AGW Observer

Observations of anthropogenic global warming

New research from last week 5/2011

Posted by Ari Jokimäki on February 7, 2011

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

Published last week:

Possibly no vegetation in Antarctic peninsula during pliocene interglacials

How likely was a green Antarctic Peninsula during warm Pliocene interglacials? A critical reassessment based on new palynofloras from James Ross Island – Salzmann et al. (2011) “The question of whether Pliocene climate was warm enough to support a substantial vegetation cover on Antarctica is of great significance to the ongoing and controversial debate on the stability or dynamism of Antarctic ice sheets during warm periods with high atmospheric greenhouse gas concentrations. Here we present a systematic palynological comparison of pollen and dinoflagellate cyst assemblages from Early Pliocene diamictites and underlying late Cretaceous sediments collected from James Ross Island, northern Antarctic Peninsula. The diamictites are dated using a combination of 40Ar/39Ar and 87Sr/86Sr isotope ages on interbedded lavas and pristine bivalves. Well preserved pectinid shells and cheilostome bryozoans suggest that the palynomorph-bearing sediments were probably deposited during warmer Pliocene interglacials and later amalgamated into a diamtictite formed by a major ice advance during cold glacial cycle. The palynological analyses presented herein do not identify any in-situ pollen and spores which indicate the presence of a substantial vegetation cover. Our study suggests a local (i.e. James Ross Island) provenance for most of the diamictites, whilst sediments from the western coast might have been delivered by ice sheets from the Antarctic Peninsula. Whilst the acritarch Leiosphaeridia might imply the presence of sea-ice and near-modern climate conditions during the Late Neogene, the presence of the dinoflagellate cyst Bitectatodinium tepikiense at one location suggests that sea surface temperatures might have been substantially warmer during some interglacials. The absence of in-situ pollen and spores in the James Ross Island diamictites cannot be taken as proof of non-existence of vegetation. However, the combined palynological and geological evidence presented in this paper makes the presence of a substantial Pliocene vegetation cover on James Ross Island unlikely and supports previous reconstructions of a permanent ice sheet on the Antarctic Peninsula throughout the Late Neogene.” Ulrich Salzmann, James B. Riding, Anna E. Nelson, and John L. Smellie, Palaeogeography, Palaeoclimatology, Palaeoecology, doi:10.1016/j.palaeo.2011.01.028.

Age of blue-ice moraines suggests that WAIS survived last interglacial

Do blue-ice moraines in the Heritage Range show the West Antarctic ice sheet survived the last interglacial? – Fogwill et al. (2011) “We present a hypothesis that best explains cosmogenic isotope data on blue-ice moraines in the Heritage Range, West Antarctica. The age of the moraines implies that they, and the related ice-sheet surface with which they are associated, have persisted on the flanks of nunataks throughout at least the last interglacial/glacial cycle. The implication is that although the West Antarctic Ice Sheet (WAIS) may have fluctuated in thickness during glacial cycles, the central dome has remained intact for at least 200 kyr and possibly even for 400 kyr. Such a finding, if substantiated, would contribute to our understanding of the sensitivity of the WAIS to climate change. Further it would be a powerful geomorphic constraint on models of the past behaviour of the ice sheet during glacial cycles and thus those predicting the future of the ice sheet in a warming world.” Christopher J. Fogwill, Andrew S. Hein, Michael J. Bentley, and David E. Sugden, Palaeogeography, Palaeoclimatology, Palaeoecology, doi:10.1016/j.palaeo.2011.01.027.

Review of mountain water resources

Climate change and mountain water resources: overview and recommendations for research, management and policy – Viviroli et al. (2011) “Mountains are essential sources of freshwater for our world, but their role in global water resources could well be significantly altered by climate change. How well do we understand these potential changes today, and what are implications for water resources management, climate change adaptation, and evolving water policy? To answer above questions, we have examined 11 case study regions with the goal of providing a global overview, identifying research gaps and formulating recommendations for research, management and policy. After setting the scene regarding water stress, water management capacity and scientific capacity in our case study regions, we examine the state of knowledge in water resources from a highland-lowland viewpoint, focusing on mountain areas on the one hand and the adjacent lowland areas on the other hand. Based on this review, research priorities are identified, including precipitation, snow water equivalent, soil parameters, evapotranspiration and sublimation, groundwater as well as enhanced warming and feedback mechanisms. In addition, the importance of environmental monitoring at high altitudes is highlighted. We then make recommendations how advancements in the management of mountain water resources under climate change could be achieved in the fields of research, water resources management and policy as well as through better interaction between these fields. We conclude that effective management of mountain water resources urgently requires more detailed regional studies and more reliable scenario projections, and that research on mountain water resources must become more integrative by linking relevant disciplines. In addition, the knowledge exchange between managers and researchers must be improved and oriented towards long-term continuous interaction.” Viviroli, D., Archer, D. R., Buytaert, W., Fowler, H. J., Greenwood, G. B., Hamlet, A. F., Huang, Y., Koboltschnig, G., Litaor, M. I., López-Moreno, J. I., Lorentz, S., Schädler, B., Schreier, H., Schwaiger, K., Vuille, M., and Woods, R., Hydrol. Earth Syst. Sci., 15, 471-504, doi:10.5194/hess-15-471-2011, 2011. [full text]

Temperature extremes change in observations and climate model

Global changes in indices describing moderate temperature extremes from the daily output of a climate model – Russo & Sterl (2011) “Climate change indices derived from daily climate model temperature output are computed and analyzed to study the change of moderate climatic extremes between 1950 and 2100. We used output from the Ensemble Simulations of Extreme Weather Events Under Nonlinear Climate Change (ESSENCE) project, in which a 17-member ensemble simulation of climate change in response to the SRES A1b scenario has been carried out using the ECHAM5/MPI-OM climate model developed at the Max-Planck-Institute for Meteorology in Hamburg. The large size of the data set gives the opportunity to accurately detect the change of extreme climate indicators. We choose indices describing moderately extreme temperatures from the Expert Team on Climate Change Detection, Monitoring and Indices, focusing on percentile-based and duration indices. Additionally, we define some new indices measuring the intensity of daily temperature extremes. To study extremes within different consecutive 50 year time intervals (1950–2000, 2001–2050, and 2051–2100), we use corresponding reference periods (1961–1990, 2011–2040, and 2061–2090, respectively). Trends of the indices within each of the three 50-year periods are estimated using the Mann-Kendall slope estimator. The trends found in our model output for the period 1950–2000 compare well with those reported in the literature from observations. Future trend patterns resemble those from the 1950–2000 period, but have larger amplitudes. This suggests that the pattern of extreme temperature change might already emerge from the weather noise. Outside the tropics, the trend of indices defined from minimum daily temperatures is greater in absolute value than the trend of indicators related to maximum daily temperatures. The trend of the annual temperature range (Tmax − Tmin) is positive or close to zero over the tropics and negative over the extratropics, indicating that the value of the yearly maximum temperature is increasing faster than the minimum temperature in the tropics and vice versa in the extratropics. Finally, using the empirical distribution, we study the probability distribution functions (PDFs) of the occurrence of cold nights and warm days for nine regions. All PDFs shift in the direction of warming.” Russo, S., and A. Sterl (2011), J. Geophys. Res., 116, D03104, doi:10.1029/2010JD014727.

Stratospheric cooling distracts ozone measurements

Quantifying stratospheric ozone trends: Complications due to stratospheric cooling – McLinden & Fioletov (2011) “Recent studies suggest that ozone turnaround (the second stage of ozone recovery) is near. Determining precisely when this occurs, however, will be complicated by greenhouse gas-induced stratospheric cooling as ozone trends derived from profile data in different units and/or vertical co-ordinates will not agree. Stratospheric cooling leads to simultaneous trends in air density and layer thicknesses, confounding the interpretation of ozone trends. A simple model suggests that instruments measuring ozone in different units may differ as to the onset of turnaround by a decade, with some indicting a continued decline while others an increase. This concept was illustrated by examining the long-term (1979–2005) ozone trends in the SAGE (Stratospheric Aerosol and Gas Experiment) and SBUV (Solar Backscatter Ultraviolet) time series. Trends from SAGE, which measures number density as a function of altitude, and SBUV, which measures partial column as a function of pressure, are known to differ by 4–6%/decade in the upper stratosphere. It is shown that this long-standing difference can be reconciled to within 2%/decade when the trend in temperature is properly accounted for.” McLinden, C. A., and V. Fioletov (2011), Geophys. Res. Lett., 38, L03808, doi:10.1029/2010GL046012.

No evidence of cyclicity of D-O events

Characterizing the statistical properties and interhemispheric distribution of Dansgaard-Oeschger events – Thomas et al. (2011) “Ice core records from Greenland show times of rapid warming, called Dansgaard-Oeschger events, during the most recent glacial period. Characterizing the nature of Dansgaard-Oeschger events is critical to our understanding of past glacial climates, as well as modern climate volatility. Here we present new methods for statistically evaluating two important characteristics of these rapid warming events which have been highly debated in the scientific community: whether their occurrence is cyclical and whether they have a regional or global distribution. We find that there is not enough evidence to conclude that Dansgaard-Oeschger events are cyclical; yet, importantly, there is a statistically significant lagged correlation between the Antarctica and Greenland records. These results may suggest that rapid warming events in Greenland are driven by internal climate variability and strongly imply that rapid climate changes in Greenland are led by smaller amplitude changes in Antarctica through an oceanic teleconnection.” Thomas, A. M., S. Rupper, and W. F. Christensen (2011), J. Geophys. Res., 116, D03103, doi:10.1029/2010JD014834.

Ship aerosol plumes cause changes in clouds

Microphysical and macrophysical responses of marine stratocumulus polluted by underlying ships: Evidence of cloud deepening – Christensen & Stephens (2011) “Ship tracks observed by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) were analyzed to determine the extent to which aerosol plumes from ships passing below marine stratocumulus alter the microphysical and macrophysical properties of the clouds. Moderate Resolution Imaging Spectroradiometer (MODIS) imagery was used to distinguish ship tracks embedded in closed, open, and undefined mesoscale cellular cloud structures. The impact of aerosol on the microphysical cloud properties in both the closed and open cell regimes were consistent with the changes predicted by the Twomey hypothesis. For the macrophysical changes, differences were observed between regimes. In the open cell regime, polluted clouds had significantly higher cloud tops (16%) and more liquid water (39%) than nearby unpolluted clouds. However, in the closed cell regime, polluted clouds exhibited no change in cloud top height and had less liquid water (−6%). Both microphysical (effective radius) and macrophysical (liquid water path) cloud properties contribute to a fractional change in cloud optical depth; in the closed cell regime the microphysical contribution was 3 times larger than the macrophysical contribution. However, the opposite was true in the open cell regime where the macrophysical contribution was nearly 2 times larger than the microphysical contribution because the aerosol probably increased cloud coverage. The results presented here demonstrate key differences aerosols have on the microphysical and macrophysical responses of boundary layer clouds between mesoscale stratocumulus convective regimes.” Christensen, M. W., and G. L. Stephens (2011), J. Geophys. Res., 116, D03201, doi:10.1029/2010JD014638.

Snow melts earlier in Eurasian Arctic

Change in spring snowmelt timing in Eurasian Arctic rivers – Tan et al. (2011) “Changes in the amount and timing of the discharge of major Eurasian Arctic rivers have been well documented, but whether or not these changes can be attributed to climatic factors or to the construction of manmade reservoirs remains unclear. Here we endeavor to identify the key processes (snow cover and air temperature) that have regulated seasonal streamflow fluctuations in the Eurasian Arctic over the last half-century (1958–1999) and to understand the regional coherence of timing trends, using a set of Eurasian Arctic rivers selected specifically because they are free of known effects of dams. We find a shift toward earlier onset of spring runoff as measured by a modest change in the spring pulse onset (26 of 45 stations) and a strong change in the centroid of timing (39 of 45 stations). Winter streamflows increased over the period of record in most rivers, suggesting that trends observed by others in larger regulated Eurasian Arctic rivers may not be entirely attributable to reservoir construction. Upward trends in air temperature appeared to have had the largest impact on spring and summer flows for tributaries in the coldest of the major Eurasian Arctic river basins (e.g., the Lena). While the overall duration of snow cover has not significantly changed across the Eurasian Arctic, snow cover disappearance has trended earlier in the year and appears to be related to the increased May and snowmelt season fractional flows.” Tan, A., J. C. Adam, and D. P. Lettenmaier (2011), J. Geophys. Res., 116, D03101, doi:10.1029/2010JD014337.

Warming Atlantic cools the Pacific

Tropical Pacific response to 20th century Atlantic warming – Kucharski et al. (2011) “The analysis of a series of regionally coupled ocean-atmospheric simulations suggests that the Atlantic warming that has occurred in the 20th century may have reduced the concomitant warming in the eastern tropical Pacific. The Pacific response to the Atlantic warming shows La Nina-like features even in the presence of greenhouse gas (GHG) forcing. The physical mechanism for the Atlantic warming influence on the tropical Pacific is a change in the Walker circulation that results in easterly surface wind anomalies in the central-west Pacific. Coupled ocean-atmosphere processes then amplify the signal. The possibility of an Atlantic Ocean induced cooling of the eastern tropical Pacific is complementary to the hypothesis that the GHG forcing itself may have caused the observed relative eastern Pacific cooling. It is argued that the uncertainties in the projected future mean state in the Pacific may be partly due to the competition of the GHG induced warming and the Atlantic induced cooling.” Kucharski, F., I.-S. Kang, R. Farneti, and L. Feudale (2011), Geophys. Res. Lett., 38, L03702, doi:10.1029/2010GL046248.

More nanodiamond evidence for impact hypothesis of YD event

Discovery of a nanodiamond-rich layer in the Greenland ice sheet – Kurbatov et al. (2011) “We report the discovery in the Greenland ice sheet of a discrete layer of free nanodiamonds (NDs) in very high abundances, implying most likely either an unprecedented influx of extraterrestrial (ET) material or a cosmic impact event that occurred after the last glacial episode. From that layer, we extracted n-diamonds and hexagonal diamonds (lonsdaleite), an accepted ET impact indicator, at abundances of up to about 5×106 times background levels in adjacent younger and older ice. The NDs in the concentrated layer are rounded, suggesting they most likely formed during a cosmic impact through some process similar to carbon-vapor deposition or high-explosive detonation. This morphology has not been reported previously in cosmic material, but has been observed in terrestrial impact material. This is the first highly enriched, discrete layer of NDs observed in glacial ice anywhere, and its presence indicates that ice caps are important archives of ET events of varying magnitudes. Using a preliminary ice chronology based on oxygen isotopes and dust stratigraphy, the ND-rich layer appears to be coeval with ND abundance peaks reported at numerous North American sites in a sedimentary layer, the Younger Dryas boundary layer (YDB), dating to 12.9±0.1 ka. However, more investigation is needed to confirm this association.” Kurbatov, Andrei V.; Mayewski, Paul A.; Steffensen, Jorgen P.; West, Allen; Kennett, Douglas J.; Kennett, James P.; Bunch, Ted E.; Handley, Mike; Introne, Douglas S.; Que Hee, Shane S.; Mercer, Christopher; Sellers, Marilee; Shen, Feng; Sneed, Sharon B.; Weaver, James C.; Wittke, James H.; Stafford, Thomas W.; Donovan, John J.; Xie, Sujing; Razink, Joshua J.; Stich, Adrienne; Kinzie, Charles R.; Wolbach, Wendy S., Journal of Glaciology, Volume 56, Number 199, December 2010 , pp. 747-757(11), DOI: 10.3189/002214310794457191. [full text]


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