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Observations of anthropogenic global warming

Archive for August, 2012

New research from last week 34/2012

Posted by Ari Jokimäki on August 27, 2012

Last week scientists were seeking answer to the question: “what is climate”. This question is not so universal that “42” would be correct answer. Also, the answer they got is slightly more complicated than that. Here is what they came up with: −266, 1500, 42, 50–60, 23.4, −0.46, 1000, 8175, 2, 16, 2000, 2, 230, 1, 10-20, 1294±545, 4.05, 0.1-0.2. Looking at the result, we notice that there is a 42 in there. We hypothesize that this is due to climate being a subset of universe. Even though you already know the answer, read the abstracts below anyway, as they might hold some further interesting information.

Year-round mid-tropospheric warming and spring and summer lower stratospheric cooling have occurred over Antarctica

Half-century air temperature change above Antarctica: Observed trends and spatial reconstructions – Screen & Simmonds (2012)

Abstract: “This study provides a comprehensive analysis of observed 50-year (1961–2010) seasonal air temperature trends from radiosonde ascents above Antarctica. Comparisons between multiple radiosonde data sets (homogenized in different ways) at each of eight Antarctic stations reveals substantial differences in the upper-air temperature trend magnitudes and their statistical significance between data sets. However, when considering the average of these data sets at each station, or averaging across all stations, a robust vertical profile of half-century temperature change emerges, characterized by mid-tropospheric warming and stratospheric cooling. Statistically significant Multistation-mean 500 hPa warming (0.1 to 0.2°C decade−1) is found in all seasons, whereas the lower stratospheric cooling has been manifest primarily in austral spring and summer, but with larger magnitudes (−1.0 to −2.0°C decade−1). We undertake the first spatial reconstructions of pan-Antarctic upper-air temperature trends. They strongly suggest that both the year-round mid-tropospheric warming and spring and summer lower stratospheric cooling have occurred above the entire continent, although their magnitudes and significance vary regionally. The reconstructed 500 hPa warming trends in winter and spring are largest over West Antarctica, the Ross Ice shelf, Victoria Land and Oates Land, and show close resemblance to those found in previously published surface temperature trend reconstructions, suggesting coupling between the surface and trends aloft. We speculate that the winter and spring mid-tropospheric warming may, in part, be driven by tropical ocean warming, analogous to proposed mechanisms for the co-located surface warming. The spring and summer lower stratospheric cooling is entirely consistent with the temperature response to ozone depletion.”

Citation: Screen, J. A., and I. Simmonds (2012), Half-century air temperature change above Antarctica: Observed trends and spatial reconstructions, J. Geophys. Res., 117, D16108, doi:10.1029/2012JD017885.

Global patterns of tropospheric nitrogen dioxide trends observed from satellite

A global single-sensor analysis of 2002–2011 tropospheric nitrogen dioxide trends observed from space – Schneider & van der A (2012)

Abstract: “A global nine-year archive of monthly tropospheric NO2 data acquired by the SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY (SCIAMACHY) instrument was analyzed with respect to trends between August 2002 and August 2011. In the past, similar studies relied on combining data from multiple sensors; however, the length of the SCIAMACHY data set now for the first time allows utilization of a consistent time series from just a single sensor for mapping NO2 trends at comparatively high horizontal resolution (0.25°). This study provides an updated analysis of global patterns in NO2 trends and finds that previously reported decreases in tropospheric NO2 over Europe and the United States as well as strong increases over China and several megacities in Asia have continued in recent years. Positive trends of up to 4.05 (±0.41) × 1015 molecules cm−2 yr−1 and up to 19.7 (±1.9) % yr−1 were found over China, with the regional mean trend being 7.3 (±3.1) % yr−1. The megacity with the most rapid relative increase was found to be Dhaka in Bangladesh. Subsequently focusing on Europe, the study further analyzes trends by country and finds significantly decreasing trends for seven countries ranging from −3.0 (±1.6) % yr−1 to −4.5 (±2.3) % yr−1. A comparison of the satellite data with station data indicates that the trends derived from both sources show substantial differences on the station scale, i.e., when comparing a station trend directly with the equivalent satellite-derived trend at the same location, but provide quite similar large-scale spatial patterns. Finally, the SCIAMACHY-derived NO2 trends are compared with equivalent trends in NO2 concentration computed using the Co-operative Programme for Monitoring and Evaluation of the Long-range Transmission of Air Pollutants in Europe (EMEP) model. The results show that the spatial patterns in trends computed from both data sources mostly agree in Central and Western Europe, whereas substantial differences are found in Eastern Europe.”

Citation: Schneider, P., and R. J. van der A (2012), A global single-sensor analysis of 2002–2011 tropospheric nitrogen dioxide trends observed from space, J. Geophys. Res., 117, D16309, doi:10.1029/2012JD017571.

European ecosystems might be unlikely to contribute to mitigating the effects of climate change

The European land and inland water CO2, CO, CH4 and N2O balance between 2001 and 2005 – Cao et al. (2012) [FULL TEXT]

Abstract: “Globally, terrestrial ecosystems have absorbed about 30% of anthropogenic greenhouse gas emissions over the period 2000–2007 and inter-hemispheric gradients indicate that a significant fraction of terrestrial carbon sequestration must be north of the Equator. We present a compilation of the CO2, CO, CH4 and N2O balances of Europe following a dual constraint approach in which (1) a land-based balance derived mainly from ecosystem carbon inventories and (2) a land-based balance derived from flux measurements are compared to (3) the atmospheric data-based balance derived from inversions constrained by measurements of atmospheric GHG (greenhouse gas) concentrations. Good agreement between the GHG balances based on fluxes (1294 ± 545 Tg C in CO2-eq yr−1), inventories (1299 ± 200 Tg C in CO2-eq yr−1) and inversions (1210 ± 405 Tg C in CO2-eq yr−1) increases our confidence that the processes underlying the European GHG budget are well understood and reasonably sampled. However, the uncertainty remains large and largely lacks formal estimates. Given that European net land to atmosphere exchanges are determined by a few dominant fluxes, the uncertainty of these key components needs to be formally estimated before efforts could be made to reduce the overall uncertainty. The net land-to-atmosphere flux is a net source for CO2, CO, CH4and N2O, because the anthropogenic emissions by far exceed the biogenic sink strength. The dual-constraint approach confirmed that the European biogenic sink removes as much as 205 ± 72 Tg C yr−1 from fossil fuel burning from the atmosphere. However, This C is being sequestered in both terrestrial and inland aquatic ecosystems. If the C-cost for ecosystem management is taken into account, the net uptake of ecosystems is estimated to decrease by 45% but still indicates substantial C-sequestration. However, when the balance is extended from CO2 towards the main GHGs, C-uptake by terrestrial and aquatic ecosystems is offset by emissions of non-CO2 GHGs. As such, the European ecosystems are unlikely to contribute to mitigating the effects of climate change.”

Citation: Luyssaert, S., Abril, G., Andres, R., Bastviken, D., Bellassen, V., Bergamaschi, P., Bousquet, P., Chevallier, F., Ciais, P., Corazza, M., Dechow, R., Erb, K.-H., Etiope, G., Fortems-Cheiney, A., Grassi, G., Hartmann, J., Jung, M., Lathière, J., Lohila, A., Mayorga, E., Moosdorf, N., Njakou, D. S., Otto, J., Papale, D., Peters, W., Peylin, P., Raymond, P., Rödenbeck, C., Saarnio, S., Schulze, E.-D., Szopa, S., Thompson, R., Verkerk, P. J., Vuichard, N., Wang, R., Wattenbach, M., and Zaehle, S.: The European land and inland water CO2, CO, CH4 and N2O balance between 2001 and 2005, Biogeosciences, 9, 3357-3380, doi:10.5194/bg-9-3357-2012, 2012.

Lumberjacks to blame for the collapse of Mayan civilization?

Pre-Columbian deforestation as an amplifier of drought in Mesoamerica – Cook et al. (2012)

Abstract: “Droughts in pre-Columbian Mesoamerica caused significant societal disruptions during the Late Classic and Post-Classic Periods. While the primary causes of these droughts are still debated, it has been speculated that they may be linked to extensive deforestation associated with high population densities during these intervals. Here we show that pre-Columbian deforestation would have biased the climate in Mesoamerica towards a drier mean state, amplifying drought in the region. In climate model simulations using a pre-Columbian land cover reconstruction, annual precipitation decreases by 5%–15% throughout southern Mexico and the Yucatán compared to simulations using either natural forest cover or forest regrowth associated with population declines after 1500 C.E. These changes are driven primarily by large reductions (10%–20%) in precipitation during the late summer wet season (August–September). When compared to precipitation changes estimated to have occurred during the Maya collapse, our results suggest that deforestation could account for up to sixty percent of the mean drying during this interval. Many regions previously deforested in the pre-Columbian era are now under dense forest cover, indicating potential future climate impacts should tropical deforestation of these areas accelerate.”

Citation: Cook, B. I., K. J. Anchukaitis, J. O. Kaplan, M. J. Puma, M. Kelley, and D. Gueyffier (2012), Pre-Columbian deforestation as an amplifier of drought in Mesoamerica, Geophys. Res. Lett., 39, L16706, doi:10.1029/2012GL052565.

Best skill in decadal climate prediction in Indian Ocean due to low internal to external forcing ratio

The Indian Ocean: the region of highest skill worldwide in decadal climate prediction – Guemas et al. (2012)

Abstract: “The Indian Ocean stands out as the region where the state-of-the-art decadal climate predictions of sea surface temperature (SST) perform the best worldwide for forecast times ranging from the second to the ninth year, according to correlation and RMSE (Root Mean Square Error) scores. This paper investigates the reasons for this high skill, by assessing the contributions from the initial conditions, greenhouse gases, solar activity and volcanic aerosols. The comparison between the SST correlation skill in uninitialized historical simulations and hindcasts initialized from estimates of the observed climate state shows that the high Indian Ocean skill is largely explained by the varying radiative forcings, the latter finding being supported by a set of additional sensitivity experiments. The long-term warming trend is the primary contributor to the high skill, though not the only one. Volcanic aerosols bring additional skill in this region as shown by the comparison between initialized hindcasts taking into account or not the effect of volcanic stratospheric aerosols and by the drop in skill when filtering out their effect in hindcasts which take them into account. Indeed, the Indian Ocean is shown to be the region where the ratio of the internally-generated over the externally-forced variability is the lowest, where the amplitude of the internal variability has been estimated by removing the effect of long-term warming trend and volcanic aerosols by a multiple least-square linear regression on observed SSTs.”

Citation: Virginie Guemas, Susanna Corti, J. García-Serrano, F. J. Doblas-Reyes, Magdalena Balmaseda and Linus Magnusson, Journal of Climate 2012, doi:

Sunspot minima contribute to cold winters in central Europe

Solar influence on winter severity in central Europe – Sirocko et al. (2012)

Abstract: “The last two winters in central Europe were unusually cold in comparison to the years before. Meteorological data, mainly from the last 50 years, and modelling studies have suggested that both solar activity and El Niño strength may influence such central European winter coldness. To investigate the mechanisms behind this in a statistically robust way and to test which of the two factors was more important during the last 230 years back into the Little Ice Age, we use historical reports of freezing of the river Rhine. The historical data show that 10 of the 14 freeze years occurred close to sunspot minima and only one during a year of moderate El Niño. This solar influence is underpinned by corresponding atmospheric circulation anomalies in reanalysis data covering the period 1871 to 2008. Accordingly, weak solar activity is empirically related to extremely cold winter conditions in Europe also on such long time scales. This relationship still holds today, however the average winter temperatures have been rising during the last decades.”

Citation: Sirocko, F., H. Brunck, and S. Pfahl (2012), Solar influence on winter severity in central Europe, Geophys. Res. Lett., 39, L16704, doi:10.1029/2012GL052412.

Significant climate effects occur within days of a stepwise increase in atmospheric CO2 or solar irradiance

Climate response to changes in atmospheric carbon dioxide and solar irradiance on the time scale of days to weeks – Cao et al. (2012) [FULL TEXT]

Abstract: “Recent studies show that fast climate response on time scales of less than a month can have important implications for long-term climate change. In this study, we investigate climate response on the time scale of days to weeks to a step-function quadrupling of atmospheric CO2 and contrast this with the response to a 4% increase in solar irradiance. Our simulations show that significant climate effects occur within days of a stepwise increase in both atmospheric CO2 content and solar irradiance. Over ocean, increased atmospheric CO2 warms the lower troposphere more than the surface, increasing atmospheric stability, moistening the boundary layer, and suppressing evaporation and precipitation. In contrast, over ocean, increased solar irradiance warms the lower troposphere to a much lesser extent, causing a much smaller change in evaporation and precipitation. Over land, both increased CO2 and increased solar irradiance cause rapid surface warming that tends to increase both evaporation and precipitation. However, the physiological effect of increased atmospheric CO2 on plant stomata reduces plant transpiration, drying the boundary layer and decreasing precipitation. This effect does not occur with increased solar irradiance. Therefore, differences in climatic effects from CO2 versus solar forcing are manifested within days after the forcing is imposed.”

Citation: Long Cao et al 2012 Environ. Res. Lett. 7 034015 doi:10.1088/1748-9326/7/3/034015.

Strong mass loss at low elevations has had dynamic impact on the entire Greenland ice sheet

Dynamic inland propagation of thinning due to ice loss at the margins of the Greenland ice sheet – Wang et al. (2012) [FULL TEXT]

Abstract: “Mass-balance analysis of the Greenland ice sheet based on surface elevation changes observed by the European Remote-sensing Satellite (ERS) (1992-2002) and Ice, Cloud and land Elevation Satellite (ICESat) (2003-07) indicates that the strongly increased mass loss at lower elevations (<2000 m) of the ice sheet, as observed during 2003-07, appears to induce interior ice thinning at higher elevations. In this paper, we perform a perturbation experiment with a three-dimensional anisotropic ice-flow model (AIF model) to investigate this upstream propagation. Observed thinning rates in the regions below 2000 m elevation are used as perturbation inputs. The model runs with perturbation for 10 years show that the extensive mass loss at the ice-sheet margins does in fact cause interior thinning on short timescales (i.e. decadal). The modeled pattern of thinning over the ice sheet agrees with the observations, which implies that the strong mass loss since the early 2000s at low elevations has had a dynamic impact on the entire ice sheet. The modeling results also suggest that even if the large mass loss at the margins stopped, the interior ice sheet would continue thinning for 300 years and would take thousands of years for full dynamic recovery.”

Citation: Wang, Weili; Li, Jun; Zwally, H. Jay, Journal of Glaciology, Volume 58, Number 210, August 2012 , pp. 734-740(7), DOI:

Ice regimes in thermokarst lakes of northern Alaska shifting from bedfast ice to floating ice

Shifting balance of thermokarst lake ice regimes across the Arctic Coastal Plain of northern Alaska – Arp et al. (2012)

Abstract: “The balance of thermokarst lakes with bedfast- and floating-ice regimes across Arctic lowlands regulates heat storage, permafrost thaw, winter-water supply, and over-wintering aquatic habitat. Using a time-series of late-winter synthetic aperture radar (SAR) imagery to distinguish lake ice regimes in two regions of the Arctic Coastal Plain of northern Alaska from 2003–2011, we found that 18% of the lakes had intermittent ice regimes, varying between bedfast-ice and floating-ice conditions. Comparing this dataset with a radar-based lake classification from 1980 showed that 16% of the bedfast-ice lakes had shifted to floating-ice regimes. A simulated lake ice thinning trend of 1.5 cm/yr since 1978 is believed to be the primary factor driving this form of lake change. The most profound impacts of this regime shift in Arctic lakes may be an increase in the landscape-scale thermal offset created by additional lake heat storage and its role in talik development in otherwise continuous permafrost as well as increases in over-winter aquatic habitat and winter-water supply.”

Citation: Arp, C. D., B. M. Jones, Z. Lu, and M. S. Whitman (2012), Shifting balance of thermokarst lake ice regimes across the Arctic Coastal Plain of northern Alaska, Geophys. Res. Lett., 39, L16503, doi:10.1029/2012GL052518.

There might be a threshold in atmospheric carbon dioxide beyond which the Hadley circulation shrinks drastically

Drastic shrinking of the Hadley circulation during the mid-Cretaceous Supergreenhouse – Hasegawa et al. (2012) [FULL TEXT]

Abstract: “Understanding the behavior of the global climate system during extremely warm periods is one of the major themes of paleoclimatology. Proxy data demonstrate that the equator-to-pole temperature gradient was much lower during the mid-Cretaceous “supergreenhouse” period than at present, implying larger meridional heat transport by atmospheric and/or oceanic circulation. However, reconstructions of atmospheric circulation during the Cretaceous have been hampered by a lack of appropriate datasets based on reliable proxies. Desert distribution directly reflects the position of the subtropical high-pressure belt, and the prevailing surface-wind pattern preserved in desert deposits reveals the exact position of its divergence axis, which marks the poleward margin of the Hadley circulation. We reconstructed temporal changes in the latitude of the subtropical high-pressure belt and its divergence axis during the Cretaceous based on spatio-temporal changes in the latitudinal distribution of deserts and prevailing surface-wind patterns in the Asian interior. We found a poleward shift in the subtropical high-pressure belt during the early and late Cretaceous, suggesting a poleward expansion of the Hadley circulation. In contrast, an equatorward shift of the belt was found during the mid-Cretaceous “supergreenhouse” period, suggesting drastic shrinking of the Hadley circulation. These results, in conjunction with recent observations, suggest the existence of a threshold in atmospheric CO2 level and/or global temperature, beyond which the Hadley circulation shrinks drastically.”

Citation: Hasegawa, H., Tada, R., Jiang, X., Suganuma, Y., Imsamut, S., Charusiri, P., Ichinnorov, N., and Khand, Y.: Drastic shrinking of the Hadley circulation during the mid-Cretaceous Supergreenhouse, Clim. Past, 8, 1323-1337, doi:10.5194/cp-8-1323-2012, 2012.

Finally evidence for 8.2 ka event related glacier advance from Alps

The 8.2 ka event—Calendar-dated glacier response in the Alps – Nicolussi & Schlüchter (2012)

Abstract: “Evidence for an 8.2 ka event–related advance for an Alpine glacier was missing for a long time. In the light of dendrochronological analyses for tree remains found in front of the Mont Miné Glacier, Swiss Alps, we present evidence for such an advance related to the 8.2 ka event. Calendar dates established for dozens of tree remains place this glacier advance ∼8175 yr before A.D. 2000. Therefore, this 8.2 ka advance response of the Mont Miné Glacier terminated a nearly millennial-long retreat period with a glacier always shorter than today.”

Citation: Kurt Nicolussi and Christian Schlüchter, Geology, v. 40 no. 9 p. 819-822, doi: 10.1130/G32406.1.

Incidence of extreme floods in New Zealand and the UK has been largely asynchronous during the Holocene

New Zealand and UK Holocene flooding demonstrates interhemispheric climate asynchrony – Macklin et al. (2012)

Abstract: “The timing and controls of interhemispheric Holocene climate change have remained poorly understood, primarily because of the absence of well-dated and continuous climatic records in terrestrial environments. Here we report a new probability-based meta-analysis of 1185 14C dates from fluvial sedimentary sequences in New Zealand and the UK, which provides a robust means of identifying centennial- and multicentennial-length episodes of Holocene river flooding. Statistical analysis shows that prior to large-scale human impact, which began at ca. 1000 cal. yr B.P., the incidence of extreme floods in New Zealand and the UK has been largely asynchronous during the Holocene. Major periods of flooding are controlled by large-scale shifts in atmospheric circulation, which alter the frequency of extreme precipitation events. Our novel synthesis demonstrates that short-term climate change, of sufficient magnitude to modify flooding regimes, was out of phase in the temperate maritime regions of the Northern and Southern Hemispheres during much of the Holocene. This supports recent evidence from both glacial and marine records that Holocene climate changes may have been antiphased between the polar regions and that this could have been related to variation in the strength of deep water formation.”

Citation: Mark G. Macklin, Ian C. Fuller, Anna F. Jones and Mark Bebbington, Geology, v. 40 no. 9 p. 775-778, doi: 10.1130/G33364.1.

Observed trends in climate indices cannot be explained by natural forcings alone

Evaluating global climate responses to different forcings using simple indices – Drost & Karoly (2012)

Abstract: “Previous studies have shown that various climate indices based on surface temperature can be used in detection and attribution studies of climate change. Besides global mean surface temperature, these indices are the contrast between surface temperature over land and over oceans, the temperature contrast between the Northern and Southern Hemispheres, the meridional temperature gradient in the Northern Hemisphere and the magnitude of the annual cycle of temperatures over land. The indices vary independently from the global mean at decadal timescales, yet show common responses to anthropogenic climate change. Collectively they are more useful in detecting and attributing climate change than global mean surface temperature alone. We use CMIP5 model data and investigate to what extent observed trends in surface temperature can be attributed to natural and anthropogenic forcings. The multi-model ensemble mean trend for all indices, except for NS, are either at or exceed the 5%–95% confidence interval for no trend. These trends cannot be explained by natural forcings only and additional forcings are required to replicate observed trends. Historical simulations with greenhouse gas forcings only resulted generally in trends in the indices that were larger than those in simulations with all historical forcings and observed. The difference in the trends in the indices between the simulations with all historical forcings and with greenhouse gas forcing only are ascribed to the effect of aerosols.”

Citation: Drost, F. and D. Karoly (2012), Evaluating global climate responses to different forcings using simple indices, Geophys. Res. Lett., 39, L16701, doi:10.1029/2012GL052667.

Brightening of the global cloud field by nitric acid might be important factor in aerosol cooling

Brightening of the global cloud field by nitric acid and the associated radiative forcing – Makkonen et al. (2012) [FULL TEXT]

Abstract: “Clouds cool Earth’s climate by reflecting 20% of the incoming solar energy, while also trapping part of the outgoing radiation. The effect of human activities on clouds is poorly understood, but the present-day anthropogenic cooling via changes of cloud albedo and lifetime could be of the same order as warming from anthropogenic addition in CO2. Soluble trace gases can increase water condensation to particles, possibly leading to activation of smaller aerosols and more numerous cloud droplets. We have studied the effect of nitric acid on the aerosol indirect effect with the global aerosol-climate model ECHAM5.5-HAM2. Including the nitric acid effect in the model increases cloud droplet number concentrations globally by 7%. The nitric acid contribution to the present-day cloud albedo effect was found to be −0.32 W m−2 and to the total indirect effect −0.46 W m−2. The contribution to the cloud albedo effect is shown to increase to −0.37 W m−2 by the year 2100, if considering only the reductions in available cloud condensation nuclei. Overall, the effect of nitric acid can play a large part in aerosol cooling during the following decades with decreasing SO2 emissions and increasing NOx and greenhouse gases.”

Citation: Makkonen, R., Romakkaniemi, S., Kokkola, H., Stier, P., Räisänen, P., Rast, S., Feichter, J., Kulmala, M., and Laaksonen, A.: Brightening of the global cloud field by nitric acid and the associated radiative forcing, Atmos. Chem. Phys., 12, 7625-7633, doi:10.5194/acp-12-7625-2012, 2012.

Glaciers are shrinking in Big Naryn basin in Central Asia

Glacier changes in the Big Naryn basin, Central Tian Shan – Hagg et al. (2012)

Abstract: “A glacier inventory referring to the year 2007 was created for the Big Naryn basin based on satellite imagery. The 507 glaciers had a total area of 471 km². Compared to the Soviet glacier inventory based on data from the mid 20th century, the total glacier area decreased by 23.4%. The shrinkage varies from 14% to 42% between individual mountain ranges. We discuss the possible causes for this considerable variation by analyzing and interpreting topographic parameters and differences between seven sub-regions. On three glaciers, ice thickness was derived by ground penetrating radar (GPR) measurements on the glacier tongues and by surface slope using a simplified ice mechanical approach on the upper parts. We estimate the total ice volume of the basin for both inventories using volume-area scaling. Our results show a current glacier volume of 26.0-33.3 km³. A total of 6.6-8.4 km³ (20%) have been lost since the mid 20th century. The water equivalent of 5.9-7.6 km³ was transformed into excess discharge and contributed to at least 7.3-9.2% of total runoff in the considered period.”

Citation: W. Hagg, C. Mayer, A. Lambrecht, D. Kriegel, E. Azizov, Global and Planetary Change,

Elevated carbon dioxide may affect hydrological cycle by decreasing plant respiration

Deep-time evidence of a link between elevated CO2 concentrations and perturbations in the hydrological cycle via drop in plant transpiration – Steinthorsdottir et al. (2012)

Abstract: “The physiological effects of high CO2 concentrations, i.e., [CO2], on plant stomatal responses may be of major importance in understanding the consequences of climate change, by causing increases in runoff through suppression of plant transpiration. Radiative forcing by high [CO2] has been the main consideration in models of global change to the exclusion of plant physiological forcing, but this potentially underestimates the effects on the hydrological cycle, and the consequences for ecosystems. We tested the physiological responses of fossil plants from the Triassic–Jurassic boundary transition (Tr–J) succession of East Greenland. This interval marks a major high CO2-driven environmental upheaval, with faunal mass extinctions and significant floral turnover. Our results show that both stomatal size (expressed in fossil material as SL, the length of the stomatal complex opening) and stomatal density (SD, the number of stomata per mm2) decreased significantly during the Tr–J. We estimate, using a leaf gas-exchange model, that the decreases in SD and SL resulted in a 50%–60% drop in stomatal and canopy transpiration at the Tr–J. We also present new field evidence indicating simultaneous increases in runoff and erosion rates. We propose that the consequences of stomatal responses to elevated [CO2] may lead to locally increased runoff and erosion, and may link terrestrial and marine biodiversity loss via the hydrological cycle.”

Citation: Margret Steinthorsdottir, F. Ian Woodward, Finn Surlyk and Jennifer C. McElwain, Geology, v. 40 no. 9 p. 815-818, doi: 10.1130/G33334.1.

Record low temperature minimums decreasing and record high maximums increasing in United States

Trends in record-breaking temperatures for the conterminous United States – Rowe & Derry (2012)

Abstract: “In an unchanging climate, record-breaking temperatures are expected to decrease in frequency over time, as established records become increasingly more difficult to surpass. This inherent trend in the number of record-breaking events confounds the interpretation of actual trends in the presence of any underlying climate change. Here, a simple technique to remove the inherent trend is introduced so that any remaining trend can be examined separately for evidence of a climate change. As this technique does not use the standard definition of a broken record, our records* are differentiated by an asterisk. Results for the period 1961–2010 indicate that the number of record* low daily minimum temperatures has been significantly and steadily decreasing nearly everywhere across the United States while the number of record* high daily minimum temperatures has been predominantly increasing. Trends in record* low and record* high daily maximum temperatures are generally weaker and more spatially mixed in sign. These results are consistent with other studies examining changes expected in a warming climate.”

Citation: Rowe, C. M. and L. E. Derry (2012), Trends in record-breaking temperatures for the conterminous United States, Geophys. Res. Lett., 39, L16703, doi:10.1029/2012GL052775.

Early 20th century abruptly ended a 1500-year period favoring Castle Creek Glacier expansion

Late Holocene glacier expansion in the Cariboo and northern Rocky Mountains, British Columbia, Canada – Maurer et al. (2012)

Abstract: “Castle Creek Glacier in the Cariboo Mountains of British Columbia remained close to its Little Ice Age limit for most of the past 1500 years, without significant recession until the 20th century. This conclusion is based on radiocarbon-dated detrital and in-situ plant material overrun by the glacier, and the sedimentary record from informally named On–off Lake, which received clastic sediments only when Castle Creek Glacier crossed a hydrologic divide 330 m upvalley of the Little Ice Age limit. Plant macrofossils recovered from the transition between basal inorganic silt and overlying organic silty clay in a sediment core from the lake indicate that the glacier first retreated behind the divide ca. 10.92–9.70 ka. Ages of 8.97–8.61 and 5.58–5.53 ka on detrital wood from the glacier’s forefield may record earlier advances, but the first unequivocal evidence of glacier expansion is from an overridden stump with an age of 4.96–4.45 ka. Continuous accumulation of gyttja within On–off Lake, however, indicates that Castle Creek Glacier did not cross the hydrologic divide at any time during the first half of the Holocene. Glacigenic sediments began to accumulate in the lake between 2.73 and 2.49 ka, indicating that Castle Creek Glacier expanded beyond the hydrologic divide at that time. A coincident advance is also recorded in the northern Rocky Mountains of British Columbia at Kwadacha Glacier, which overran a vegetated surface at 2.69–2.36 ka. Clastic sedimentation in On–off Lake ceased soon after the Bridge River volcanic eruption (2.70–2.35 ka), indicating that Castle Creek glacier retreat to a position upvalley of the divide at that time. Sedimentation resumed before 1.87–1.72 ka when the glacier advanced again past the hydrologic divide. Following a second retreat, Castle Creek Glacier advanced across the divide a final time at ca. 1.54–1.42 ka. The snout of the glacier remained less than 330 m upvalley of the Little Ice Age moraine until the early twentieth century when annual moraines indicate rapid frontal recession to a position upvalley of the hydrologic divide. These data collectively indicate that glaciers in the Cariboo Mountains of British Columbia nearly achieved their all-time Holocene limits as early as 2.73–2.49 ka and climatic conditions in the early 20th century abruptly ended a 1500-year period favoring glacier expansion.”

Citation: Malyssa K. Maurer, Brian Menounos, Brian H. Luckman, Gerald Osborn, John J. Clague, Matthew J. Beedle, Rod Smith, Nigel Atkinson, Quaternary Science Reviews, Volume 51, 19 September 2012, Pages 71–80,

Satellite observations of Antarctic sea ice thickness and volume

Satellite observations of Antarctic sea ice thickness and volume – Kurtz & Markus (2012)

Abstract: “We utilize satellite laser altimetry data from NASA’s Ice, Cloud, and land Elevation Satellite (ICESat) combined with passive microwave measurements to analyze basin-wide changes in Antarctic sea ice thickness and volume over a 5 year period from 2003–2008. Sea ice thickness exhibits a small negative trend while area increases in the summer and fall balanced losses in thickness leading to small overall volume changes. Using a 5 year time series, we show that only small ice thickness changes of less than −0.03 m/yr and volume changes of −266 km3/yr and 160 km3/yr occurred for the spring and summer periods, respectively. These results are in stark contrast to the much greater observed losses in Arctic sea ice volume and illustrate the different hemispheric changes of the polar sea ice covers in recent years. The uncertainties in the calculated thickness and volume trends are large compared to the observed basin-scale trends. This masks the determination of a long-term trend or cyclical variability in the sea ice cover. It is found that lengthening of the observation time series along with better determination of the interannual variability of sea ice and snow densities will allow for a more statistically significant determination of long-term sea ice thickness and volume trends in the Southern Ocean.”

Citation: Kurtz, N. T., and T. Markus (2012), Satellite observations of Antarctic sea ice thickness and volume, J. Geophys. Res., 117, C08025, doi:10.1029/2012JC008141.


Periodic Fluctuations in the Numbers of Animals: Their Causes and Effects – Elton (1924) [FULL TEXT]

Abstract: “I. Four main points are dealt with :– (a) The widespread existence of fluctuations in the numbers of animals. (b) The existence, in many birds and mammals, of periodic fluctuations (p.f.). (c) The cause of the latter, which must be some periodic climatic change acting over wide areas. (d) The effects of fluctuations in general, and in particular of the p.f., on the method of evolution and other biological phenomena. 2. A short sketch is given of what is known about short- period climatic cycles (2 to 20 years), and their causes. 3. P.f. of lemmings have an average period of about 3½ years. The maxima in numbers occur synchronously in North America and Europe, and probably all round the arctic regions. The varying hare in Canada has a period of 10 to 11 years. 5. The only regular periods shown by the animals dealt with are the short one of 3½ years and the longer one of 10 to 11 years. The former is probably more marked in the arctic and the other further south. 6. The sandgrouse p.f. point to the existence of an 11-year climatic cycle in the deserts of Central Asia. 7. The effects of these p.f. on evolution must be very great, although at present problematical; but the following suggestions are made :– (a) Natural selection of some characters must be periodic. (b) There will be different types of natural selection at the maxima and minima of numbers. (c) The struggle for existence, and therefore natural selection, tend to cease temporarily during the rapid expansion in numbers from a minimum, and new mutations have then a chance to get established and spread, i.e. without the aid of natural selection. This might happen only rarely. (d) This would explain the origin and survival of non adaptive characters in a species. (e) On the other hand periodic reduction in numbers will act as an important factor causing uniformity in the species. (f) The opposing factors (c) and (e) will vary much in different species, and the problem will require the combined attentions of mathematicians, and of ecologists working on the methods of regulation of the numbers of animals. (g) This mechanical uniformity factor, since it acts independently of natural selection, explains how a particular structure or habit may evolve, when it only has a general adaptive significance.”

Citation: C. S. Elton, The Journal of Experimental Biology, 2, 119-163, October 1924.

When each paper is published, it is notified in AGW Observer Facebook page and Twitter page. Here’s the archive for the research papers of previous weeks. If this sort of thing interests you, be sure to check out A Few Things Illconsidered. They also have a weekly posting containing lots of links to new research and other climate related news.


Posted in Climate science | 1 Comment »

Climate skeptic claims prebunked by Keeling

Posted by Ari Jokimäki on August 23, 2012

If you have followed discussions about global warming, you probably have seen claims that because atmospheric carbon dioxide concentration is measured on the top of a volcano (actually on the side – the measurement station is at the elevation of 3400m while the top of the mountain is at the elevation of over 4100m), and that volcanos emit carbon dioxide, the carbon dioxide measurements cannot be trusted.  Thus the argument concludes that we don’t know if atmospheric carbon dioxide concentration is rising or not. Here we take a look at what Charles David Keeling (1928 – 2005) wrote long ago.

Charles David Keeling in the lab

As many of you probably know, Keeling was the one who arranged atmospheric carbon dioxide measurements starting in the 1950s, that resulted in the famous Keeling Curve, which describes the evolution of atmospheric carbon dioxide as measured in Hawaii, on top of a volcano called Mauna Loa. The measurement site was selected, because Hawaii is located in the middle of an ocean and far away from disturbing carbon dioxide sources. Also, the elevation of the location of the station ensures that measured air masses are representative of large areas. However, as the Keeling Curve is famous and is drawn from the measurements that originate at a site that has volcanic vents nearby, it is quite natural that there are claims made that the presence of the volcano somehow invalidates all our knowledge of atmospheric carbon dioxide. Many readers of course know that it isn’t so, but here we look at what Keeling wrote about the issue in 1960. It turns out he had already debunked the claims, even before those claims were made.

In 1960, Keeling published the paper The Concentration and Isotopic Abundances of Carbon Dioxide in the Atmosphere (full text freely available in the linked abstract page). In this paper he discussed results from carbon dioxide measurements during a few years of observtions. Early in the paper he says:

“Three gas analysers, as described by SMITH (1953), equipped with strip chart recorders, have been employed to measure the concentration of carbon dioxide continuously at stations in Antarctica, Hawaii, and California.”

So already from the beginning of Keeling’s measurements there were other measurement stations besides Mauna Loa. End of story? Well, pretty much so for those claims, but anyway, let’s take a look at what other things Keeling has to say on the subject.

Despite the reality, what if Mauna Loa was the only atmospheric carbon dioxide measuring station as those claims suggest? Would carbon dioxide measurements be suspect because of that? Keeling discusses this too. Keeling notes that there was local contamination in all of the measurement stations. In the Antarctica station there was some combustion of fuel near the station:

“It could be readily spotted from the significant fluctuations in the otherwise steady trace of the recorder pen and was eliminated from consideration in the initial reading of the charts.”

In Mauna Loa, there also was some extra variability in the measurement record:

“This is attributed to release of carbon dioxide by nearby volcanic vents; combustion on the island associated with agricultural, industrial, and domestic activities; and lower concentration of carbon dioxide in the air transported to the station by upslope winds.”

It seems that Keeling was well aware that “Mauna Loa is a volcano”. He also identified some other sources of contamination. Not only was Keeling aware of the situation, he also knew how to correct it:

“The values reported here are averages of data for periods of downslope winds or strong lateral winds when the concentration remained nearly constant for several hours or more.”

At a California measurement station there was an interesting situation. The measured carbon dioxide concentration was found to be highly variable:

“Highest concentrations occur during light winds from the north, from the direction of Los Angeles; lowest concentrations when the wind is from the west or southwest and of moderate force or greater.”

Highest concentrations when winds were blowing from a large city? Why is that? Could it be that there is carbon dioxide coming from human actions?

Keeling then proceeds to discuss seasonal variation which he finds in the Northern Hemisphere but not in the Southern Hemisphere. Based on carbon-13 measurements, he concludes that the seasonal variation found in the Northern Hemisphere is from the activity of land plants. He also notes that timing of maximum and minimum concentrations match the timing of the land vegetation activity in the Northern Hemisphere. Keeling explains the absence of seasonal variability in the Southern Hemisphere by the smaller area of vegetation in the Southern Hemisphere.

Getting back to the claims of CO2 record contamination, Keeling then discusses the interannual trends in carbon dioxide concentration:

“Where data extend beyond one year, averages for the second year are higher than for the first year. At the South Pole, where the longest record exists, the concentration has increased at the rate of about 1.3 p.p.m. per year.”

Note that Keeling reported the first clear increase in carbon dioxide concentration from the South Pole, not from Mauna Loa.

So, already back in 1960, Keeling knew that Mauna Loa was a volcano. He also knew how to correct the problems that the volcano caused for carbon dioxide measurements. He also knew that the volcanic problems wouldn’t matter anyway because there were other measurement stations that were nowhere near any volcanos, and those stations show the same thing as Mauna Loa station – atmospheric carbon dioxide concentration is rising.

Posted in AGW evidence, Climate claims, Climate science | 3 Comments »

New research from last week 33/2012

Posted by Ari Jokimäki on August 20, 2012

What happens when we dump greenhouse gases to atmosphere? Temperature rises, there will be more heat waves, ice and snow melts, sea level rises, there are changes in clouds and other climate feedbacks such as methane bursting out from ocean sediments, forest fire frequency changes, hydrological cycle changes, biosphere reacts, and economy is affected. Below you will find new research on each of these subjects.

Arctic sea ice loss has created negative NAO-like conditions to atmospheric circulation

The atmospheric response to three decades of observed Arctic sea ice loss – Screen et al. (2012)

Abstract: “Arctic sea ice is declining at an increasing rate with potentially important repercussions. In order to understand better the atmospheric changes that may have occurred in response to Arctic sea ice loss, we present results from atmospheric general circulation model (AGCM) experiments in which the only time-varying forcings prescribed were observed variations in Arctic sea ice and accompanying changes in Arctic sea surface temperatures from 1979 to 2009. We utilize two independent AGCMs in order to assess the robustness of the response across different models. The results suggest that the atmospheric impacts of Arctic sea ice loss have been manifest most strongly within the maritime and coastal Arctic, and in the lowermost atmosphere. Sea ice loss has driven increased energy transfer from the ocean to the atmosphere, enhanced warming and moistening of the lower troposphere, has decreased the strength of the surface inversion, and increased lower-tropospheric thickness; all these changes are most pronounced in autumn and early winter (September-December). The early winter (November-December) atmospheric circulation response resembles the negative phase of the North Atlantic Oscillation (NAO); however, the NAO-type response is quite weak and is often masked by intrinsic (unforced) atmospheric variability. We also find some evidence of a late winter (March-April) polar stratospheric cooling response to sea ice loss, which may have important implications for polar stratospheric ozone concentrations. The attribution and quantification of other aspects of the possible atmospheric response are hindered by model sensitivities and large intrinsic variability. The potential remote responses to Arctic sea ice change are currently hard to confirm and remain uncertain.”

Citation: James A. Screen and Ian Simmonds, Clara Deser and Robert Tomas, Journal of Climate 2012, doi:

Small decline in total cloud cover over land areas since 1971

A 39-Year Survey of Cloud Changes from Land Stations Worldwide 1971-2009: Long-Term Trends, Relation to Aerosols, and Expansion of the Tropical Belt – Eastman & Warren (2012) [FULL TEXT]

Abstract: “An archive of land-based, surface-observed cloud reports has been updated and now spans 39 years from 1971 through 2009. Cloud-type information at weather stations is available in individual reports or in long-term, seasonal, and monthly averages. A shift to a new data source and the automation of cloud reporting in some countries has reduced the number of available stations; however this dataset still represents most of the global land area. Global average trends of cloud cover suggest a small decline in total cloud cover, on the order of 0.4% per decade. Declining clouds in middle latitudes at high and middle levels appear responsible for this trend. An analysis of zonal cloud cover changes suggests poleward shifts of the jet streams in both hemispheres. The observed displacement agrees with other studies. Changes seen in cloud types associated with the Indian monsoon are consistent with previous work suggesting that increased pollution (black carbon) may be affecting monsoonal precipitation, causing drought in North India. A similar analysis over northern China does not show an obvious aerosol connection. Past reports claiming a shift from stratiform to cumuliform cloud types over Russia were apparently partially based on spurious data. When the faulty stations are removed, a tradeoff of stratiform and cumuliform cloud cover is still observed, but muted, over much of northern Eurasia.”

Citation: Ryan Eastman and Stephen G. Warren, Journal of Climate 2012, doi:

Sea level is predicted to rise at least 80cm by 2100 and continues to rise at least next 200 years

Lower bounds to future sea-level rise – Zecca & Chiari (2012)

Abstract: “Sea-level rise is among the most important changes expected as a consequence of anthropogenic global warming. Climate model-based projections made until the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) yield a 21st century rise spanning nearly 20–60 cm. However, it is known that current climate models are likely to underestimate sea-level change in response to rapid climatic variations. Recent alternative semi-empirical approaches predict a much higher sea-level rise than the IPCC AR4 projections. Nevertheless, the underway depletion of conventional fossil fuels might, at least in principle, constrain future fossil CO2 emissions and, in turn, affect also the extent of sea-level rise. Here we project 2000–2200 sea-level rise with a semi-empirical method coupled to a simple climate model that is run under a range of fossil-fuel exhaustion scenarios. We find that, in spite of fossil-fuel depletion, sea level is predicted to rise by at least ~ 80 cm at the end of this century and is expected to continue rising for at least the next two hundred years. The present results support the need for prompt and substantial emission cuts in order to slow down future sea-level rise and implement adaptation measures.”

Citation: Antonio Zecca, Luca Chiari, Global and Planetary Change,

Ocean circulation promotes methane release from gas hydrate outcrops

Ocean circulation promotes methane release from gas hydrate outcrops at the NEPTUNE Canada Barkley Canyon node – Thomsen et al. (2012)

Abstract: “The NEPTUNE Canada cabled observatory network enables non-destructive, controlled experiments and time-series observations with mobile robots on gas hydrates and benthic community structure on a small plateau of about 1 km2 at a water depth of 870 m in Barkley Canyon, about 100 km offshore Vancouver Island, British Columbia. A mobile Internet operated vehicle was used as an instrument platform to monitor and study up to 2000 m2 of sediment surface in real-time. In 2010 the first mission of the robot was to investigate the importance of oscillatory deep ocean currents on methane release at continental margins. Previously, other experimental studies have indicated that methane release from gas hydrate outcrops is diffusion-controlled and should be much higher than seepage from buried hydrate in semipermeable sediments. Our results show that periods of enhanced bottom currents associated with diurnal shelf waves, internal semidiurnal tides, and also wind-generated near-inertial motions can modulate methane seepage. Flow dependent destruction of gas hydrates within the hydrate stability field is possible from enhanced bottom currents when hydrates are not covered by either seafloor biota or sediments. The calculated seepage varied between 40–400 μmol CH4 m−2 s−1. This is 1–3 orders of magnitude higher than dissolution rates of buried hydrates through permeable sediments and well within the experimentally derived range for exposed gas hydrates under different hydrodynamic boundary conditions. We conclude that submarine canyons which display high hydrodynamic activity can become key areas of enhanced seepage as a result of emerging weather patterns due to climate change.”

Citation: Thomsen, L., C. Barnes, M. Best, R. Chapman, B. Pirenne, R. Thomson, and J. Vogt (2012), Ocean circulation promotes methane release from gas hydrate outcrops at the NEPTUNE Canada Barkley Canyon node, Geophys. Res. Lett., 39, L16605, doi:10.1029/2012GL052462.

Climate in Romania has become warmer during the last decades

Changes in daily extreme temperatures in the extra-Carpathians regions of Romania – Croitoru & Piticar (2012)

Abstract: “Changes in daily extreme temperatures have been identified in many studies conducted at local, regional or global scales. For Romanian territory, only little research on this issue was done. In this article, the extra-Carpathians regions of Romania located southward and eastward from the Carpathians Chain were considered. This study is focused on analyzing daily extreme temperature trends at a regional scale (eastern, southern and southeastern regions of Romania) across 50 years (1961–2010). Data sets of daily minimum and maximum temperature recorded in 14 weather stations were analyzed. The main goal was to find changes in extreme daily temperatures using a set of 20 indices adopted from the core indices developed by ETCCDMI with appropriate modifications to suit to the analyzed territory. The main results suggest that regional temperature trends at the scale of extra-Carpathians areas of Romania are similar to those calculated for global and European continental scales; the climate has become warmer during the last decades. It has been identified that both extreme daily maximum and minimum temperatures have increased in the analyzed areas. For all the indices related to hot temperature most trends are significantly positive. The strongest increase was detected for hot related extremes such as summer days and tropical nights as well as for maximum values of maximum and minimum daily temperatures. For indices related to cold there are different sign slopes, but negative slopes prevail, especially for number of days under a defined threshold. This is also an evidence of the important warming in the area. Generally, it was found that the daily maximum temperature is getting more extreme, whereas the minimum is getting less extreme.”

Citation: Adina-Eliza Croitoru, Adrian Piticar, International Journal of Climatology, DOI: 10.1002/joc.3567.

Antarctic sea ice variability and trends, 1979–2010

Antarctic sea ice variability and trends, 1979–2010 – Parkinson & Cavalieri (2012) [FULL TEXT]

Abstract: “In sharp contrast to the decreasing sea ice coverage of the Arctic, in the Antarctic the sea ice cover has, on average, expanded since the late 1970s. More specifically, satellite passive-microwave data for the period November 1978–December 2010 reveal an overall positive trend in ice extents of 17 100 ± 2300 km2 yr−1. Much of the increase, at 13 700 ± 1500 km2 yr−1, has occurred in the region of the Ross Sea, with lesser contributions from the Weddell Sea and Indian Ocean. One region, that of the Bellingshausen/Amundsen Seas, has (like the Arctic) instead experienced significant sea ice decreases, with an overall ice extent trend of −8200 ± 1200 km2 yr−1. When examined through the annual cycle over the 32-yr period 1979–2010, the Southern Hemisphere sea ice cover as a whole experienced positive ice extent trends in every month, ranging in magnitude from a low of 9100 ± 6300 km2 yr−1 in February to a high of 24 700 ± 10 000 km2 yr−1 in May. The Ross Sea and Indian Ocean also had positive trends in each month, while the Bellingshausen/Amundsen Seas had negative trends in each month, and the Weddell Sea and western Pacific Ocean had a mixture of positive and negative trends. Comparing ice-area results to ice-extent results, in each case the ice-area trend has the same sign as the ice-extent trend, but the magnitudes of the two trends differ, and in some cases these differences allow inferences about the corresponding changes in sea ice concentrations. The strong pattern of decreasing ice coverage in the Bellingshausen/Amundsen Seas region and increasing ice coverage in the Ross Sea region is suggestive of changes in atmospheric circulation. This is a key topic for future research.”

Citation: Parkinson, C. L. and Cavalieri, D. J.: Antarctic sea ice variability and trends, 1979–2010, The Cryosphere, 6, 871-880, doi:10.5194/tc-6-871-2012, 2012.

Arctic sea ice variability and trends, 1979–2010

Arctic sea ice variability and trends, 1979–2010 – Cavalieri & Parkinson (2012) [FULL TEXT]

Abstract: “Analyses of 32 yr (1979–2010) of Arctic sea ice extents and areas derived from satellite passive microwave radiometers are presented for the Northern Hemisphere as a whole and for nine Arctic regions. There is an overall negative yearly trend of −51.5 ± 4.1 × 103 km2 yr−1 (−4.1 ± 0.3% decade−1) in sea ice extent for the hemisphere. The yearly sea ice extent trends for the individual Arctic regions are all negative except for the Bering Sea: −3.9 ± 1.1 × 103 km2 yr−1 (−8.7 ± 2.5% decade−1) for the Seas of Okhotsk and Japan, +0.3 ± 0.8 × 103 km2 yr−1 (+1.2 ± 2.7% decade−1) for the Bering Sea, −4.4 ± 0.7 × 103 km2 yr−1 (−5.1 ± 0.9% decade−1) for Hudson Bay, −7.6 ± 1.6 × 103 km2 yr−1 (−8.5 ± 1.8% decade−1) for Baffin Bay/Labrador Sea, −0.5 ± 0.3 × 103 km2 yr−1 (−5.9 ± 3.5% decade−1) for the Gulf of St. Lawrence, −6.5 ± 1.1 × 103 km2 yr−1 (−8.6 ± 1.5% decade−1) for the Greenland Sea, −13.5 ± 2.3 × 103 km2 yr−1 (−9.2 ± 1.6% decade−1) for the Kara and Barents Seas, −14.6 ± 2.3 × 103 km2 yr−1 (−2.1 ± 0.3% decade−1) for the Arctic Ocean, and −0.9 ± 0.4 × 103 km2 yr−1 (−1.3 ± 0.5% decade−1) for the Canadian Archipelago. Similarly, the yearly trends for sea ice areas are all negative except for the Bering Sea. On a seasonal basis for both sea ice extents and areas, the largest negative trend is observed for summer with the next largest negative trend being for autumn. Both the sea ice extent and area trends vary widely by month depending on region and season. For the Northern Hemisphere as a whole, all 12 months show negative sea ice extent trends with a minimum magnitude in May and a maximum magnitude in September, whereas the corresponding sea ice area trends are smaller in magnitude and reach minimum and maximum values in March and September.”

Citation: Cavalieri, D. J. and Parkinson, C. L.: Arctic sea ice variability and trends, 1979–2010, The Cryosphere, 6, 881-889, doi:10.5194/tc-6-881-2012, 2012.

Decrease in biomass burning after year 1500 is similar in duration and timing to Little Ice Age

Climatic control of the biomass-burning decline in the Americas after AD 1500 – Power et al. (2012) [FULL TEXT]

Abstract: “The significance and cause of the decline in biomass burning across the Americas after AD 1500 is a topic of considerable debate. We synthesized charcoal records (a proxy for biomass burning) from the Americas and from the remainder of the globe over the past 2000 years, and compared these with paleoclimatic records and population reconstructions. A distinct post-AD 1500 decrease in biomass burning is evident, not only in the Americas, but also globally, and both are similar in duration and timing to ‘Little Ice Age’ climate change. There is temporal and spatial variability in the expression of the biomass-burning decline across the Americas but, at a regional–continental scale, ‘Little Ice Age’ climate change was likely more important than indigenous population collapse in driving this decline.”

Citation: M J Power, F E Mayle, P J Bartlein, J R Marlon, R S Anderson, H Behling, K J Brown, C Carcaillet, D Colombaroli, D G Gavin, D J Hallett, S P Horn, L M Kennedy, C S Lane, C J Long, P I Moreno, C Paitre, G Robinson, Z Taylor, M K Walsh, The Holocene August 14, 2012 0959683612450196, doi: 10.1177/0959683612450196.

Domestic tourism increases in northern Spain and decreases in southern Spain with climate change

Climate change and summer mass tourism: the case of Spanish domestic tourism – Bujosa & Rosselló (2012)

Abstract: “This paper investigates the impact of climate change on destination choice decisions in a context of domestic coastal tourism in Spain. Destinations are characterized in terms of travel cost and coastal ‘attractors’, such as temperature and beach-related attributes. By means of a discrete choice model based on the random utility theory, these variables are used to explain the observed pattern of interprovincial domestic trips, showing trade-offs between temperature and attractiveness in the probability of a particular destination being chosen. The model is used to investigate the impact of two climate change scenarios on the allocation of domestic tourism within Spain. The findings show that while Spain’s northern colder provinces would benefit from rising temperatures, provinces in the south would experience a decrease in the frequency of trips.”

Citation: Angel Bujosa and Jaume Rosselló, Climatic Change, 2012, DOI: 10.1007/s10584-012-0554-x.

Satellite measurements of soil moisture

A method to improve satellite soil moisture retrievals based on Fourier analysis – Du (2012)

Abstract: “Knowledge of the spatial distribution and temporal changes of the global soil moisture for a long period of time is crucial to the understanding of climate changes and hydrological processes. By applying Fourier analysis to the time-series observations from the space-borne passive microwave sensors, this paper proposes a method to extract the high-frequency part of the satellite observed signals that reflect the soil moisture changes and help to generate the historical soil moisture datasets with an improved accuracy. The method is applied to the observations from Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E). Validations using field sampled soil moisture from two watersheds in the U.S. indicate that the method can effectively improve the sensitivity of current National Aeronautics and Space Administration (NASA) soil moisture products to the temporal changes of the surface soil moisture, with the correlation coefficients of the retrievals and measurements increased from 0.462 to 0.595 and 0.403 to 0.613 for the two watersheds, respectively.”

Citation: Du, J. (2012), A method to improve satellite soil moisture retrievals based on Fourier analysis, Geophys. Res. Lett., 39, L15404, doi:10.1029/2012GL052435.

Heat waves have increased in western Turkey

Summer heat waves over western Turkey between 1965 and 2006 – Unal et al. (2012)

Abstract: “Global warming is one of the greatest environmental, economic, and social threats in the world. There are many assessments to estimate climate variability over many regions. A change in the Earth’s surface temperature leads to increase in extreme temperature events, which are harmful to the ecosystem, and moreover, they create danger on human health. In this study, we have selected the western part of Turkey as the study area, since climate change projections for Turkey point out that the highest temperature change can be expected on this region during summer, and the Turkish population is very dense here to be affected by extreme events. We have used apparent temperatures to define the heat waves which we have determined their frequencies for the summer months (June–August) of 1965–2006. Since the regional comparisons of station results are intended, we selected the 90th percentile value for each station as a threshold value to be used in the delineation of heat waves. Then, the number of heat waves is determined by imposing the constraint that apparent temperatures stay above the threshold value at least for three consecutive days. Then, the changes in the number of hot days and heat waves and also their durations are analyzed by using the linear least square method. We have found that the number of hot days, heat waves, and heat wave durations is increased between 1965 and 2006 on the western part of Turkey. Additionally, their rate of change is larger within the last decade and extremes are frequently observed after 1998. Regional distributions show that the tendency of the number of heat wave events increases towards the southern latitudes of the domain. Moreover, we investigated the relationship between the number of hot days and the sea surface temperatures of the Mediterranean Sea and Black Sea. Correlation analyses are carried out by the number of hot days and averaged sea surface temperatures on the regions of the western, central, and eastern Mediterranean Sea and the Black Sea. It is found that the number of hot days of west Turkey is better correlated with the sea surface temperatures averaged over eastern Mediterranean and Black Seas. The number of heat waves is found significantly correlated with the fire occurrences for most of the stations.”

Citation: Yurdanur Sezginer Unal, Elcin Tan and S. Sibel Mentes, Theoretical and Applied Climatology, 2012, DOI: 10.1007/s00704-012-0704-0.

Snow cover is expected to decrease in China with climate change

Projection of snow cover changes over China under RCP scenarios – Ji & Kang (2012)

Abstract: “Snow cover changes in the middle (2040–2059) and end (2080–2099) of the twenty-first century over China were investigated with a regional climate model, nested within the global model BCC_CSM1.1. The simulations had been conducted for the period of 1950–2099 under the RCP4.5 and RCP8.5 scenarios. Results show that the model perform well in representing contemporary (1986–2005) spatial distributions of snow cover days (SCDs) and snow water equivalent (SWE). However, some differences between observation and simulation were detected. Under the RCP4.5 scenarios, SCDs are shortened by 10–20 and 20–40 days during the middle and end of the twenty-first century, respectively. Whereas simulated SWE is lowered by 0.1–10 mm in most areas over the Tibetan Plateau (TP). On the other hand, the spatial distributions of SWE are reversed between the middle and end terms in the northeast China. Furthermore, compared with the changes of RCP4.5 scenario, SCDs are reduced by 5–20 days in the middle period under RCP8.5 scenario with even larger decreasing amplitude in the end term. SWE was lowered by 0.1–2.5 mm in most areas except the northeast of China in middle term under RCP8.5 scenario. The great center of SCDs and SWE changes are always located over TP. The regional mean of SCDs and SWE for the TP and for China display a declining trend from 2006 to 2099 with more pronounced changes in the TP than in China as a whole. Under the RCP8.5 scenario, the changes are enhanced compared to those under RCP4.5.”

Citation: Zhenming Ji and Shichang Kang, Climate Dynamics, 2012, DOI: 10.1007/s00382-012-1473-2.

Using satellite measurements in mosquito population dynamics studies

Satellite microwave remote sensing for environmental modeling of mosquito population dynamics – Chuang et al. (2012)

Abstract: “Environmental variability has important influences on mosquito life cycles and understanding the spatial and temporal patterns of mosquito populations is critical for mosquito control and vector-borne disease prevention. Meteorological data used for model-based predictions of mosquito abundance and life cycle dynamics are typically acquired from ground-based weather stations; however, data availability and completeness are often limited by sparse networks and resource availability. In contrast, environmental measurements from satellite remote sensing are more spatially continuous and can be retrieved automatically. This study compared environmental measurements from the NASA Advanced Microwave Scanning Radiometer on EOS (AMSR-E) and in situ weather station data to examine their ability to predict the abundance of two important mosquito species (Aedes vexans and Culex tarsalis) in Sioux Falls, South Dakota, USA from 2005 to 2010. The AMSR-E land parameters included daily surface water inundation fraction, surface air temperature, soil moisture, and microwave vegetation opacity. The AMSR-E derived models had better fits and higher forecasting accuracy than models based on weather station data despite the relatively coarse (25-km) spatial resolution of the satellite data. In the AMSR-E models, air temperature and surface water fraction were the best predictors of Aedes vexans, whereas air temperature and vegetation opacity were the best predictors of Cx. tarsalis abundance. The models were used to extrapolate spatial, seasonal, and interannual patterns of climatic suitability for mosquitoes across eastern South Dakota. Our findings demonstrate that environmental metrics derived from satellite passive microwave radiometry are suitable for predicting mosquito population dynamics and can potentially improve the effectiveness of mosquito-borne disease early warning systems.”

Citation: Ting-Wu Chuang, Geoffrey M. Henebry, John S. Kimball, Denise L. VanRoekel-Patton, Michael B. Hildreth, Michael C. Wimberly, Remote Sensing of Environment, Volume 125, October 2012, Pages 147–156,

CLASSIC OF THE WEEK: Yokoyama (1911)

Climatic Changes in Japan since the Pliocene Epoch – Yokoyama (1911) [FULL TEXT]

Abstract: No abstract. Discusses the climate of Japan during glacial and interglacial ages. Carbon dioxide is mentioned as a possible cause for climate change.

Citation: Yokoyama, Matajiro, The Journal of the College of Science, Imperial University of Tokyo, Japan, v32 art5, 1911.10.2, pp. 1-16.

When each paper is published, it is notified in AGW Observer Facebook page and Twitter page. Here’s the archive for the research papers of previous weeks. If this sort of thing interests you, be sure to check out A Few Things Illconsidered. They also have a weekly posting containing lots of links to new research and other climate related news.

Posted in Climate science | 1 Comment »

New research from last week 32/2012

Posted by Ari Jokimäki on August 13, 2012

Mankind puts dust to atmosphere and all other sorts of air pollution, which pollutes trees so that we can’t do climate reconstructions anymore. Trees emit methane which is then measured from sea by Japanese researchers who also think that tsunamis should be detected by satellites which also measure net primary productivity, which is a good idea because climate did have an effect on ecosystems also in past. Meanwhile, we fiddle with our miniaturized radiance cameras and debate if ice surface is melting over large areas of Greenland, which is in Arctic where there just recently were record ozone loss. I guess Arctic is such a big place that it is easy to lose lot of things there, such as ice and ozone. Anyway, at the end we just feed everything to climate models, which by the way have very good quality software.

Miniaturized radiance cameras measuring underwater multi-spectral radiances in all directions

Underwater radiance distributions measured with miniaturized multispectral radiance cameras – Antoine et al. (2012) [FULL TEXT]

Abstract: “Miniaturized radiance cameras measuring underwater multi-spectral radiances in all directions at high-radiometric accuracy – the CE600 – are presented. The camera design is described, as well as the main steps of its optical and radiometric characterization and calibration. The results show excellent optical quality of the specifically designed fisheye objective. They also show the low noise and excellent linearity of the Complementary Metal Oxide Semiconductor (CMOS) detector array that is used. Initial results obtained in various oceanic environments demonstrate the potential of this instrument to provide new measurements of the underwater radiance distribution from the sea surface to dim-lighted layers at depth. Excellent agreement is obtained between nadir radiances measured with the camera and commercial radiometers. Comparison of the upwelling radiances distributions measured with the CE600 and those obtained with another radiance camera also show a very close agreement. The CE600 measurements allow all apparent optical properties (AOPs) to be determined from integration of the radiances distributions, and inherent optical properties (IOPs) to be determined from inversion of the AOPs. This possibility represents a significant advance for marine optics, by tying all optical properties to the radiometric standard and avoiding deployment of complex instrument packages to collect AOPs and IOPs simultaneously (except when it comes to partitioning IOPs into their component parts).”

Citation: David Antoine, André Morel, Edouard Leymarie, Amel Houyou, Bernard Gentili, Stéphane Victori, Jean-Pierre Buis, Nicolas Buis, Sylvain Meunier, Marius Canini, Didier Crozel, Bertrand Fougnie, and Patrice Henry, Journal of Atmospheric and Oceanic Technology 2012, doi:

Too early to infer a global net primary productivity decline since 2000

Too early to infer a global NPP decline since 2000 – Ahlström et al. (2012)

Abstract: “The global terrestrial carbon cycle plays a pivotal role in regulating the atmospheric composition of greenhouse gases. It has recently been suggested that the upward trend in net primary production (NPP) seen during the 1980’s and 90’s has been replaced by a negative trend since 2000 induced by severe droughts mainly on the southern hemisphere. Here we compare results from an individual-based global vegetation model to satellite-based estimates of NPP and top-down reconstructions of net biome production (NBP) based on inverse modelling of observed CO2 concentrations and CO2 growth rates. We find that simulated NBP exhibits considerable covariation on a global scale with interannual fluctuations in atmospheric CO2. Our simulations also suggest that droughts in the southern hemisphere may have been a major driver of NPP variations during the past decade. The results, however, do not support conjecture that global terrestrial NPP has entered a period of drought-induced decline.”

Citation: Ahlström, A., P. A. Miller, and B. Smith (2012), Too early to infer a global NPP decline since 2000, Geophys. Res. Lett., 39, L15403, doi:10.1029/2012GL052336.

Air pollution masks climate signals in tree rings

Climatic isotope signals in tree rings masked by air pollution: A case study conducted along the Mont Blanc Tunnel access road (Western Alps, Italy) – Leonelli et al. (2012)

Abstract: “Three sites at about 1400 m a.s.l., were chosen for this study along the Mt. Blanc Motorway in Italy. Chronologies of stable isotope ratios (δ13C, δ18O, δ15N), total N concentration and ring width of Larix decidua Mill. were analyzed to observe changes in growth and climatic signals in tree rings after significant changes in air pollution emissions occurred locally over time. The tunnel opened in 1968 and was closed for three years from March 1999 to March 2002. The obtained series from the three sites (Close = C, High = H and Far = F from the highway) for the analyzed periods, 1950–1970 (only sites H and F) and 1985–2008 (all sites), did not show any particular long-term change except site H that showed significant changes in δ18O (enrichment), δ15N (depletion) and total N (increase). δ13C values at site C were enriched in the first year of the tunnel closure (1999), showing an opposite trend in δ13C at site C, in comparison to the two control sites H and F, which cannot be explained by climatic factors. Since no great differences in δ18O were recorded in 1999, this enrichment in δ13C could be related to an enhancement in photosynthetic rate during periods of low air pollution loads. Opposite to δ15N, total N concentration shows a generally good correlation between sites, and site F was measured as the most N enriched. In a correlation analysis performed on the two study periods between the climatic parameters and ring width, we did not find any clear relationships, whereas for the series of stable isotopes and total N, we found the strongest and most significant relationships only between δ13C and summer (June to August) temperature (positive correlations) and precipitation (negative correlations) at sites H and F. These same relationships at site C were, instead, mostly insignificant, indicating an alteration of the climatic signal recorded in the δ13C chronology, caused by direct exposure to the high level of air pollution at this site. Given that site C is more affected by pollution with respect to the other two sites (whereas the same climatic conditions influence tree growth at all sites), the lack of a climatic signal in the δ13C chronology at this site can be ascribed to air pollution. Few other long-term changes were recorded by tree rings (e.g. at site H), indicating that trees probably record better the pollution events or the worsening of the environmental conditions rather than a lack of pollution for a relatively short time period in a polluted environment.”

Citation: Giovanni Leonelli, Giovanna Battipaglia, Rolf T.W. Siegwolf, Matthias Saurer, Umberto Morra di Cella, Paolo Cherubini, Manuela Pelfini, Atmospheric Environment, Volume 61, December 2012, Pages 169–179,

Climate models all have very low defect densities compared to similarly sized open-source projects

Assessing climate model software quality: a defect density analysis of three models – Pipitone & Easterbrook (2012) [FULL TEXT]

Abstract: “A climate model is an executable theory of the climate; the model encapsulates climatological theories in software so that they can be simulated and their implications investigated. Thus, in order to trust a climate model, one must trust that the software it is built from is built correctly. Our study explores the nature of software quality in the context of climate modelling. We performed an analysis of defect reports and defect fixes in several versions of leading global climate models by collecting defect data from bug tracking systems and version control repository comments. We found that the climate models all have very low defect densities compared to well-known, similarly sized open-source projects. We discuss the implications of our findings for the assessment of climate model software trustworthiness.”

Citation: Pipitone, J. and Easterbrook, S.: Assessing climate model software quality: a defect density analysis of three models, Geosci. Model Dev., 5, 1009-1022, doi:10.5194/gmd-5-1009-2012, 2012.

Trees produce methane in their cores with assistance of microorganisms

Elevated methane concentrations in trees of an upland forest – Covey et al. (2012)

Abstract: “There is intense debate about whether terrestrial vegetation contributes substantially to global methane emissions. Although trees may act as a conduit for methane release from soils to atmosphere, the debate centers on whether vegetation directly produces methane by an uncharacterized, abiotic mechanism. A second mechanism of direct methane production in plants occurs when methanogens – microorganisms in the domain Archaea – colonize the wood of living trees. In the debate this biotic mechanism has largely been ignored, yet conditions that promote anaerobic activity in living wood, and hence potentially methane production, are prevalent across forests. We find average, growing season, trunk-gas methane concentrations >15,000 μL·L−1 in common, temperate-forest species. In upland habitat (where soils are not a significant methane source), concentrations are 2.3-times greater than in lowland areas, and wood cores produce methane in anaerobic, lab-assays. Emission rate estimates from our upland site are 52 ± 9.5 ng CH4 m−2 s−1; rates that are of a similar magnitude to the soil methane sink in temperate forest, and equivalent in global warming potential to ∼18% of the carbon likely sequestered by this forest. Microbial infection of one of the largest, biogenic sinks for carbon dioxide, living trees, might result in substantial, biogenic production of methane.”

Citation: Covey, K. R., S. A. Wood, R. J. Warren II, X. Lee, and M. A. Bradford (2012), Elevated methane concentrations in trees of an upland forest, Geophys. Res. Lett., 39, L15705, doi:10.1029/2012GL052361.

Ice surface melt area might cover whole Greenland ice sheet within decade

Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers – Box et al. (2012) [FULL TEXT]

Abstract: “Greenland ice sheet mass loss has accelerated in the past decade responding to combined glacier discharge and surface melt water runoff increases. During summer, absorbed solar energy, modulated at the surface primarily by albedo, is the dominant factor governing surface melt variability in the ablation area. Using satellite-derived surface albedo with calibrated regional climate modeled surface air temperature and surface downward solar irradiance, we determine the spatial dependence and quantitative impact of the ice sheet albedo feedback over 12 summer periods beginning in 2000. We find that, while albedo feedback defined by the change in net solar shortwave flux and temperature over time is positive over 97% of the ice sheet, when defined using paired annual anomalies, a second-order negative feedback is evident over 63% of the accumulation area. This negative feedback damps the accumulation area response to warming due to a positive correlation between snowfall and surface air temperature anomalies. Positive anomaly-gauged feedback concentrated in the ablation area accounts for more than half of the overall increase in melting when satellite-derived melt duration is used to define the timing when net shortwave flux is sunk into melting. Abnormally strong anticyclonic circulation, associated with a persistent summer North Atlantic Oscillation extreme since 2007, enabled three amplifying mechanisms to maximize the albedo feedback: (1) increased warm (south) air advection along the western ice sheet increased surface sensible heating that in turn enhanced snow grain metamorphic rates, further reducing albedo; (2) increased surface downward shortwave flux, leading to more surface heating and further albedo reduction; and (3) reduced snowfall rates sustained low albedo, maximizing surface solar heating, progressively lowering albedo over multiple years. The summer net infrared and solar radiation for the high elevation accumulation area approached positive values during this period. Thus, it is reasonable to expect 100% melt area over the ice sheet within another similar decade of warming.”

Citation: Box, J. E., Fettweis, X., Stroeve, J. C., Tedesco, M., Hall, D. K., and Steffen, K.: Greenland ice sheet albedo feedback: thermodynamics and atmospheric drivers, The Cryosphere, 6, 821-839, doi:10.5194/tc-6-821-2012, 2012.

Methane measurements in the water and sediments of Sea of Japan

Methane in water columns and sediments of the north western Sea of Japan – Vereshchagina et al. (2012)

Abstract:“This paper presents the results of methane measurements in water and sediments, first performed along the north western continental slope and abyssal plain of the Sea of Japan. Methane concentrations in the study area were very low. However, some features of its distribution are revealed. The highest dissolved methane concentrations (10–14 nmol kg−1) are characteristic of the pycnocline layer at a depth of 30–50 m in the northern shallow stations. With increasing depth, the methane is reduced to minimum values (0.5–1.0 nmol kg−1). The greatest variability in methane concentrations was observed in the layers at 0–500 m, which can be explained by the hydrodynamic conditions of the environment on the slope. Methane plumes (1.7 and 1.3 nmol·kg−1) on the northern section were recorded at the depth of 1,250 and 1,495 m, respectively. Plumes (1.2 nmol kg−1) are also observed on near bottom layers at the deepest (more than 3,000 m) stations. CH4 concentration in bottom sediments is also low (from 1 nmol kg−1 at 7 cm level to 752 nmol kg−1 at the 53 cm level of the core sediment in the northern part). Reduced sediments in the southern part of the study region have maximal methane concentration for sediment (2,549 nmol kg−1) at the horizon 44 cm bsf (below sea floor) with a smell of H2S. These results suppose a close relation of CH4 to sediment properties. A few stations with the maximum methane (86–101 nmol kg−1) in the surface sediment layer are at the foot of a steep slope. Herewith, the highest abundance of some pericarid species was observed at the points with the highest values of methane concentrations in the surface sediment layer. Weak methane seepage can cause anoxic marine waters. Methane emission from water to the atmosphere is low because of its close to equilibrium concentration in surface water. An improved formula for calculating the methane flux of water into the atmosphere, taking into account high wind speeds is presented in the paper.”

Citation: Olga F. Vereshchagina, Elena V. Korovitskaya, Galina I. Mishukova, Deep Sea Research Part II: Topical Studies in Oceanography,

Tsunami detection from satellite altimetry – 2011 tsunami in Japan as test case

Could satellite altimetry have improved early detection and warning of the 2011 Tohoku tsunami? – Hamlington et al. (2012)

Abstract: “The 2011 Tohoku tsunami devastated Japan and affected coastal populations all around the Pacific Ocean. Accurate early warning of an impending tsunami requires the detection of the tsunami in the open ocean. While the lead-time was not sufficient for use in warning coastal populations in Japan, satellite altimetry observations of the tsunami could have been used to improve predictions and warnings for other affected areas. By comparing to both model results and historical satellite altimeter data, we use near-real-time satellite altimeter measurements to demonstrate the potential for detecting the 2011 Tohoku tsunami within a few hours of the tsunami being generated. We show how satellite altimeter data could be used to both directly detect tsunamis in the open ocean and also improve predictions made by models.”

Citation: Hamlington, B. D., R. R. Leben, O. A. Godin, E. Gica, V. V. Titov, B. J. Haines, and S. D. Desai (2012), Could satellite altimetry have improved early detection and warning of the 2011 Tohoku tsunami?, Geophys. Res. Lett., 39, L15605, doi:10.1029/2012GL052386.

25% of dust in Earth’s atmosphere is from human actions

Global-scale attribution of anthropogenic and natural dust sources and their emission rates based on MODIS Deep Blue aerosol products – Ginoux et al. (2012)

Abstract: “Our understanding of the global dust cycle is limited by a dearth of information about dust sources, especially small-scale features which could account for a large fraction of global emissions. Here we present a global-scale high-resolution (0.1°) mapping of sources based on Moderate Resolution Imaging Spectroradiometer (MODIS) Deep Blue estimates of dust optical depth in conjunction with other data sets including land use. We ascribe dust sources to natural and anthropogenic (primarily agricultural) origins, calculate their respective contributions to emissions, and extensively compare these products against literature. Natural dust sources globally account for 75% of emissions; anthropogenic sources account for 25%. North Africa accounts for 55% of global dust emissions with only 8% being anthropogenic, mostly from the Sahel. Elsewhere, anthropogenic dust emissions can be much higher (75% in Australia). Hydrologic dust sources (e.g., ephemeral water bodies) account for 31% worldwide; 15% of them are natural while 85% are anthropogenic. Globally, 20% of emissions are from vegetated surfaces, primarily desert shrublands and agricultural lands. Since anthropogenic dust sources are associated with land use and ephemeral water bodies, both in turn linked to the hydrological cycle, their emissions are affected by climate variability. Such changes in dust emissions can impact climate, air quality, and human health. Improved dust emission estimates will require a better mapping of threshold wind velocities, vegetation dynamics, and surface conditions (soil moisture and land use) especially in the sensitive regions identified here, as well as improved ability to address small-scale convective processes producing dust via cold pool (haboob) events frequent in monsoon regimes.”

Citation: Ginoux, P., J. M. Prospero, T. E. Gill, N. C. Hsu, and M. Zhao (2012), Global-scale attribution of anthropogenic and natural dust sources and their emission rates based on MODIS Deep Blue aerosol products, Rev. Geophys., 50, RG3005, doi:10.1029/2012RG000388.

Past millennial scale climate variability had profound effect on the terrestrial ecosystems in SE Europe

Responses of terrestrial ecosystems to Dansgaard-Oeshger cycles and Heinrich-events: A 28,000-year record of environmental changes from SE Hungary – Sümegi et al. (2012)

Abstract: “According to the findings of a complex sedimentological, geochemical, malacological and pollen study implemented on a core sequence of an alkaline lake (Fehér Lake), interstadials in the SE Great Hungarian Plain were characterized by increased boreal woodland cover during Marine Isotope Stage 2 (MIS 2: 29,700-14,500 cal BP). These interstadials were dated to 26,420-27,970, 23,185-24,880, and 18,810-20,770 cal BP, and correlate well with the Dansgaard-Oeschger (DO) interstadials 2 and 3 and the post LGM warm interval seen in the Greenland ice core oxygen isotope records. Intervening cold phases, on the other hand, were found between 24,880-26,420 and 20,770-23,185 cal BP, correlating with Heinrich event 2 and the LGM. These data overall confirm that millennial scale climate variability during Marine Isotope Stage 2 had profound effect on the terrestrial ecosystems in the continental interior of SE Europe, leading to periodic boreal woodland expansions and contractions and wildfires.”

Citation: Pál Sümegi, Enikő Magyari, Péter Dániel, Mihály Molnár, Tünde Törőcsik, Quaternary International,

Record-breaking ozone loss in the Arctic winter 2010/2011

Record-breaking ozone loss in the Arctic winter 2010/2011: comparison with 1996/1997 – Kuttippurath et al. (2012) [FULL TEXT]

Abstract: “We present a detailed discussion of the chemical and dynamical processes in the Arctic winters 1996/1997 and 2010/2011 with high resolution chemical transport model (CTM) simulations and space-based observations. In the Arctic winter 2010/2011, the lower stratospheric minimum temperatures were below 195 K for a record period of time, from December to mid-April, and a strong and stable vortex was present during that period. Simulations with the Mimosa-Chim CTM show that the chemical ozone loss started in early January and progressed slowly to 1 ppmv (parts per million by volume) by late February. The loss intensified by early March and reached a record maximum of ~2.4 ppmv in the late March–early April period over a broad altitude range of 450–550 K. This coincides with elevated ozone loss rates of 2–4 ppbv sh−1 (parts per billion by volume/sunlit hour) and a contribution of about 30–55% and 30–35% from the ClO-ClO and ClO-BrO cycles, respectively, in late February and March. In addition, a contribution of 30–50% from the HOx cycle is also estimated in April. We also estimate a loss of about 0.7–1.2 ppmv contributed (75%) by the NOx cycle at 550–700 K. The ozone loss estimated in the partial column range of 350–550 K exhibits a record value of ~148 DU (Dobson Unit). This is the largest ozone loss ever estimated in the Arctic and is consistent with the remarkable chlorine activation and strong denitrification (40–50%) during the winter, as the modeled ClO shows ~1.8 ppbv in early January and ~1 ppbv in March at 450–550 K. These model results are in excellent agreement with those found from the Aura Microwave Limb Sounder observations. Our analyses also show that the ozone loss in 2010/2011 is close to that found in some Antarctic winters, for the first time in the observed history. Though the winter 1996/1997 was also very cold in March–April, the temperatures were higher in December–February, and, therefore, chlorine activation was moderate and ozone loss was average with about 1.2 ppmv at 475–550 K or 42 DU at 350–550 K, as diagnosed from the model simulations and measurements.”

Citation: Kuttippurath, J., Godin-Beekmann, S., Lefèvre, F., Nikulin, G., Santee, M. L., and Froidevaux, L.: Record-breaking ozone loss in the Arctic winter 2010/2011: comparison with 1996/1997, Atmos. Chem. Phys., 12, 7073-7085, doi:10.5194/acp-12-7073-2012, 2012.

CLASSIC OF THE WEEK: Rubens & Aschkinass (1898)

Observations on the Absorption and Emission of Aqueous Vapor and Carbon Dioxide in the Infra-Red Spectrum – Rubens & Aschkinass (1898) [FULL TEXT]

Abstract: No abstract.

Citation: Rubens, H., Aschkinass, E., Astrophysical Journal, vol. 8, p.176, DOI: 10.1086/140516.

When each paper is published, it is notified in AGW Observer Facebook page and Twitter page. Here’s the archive for the research papers of previous weeks. If this sort of thing interests you, be sure to check out A Few Things Illconsidered. They also have a weekly posting containing lots of links to new research and other climate related news.

Posted in Climate science | 1 Comment »

New research from last week 31/2012

Posted by Ari Jokimäki on August 6, 2012

If you prefer new peer-reviewed science over non-peer-reviewed PR papers, this is the post for you. Apart from scientists themselves, peer-reviewers, and journal editors, you are the first people on Earth to know about the things presented below.

Tree-ring proxies can provide reliable indicators of temperature variability even in rapidly warming climate

Tree-ring reconstructed summer temperatures from northwestern North America during the last nine centuries – Anchukaitis et al. (2012)

Abstract: “Northwestern North America has one of the highest rates of recent temperature increase in the world, but the putative ‘divergence problem’ in dendroclimatology potentially limits the ability of tree-ring proxy data at high latitudes to provide long-term context for current anthropogenic change. Here, we reconstruct summer temperatures from a Picea glauca maximum latewood density (MXD) chronology that shows a stable relationship to regional temperatures and spans most of the last millennium at the Firth River in northeastern Alaska. We estimate that the warmest epoch in the last nine centuries occurs during the late 20th century, with average temperatures over the last thirty years of our reconstruction (1973 to 2002 CE) approximately 1.3 ± 0.4°C warmer than the long-term preindustrial mean (1100 to 1850 CE), a change associated with rapid increases in greenhouse gases. Prior to the late 20th century, multidecadal temperature fluctuations covary broadly with changes in natural radiative forcing. Our findings emphasize that tree-ring proxies can provide reliable indicators of temperature variability even in a rapidly warming climate.”

Citation: Kevin J. Anchukaitis, Rosanne D. D’Arrigo, and Laia Andreu-Hayles, David Frank and Anne Verstege, Ashley Curtis, Brendan M. Buckley, Gordon C. Jacoby, and Edward R. Cook, Journal of Climate 2012, doi:

Global coverage for carbon dioxide measurements from satellites

Patterns of CO2 variability from global satellite data – Ruzmaikin et al. (2012)

Abstract: “We present an analysis of the global mid-tropospheric CO2 retrieved for all-sky (clear and cloudy) conditions from measurements by the Atmospheric Infrared Radiation Sounder on board the Aqua satellite in 2003-2009. The global data coverage allows us to identify the set of CO2 spatial patterns and their time variability by applying the Principal Component Analysis and the Empirical Mode Decomposition. The first, dominant pattern represents 93% of the variability and exhibits the linear trend of 2 ± 0.2 ppm/year, as well as annual and interannual dependencies. The single-site record of CO2 at Mauna Loa compares well with variability of this pattern. The first principal component is phase-shifted relative to the Southern Oscillation indicating a causative relationship between the atmospheric CO2 and the ENSO. The higher-order patterns show regional details of CO2 distribution and display the semi-annual oscillation. We also compare the CO2 distributions with the distribution of two major characteristics of air transport: the vertical velocity and potential temperature surfaces at the same height. In agreement with modeling, CO2 concentration closely traces the potential temperature surfaces (isentropes) in mid and high latitudes. However its vertical transport in the tropics, where these surfaces are mostly horizontal, is suppressed. Our results are in agreement with the previous results on annual and interannual CO2 time variability obtained by using the network flask data. This knowledge of the global CO2 spatial patterns can be useful in climate analyses and potentially in the challenging task of connecting CO2 sources and sinks with its distribution in the atmosphere.”

Citation: Alexander Ruzmaikin, Hartmut H. Aumann, and Thomas S. Pagano, Journal of Climate 2012, doi:

Southeast Australia autumn rainfall reduction might be due to poleward shift of ocean-atmosphere circulation

Southeast Australia autumn rainfall reduction: A climate-change induced poleward shift of ocean-atmosphere circulation – Cai & Cowan (2012)

Abstract: “Since the 1950s, annual rainfall over southeast Australia (SEA) has decreased considerably with a maximum decline in the austral autumn season (March-May), particularly from 1980 onwards. The understanding of SEA autumn rainfall variability, the causes and associated mechanisms for the autumn reduction remain elusive. As such, a new plausible mechanism for SEA autumn rainfall variability is described, and the dynamics for the reduction are hypothesised. Firstly, there is no recent coherence between SEA autumn rainfall and the Southern Annular Mode, discounting it as a possible driver of the autumn rainfall reduction. Secondly, weak trends in the subtropical ridge intensity (STRI) cannot explain the recent autumn rainfall reduction across SEA, even though a significant relationship exists between the ridge and rainfall in April and May. With a collapse in the relationship between the autumn STRI and position in recent decades, a strengthening in the influence of the post-monsoonal winds from north of Australia has emerged, as evident by a strong post-1980 coherence with SEA pressure and rainfall. From mid-late autumn, there has been a replacement of a relative wet climate in SEA with a drier climate from northern latitudes, representing a climate shift that has contributed to the rainfall reduction. The maximum baroclinicity, as indicated by Eady growth rates, shifts polewards. An associated poleward shift of the dominant process controlling SEA autumn rainfall further enhances the reduction, particularly across southern SEA. This observed change over the past few decades is consistent with a poleward shift of the ocean and atmosphere circulation.”

Citation: Wenju Cai and Tim Cowan, Journal of Climate 2012, doi:

Satellite records have only recently reached sufficient length to detect trends in cloudiness

PATMOS-x: Results from a Diurnally-Corrected Thirty-Year Satellite Cloud Climatology – Foster & Heidinger (2012)

Abstract: “Satellite drift is an historical issue affecting the consistency of those few satellite records capable of being used for studies on climate time-scales. Here we address this issue for the PATMOS-x/AVHRR cloudiness record, which spans three decades and eleven disparate sensors. A two-harmonic sinusoidal function is fit to a mean diurnal cycle of cloudiness derived over the course of the entire AVHRR record. We validate this function against measurements from GOES sensors, finding good agreement, and then test the stability of the diurnal cycle over the course of the AVHRR record. It is found that the diurnal cycle is subject to some inter-annual variability over land, but that the differences are somewhat offset when averaged over an entire day. The fit function is used to generate daily-averaged time-series of ice, water and total cloudiness over the Tropics, where it is found that the diurnal correction affects the magnitude and even sign of long-term cloudiness trends. A statistical method is applied to determine the minimum length of time required to detect significant trends, and we find that only recently have we begun generating satellite records of sufficient length to detect trends in cloudiness.”

Citation: Michael J. Foster, Andrew Heidinger, Journal of Climate 2012, doi:

It’s not internal variability, it’s not unknown forcing, it’s mankind

Testing for the possible influence of unknown climate forcings upon global temperature increases from 1950-2000 – Anderson et al. (2012)

Abstract: “Global-scale variations in the climate system over the last half of the 20th Century, including long-term increases in global-mean near-surface temperatures, are consistent with concurrent human-induced emissions of radiatively-active gases and aerosols. However, such consistency does not preclude the possible influence of other forcing agents, including internal modes of climate variability or unaccounted for aerosol effects. To test whether other unknown forcing agents may have contributed to multi-decadal increases in global-mean near-surface temperatures from 1950-2000, data pertaining to observed changes in global-scale sea-surface temperatures and observed changes in radiatively-active atmospheric constituents are incorporated into numerical global climate models. Results indicate that the radiative forcing needed to produce the observed long-term trends in sea-surface temperatures—and global-mean near-surface temperatures—is provided predominantly by known changes in greenhouse gases and aerosols. Further, results indicate that less than 10% of the long-term historical increase in global-mean near-surface temperatures over the last half of the 20th century could have been the result of internal climate variability. In addition they indicate that less than 25% of the total radiative forcing needed to produce the observed long-term trend in global-mean near-surface temperatures could have been provided by changes in net radiative forcing from unknown sources (either positive or negative). These results, which are derived from simple energy balance requirements, emphasize the important role humans have played in modifying the global climate over the last half of the 20th Century.”

Citation: Bruce T. Anderson, Jeff R. Knight and Mark A. Ringer, Jin-Ho Yoon, Annalisa Cherchi, Journal of Climate 2012, doi:

Observations of climate feedbacks over 2000-2010 and comparisons to climate models

Observations of climate feedbacks over 2000-2010 and comparisons to climate models – Dessler (2012)

Abstract:“Feedbacks in response to climate variations during the period 2000-2010 have been calculated using reanalysis meteorological fields and top-of-atmosphere flux measurements. Over this period, the climate was stabilized by a strongly negative temperature feedback (~ −3 W/m2/K); climate variations were also amplified by a strong positive water vapor feedback (~ +1.2 W/m2/K) and smaller positive albedo and cloud feedbacks (~ +0.3 and +0.5 W/m2/K, respectively). These observations are compared to two climate model ensembles, one dominated by internal variability (the control ensemble) and the other dominated by long-term global warming (the A1B ensemble). The control ensemble produces global average feedbacks that agree within uncertainties with the observations, as well as producing similar spatial patterns. The most significant discrepancy was in the spatial pattern for the total (shortwave + longwave) cloud feedback. Feedbacks calculated from the A1B ensemble show a stronger negative temperature feedback (due to a stronger lapse-rate feedback), but that is cancelled by a stronger positive water vapor feedback. The feedbacks in the A1B ensemble tend to be more smoothly distributed in space, which is consistent with the differences between ENSO climate variations and long-term global warming. The sum of all of the feedbacks, sometimes referred to as the thermal damping rate, is −1.15±0.88 W/m2/K in the observations, −0.60±0.37 W/m2/K in the control ensemble. Within the control ensemble, models that more accurately simulate ENSO tend to produce thermal damping rates closer to the observations. The A1B ensemble average thermal damping rate is −1.26±0.45 W/m2/K.”

Citation: A. E. Dessler, Journal of Climate 2012, doi:

Simulating the effects of methane disaster scenario

Damage of land biosphere due to intense warming by 1000-fold rapid increase in atmospheric methane: Estimation with a climate-carbon cycle model – Obata & Shibata (2012)

Abstract: “Decadal timescale responses of climate and the global carbon cycle to warming associated with rapid increases in atmospheric methane from a massive methane release from marine sedimentary methane hydrates are investigated with a coupled climate-carbon cycle model. A 1000-fold methane increase (from <1 to 1000 ppmv) causes surface air temperatures to increase with a global warming of >6°C within 80 years. The amount of carbon stored in the land biosphere decreases by >25%. This is mostly due to a large decrease in tropical net primary production during the first few years (~−40%), which is caused by a decrease in photosynthesis and an increase in plant maintenance respiration with the early warming of ~3°C, leading to tropical forest dieback (>20%) and the largest decrease in vegetation carbon of >50% (~80% of the decrease in global vegetation carbon). The decrease in global land carbon is also partly due to forest diebacks (mainly boreal forest dieback by heat stress) at northern middle latitudes. In contrast, vegetation increases by >50% at northern high latitudes because of the amelioration to warm and wet conditions. Sensitivity experiments show that the warming of >6°C consists mainly of >5°C by the 1000-fold atmospheric methane and an additional increase of 1°C by the atmospheric CO2 increase due to the land CO2 release, and that the CO2 fertilization of land plants prevents further warming of 1°C by limiting the atmospheric CO2 increase. The large decrease in land biomass estimated in this study suggests a critical situation for the land ecosystem or agricultural production especially in the tropics.”

Citation: Atsushi Obata and Kiyotaka Shibata, Journal of Climate 2012, doi:

Extracting seasonal climate information from Antarctic ice cores

Seasonal climate information preserved in West Antarctic ice core water isotopes: relationships to temperature, large-scale circulation, and sea ice – Küttel et al. (2012) [FULL TEXT]

Abstract: “As part of the United States’ contribution to the International Trans-Antarctic Scientific Expedition (ITASE), a network of precisely dated and highly resolved ice cores was retrieved from West Antarctica. The ITASE dataset provides a unique record of spatial and temporal variations of stable water isotopes (δ18O and δD) across West Antarctica. We demonstrate that, after accounting for water vapor diffusion, seasonal information can be successfully extracted from the ITASE cores. We use meteorological reanalysis, weather station, and sea ice data to assess the role of temperature, sea ice, and the state of the large-scale atmospheric circulation in controlling seasonal average water isotope variations in West Antarctica. The strongest relationships for all variables are found in the cores on and west of the West Antarctic Ice Sheet Divide and during austral fall. During this season positive isotope anomalies in the westernmost ITASE cores are strongly related to a positive pressure anomaly over West Antarctica, low sea ice concentrations in the Ross and Amundsen Seas, and above normal temperatures. Analyses suggest that this seasonally distinct climate signal is due to the pronounced meridional oriented circulation and its linkage to enhanced sea ice variations in the adjacent Southern Ocean during fall, both of which also influence local to regional temperatures.”

Citation: Marcel Küttel, Eric J. Steig, Qinghua Ding, Andrew J. Monaghan and David S. Battisti, Climate Dynamics, 2012, DOI: 10.1007/s00382-012-1460-7.

Abrupt climate changes in Northern hemisphere during MWP but not during LIA

Abrupt temperature changes during the last 1,500 years – Matyasovszky & Ljungqvist (2012)

Abstract: “We investigate the occurrence of abrupt changes in a total of 35 different proxy records from the extra-tropical Northern Hemisphere for the last ~1,500 years. The proxy records include ice-core δ18O, speleothem, tree ring width/density, marine sediment and lake sediment records with annual, sub-decadal or decadal resolutions. The aim is to explore the spatio–temporal distribution of abrupt climate changes using a kink point analysis technique. A clustering of warm kink points (the kink points with the highest temperatures) around AD 1000 appears corresponding to the Medieval Warm Period and indicates a geographically widespread temperature peak at that time. Kink points around AD 1000 are somewhat more numerous on higher latitudes than on lower latitudes. There are some tendencies for the coldest kink points (the kink points with the lowest temperatures) to be clustered in the ninetenth century, but they are generally more unevenly spaced in time than the warm peaks around AD 1000. The relative lack of kink points detected during the 1500 s–1700 s, likely the coldest part of the Little Ice Age, implies that this cold period was relatively stable and without abrupt events. A possible cluster of kink points on lower latitudes in the early ninth century is also found. No clear difference in the timing of kink points between the different proxy types can be observed.”

Citation: István Matyasovszky and Fredrik Charpentier Ljungqvist, Theoretical and Applied Climatology, 2012, DOI: 10.1007/s00704-012-0725-8.

Warming of 2K impacts Europe economy only moderately but 4K warming impact is clearly negative

Impacts and adaptation to climate change in European economies – Aaheim et al. (2012)

Abstract: “This paper evaluates the impacts of climate change to European economies under an increase in global mean temperature at +2 °C and +4 °C. It is based on a summary of conclusions from available studies of how climate change may affect various sectors of the economies in different countries. We apply a macroeconomic general equilibrium model, which integrates impacts of climate change on different activities of the economies. Agents adapt by responding to the changes in market conditions following the climatic changes, thus bringing consistency between economic behaviour and adaptation to climate change. Europe is divided into 85 sub-regions in order to capture climate variability and variations in vulnerabilities within countries. We find that the impacts in the +2 °C are moderate throughout Europe, with positive impacts on GDP in some sub-regions and negative impacts down to 0.1 per cent per year in others. At +4 °C, GDP is negatively affected throughout Europe, and most substantially in the southern parts, where it falls by up to 0.7 per cent per year in some sub-regions. We also find that climate change causes differentiations in wages across Europe, which may cause migration from southern parts of Europe to northern parts, especially to the Nordic countries.”

Citation: Asbjørn Aaheim, Helene Amundsen, Therese Dokken, Taoyuan Wei, Global Environmental Change, 2012,

Aerosols cause solar dimming so rice yields decrease despite of warming climate

Increasing concentrations of aerosols offset the benefits of climate warming on rice yields during 1980–2008 in Jiangsu Province, China – Shuai et al. (2012)

Abstract: “The impacts of climate change on crop yield have increasingly been of concern. In this study, we investigated the impacts of trends in sunshine duration (S) and maximum temperature (T max) on rice yields in Jiangsu Province at both the provincial and county level during the period from 1980 to 2008. The results showed that although S and T max both were positively correlated with rice yields, the combined impacts of the decreasing trend of S (0.37 h/decade) and the increasing trend of T max (0.34 °C/decade) in August caused a reduction of 0.16 t ha−1 in rice yields (approximately 1.8 %) in Jiangsu Province, and the trend of S had played a dominant role in the yield losses. Further analyses suggest that the increasing concentration of aerosols from rapid economic development in Jiangsu Province has caused a significant solar dimming at least since 1960, making mitigations and adaptation measurements on regional haze impact imperative. Our study provides a prototype for detecting negative feedback on agricultural production caused by intensified anthropogenic activities that aim only to create rapid economic development.”

Citation: Jiabing Shuai, Zhao Zhang, Xiaofei Liu, Yi Chen, Pin Wang and Peijun Shi, Regional Environmental Change, 2012, DOI: 10.1007/s10113-012-0332-3.

Analysis of aerosol and ozone forcing between 1850 and 2100

Aerosol and ozone changes as forcing for climate evolution between 1850 and 2100 – Szopa et al. (2012) [FULL TEXT]

Abstract: “Global aerosol and ozone distributions and their associated radiative forcings were simulated between 1850 and 2100 following a recent historical emission dataset and under the representative concentration pathways (RCP) for the future. These simulations were used in an Earth System Model to account for the changes in both radiatively and chemically active compounds, when simulating the climate evolution. The past negative stratospheric ozone trends result in a negative climate forcing culminating at −0.15 W m−2 in the 1990s. In the meantime, the tropospheric ozone burden increase generates a positive climate forcing peaking at 0.41 W m−2. The future evolution of ozone strongly depends on the RCP scenario considered. In RCP4.5 and RCP6.0, the evolution of both stratospheric and tropospheric ozone generate relatively weak radiative forcing changes until 2060–2070 followed by a relative 30 % decrease in radiative forcing by 2100. In contrast, RCP8.5 and RCP2.6 model projections exhibit strongly different ozone radiative forcing trajectories. In the RCP2.6 scenario, both effects (stratospheric ozone, a negative forcing, and tropospheric ozone, a positive forcing) decline towards 1950s values while they both get stronger in the RCP8.5 scenario. Over the twentieth century, the evolution of the total aerosol burden is characterized by a strong increase after World War II until the middle of the 1980s followed by a stabilization during the last decade due to the strong decrease in sulfates in OECD countries since the 1970s. The cooling effects reach their maximal values in 1980, with −0.34 and −0.28 W m−2 respectively for direct and indirect total radiative forcings. According to the RCP scenarios, the aerosol content, after peaking around 2010, is projected to decline strongly and monotonically during the twenty-first century for the RCP8.5, 4.5 and 2.6 scenarios. While for RCP6.0 the decline occurs later, after peaking around 2050. As a consequence the relative importance of the total cooling effect of aerosols becomes weaker throughout the twenty-first century compared with the positive forcing of greenhouse gases. Nevertheless, both surface ozone and aerosol content show very different regional features depending on the future scenario considered. Hence, in 2050, surface ozone changes vary between −12 and +12 ppbv over Asia depending on the RCP projection, whereas the regional direct aerosol radiative forcing can locally exceed −3 W m−2.”

Citation: Sophie Szopa, Y. Balkanski, M. Schulz, S. Bekki, D. Cugnet, A. Fortems-Cheiney, S. Turquety, A. Cozic, C. Déandreis and D. Hauglustaine, et al., Climate Dynamics, 2012, DOI: 10.1007/s00382-012-1408-y.

Western North American tree populations already lag behind their optimal climate niche

Tracking suitable habitat for tree populations under climate change in western North America – Gray & Hamann (2012)

Abstract: “An important criticism of bioclimate envelope models is that many wide-ranging species consist of locally adapted populations that may all lag behind their optimal climate habitat under climate change, and thus should be modeled separately. Here, we apply a bioclimate envelope model that tracks habitat of individual populations to estimate adaptational lags for 15 wide-ranging forest tree species in western North America. An ensemble classifier modeling approach (RandomForest) was used to spatially project the climate space of tree populations under observed climate trends (1970s to 2000s) and multi-model projections for the 2020s, 2050s and 2080s. We find that, on average, populations already lag behind their optimal climate niche by approximately 130 km in latitude, or 60 m in elevation. For the 2020s we expect an average lag of approximately 310 km in latitude or 140 m in elevation, with the most pronounced geographic lags in the Rocky Mountains and the boreal forest. We show that our results could in principle be applied to guide assisted migration of planting stock in reforestation programs using a general formula where 100 km north shift is equivalent to approximately 44 m upward shift in elevation. However, additional non-climatic factors should be considered when matching reforestation stock to suitable planting environments.”

Citation: Laura K. Gray and Andreas Hamann, Climatic Change, 2012, DOI: 10.1007/s10584-012-0548-8.

Arctic Ocean contributes to Arctic amplification by losing heat to atmosphere when sea ice retreats

Heat budget of the upper Arctic Ocean under a warming climate – Graham & Vellinga (2012)

Abstract: “The heat budget of the upper Arctic Ocean is examined in an ensemble of coupled climate models under idealised increasing CO2 scenarios. All of the experiments show a strong amplification of surface air temperatures but a smaller increase in sea surface temperature than the rest of the world as heat is lost to the atmosphere as the sea-ice cover is reduced. We carry out a heat budget analysis of the Arctic Ocean in an ensemble of model runs to understand the changes that occur as the Arctic becomes ice free in summer. We find that as sea-ice retreats heat is lost from the ocean surface to the atmosphere contributing to the amplification of Arctic surface temperatures. Furthermore, heat is mixed upwards into the mixed layer as a result of increased upper ocean mixing and there is increased advection of heat into the Arctic as the ice edge retreats. Heat lost from the upper Arctic Ocean to the atmosphere is therefore replenished by mixing of warmer water from below and by increased advection of warm water from lower latitudes. The ocean is therefore able to contribute more to Arctic amplification.”

Citation: Tim Graham and Michael Vellinga, Climate Dynamics, 2012, DOI: 10.1007/s00382-012-1454-5.

How Little Ice Age showed up in Antarctica?

Little Ice Age climate and oceanic conditions of the Ross Sea, Antarctica from a coastal ice core record – Rhodes et al. (2012) [FULL TEXT]

Abstract: “Increasing paleoclimatic evidence suggests that the Little Ice Age (LIA) was a global climate change event. Understanding the forcings and associated climate system feedbacks of the LIA is made difficult by the scarcity of Southern Hemisphere paleoclimate records. We use a new glaciochemical record of a coastal ice core from Mt. Erebus Saddle, Antarctica, to reconstruct atmospheric and oceanic conditions in the Ross Sea sector of Antarctica over the past five centuries. The LIA is identified in stable isotope (δD) and lithophile element records, which respectively demonstrate that the region experienced 1.6 ± 1.4 °C cooler average temperatures prior to 1850 AD than during the last 150 yr and strong (>57 m s−1) prevailing katabatic winds between 1500 and 1800 AD. Al and Ti concentration increases of an order of magnitude (>120 ppb Al) are linked to enhanced aeolian transport of complex silicate minerals and represent the strongest katabatic wind events of the LIA. These events are associated with three 12–30 yr intervals of cooler temperatures at ca. 1690 AD, 1770 AD and 1840 AD. Furthermore, ice core concentrations of the biogenic sulphur species MS suggest that biological productivity in the Ross Sea polynya was ~80% higher prior to 1875 AD than at any subsequent time. We propose that cooler Antarctic temperatures promoted stronger katabatic winds across the Ross Ice Shelf, resulting in an enlarged Ross Sea polynya during the LIA.”

Citation: Rhodes, R. H., Bertler, N. A. N., Baker, J. A., Steen-Larsen, H. C., Sneed, S. B., Morgenstern, U., and Johnsen, S. J.: Little Ice Age climate and oceanic conditions of the Ross Sea, Antarctica from a coastal ice core record, Clim. Past, 8, 1223-1238, doi:10.5194/cp-8-1223-2012, 2012.

CLASSIC OF THE WEEK: Chamberlin (1898)

The Influence of Great Epochs of Limestone Formation upon the Constitution of the Atmosphere – Chamberlin (1898) [FULL TEXT]

Abstract: No abstract. Quote from the beginning of the article: “THE virtues of carbon dioxide are in inverse ratio to the sinister reputation which “a little knowledge” and a narrow homocentric point of view have given it. As a constituent of the atmosphere it is as necessary to the maintenance of life as oxygen because it is the food of plants and they in turn are the food of animals. Its peculiar competency to retain the heat of the sun renders it a decisive factor in the maintenance of that measurable constancy and geniality of temperature upon which the existence of life depends. It is a leading agency in the disintegration of crystalline rock and is a necessary factor in other geologic changes. It is an essential link in a chain of vital processes which involve all the constituents of the atmosphere. Inherently it may be no more necessary to these processes, save in its thermal nature, than is oxygen, but being the minimum factor in the atmosphere it becomes regulative and decisive, because variations in it affect the whole cycle of processes dependent on it, while similar variations in the major constituents may have no appreciable effect.”

Citation: T. C. Chamberlin, The Journal of Geology, Vol. 6, No. 6 (Sep. – Oct., 1898) (pp. 609-621).

When each paper is published, it is notified in AGW Observer Facebook page and Twitter page. Here’s the archive for the research papers of previous weeks. If this sort of thing interests you, be sure to check out A Few Things Illconsidered. They also have a weekly posting containing lots of links to new research and other climate related news.

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Papers on time of observation bias

Posted by Ari Jokimäki on August 1, 2012

This is a list of the time of observation bias in temperature measurements. The list is not complete, and will most likely be updated in future in order to make it more thorough and more representative.

Note that list of papers on global surface temperature contains papers relevant to this list also.

UPDATE (August 1, 2012): Kreil (1854) and Kreil (1854) added. Thanks to Victor Venema for pointing them out.

Bias in Minimum Temperature Introduced by a Redefinition of the Climatological Day at the Canadian Synoptic Stations – Vincent et al. (2009) “On 1 July 1961, the climatological day was redefined to end at 0600 UTC (coordinated universal time) at all synoptic (airport) stations in Canada. Prior to that, the climatological day ended at 1200 UTC for maximum temperature and 0000 UTC for minimum temperature. This study shows that the redefinition of the climatological day in 1961 has created a cold bias in the annual and seasonal means of daily minimum temperatures across the country while the means of daily maximum temperatures were not affected. Hourly temperatures taken at 121 stations for 1953–2007 are used to determine the magnitude of the bias and its spatial variation. It was found that the bias is more pronounced in the eastern regions; its annual mean varies from −0.2° in the west to −0.8°C in the east. Not all days are affected by this change in observing time, and the annual percentage of affected days ranges from 15% for locations in the west to 38% for locations in the east. An approach based on hourly values is proposed for adjusting the affected daily minimum temperatures over 1961–2007. The adjustment on any individual day varies from 0.5° to 12.5°C. The impact of the adjustment is assessed by examining the trends in the annual mean of the daily minimum temperatures for 1950–2007. Overall, with the adjustment, the trends are becoming either more positive or are reversing from negative to positive, and they have changed by as much as 1°C in numerous locations in the eastern regions.” Vincent, Lucie A., Ewa J. Milewska, Ron Hopkinson, Leslie Malone, 2009: Bias in Minimum Temperature Introduced by a Redefinition of the Climatological Day at the Canadian Synoptic Stations. J. Appl. Meteor. Climatol., 48, 2160–2168. doi: [FULL TEXT]

A method to infer time of observation at US Cooperative Observer Network stations using model analyses – Belcher & DeGaetano (2005) “A method to estimate the time of observation employed at US Cooperative Observer Network stations has been developed using rapid update cycle model analyses. This method uses the day-to-day variability in model temperature biases to estimate observation schedules on a time scale of weeks, making it ideal for use in ‘real-time’ applications. Observation time estimates from a two-category system (morning and ‘non-morning’) and three-category system (morning, afternoon and midnight) were both evaluated. The performance of the two-category system was compared with existing techniques that employ this system on monthly time scales. The results were comparable, showing dependence on season and climatological characteristics, but reveal an ability to reach high levels of accuracy (>90% of stations have observation schedules correctly estimated) over similar time periods (10–50 days). To our knowledge, the evaluation of three-category estimation performance for the time scales investigated has not been documented. Accuracy remained high for morning and midnight stations (>90%), and decreased for stations with afternoon observation schedules (85–65%). Additionally, the three-category estimation technique was extended to four categories in order to identify observers who shift temperature records temporally. The accuracy of detecting shifted records within the context of the four-category estimation technique was comparable to the performance of the three-category system, with shifted observations correctly identified more than 75% of the time in most cases.” Brian N. Belcher, Arthur T. DeGaetano, International Journal of Climatology, Volume 25, Issue 9, pages 1237–1251, July 2005, DOI: 10.1002/joc.1183. [FULL TEXT]

An evaluation of the time of observation bias adjustment in the U.S. Historical Climatology Network – Vose et al. (2003) “The U.S. Historical Climatology Network (HCN) database contains statistical adjustments that address historical changes in observation time at each observing station in the network. A paper in 2002 suggested that these adjustments cause HCN temperature trends to be “spuriously” warm relative to other datasets for the United States. To test this hypothesis, this paper evaluates the reliability of these “time of observation bias” adjustments in HCN. The results indicate that HCN station history information is reasonably complete and that the bias adjustment models have low residual errors. In short, the time of observation bias adjustments in HCN appear to be robust.” Vose, R. S., C. N. Williams Jr., T. C. Peterson, T. R. Karl, and D. R. Easterling (2003), An evaluation of the time of observation bias adjustment in the U.S. Historical Climatology Network, Geophys. Res. Lett., 30(20), 2046, doi:10.1029/2003GL018111.

A Method for Operational Detection of Daily Observation-Time Changes – Belcher & DeGaetano (2003) “A method to detect observation-time changes within weeks to months of their occurrence was developed using hourly observations from a set of 32 first-order stations across the United States. The procedure operationally requires only daily maximum and minimum temperatures. Development of the detection procedure depends on the utilization of nonclimatic biases that are artificially introduced into simulated daily temperature datasets constructed from hourly data at each of the 32 development stations. These biases are quantified by using interdiurnal temperature differences, which are used as the basis of observation-time-change detection. The procedure is tested on simulated daily temperature datasets constructed from hourly data at nine independent first-order stations and is applied to actual daily temperature observations from a sample of stations that make up the Cooperative Observer Network. The probability of detection is largest over the Midwest and High Plains regions of the United States and is smallest for maritime stations in the southwestern and southeastern regions of the United States. False-alarm occurrence is highest over the southern United States, particularly in the southeastern region and southern California. Overall detection performance is improved in all regions by incorporating more data into the detection tests, but the median amount of time between the occurrence of an observation-time change and its detection also increases as a result.” Belcher, Brian N., Arthur T. DeGaetano, 2003: A Method for Operational Detection of Daily Observation-Time Changes. J. Appl. Meteor., 42, 1823–1836. doi:;2. [FULL TEXT]

Observation-Time-Dependent Biases and Departures for Daily Minimum and Maximum Air Temperatures – Janis (2002) “Non-calendar-day observations of 24-h minimum and maximum air temperatures can be considerably different from calendar-day or midnight observations. This paper examines the influence of time-of-observation on 24-h temperature observations. Diurnal minimum and maximum temperatures measured at common observation times (0700 and 1700 LST) are compared with minimum and maximum temperatures measured at midnight. The principal methods make use of hourly temperature observations, sampled over 24-h moving windows, to approximate once-daily observations. Surprisingly, non-calendar-day observations are similar to calendar-day observations on a majority of days. When differences do occur, however, they can be large and of either sign. Differences between 1700 LST observations and midnight observations are typically smaller than those arising from 0700 LST observations. Daily differences can be grouped by temperature extrema recorded on the incorrect day (a bookkeeping problem) or temperature extrema recorded on two successive days (bias). Bias scenarios arise when very cold mornings or very warm afternoons influence the temperature measured on successive days. Locations or seasons with the least day-to-day temperature variability often display the least time-of-daily-observation influence on temperature. Determining those days on which large departures and biases are likely to occur is possible by measuring day-to-day temperature persistence. First-order differences of daily time series may be used explicitly in adjustment procedures for morning observations of maximum temperature. Otherwise, first-order differences may be used to determine those days on which large observation-time differences are likely or those days on which observation-time dependencies are trivial.” Janis, Michael J., 2002: Observation-Time-Dependent Biases and Departures for Daily Minimum and Maximum Air Temperatures. J. Appl. Meteor., 41, 588–603. doi:;2. [FULL TEXT]

A Method to Infer Observation Time Based on Day-to-Day Temperature Variations – DeGaetano (1999) “A method to infer the observation time of a station at annual resolution is developed and tested at stations in the United States. The procedure is based on a tendency for the percentiles of the monthly distribution of positive day-to-day maximum temperature changes (i.e., day n + 1 > day n) to exceed the corresponding absolute percentiles of the distribution of negative day-to-day changes at afternoon stations. Similarly absolute percentiles of negative day-to-day minimum temperature change tend to exceed the corresponding positive interdiurnal changes at morning observation sites. Equal percentiles are generally found at stations that use a midnight observation hour. Based on annual and seasonal summations of these monthly percentile differences, discriminant functions are developed that are capable of differentiating between afternoon, morning, and midnight observation schedules. Across the majority of the United States observation time is correctly classified in over 90% of the station-years tested. Classification success is generally highest for morning and afternoon observations and somewhat lower for midnight observations. Although geographic biases in classification success are not apparent, the procedure’s ability to estimate observation time decreases considerably at stations where the average annual interdiurnal temperature range is less than 1.7°C. In the United States such stations are limited to coastal California, parts of Arizona, and extreme southern portions of Texas and Florida. Application of the procedure to a subset of U.S. climatic normals stations indicates the presence of errors in the corresponding observation time metadata file.” DeGaetano, Arthur T., 1999: A Method to Infer Observation Time Based on Day-to-Day Temperature Variations. J. Climate, 12, 3443–3456. doi:;2. [FULL TEXT]

Standardization of weekly growingdegreedayaccumulationsbasedondifferencesin temperature observation time and method – DeGaetano & Knapp (1993) “Efforts to develop comparable growingdegreeday (GDD) accumulations across the US-Canadian border have revealed significant anomalies resulting from differencesin observing times among US stations and reporting practices between US and Canadian stations. Simulations using hourly temperature data indicate that the period required to reach a given GDD threshold value during a growing season often varies by 2 weeks or more solely because of observation time differences. Previous work on methods to adjust such biases has concentrated on seasonal totals and long-term averages. In this study, empirical methods are developed to standardize weekly GDD accumulations to a common observing time. Hourly data for a 10 year period from five northeastern United States stations are used in the development of the adjustment procedure. However, only daily maximum and minimum temperatures are needed to implement the adjustment scheme. Different weekly adjustment factors are used for each month from March through November. In addition, the weekly adjustment factors are decreased in magnitude during individual spring and autumn weeks in which fewer than 25 degreedays (13.9°C GDD) accumulate. Correction factors are also reduced during summer weeks which exhibit minimal day-to-day variation in temperature. An additional adjustment is applied to observations taken in the late afternoon and evening to ensure that the maximum temperature observed at these stations has occurred on the same day as that reported by morning observing sites. Validation trials using data from six independent stations indicate that average weekly differences of as much as 10 GDD (5.6°C GDD) are reduced to less than 1 GDD (0.6°C GDD). After applying the standardization procedures, GDD values basedon different observation times and the Canadian observation practice accumulate at similar rates.” Arthur T. DeGaetano, Warren W. Knapp, Agricultural and Forest Meteorology, Volume 66, Issues 1–2, September 1993, Pages 1–19,

A Model to Estimate the Time of Observation Bias Associated with Monthly Mean Maximum, Minimum and Mean Temperatures for the United States – Karl et al. (1986) “Hourly data for 79 stations in the United States are used to develop an empirical model which can be used to estimate the time of observation bias associated with different observation schedules. The model is developed for both maximum and minimum monthly average temperature as well as monthly mean temperature. The model was tested on 28 independent stations, and the results were very good. Using seven years of hourly data the standard errors of estimate using the model were only moderately higher than the standard errors of estimate of the true time of observation bias. The physical characteristics of the model directly include a measure of mean monthly interdiurnal temperature differences, analemma information, and the effects of the daily temperature range due to solar forcing. A self-contained computer program has been developed which allows a user to estimate the time of observation bias anywhere in the contiguous United States without the costly exercise of accusing 24-hourly observations at first-order stations.” Karl, Thomas R., Claude N. Williams, Pamela J. Young, Wayne M. Wendland, 1986: A Model to Estimate the Time of Observation Bias Associated with Monthly Mean Maximum, Minimum and Mean Temperatures for the United States. J. Climate Appl. Meteor., 25, 145–160. doi:;2. [FULL TEXT]

An Adjustment for the Effects of Observation Time on Mean Temperature and Degree-Day Computations – Byrd (1985) “Biases in mean temperatures due to differing times of daily maximum and minimum temperature observation cause problems in evaluation of temporal and spatial anomalies in temperature and derived degree day values. These biases were examined using six years (1973–78) of digitized hourly temperature data taken at Oneonta, New York. An annual mean temperature difference of 2.5°F is noted between means computed with the 0600 LST and 1500 IST observation times, with individual monthly differences as high as 4.4°F. Maximum seasonal degree day biases were 743 heating degree days (HDD) (10.2%), 169 cooling degree days (CDD) (43.3%), and 299 growing degree days (GDD) (14.3%). A modified version of the Blackburn method for adjusting mean temperature data for observation time bias is presented. The modified method involves adjusting data to a “true” mean obtained by averaging all hourly temperature values for the 24-hour period ending at midnight, rather than adjusting to the midnight standard observational mean obtained by averaging the maximum and minimum values over the same period. The adjustments are applied to mean temperatures from stations with different observation times in the region around Oneonta, resulting in spatial analysis fields which are believed to be more representative than those using the published data. This suggests that application of such an adjustment scheme results in a more homogeneous climatological data set.” Byrd, Gregory P., 1985: An Adjustment for the Effects of Observation Time on Mean Temperature and Degree-Day Computations. J. Climate Appl. Meteor., 24, 869–874. doi:;2. [FULL TEXT]

A Practical Method of Correcting Monthly Average Temperature Biases Resulting from Differing Times of Observation – Blackburn (1983) “Biases in monthly average temperatures reported by cooperative weather observers arise from once-daily observations of maximum and minimum temperatures at times of day other than local midnight. A scheme for adjusting these reports to eliminate the biases and make them conform to the midnight-to-midnight reports of first-order weather stations is described. This scheme has been applied to climatological reports of the Washington, DC, cooperative network.” Blackburn, Thomas, 1983: A Practical Method of Correcting Monthly Average Temperature Biases Resulting from Differing Times of Observation. J. Climate Appl. Meteor., 22, 328–330. doi:;2. [FULL TEXT]

Time of Observation Temperature Bias and “Climatic Change” – Schaal & Dale (1977) “Historical changes in time of once daily maximum and minimum temperature observations at cooperative climatological stations from 1905 to 1975 have introduced a systematic bias in mean temperatures. Unless corrected, this bias may be interpreted incorrectly as climatic “cooling” and may also affect the assessment of agricultural production potential and fossil fuel needs. Maximum and minimum temperature data for two years from the National Weather Service station at Indianapolis International Airport were used to evaluate the differences between mean temperatures obtained by terminating the 24 h period at the midnight observation and the mean temperatures obtained by terminating the 24 h period at 0700 and 1900 hours, typical observation times for AM and PM observing stations. The greatest mean temperature bias occurs in March when a 1900 observation day yields a monthly mean temperature 1.3°F above a midnight observation, and a 0700 observational day gives a −1.3°F bias. Since the number of AM observing stations in Indiana have increased from 10% of the total number of temperature stations in 1925 to 55% in 1975, the March mean temperature shows a decrease of 1.2°F in the last 40 years, solely because of the change in substation observational times. Unless the time of observation bias is considered, the mixture of AM and PM observations complicates interpretation of areal temperature anomaly patterns. This bias is accumulated in monthly, seasonal or annual values of the mean temperature-derived variables-heating degree days, cooling degree days and growing degree days—and may provide misleading information for applications in industry and agriculture.” Schaal, Lawrence A., Robert F. Dale, 1977: Time of Observation Temperature Bias and “Climatic Change”. J. Appl. Meteor., 16, 215–222. doi:;2. [FULL TEXT]

Effect of Observation Time on Mean Temperature Estimation – Baker et al. (1975) “The increased interest and application of heating degree days (HDD) and growing degree days (GDD) prompted this study into the effect of different observation times upon the mean daily temperature. The study was based upon three years of hourly air temperatures measured at St. Paul. These data were used to calculate 1) a true daily mean, 2) a mean of the maximum and minimum between successive midnights as observed at first order stations, and 3) a mean of the maximum and minimum observed at all other hours of the day to simulate cooperative station means. Comparisons of the annual and monthly mean temperatures showed deviations can be of such magnitude as to discourage comparison of station temperatures and temperature-derived quantities such as HDD and GDD unless observation times are the same or corrections are applied.” Baker, Donald G., 1975: Effect of Observation Time on Mean Temperature Estimation. J. Appl. Meteor., 14, 471–476. doi:;2. [FULL TEXT]

Temperature adjustments for discrepancies due to time of observation – Weaver & Miller (1970) Doesn’t seem to be available online in any form. Weaver, C. R., and M. E. Miller, 1970, Type-written communication directed to Director, National Climatic Center, 7 pp plus attachments, dated 23 November.

Effects of changing observation time on mean temperature – Mitchell (1958) Doesn’t seem to be available online in any form. Mitchell, J. M. Jr., 1958, Bull. Amer. Meteor. Soc., 39, 83-89.

The effect of time of observation on mean temperature – Rumbaugh (1934) No abstract. RUMBAUGH, W. F., 1934: THE EFFECT OF TIME OF OBSERVATION ON MEAN TEMPERATURE1. Mon. Wea. Rev., 62, 375–376. doi:;2. [FULL TEXT]

Report on the temperatures and vapor tensions of the United States reduced to a homogeneous system of 24 hourly observations for the 33-year interval, 1873-1905 – Bigelow (1909) No abstract. Bigelow, F. H., 1909, Bull S.W.B. No. 408, U. S. Weather Bureau, Washington D. C.. [FULL TEXT]

On the difference produced in the mean temperature derived from daily maximum and minimum readings, as depending on the time at which the thermometers are read – Ellis (1890) No abstract. William Ellis F.R.A.S., Quarterly Journal of the Royal Meteorological Society, Volume 16, Issue 76, pages 213–220, October 1890, DOI: 10.1002/qj.4970167605.

Mehrjährige Beobachtungen in Wien vom Jahre 1775 bis 1850 – Kreil (1854) Doesn’t seem to be available online in any form. Kreil K, 1854. Mehrjährige Beobachtungen in Wien vom Jahre 1775 bis 1850. Jahrbücher der k.k. Central-Anstalt für Meteorologie und Erdmagnetismus. I. Band – Jg 1848 und 1849, 35-74.

Mehrjährige Beobachtungen in Mailand vom Jahre 1763 bis 1850 – Kreil (1854) Doesn’t seem to be available online in any form. Kreil K, 1854. Mehrjährige Beobachtungen in Mailand vom Jahre 1763 bis 1850. Jahrbücher der k.k. Central-Anstalt für Meteorologie und Erdmagnetismus. I. Band – Jg 1848 und 1849, 75-114..

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