New research from last week 52/2012
Posted on 31 December 2012 by Ari Jokimäki
Here it is - the last post in the New research from last week series. I thank all researchers for providing continuous stream of interesting science to include to weekly batches. I also thank all readers for their interest in the series. New research reporting will continue in some form, which is currently uncertain. I probably will continue pointing out some interesting papers in my Twitter feed, but I expect that even there will be a quiet period in coming weeks. Happy new year for all climate science fans everywhere!
Time-varying climate sensitivity from regional feedbacks
Abstract:"The sensitivity of global climate with respect to forcing is generally described in terms of the global climate feedback—the global radiative response per degree of global annual mean surface temperature change. While the global climate feedback is often assumed to be constant, its value—diagnosed from global climate models—shows substantial time-variation under transient warming. Here we propose that a reformulation of the global climate feedback in terms of its contributions from regional climate feedbacks provides a clear physical insight into this behavior. Using (i) a state-of-the-art global climate model and (ii) a low-order energy balance model, we show that the global climate feedback is fundamentally linked to the geographic pattern of regional climate feedbacks and the geographic pattern of surface warming at any given time. Time-variation of the global climate feedback arises naturally when the pattern of surface warming evolves, actuating regional feedbacks of different strengths. This result has substantial implications for our ability to constrain future climate changes from observations of past and present climate states. The regional climate feedbacks formulation reveals fundamental biases in a widely-used method for diagnosing climate sensitivity, feedbacks and radiative forcing—the regression of the global top-of-atmosphere radiation flux on global surface temperature. Further, it suggests a clear mechanism for the ‘efficacies’ of both ocean heat uptake and radiative forcing."
Citation: Kyle C. Armour, Cecilia M. Bitz, Gerard H. Roe, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-12-00544.1.
West Antarctic rapid glacier retreat may be exceptional during the Holocene
Abstract:"Ice loss from the marine-based, potentially unstable West Antarctic Ice Sheet (WAIS) contributes to current sea-level rise and may raise sea level by ≤3.3 m or even ≤5 m in the future. Over the past few decades, glaciers draining the WAIS into the Amundsen Sea Embayment (ASE) have shown accelerated ice flow, rapid thinning, and fast retreat of the grounding line (GL). However, the long-term context of this ice loss is poorly constrained, limiting our ability to accurately predict future WAIS behavior. Here we present a new chronology for WAIS retreat from the inner continental shelf of the eastern ASE, based on radiocarbon dates from three marine sediment cores. The ages document a retreat of the GL to within ∼100 km of its modern position before ca. 10,000 calibrated (cal.) yr B.P. This early deglaciation is consistent with ages for GL retreat from the western ASE. Our new data demonstrate that, in contrast to the Ross Sea, WAIS retreat from the ASE shelf was largely complete by the start of the Holocene. Our results further suggest either slow GL retreat from the inner ASE shelf throughout the Holocene, or that any episodes of fast GL retreat must have been short-lived. Thus, today’s rapid retreat may be exceptional during the Holocene and may originate in recent changes in regional climate, ocean circulation, or ice-sheet dynamics."
Citation: Claus-Dieter Hillenbrand, Gerhard Kuhn, James A. Smith, Karsten Gohl, Alastair G.C. Graham, Robert D. Larter, Johann P. Klages, Rachel Downey, Steven G. Moreton, Matthias Forwick and David G. Vaughan, Geology, v. 41 no. 1 p. 35-38, doi: 10.1130/G33469.1.
Late Pleistocene tropical Pacific temperatures suggest higher climate sensitivity than currently thought
Abstract: "Understanding how global temperature changes with increasing atmospheric greenhouse gas concentrations, or climate sensitivity, is of central importance to climate change research. Climate models provide sensitivity estimates that may not fully incorporate slow, long-term feedbacks such as those involving ice sheets and vegetation. Geological studies, on the other hand, can provide estimates that integrate long- and short-term climate feedbacks to radiative forcing. Because high latitudes are thought to be most sensitive to greenhouse gas forcing owing to, for example, ice-albedo feedbacks, we focus on the tropical Pacific Ocean to derive a minimum value for long-term climate sensitivity. Using Mg/Ca paleothermometry from the planktonic foraminifera Globigerinoides ruber from the past 500 k.y. at Ocean Drilling Program (ODP) Site 871 in the western Pacific warm pool, we estimate the tropical Pacific climate sensitivity parameter (λ) to be 0.94–1.06 °C (W m−2)−1, higher than that predicted by model simulations of the Last Glacial Maximum or by models of doubled greenhouse gas concentration forcing. This result suggests that models may not yet adequately represent the long-term feedbacks related to ocean circulation, vegetation and associated dust, or the cryosphere, and/or may underestimate the effects of tropical clouds or other short-term feedback processes."
Citation: Kelsey A. Dyez and A. Christina Ravelo, Geology, v. 41 no. 1 p. 23-26, doi: 10.1130/G33425.1.
Dynamics played a major role for the Arctic ozone deficit in 2011
Highlights:•Good model agreement with observations; •The model reproduces the Arctic ozone deficit in 2011; •Dynamics play a major role for the ozone deficit in 2011.
Abstract:"Arctic column ozone reached record low values (∼310 DU) during March of 2011, exposing Arctic ecosystems to enhanced UV-B. We identify the cause of this anomaly using the Oslo CTM2 atmospheric chemistry model driven by ECMWF meteorology to simulate Arctic ozone from 1998 through 2011. CTM2 successfully reproduces the variability in column ozone, from week to week, and from year to year, correctly identifying 2011 as an extreme anomaly over the period. By comparing parallel model simulations, one with all Arctic ozone chemistry turned off on January 1, we find that chemical ozone loss in 2011 is enhanced relative to previous years, but it accounted for only 23% of the anomaly. Weakened transport of ozone from middle latitudes, concurrent with an anomalously strong polar vortex, was the primary cause of the low ozone When the zonal winds relaxed in mid-March 2011, Arctic column ozone quickly recovered."
Citation: Isaksen, I. S. A., et al. (2012), Attribution of the Arctic ozone column deficit in March 2011, Geophys. Res. Lett., 39, L24810, doi:10.1029/2012GL053876.
Accelerated loss of alpine glaciers in the Kodar Mountains of SE Siberia
Highlights:► First ever multi-year study of glacier change from the Kodar Mountains, SE Siberia ► Small decline in glacier area from the 1960s to 1995 followed by dramatic reduction ► Reduction coincides with a marked summer warming trend that began in the 1980s ► Topography and supra-glacial debris cover modulate glacier response ► These glaciers may transition into a type of rock glacier within a few decades.
Abstract: "The recession of mountain glaciers around the world has been linked to anthropogenic climate change and small glaciers (e.g. < 2 km2) are thought to be particularly vulnerable, with reports of their disappearance from several regions. However, the response of small glaciers to climate change can be modulated by non-climatic factors such as topography and debris cover and there remain a number of regions where their recent change has evaded scrutiny. This paper presents results of the first multi-year remote sensing survey of glaciers in the Kodar Mountains, the only glaciers in SE Siberia, which we compare to previous glacier inventories from this continental setting that reported total glacier areas of 18.8 km2 in ca. 1963 (12.6 km2 of exposed ice) and 15.5 km2 in 1974 (12 km2 of exposed ice). Mapping their debris-covered termini is difficult but delineation of debris-free ice on Landsat imagery reveals 34 glaciers with a total area of 11.72 ± 0.72 km2 in 1995, followed by a reduction to 9.53 ± 0.29 km2 in 2001 and 7.01 ± 0.23 km2in 2010. This represents a ~ 44% decrease in exposed glacier ice between ca. 1963 and 2010, but with 40% lost since 1995 and with individual glaciers losing as much as 93% of their exposed ice. Thus, although continental glaciers are generally thought to be less sensitive than their maritime counterparts, a recent acceleration in shrinkage of exposed ice has taken place and we note its coincidence with a strong summer warming trend in the region initiated at the start of the 1980s. Whilst smaller and shorter glaciers have, proportionally, tended to shrink more rapidly, we find no statistically significant relationship between shrinkage and elevation characteristics, aspect or solar radiation. This is probably due to the small sample size, limited elevation range, and topographic setting of the glaciers in deep valleys-heads. Furthermore, many of the glaciers possess debris-covered termini and it is likely that the ablation of buried ice is lagging the shrinkage of exposed ice, such that a growth in the proportion of debris cover is occurring, as observed elsewhere. If recent trends continue, we hypothesise that glaciers could evolve into a type of rock glacier within the next few decades, introducing additional complexity in their response and delaying their potential demise."
Citation: Chris R. Stokes, Maria Shahgedanova, Ian S. Evans, Victor V. Popovnin, Global and Planetary Change, http://dx.doi.org/10.1016/j.gloplacha.2012.12.010.
Central West Antarctica among the most rapidly warming regions on Earth
Abstract:"There is clear evidence that the West Antarctic Ice Sheet is contributing to sea-level rise. In contrast, West Antarctic temperature changes in recent decades remain uncertain. West Antarctica has probably warmed since the 1950s, but there is disagreement regarding the magnitude, seasonality and spatial extent of this warming. This is primarily because long-term near-surface temperature observations are restricted to Byrd Station in central West Antarctica, a data set with substantial gaps. Here, we present a complete temperature record for Byrd Station, in which observations have been corrected, and gaps have been filled using global reanalysis data and spatial interpolation. The record reveals a linear increase in annual temperature between 1958 and 2010 by 2.4±1.2 °C, establishing central West Antarctica as one of the fastest-warming regions globally. We confirm previous reports of West Antarctic warming, in annual average and in austral spring and winter, but find substantially larger temperature increases. In contrast to previous studies, we report statistically significant warming during austral summer, particularly in December–January, the peak of the melting season. A continued rise in summer temperatures could lead to more frequent and extensive episodes of surface melting of the West Antarctic Ice Sheet. These results argue for a robust long-term meteorological observation network in the region."
Citation: David H. Bromwich, Julien P. Nicolas, Andrew J. Monaghan, Matthew A. Lazzara, Linda M. Keller, George A. Weidner & Aaron B. Wilson, Nature Geoscience, 2012, doi:10.1038/ngeo1671.
Other studies from last week
CLASSIC OF THE WEEK: Williamson (1769)
Abstract:No abstract. First paragraph: "It is generally remarked by people who have resided long in Pennsylvania and the neighbouring Colonies, that within the last forty or fifty years there has been a very observable Change of Climate, that our winters are not so intensely cold, nor our summers so disagreeably warm as they have been."
Citation: Hugh Williamson, Transactions of the American Philosophical Society, Vol. 1, (Jan. 1, 1769 - Jan. 1, 1771) (pp. 272-280).
This is a cross-post from AGW Observer. About this series. 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.