Hope Jahren, Roger M.H. Smith and Nathan D. Sheldon, GSA Bulletin, v. 118 no. 11-12 p. 1398-1411, doi: 10.1130/B26011.1. [Full text]

Climate simulation of the latest Permian: Implications for mass extinction – Kiehl & Shields (2005) “Life at the Permian-Triassic boundary (ca. 251 Ma) underwent the largest disruption in Earth’s history. Paleoclimatic data indicate that Earth was significantly warmer than present and that much of the ocean was anoxic or euxinic for an extended period of time. We present results from the first fully coupled comprehensive climate model using paleogeography for this time period. The coupled climate system model simulates warm high-latitude surface air temperatures related to elevated carbon dioxide levels and a stagnate global ocean circulation in concert with paleodata indicating low oxygen levels at ocean depth. This is the first climate simulation that captures these observed features of this time period.” Jeffrey T. Kiehl and Christine A. Shields, Geology, v. 33 no. 9 p. 757-760, doi: 10.1130/G21654.1. [Full text]

How to kill (almost) all life: the end-Permian extinction event – Benton & Twitchett (2003) “The biggest mass extinction of the past 600 million years (My), the end-Permian event (251 My ago), witnessed the loss of as much as 95% of all species on Earth. Key questions for biologists concern what combination of environmental changes could possibly have had such a devastating effect, the scale and pattern of species loss, and the nature of the recovery. New studies on dating the event, contemporary volcanic activity, and the anatomy of the environmental crisis have changed our perspectives dramatically in the past five years. Evidence on causation is equivocal, with support for either an asteroid impact or mass volcanism, but the latter seems most probable. The extinction model involves global warming by 6°C and huge input of light carbon into the ocean-atmosphere system from the eruptions, but especially from gas hydrates, leading to an ever-worsening positive-feedback loop, the ‘runaway greenhouse’.” Michael J. Benton, Richard J. Twitchett, Trends in Ecology & Evolution, Volume 18, Issue 7, July 2003, Pages 358-365, doi:10.1016/S0169-5347(03)00093-4. [Full text]

Land-plant diversity and the end-Permian mass extinction – Rees (2002) “The Permian and Triassic represent a time of major global climate change from icehouse to hothouse conditions and significant (∼25°) northward motion of landmasses amalgamated in essentially one supercontinent, Pangea. The greatest of all mass extinctions occurred around the Permian-Triassic boundary (251 Ma), although there is no consensus regarding the cause(s). Recent studies have suggested a meteor impact and worldwide die-off of vegetation, on the basis of sparse local observations. However, new analyses of global Permian and Triassic plant data in a paleogeographic context show that the scale and timing of effects varied markedly between regions. The patterns are best explained by differences in geography, climate, and fossil preservation, not by catastrophic events. Caution should be exercised when extrapolating local observations to global-scale interpretations. At the other extreme, global compilations of biotic change through time can be misleading if the effects of geography, climate, and preservation bias are not considered.” P. McAllister Rees, Geology, v. 30 no. 9 p. 827-830, doi: 10.1130/0091-7613(2002)​030​2.0.CO;2. [Full text]

Ocean stagnation and end-Permian anoxia – Hotinski et al. (2001) “Ocean stagnation has been invoked to explain the widespread occurrence of organic-carbon–rich, laminated sediments interpreted to have been deposited under anoxic bottom waters at the time of the end-Permian mass extinction. However, to a first approximation, stagnation would severely reduce the upwelling supply of nutrients to the photic zone, reducing productivity. Moreover, it is not obvious that ocean stagnation can be achieved. Numerical experiments performed with a three-dimensional global ocean model linked to a biogeochemical model of phosphate and oxygen cycling indicate that a low equator to pole temperature gradient could have produced weak oceanic circulation and widespread anoxia in the Late Permian ocean. We find that polar warming and tropical cooling of sea-surface temperatures cause anoxia throughout the deep ocean as a result of both lower dissolved oxygen in bottom source waters and increased nutrient utilization. Buildup of quantities of H2S and CO2 in the Late Permian ocean sufficient to directly cause a mass extinction, however, would have required large increases in the oceanic nutrient inventory.” Roberta M. Hotinski, Karen L. Bice, Lee R. Kump, Raymond G. Najjar and Michael A. Arthur, Geology, v. 29 no. 1 p. 7-10, doi: 10.1130/0091-7613(2001)​029​2.0.CO;2. [Full text]

Pattern of Marine Mass Extinction Near the Permian-Triassic Boundary in South China – Jin et al. (2000) “The Meishan section across the Permian-Triassic boundary in South China is the most thoroughly investigated in the world. A statistical analysis of the occurrences of 162 genera and 333 species confirms a sudden extinction event at 251.4 million years ago, coincident with a dramatic depletion of δ13Ccarbonate and an increase in microspherules.” Y. G. Jin, Y. Wang, W. Wang, Q. H. Shang, C. Q. Cao and D. H. Erwin, Science 21 July 2000: Vol. 289 no. 5478 pp. 432-436, DOI: 10.1126/science.289.5478.432. [Full text]

U/Pb Zircon Geochronology and Tempo of the End-Permian Mass Extinction – Bowring et al. (1998) “The mass extinction at the end of the Permian was the most profound in the history of life. Fundamental to understanding its cause is determining the tempo and duration of the extinction. Uranium/lead zircon data from Late Permian and Early Triassic rocks from south China place the Permian-Triassic boundary at 251.4 ± 0.3 million years ago. Biostratigraphic controls from strata intercalated with ash beds below the boundary indicate that the Changhsingian pulse of the end-Permian extinction, corresponding to the disappearance of about 85 percent of marine species, lasted less than 1 million years. At Meishan, a negative excursion in δ13C at the boundary had a duration of 165,000 years or less, suggesting a catastrophic addition of light carbon.” S. A. Bowring, D. H. Erwin, Y. G. Jin, M. W. Martin, K. Davidek and W. Wang, Science 15 May 1998: Vol. 280 no. 5366 pp. 1039-1045, DOI: 10.1126/science.280.5366.1039.

Oceanic Anoxia and the End Permian Mass Extinction – Wignall & Twitchett (1996) “Data on rocks from Spitsbergen and the equatorial sections of Italy and Slovenia indicate that the world’s oceans became anoxic at both low and high paleolatitudes in the Late Permian. Such conditions may have been responsible for the mass extinction at this time. This event affected a wide range of shelf depths and extended into shallow water well above the storm wave base.” Paul B. Wignall, Richard J. Twitchett, Science 24 May 1996: Vol. 272 no. 5265 pp. 1155-1158, DOI: 10.1126/science.272.5265.1155.

Comparative Earth History and Late Permian Mass Extinction – Knoll et al. (1996) “The repeated association during the late Neoproterozoic Era of large carbon-isotopic excursions, continental glaciation, and stratigraphically anomalous carbonate precipitation provides a framework for interpreting the reprise of these conditions on the Late Permian Earth. A paleoceanographic model that was developed to explain these stratigraphically linked phenomena suggests that the overturn of anoxic deep oceans during the Late Permian introduced high concentrations of carbon dioxide into surficial environments. The predicted physiological and climatic consequences for marine and terrestrial organisms are in good accord with the observed timing and selectivity of Late Permian mass extinction.” A. H. Knoll, R. K. Bambach, D. E. Canfield, J. P. Grotzinger, Science 26 July 1996: Vol. 273 no. 5274 pp. 452-457, DOI: 10.1126/science.273.5274.452.

Synchrony and Causal Relations Between Permian-Triassic Boundary Crises and Siberian Flood Volcanism – Renne et al. (1995) “The Permian-Triassic boundary records the most severe mass extinctions in Earth’s history. Siberian flood volcanism, the most profuse known such subaerial event, produced 2 million to 3 million cubic kilometers of volcanic ejecta in approximately 1 million years or less. Analysis of 40Ar/39Ar data from two tuffs in southern China yielded a date of 250.0 ± 0.2 million years ago for the Permian-Triassic boundary, which is comparable to the inception of main stage Siberian flood volcanism at 250.0 ± 0.3 million years ago. Volcanogenic sulfate aerosols and the dynamic effects of the Siberian plume likely contributed to environmental extrema that led to the mass extinctions.” Paul R. Renne, Michael T. Black, Zhang Zichao, Mark A. Richards and Asish R. Basu, Science 8 September 1995: Vol. 269 no. 5229 pp. 1413-1416, DOI: 10.1126/science.269.5229.1413. [Full text]

Synchronism of the Siberian Traps and the Permian-Triassic Boundary – Campbell et al. (1992) “Uranium-lead ages from an ion probe were taken for zircons from the ore-bearing Noril’sk I intrusion that is comagmatic with, and intrusive to, the Siberian Traps. These values match, within an experimental error of ±4 million years, the dates for zircons extracted from a tuff at the Permian-Triassic (P-Tr) boundary. The results are consistent with the hypothesis that the P-Tr extinction was caused by the Siberian basaltic flood volcanism. It is likely that the eruption of these magmas was accompanied by the injection of large amounts of sulfur dioxide into the upper atmosphere, which may have led to global cooling and to expansion of the polar ice cap. The P-Tr extinction event may have been caused by a combination of acid rain and global cooling as well as rapid and extreme changes in sea level resulting from expansion of the polar ice cap.” I. H. Campbell, G. K. Czamanske, V. A. Fedorenko, R. I. Hill and V. Stepanov, Science 11 December 1992: Vol. 258 no. 5089 pp. 1760-1763, DOI: 10.1126/science.258.5089.1760.

The End-Permian mass extinction: What really happened and did it matter? – Erwin (1989) “Marine communities of the Paleozoic differ markedly from those of the post-Paleozoic, a dichotomy long recognized as the most fundamental change between the Cambrian metazoan radiation and the present. The end-Permian mass extinction of about 54% of marine families eliminated many of the groups that dominated Paleozoic communities. Correlative changes occurred in terrestrial vertebrate and plant communities, but there is no clear evidence that these changes are related to the marine extinction. The marine extinction occurred during a period of physical change, and a variety of extinction mechanisms have been proposed, most related to a major Late Permian marine regression or to climatic changes. Unfortunately, the regression has made it difficult to gather data on the rate, timing and pattern of extinction, and the available data exclude only a few hypotheses. Thus the largest mass extinction, and the one with the greatest evolutionary importance, is also the most poorly understood.” Douglas H. Erwin, Trends in Ecology & Evolution, Volume 4, Issue 8, August 1989, Pages 225–229, http://dx.doi.org/10.1016/0169-5347(89)90165-1.

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New research from last week 1/2012

Posted by Ari Jokimäki on January 9, 2012

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.

In this week’s papers El Niño does some moonlighting in Europe. In New Zealand they found some unused sea level measurement stations while in Netherlands they apparently run out of official weather stations and started using weather amateur stations. The pines from Spain are showing the decline, but are doing so selectively. In Australia, they apparently didn’t notice YD event at all. There’s yet another effort with cosmic ray and climate connection. We also learn how to tell apart climate signal and noise. But did you know that female corals don’t like climate change? Or that some Malaria species do seem to like it at least in Thar Desert? This is not all, we have studies also on Paris-London westerly index, dark aerosols, inland waters, and carbon in Siberia. However, this is just a scratch of the surface as there are hundreds of papers published every week relating to climate.

AGW Observer takes over Skeptical Science!

From now on, this “New research from last week” series will also be published in Skeptical Science. This has also prompted me to change the outlook of this post a little, as you can see above and below.


El Niño fiddles with European and North Atlantic weather

Central Pacific El Niño, the “subtropical bridge,” and Eurasian climate – Graf & Zanchettin (2012)

Abstract: “This study contributes to the discussion on possible effects of El Niño on North Atlantic/European regional climates. We use NCEP/NCAR reanalysis data to show how the two different types of El Niños (the central Pacific, or CP, and the east Pacific, or EP) result in remarkably different European winter temperature anomalies, specifically weak warming during EP and significant cooling during CP El Niños, the latter being associated with a negative phase of the winter North Atlantic Oscillation (NAO). Our results diverge from former suggestions addressing the weakened stratospheric polar vortex as the dominant factor contributing to the El Niño/NAO teleconnection. We propose a tropospheric bridge as the mechanism primarily responsible for the establishment of a negative NAO phase and of associated cold European winters. This mechanism includes the subtropical jet (STJ) waveguide being activated only during CP El Niños, when anomalous convective heating occurs near the edge of the Pacific warm pool. Under these conditions the STJ is enhanced by planetary wave flux divergence in the subtropical upper troposphere, providing favorable conditions for the propagation of a wave number 5 disturbance around the subtropical Northern Hemisphere. This wave contributes to weakening of the Azores High and, hence, to the negative NAO phase. As global warming scenarios project an increase in the frequency of CP El Niño events, the distinctive nature of this mechanism implies that the probability of cold European winters may increase as well in future decades.”

Citation: Graf, H.-F., and D. Zanchettin (2012), J. Geophys. Res., 117, D01102, doi:10.1029/2011JD016493.


Improvements to sea level trend analysis in New Zealand

Regional sea level trends in New Zealand – Hannah & Bell (2012)

Abstract: “In terms of sea level data sets able to be used for long-term sea level trend analysis, the Southern Hemisphere is a data sparse region of the world. New Zealand lies in this region, presently having four (major port) data sets used for such trend analysis. This paper describes the process followed to compute new sea level trends at another six ports, each with very discontinuous tide gauge records. In each case the tide gauge has previously only been used for precisely defining an historical local Mean Sea Level (MSL) datum. The process used involved a comparison of the old MSL datum with a newly defined datum obtained from sea level data covering the last decade. A simple linear trend was fitted between the two data points. Efforts were then made to assess possible bias in the results due to oceanographic factors such as the El Niño–Southern Oscillation (ENSO) cycle, and the Interdecadal Pacific Oscillation (IPO). This was done by taking the longer time series from the four major ports and assessing the spatially coherent variability in annual sea level using the dominant principal component from an empirical orthogonal function (EOF) analysis. The average relative sea level rise calculated from these six newly derived trends was 1.7 ± 0.1 mm yr−1, a result that is completely consistent with the analysis of the long-term gauge records. Most importantly, it offers a relatively simple method of improving our knowledge of relative sea level trends in data sparse regions of the world.”

Citation: Hannah, J., and R. G. Bell (2012), J. Geophys. Res., 117, C01004, doi:10.1029/2011JC007591.


Weather stations of Dutch weather amateurs used in urban heat island study

Estimating the Urban Heat Island in residential areas in the Netherlands using observations by weather amateurs – Wolters & Brandsma (2012)

Abstract: “A better quantification of the urban heat islands in the Netherlands is urgent, due to heat stress related problems in the recent past combined with the expected temperature rise for the coming decades. However, professional temperature observations in Dutch urban areas are scarce. Therefore, in this research we have explored the use of observations from weather stations installed and maintained by weather amateurs. From a set of over 200 stations, suitable and representative data have been selected from 20 stations, using a set of objective selection criteria based on metadata. One year of data (Jan-Dec 2010) was considered. From these data we have obtained estimates of the magnitude of the UHI in Dutch low-rise residential areas. A positive relation (linear model r-squared ≈ 0.7) was derived between the summer-averaged UHI and the (neighborhood-scale) population density around the observational sites. It was found that the UHI in summer is strongest in nighttime conditions, and increases with decreasing wind speed and decreasing cloud cover, and with increasing sea level air pressure. The summer-averaged UHI was around 0.9°C. During nighttime in a relatively warm one-month subperiod of the summer the average UHI was around 1.4°C. During spring and autumn the UHI was lower than in summer, during winter no significant UHI was observed. The agreement in results between the different stations, and the accordance of the magnitude and variation of the observed UHI to literature, show that automatic observations from weather amateurs can be sufficient quality for atmospheric research, provided that detailed metadata are available.”

Citation: Dirk Wolters and Theo Brandsma, Journal of Applied Meteorology and Climatology 2012, doi: http://dx.doi.org/10.1175/JAMC-D-11-0135.1.


Spanish pines are selective in showing the decline

Selective drought-induced decline of pine species in southeastern Spain – Sánchez-Salguero et al. (2012)

Abstract: “The negative impacts of severe drought on the growth and vigor of tree species and their relationship with forest decline have not been properly evaluated taking into account the differential responses to such stress of trees, sites and species. We evaluated these responses by quantifying the changes in radial growth of plantations of four pine species (Pinus sylvestris, Pinus nigra, Pinus pinaster, Pinus halepensis) which showed distinct decline and defoliation levels in southeastern Spain. We used dendrochronological methods, defoliation records, linear mixed models of basal area increment and dynamic factor analysis to quantify the responses of trees at the species and individual scales to site conditions and drought stress. In the region a temperature rise and a decrease in spring precipitation have led to drier conditions during the late twentieth century characterized by severe droughts in the 1990s and 2000s. As expected, the defoliation levels and the reductions in basal area increment were higher in those species more vulnerable to drought-induced xylem embolism (P. sylvestris) than in those more resistant (P. halepensis). Species adapted to xeric conditions but with high growth rates, such as P. pinaster, were also vulnerable to drought-induced decline. The reduction in basal area increment and the defoliation events occurred after consecutive severe droughts. A decrease in spring precipitation, which is the main driver of radial growth, is the most plausible cause of recent forest decline. The sharp growth reduction and widespread defoliation of the most affected pine plantations of Scots pine make their future persistence in drought-prone sites unlikely under the forecasted warmer and drier conditions.”

Citation: Raúl Sánchez-Salguero, Rafael M. Navarro-Cerrillo, J. Julio Camarero and Ángel Fernández-Cancio, Climatic Change, DOI: 10.1007/s10584-011-0372-6.

Two other studies were published last week on pine tree rings:

- Common growth signal and spatial synchrony of the chronologies of tree-rings from pines in the Baltic Sea region over the last nine centuries – Läänelaid et al. (2012)

- The tree-ring chronology of Scots pine (Pinus sylvestris L.) from the Nesvizh castle XVI–XIX cc. in central Belarus – Yermokhin (2012)


Younger Dryas cooling apparently didn’t show up in Australian region

The Younger Dryas: relevant in the Australian region? – Tibby (2012)

Abstract: “An assessment of Australian climate during the Younger Dryas Chronozone (YDC) is presented. This review focuses on securely dated records from sites of continuous deposition, placing greatest emphasis on temperature reconstructions, with records of effective precipitation (i.e. the combined effect of precipitation minus evapotranspiration) also considered. While there is a paucity of Australian records covering the last glacial interglacial transition, particularly those which directly infer temperature, sufficient data exist to examine YDC climate from southern and eastern Australia. Temperature reconstructions from Tasmania, based on both chironomid and pollen data, show no evidence for Younger Dryas cooling. By contrast, there is evidence for cooling associated with the Antarctic Cold Reversal, from Tullabardine Dam pollen data and the sediment organic content from Eagle and Platypus Tarns in Tasmania. Records from a number of eastern Australian mainland sites provide no evidence of effective precipitation shifts concurrent with the Younger Dryas Chronozone. Similarly, reconstructions of discharge from the Murray-Darling Basin, which covers a large proportion (14%) of the Australian continent, and dust transport from a larger portion of the continent also show no evidence of climate shifts concomitant with the Younger Dryas. Of research published in the past decade, only one study, located in the Great Australian Bight, claims evidence of a YDC cooling (Andres et al., 2003). By contrast, this review suggests that there is no conclusive evidence for cooling, or indeed any distinctive climate patterning, during the Younger Dryas Chronozone in Australia.”

Citation: John Tibby, Quaternary International, doi:10.1016/j.quaint.2012.01.003.


When climate change emerges from the noise of natural variability?

Time of emergence of climate signals – Hawkins & Sutton (2012) [FULL TEXT]

Abstract: “The time at which the signal of climate change emerges from the noise of natural climate variability (Time of Emergence, ToE) is a key variable for climate predictions and risk assessments. Here we present a methodology for estimating ToE for individual climate models, and use it to make maps of ToE for surface air temperature (SAT) based on the CMIP3 global climate models. Consistent with previous studies we show that the median ToE occurs several decades sooner in low latitudes, particularly in boreal summer, than in mid-latitudes. We also show that the median ToE in the Arctic occurs sooner in boreal winter than in boreal summer. A key new aspect of our study is that we quantify the uncertainty in ToE that arises not only from inter-model differences in the magnitude of the climate change signal, but also from large differences in the simulation of natural climate variability. The uncertainty in ToE is at least 30 years in the regions examined, and as much as 60 years in some regions. Alternative emissions scenarios lead to changes in both the median ToE (by a decade or more) and its uncertainty. The SRES B1 scenario is associated with a very large uncertainty in ToE in some regions. Our findings have important implications for climate modelling and climate policy which we discuss.”

Citation: Hawkins, E. and R. Sutton (2012), Geophys. Res. Lett., 39, L01702, doi:10.1029/2011GL050087.


Westerlies describe North Atlantic Oscillation back to 1692

Estimates of the North Atlantic Oscillation back to 1692 using a Paris–London westerly index – Cornes et al. (2012)

Abstract: “A westerly index for Europe is developed back to 1692 using newly recovered and corrected Mean Sea-level Pressure (MSLP) data from London and Paris. The index is compared against various instrumental and proxy indices of the North Atlantic Oscillation (NAO). In the winter, the Paris-London index depicts a spatial pattern of atmospheric circulation that is bi-modal, with centres of action that are shifted eastwards compared to the NAO. Owing to asymmetry in the NAO the Paris-London index provides a good depiction of positive NAO conditions as well as extreme negative phases of the NAO that arise from reversals of the pressure centres, but less extreme negative NAO conditions are associated with westerly index values approaching zero. The merit in using the Paris-London index lies with its consistency over time as a measure of westerly wind flow, which may not be the case with other proxy-based indices. In the summer, the Paris-London index bears a close relationship to the reconstructed high-summer NAO series of Folland et al. (2009) as well as the summer Luterbacher et al. (1999) NAO reconstruction. An important finding is that the summer NAO was highly variable during the early nineteenth century but was predominately positive on the decadal time scale during that period. Since circa 1970 the summer index has mostly been negative, indicating reduced westerlies and increased blocking conditions that are exceptional in the context of the last 250 years.”

Citation: Richard C. Cornes, Philip D. Jones, Keith R. Briffa, Timothy J. Osborn, International Journal of Climatology, DOI: 10.1002/joc.3416.


New article says cosmic rays have strong effect to climate

Cosmic rays and space weather: effects on global climate change – Dorman (2012) [FULL TEXT]

Comments: This paper makes a case for strong effect of cosmic rays on climate. However, the paper seems to ignore most of the papers showing evidence against the cosmic ray hypothesis. There are plenty of such papers. Discussion section mentions couple of them in passing but otherwise they are ignored. Paper also seems to use very old data, as is evident for example in Figures 2, 3, and 4, but newer data is not touched.

Abstract: “We consider possible effects of cosmic rays and some other space factors on the Earth’s climate change. It is well known that the system of internal and external factors formatting the climate is very unstable; decreasing planetary temperature leads to an increase of snow surface, and decrease of the total solar energy input into the system decreases the planetary temperature even more, etc. From this it follows that even energetically small factors may have a big influence on climate change. In our opinion, the most important of these factors are cosmic rays and cosmic dust through their influence on clouds, and thus, on climate.”

Citation: Dorman, L. I., Ann. Geophys., 30, 9-19, doi:10.5194/angeo-30-9-2012, 2012.


Different malaria species react differently to warming in India’s Thar Desert

Influence of climate on incidences of malaria in the Thar Desert, northwest India – Jhajharia et al. (2012)

Abstract: “Climatic variability and rise in temperature are considered as the key determinants to the transmission of malaria. In the present study, the trends in the cases of malaria caused by Plasmodium falciparum and Plasmodium vivax were investigated by using the nonparametric Mann-Kendall test after removing the effect of significant lag-1 serial correlation from the time series of cases of malaria incidence by pre-whitening in annual, seasonal, and monthly time scales at Bikaner, located in the Thar Desert of Rajasthan, in northwest India. Multi-collinearity within the datasets under consideration was investigated by means of correlation matrix, the Bartlett sphericity test, and the Kaiser-Meyer-Olkin measure of sampling adequacy, subsequent to which it was removed by using principal component analysis. Finally, artificial neural network models were employed to predict cases of malaria incidence caused by P. falciparum and P. vivax at various scales. During the last 34 years from 1975 to 2008, P. falciparum malaria incidence cases have been found to increase significantly corresponding to monthly (April and September) and seasonal (monsoon) time scales over Bikaner. On the other hand, no significant trends were observed in P. vivax malaria cases at Bikaner. Concomitant increases in P. falciparum cases of malaria incidence and observed temperature increases at Bikaner hint that P. falciparum malaria may have grown significantly under the warming climate of the Thar Desert.”

Citation: Deepak Jhajharia, Surajit Chattopadhyay, Rahul R. Choudhary, Vas Dev, Vijay P. Singh, Shankar Lal, International Journal of Climatology, DOI: 10.1002/joc.3424.


Review article on East Siberian Arctic Shelf carbon transport

On carbon transport and fate in the East Siberian Arctic land–shelf–atmosphere system – Semiletov et al. (2012) [FULL TEXT]

Abstract: “This review paper summarizes current understanding of the transport of organic carbon to, and the fate of organic carbon within, the East Siberian Arctic Shelf (ESAS), and of processes determining carbon dioxide (CO2) and methane (CH4) fluxes from the ESAS to the atmosphere achieved from analyzing the data sets obtained on 20 expeditions performed from 1999 to 2011. This study of the ESAS was aimed at investigating how redistribution of old carbon from degrading terrestrial and sub-sea permafrost and from coastal erosion contributes to the carbon pool of the ESAS, how changes in the hydrological cycle of the surrounding land and alteration of terrestrial carbon cycles affect the hydrological and biogeochemical parameters of shelf water masses, and which factors control CH4 and CO2 emissions from the ESAS. This report describes selected results achieved by a developing international scientific partnership that has been crucial at every stage of the study and will be even more important in the future.”

Citation: Igor P Semiletov et al 2012 Environ. Res. Lett. 7 015201 doi:10.1088/1748-9326/7/1/015201.


Female corals are more vulnerable to elevated carbon dioxide

An investigation of the calcification response of the scleractinian coral Astrangia poculata to elevated pCO2 and the effects of nutrients, zooxanthellae and gender – Holcomb et al. (2012) [FULL TEXT]

Abstract: “The effects of nutrients and pCO2 on zooxanthellate and azooxanthellate colonies of the temperate scleractinian coral Astrangia poculata (Ellis and Solander, 1786) were investigated at two different temperatures (16 °C and 24 °C). Corals exposed to elevated pCO2 tended to have lower relative calcification rates, as estimated from changes in buoyant weights. Experimental nutrient enrichments had no significant effect nor did there appear to be any interaction between pCO2 and nutrients. Elevated pCO2 appeared to have a similar effect on coral calcification whether zooxanthellae were present or absent at 16 °C. However, at 24 °C, the interpretation of the results is complicated by a significant interaction between gender and pCO2 for spawning corals. At 16 °C, gamete release was not observed, and no gender differences in calcification rates were observed – female and male corals showed similar reductions in calcification rates in response to elevated CO2 (15% and 19% respectively). Corals grown at 24 °C spawned repeatedly and male and female corals exhibited two different growth rate patterns – female corals grown at 24 °C and exposed to CO2 had calcification rates 39% lower than females grown at ambient CO2, while males showed a non-significant decline of 5% under elevated CO2. The increased sensitivity of females to elevated pCO2 may reflect a greater investment of energy in reproduction (egg production) relative to males (sperm production). These results suggest that both gender and spawning are important factors in determining the sensitivity of corals to ocean acidification, and considering these factors in future research may be critical to predicting how the population structures of marine calcifiers will change in response to ocean acidification.”

Citation: Holcomb, M., Cohen, A. L., and McCorkle, D. C., Biogeosciences, 9, 29-39, doi:10.5194/bg-9-29-2012, 2012.


Inland waters take in organic carbon and emit methane

Extreme organic carbon burial fuels intense methane bubbling in a temperate reservoir – Sobek et al. (2012)

Abstract: “Organic carbon (OC) burial and greenhouse gas emission of inland waters plays an increasingly evident role in the carbon balance of the continents, and particularly young reservoirs in the tropics emit methane (CH4) at high rates. Here we show that an old, temperate reservoir acts simultaneously as a strong OC sink and CH4 source, because the high sedimentation rate supplies reactive organic matter to deep, anoxic sediment strata, fuelling methanogenesis and gas bubble emission (ebullition) of CH4 from the sediment. Damming of the river has resulted in the build-up of highly methanogenic sediments under a shallow water column, facilitating the transformation of fixed CO2 to atmospheric CH4. Similar high OC burial and CH4 ebullition is expected in other reservoirs and natural river deltas.”

Citation: Sobek, S., T. DelSontro, N. Wongfun, and B. Wehrli (2012), Geophys. Res. Lett., 39, L01401, doi:10.1029/2011GL050144.


Small net positive radiative forcing of dark aerosols above bright clouds

Direct and semi-direct radiative forcing of smoke aerosols over clouds – Wilcox (2012) [FULL TEXT]

Abstract: “Observations from Earth observing satellites indicate that dark carbonaceous aerosols that absorb solar radiation are widespread in the tropics and subtropics. When these aerosols mix with clouds, there is generally a reduction of cloudiness owing to absorption of solar energy in the aerosol layer. Over the subtropical South Atlantic Ocean, where smoke from savannah burning in southern Africa resides above a persistent deck of marine stratocumulus clouds, radiative heating of the smoke layer leads to a thickening of the cloud layer. Here, satellite observations of the albedo of overcast scenes of 25 km2 size or larger are combined with additional satellite observations of clouds and aerosols to estimate the top-of-atmosphere direct radiative forcing attributable to presence of dark aerosol above bright cloud, and the negative semi-direct forcing attributable to the thickening of the cloud layer. The average positive direct radiative forcing by smoke over an overcast scene is 9.2±6.6 W m−2 for cases with an unambiguous signal of absorbing aerosol over cloud in passive ultraviolet remote sensing observations. However, cloud liquid water path is enhanced by 16.3±7.7 g m−2 across the range of values for sea surface temperature for cases of smoke over cloud. The negative radiative forcing associated with this semi-direct effect of smoke over clouds is estimated to be −5.9±3.5 W m−2. Therefore, the cooling associated with the semi-direct cloud thickening effect compensates for greater than 60 % of the direct radiative effect. Accounting for the frequency of occurrence of significant absorbing aerosol above overcast scenes leads to an estimate of the average direct forcing of 1.0±0.7 W m−2 contributed by these scenes averaged over the subtropical southeast Atlantic Ocean during austral winter. The regional average of the negative semi-direct forcing is −0.7±0.4 W m−2. Therefore, smoke aerosols overlaying the decks of overcast marine stratocumulus clouds considered here yield a small net positive radiative forcing, which results from the difference of two larger effects.”

Citation: Wilcox, E. M., Atmos. Chem. Phys., 12, 139-149, doi:10.5194/acp-12-139-2012, 2012.


CLASSIC OF THE WEEK: Schneider (1972)

Cloudiness as a Global Climatic Feedback Mechanism: The Effects on the Radiation Balance and Surface Temperature of Variations in Cloudiness – Schneider (1972) [FULL TEXT]

Abstract: “The effect of variation in cloudiness on the climate is considered in terms of 1) a relation between the radiation balance of the earth-atmosphere system and variations in the amount of cloud cover or effective cloud top height, 2) the effect on the surface temperature of variations in cloudiness, and 3) the dynamic coupling or “feedback” effects relating changes in surface temperature to the formation of clouds. The first two points are studied by numerical integration of a simple radiation flux model, and the third point is discussed qualitatively. Global-average radiation balance calculations show that an increase in the amount of low and middle level cloud cover (with cloud top height and cloud albedo fixed) decreases the surface temperature. But, this result for the global-average case does not hold near polar regions, where the albedo of the cloudy areas can he comparable to (or even smaller than) the albedo of the snow-covered cloudless areas, and where, especially in the winter season, the amount of incoming solar radiation at high latitudes is much less than the global-average value of insolation. The exact latitude at which surface cooling changes to surface warming from a given increase in cloud cover amount depends critically upon the local values of the cloud albedo and the albedo of the cloudless areas that are used in the calculation. However, an increase in effective cloud top height (with cloud cover and cloud albedo fixed) increases the surface temperature at all latitudes.”

Citation: Schneider, Stephen H., 1972, J. Atmos. Sci., 29, 1413–1422, doi: http://dx.doi.org/10.1175/1520-0469(1972)0292.0.CO;2.

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New research from last week 52/2011

Posted by Ari Jokimäki on January 2, 2012

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.

Multiyear ice turning to seasonal ice in Arctic Ocean

On the Arctic Ocean ice thickness response to changes in the external forcing – Stranne & Björk (2011) “Submarine and satellite observations show that the Arctic Ocean ice cover has undergone a large thickness reduction and a decrease in the areal extent during the last decades. Here the response of the Arctic Ocean ice cover to changes in the poleward atmospheric energy transport, F wall, is investigated using coupled atmosphere-ice-ocean column models. Two models with highly different complexity are used in order to illustrate the importance of different internal processes and the results highlight the dramatic effects of the negative ice thickness—ice volume export feedback and the positive surface albedo feedback. The steady state ice thickness as a function of F wall is determined for various model setups and defines what we call ice thickness response curves. When a variable surface albedo and snow precipitation is included, a complex response curve appears with two distinct regimes: a perennial ice cover regime with a fairly linear response and a less responsive seasonal ice cover regime. The two regimes are separated by a steep transition associated with surface albedo feedback. The associated hysteresis is however small, indicating that the Arctic climate system does not have an irreversible tipping point behaviour related to the surface albedo feedback. The results are discussed in the context of the recent reduction of the Arctic sea ice cover. A new mechanism related to regional and temporal variations of the ice divergence within the Arctic Ocean is presented as an explanation for the observed regional variation of the ice thickness reduction. Our results further suggest that the recent reduction in areal ice extent and loss of multiyear ice is related to the albedo dependent transition between seasonal and perennial ice i.e. large areas of the Arctic Ocean that has previously been dominated by multiyear ice might have been pushed below a critical mean ice thickness, corresponding to the above mentioned transition, and into a state dominated by seasonal ice.” Christian Stranne and Göran Björk, Climate Dynamics, DOI: 10.1007/s00382-011-1275-y.

Cold Arctic winters might come with ozone holes

Arctic winter 2010/2011 at the brink of an ozone hole – Sinnhuber et al. (2011) “The Arctic stratospheric winter of 2010/2011 was one of the coldest on record with a large loss of stratospheric ozone. Observations of temperature, ozone, nitric acid, water vapor, nitrous oxide, chlorine nitrate and chlorine monoxide from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) onboard ENVISAT are compared to calculations with a chemical transport model (CTM). There is overall excellent agreement between the model calculations and MIPAS observations, indicating that the processes of denitrification, chlorine activation and catalytic ozone depletion are sufficiently well represented. Polar vortex integrated ozone loss reaches 120 Dobson Units (DU) by early April 2011. Sensitivity calculations with the CTM give an additional ozone loss of about 25 DU at the end of the winter for a further cooling of the stratosphere by 1 K, showing locally near-complete ozone depletion (remaining ozone <200 ppbv) over a large vertical extent from 16 to 19 km altitude. In the CTM a 1 K cooling approximately counteracts a 10% reduction in stratospheric halogen loading, a halogen reduction that is expected to occur in about 13 years from now. These results indicate that severe ozone depletion like in 2010/2011 or even worse could appear for cold Arctic winters over the next decades if the observed tendency for cold Arctic winters to become colder continues into the future." Sinnhuber, B.-M., G. Stiller, R. Ruhnke, T. von Clarmann, S. Kellmann, and J. Aschmann (2011), Geophys. Res. Lett., 38, L24814, doi:10.1029/2011GL049784.

Some clouds go undetected by some cloud-detecting satellites

Cloud features detected by MODIS but not by CloudSat and CALIOP – Chan & Comiso (2011) “The ability to characterize the global cloud cover from space has been greatly enhanced by the availability of MODIS, CloudSat, and CALIOP data. The three sensors provide good complementary information about clouds. In this study, we investigated unexpected observations of certain types of clouds apparent in the MODIS data but not detected by CloudSat and CALIOP. Several examples are presented and generally these undetected clouds are geometrically thin, low-level clouds. In particular, they are located in the Arctic region and have optical thicknesses of less than 14, top height altitudes of below 2.5 km, and layer thickness of less than 1 km. CloudSat may miss such low-level clouds because of its coarse vertical resolution of about 500 m and it has limited sensitivity near the surface. Unexpectedly, CALIOP with a much higher vertical resolution of 30 m also misses these clouds and this is due to the cloud’s geometrically thin nature and surface proximity.” Chan, M. A. and J. C. Comiso (2011), Geophys. Res. Lett., 38, L24813, doi:10.1029/2011GL050063.

Global warming is projected to increase hydroclimate variability

Does global warming cause intensified interannual hydroclimate variability? – Seager et al. (2011) “The idea that global warming leads to more droughts and floods has become commonplace without clear indication of what is meant by this statement. Here we examine one aspect of this problem and assess whether interannual variability of precipitation (P) minus evaporation (E) becomes stronger in the 21st Century compared to the 20th Century, as deduced from an ensemble of models participating in Coupled Model Intercomparison Project 3. It is shown that indeed interannual variability of P-E does increase almost everywhere across the planet with a few notable exceptions such as southwestern North America and some subtropical regions. The variability increases most at the Equator and the high latitudes and least in the subtropics. While most interannual P-E variability arises from internal atmosphere variability the primary potentially predictable component is related to the El Niño-Southern Oscillation (ENSO). ENSO-driven interannual P-E variability clearly increases in amplitude in the tropical Pacific but elsewhere the changes are more complex. This is not surprising in that ENSO-driven P-E anomalies are primarily caused by circulation anomalies combining with the climatological humidity field. As climate warms and the specific humidity increases this term leads to an intensification of ENSO-driven P-E variability. However, ENSO-driven circulation anomalies also change, in some regions amplifying, but in others opposing and even overwhelming, the impact of rising specific humidity. Consequently there is sound scientific basis for anticipating a general increase in interannual P-E variability but the predictable component will depend in a more complex way on both thermodynamic responses to global warming and on how tropically-forced circulation anomalies alter.” Richard Seager, Naomi Naik, Laura Vogel, Journal of Climate, doi: http://dx.doi.org/10.1175/JCLI-D-11-00363.1. [Full text]

No evidence for robust link between cloud cover and solar activity/cosmic rays

Solar irradiance, cosmic rays and cloudiness over daily timescales – Laken & Čalogović (2011) “Although over centennial and greater timescales solar variability may be one of the most influential climate forcing agents, the extent to which solar activity influences climate over shorter time periods is poorly understood. If a link exists between solar activity and climate, it is likely via a mechanism connected to one (or a combination) of the following parameters: total solar irradiance (TSI), ultraviolet (UV) spectral irradiance, or the galactic cosmic ray (GCR) flux. We present an analysis based around a superposed epoch (composite) approach focusing on the largest TSI increases and decreases (the latter occurring in both the presence and absence of appreciable GCR reductions) over daily timescales. Using these composites we test for the presence of a robust link between solar activity and cloud cover over large areas of the globe using rigorous statistical techniques. We find no evidence that widespread variations in cloud cover at any tropospheric level are significantly associated with changes in the TSI, GCR or UV flux, and further conclude that TSI or UV changes occurring during reductions in the GCR flux are not masking a solar-cloud response. However, we note the detectability of any potential links is strongly constrained by cloud variability.” Laken, B. A. and J. Čalogović(2011), Geophys. Res. Lett., 38, L24811, doi:10.1029/2011GL049764.

Hypoxic and anoxic areas will very likely increase in Baltic Sea with warming climate

Hypoxia in future climates: A model ensemble study for the Baltic Sea – Meier et al. (2011) “Using an ensemble of coupled physical-biogeochemical models driven with regionalized data from global climate simulations we are able to quantify the influence of changing climate upon oxygen conditions in one of the numerous coastal seas (the Baltic Sea) that suffers worldwide from eutrophication and from expanding hypoxic zones. Applying various nutrient load scenarios we show that under the impact of warming climate hypoxic and anoxic areas will very likely increase or at best only slightly decrease (in case of optimistic nutrient load reductions) compared to present conditions, regardless of the used global model and climate scenario. The projected decreased oxygen concentrations are caused by (1) enlarged nutrient loads due to increased runoff, (2) reduced oxygen flux from the atmosphere to the ocean due to increased temperature, and (3) intensified internal nutrient cycling. In future climate a similar expansion of hypoxia as projected for the Baltic Sea can be expected also for other coastal oceans worldwide.” Meier, H. E. M., H. C. Andersson, K. Eilola, B. G. Gustafsson, I. Kuznetsov, B. Müller-Karulis, T. Neumann, and O. P. Savchuk (2011), Geophys. Res. Lett., 38, L24608, doi:10.1029/2011GL049929.

Global monsoon precipitation has intensified

Recent change of the global monsoon precipitation (1979–2008) – Wang et al. (2011) “The global monsoon (GM) is a defining feature of the annual variation of Earth’s climate system. Quantifying and understanding the present-day monsoon precipitation change are crucial for prediction of its future and reflection of its past. Here we show that regional monsoons are coordinated not only by external solar forcing but also by internal feedback processes such as El Niño-Southern Oscillation (ENSO). From one monsoon year (May to the next April) to the next, most continental monsoon regions, separated by vast areas of arid trade winds and deserts, vary in a cohesive manner driven by ENSO. The ENSO has tighter regulation on the northern hemisphere summer monsoon (NHSM) than on the southern hemisphere summer monsoon (SHSM). More notably, the GM precipitation (GMP) has intensified over the past three decades mainly due to the significant upward trend in NHSM. The intensification of the GMP originates primarily from an enhanced east–west thermal contrast in the Pacific Ocean, which is coupled with a rising pressure in the subtropical eastern Pacific and decreasing pressure over the Indo-Pacific warm pool. While this mechanism tends to amplify both the NHSM and SHSM, the stronger (weaker) warming trend in the NH (SH) creates a hemispheric thermal contrast, which favors intensification of the NHSM but weakens the SHSM. The enhanced Pacific zonal thermal contrast is largely a result of natural variability, whilst the enhanced hemispherical thermal contrast is likely due to anthropogenic forcing. We found that the enhanced global summer monsoon not only amplifies the annual cycle of tropical climate but also promotes directly a “wet-gets-wetter” trend pattern and indirectly a “dry-gets-drier” trend pattern through coupling with deserts and trade winds. The mechanisms recognized in this study suggest a way forward for understanding past and future changes of the GM in terms of its driven mechanisms.” Bin Wang, Jian Liu, Hyung-Jin Kim, Peter J. Webster and So-Young Yim, Climate Dynamics, DOI: 10.1007/s00382-011-1266-z. [Full text]

Greenland glacier has 3 positive melt feedbacks active

Three positive feedback mechanisms for ice-sheet melting in a warming climate – Ren & Leslie (2011) “Three positive feedback mechanisms that accelerate ice-sheet melting are assessed in a warming climate, using a numerical ice model driven by atmospheric climate models. The Greenland ice sheet (GrIS) is the modeling test-bed under accelerated melting conditions. The first feedback is the interaction of sea water with ice. It is positive because fresh water melts ice faster than salty water, owing primarily to the reduction in water heat capacity by solutes. It is shown to be limited for the GrIS, which has only a small ocean interface, and the grounding line of some fast glaciers becomes land-terminating during the 21st century. The second positive feedback, strain heating, is positive because it produces further ice heating inside the ice sheet. The third positive feedback, granular basal sliding, applies to all ice sheets and becomes the dominant feedback during the 21st century. A numerical simulation of Jakobshavn Isbrae over the 21st century reveals that all three feedback processes are active for this glacier. Compared with the year 2000 level, annual ice discharge into the ocean could increase by ∼1.4 km3 a-1 (∼5% of the present annual rate) by 2100. Granular basal sliding contributes ∼40% of this increase.” Ren, Diandong; Leslie, Lance M., Journal of Glaciology, Volume 57, Number 206, December 2011 , pp. 1057-1066(10), DOI: http://dx.doi.org/10.3189/002214311798843250.

Tree ring based winter temperature reconstruction from China

Tree ring-based winter temperature reconstruction for Changting, Fujian, subtropical region of Southeast China, since 1850: linkages to the Pacific Ocean – Chen et al. (2011) “Until recently, there have been very few tree-ring studies in southeast China due largely to the scarcity of old trees and the complexity of relationships between tree growth and climate in subtropical regions of China. Recent studies on the conifers in southeast China revealed that tree ring-based climate reconstructions are feasible. Here, we describe a reconstruction (AD 1850–2009) of November–February maximum temperatures for Changting, Fujian, southeast China based on tree ring width data of Pinus massiniana which considerably extends the available climatic information. Calibration and verification statistics for the period 1956–2009 show a high level of skill and account for a significant portion of the observed variance (32.9%) irrespective of which period is used to develop or verify the regression model. Split sample validation supports our use of a reconstruction model based on the full period of reliable observational data (1956–2009). Warm periods occurred during 1854–1859, 1868–1880, 1885–1899, 1906–1914, 1920–1943, 1964–1975 and 1994–present; while the periods of AD 1850–1853, 1860–1867, 1881–1884, 1900–1907, 1915–1919, 1944–1963 and 1976–1993 were relatively cold. The climate correlation analyses with gridded temperature dataset and SST revealed that our season temperature reconstruction contains the strong large-scale climate signals. Our results suggest that some warm winters of Changting are coincident with El Niño events over the past 150 years. In addition, several severely cold winters coincide with major volcanic eruptions.” Feng Chen, Yu-jiang Yuan, Wen-shou Wei, Shu-long Yu and Tong-wen Zhang, Theoretical and Applied Climatology, DOI: 10.1007/s00704-011-0563-0.

Reduced vertical mixing might cause Arctic amplification

Boundary layer stability and Arctic climate change: a feedback study using EC-Earth – Bintanja et al. (2011)“Amplified Arctic warming is one of the key features of climate change. It is evident in observations as well as in climate model simulations. Usually referred to as Arctic amplification, it is generally recognized that the surface albedo feedback governs the response. However, a number of feedback mechanisms play a role in AA, of which those related to the prevalent near-surface inversion have received relatively little attention. Here we investigate the role of the near-surface thermal inversion, which is caused by radiative surface cooling in autumn and winter, on Arctic warming. We employ idealized climate change experiments using the climate model EC-Earth together with ERA-Interim reanalysis data to show that boundary-layer mixing governs the efficiency by which the surface warming signal is ‘diluted’ to higher levels. Reduced vertical mixing, as in the stably stratified inversion layer in Arctic winter, thus amplifies surface warming. Modelling results suggest that both shortwave—through the (seasonal) interaction with the sea ice feedback—and longwave feedbacks are affected by boundary-layer mixing, both in the Arctic and globally, with the effect on the shortwave feedback dominating. The amplifying effect will decrease, however, with climate warming because the surface inversion becomes progressively weaker. We estimate that the reduced Arctic inversion has slowed down global warming by about 5% over the past 2 decades, and we anticipate that it will continue to do so with ongoing Arctic warming.” R. Bintanja, E. C. van der Linden and W. Hazeleger, Climate Dynamics, DOI: 10.1007/s00382-011-1272-1.

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