New research from last week 43/2012
Posted on 30 October 2012 by Ari Jokimäki
Last week I was on the road for few days, which resulted in rather limited collection on papers in the main section of this week's post as I ended up putting many of the papers to the other papers section (which takes considerably less effort than creating a main section entry and making related Twitter and Facebook posts). So I expect that in coming weeks the main section grows back to normal size. That being said, now that the other papers section has been with us for a few weeks, I would like to know if you prefer lot of papers in the main section or lot of papers in other papers section or both. While we are at it, go ahead and make all kinds of improvement suggestions if you have them. If I'm in a good mood, I might even take a look at some of them...
Climate sensitivity increases by 23% between the first and third CO2 doublings in a model study
Abstract: "Are equilibrium climate sensitivity and the associated radiative feedbacks a constant property of the climate system, or do they change with forcing magnitude and base climate? Using the radiative kernel technique, feedbacks and climate sensitivity are evaluated in a fully coupled general circulation model (GCM) for three successive doublings of carbon dioxide starting from present day concentrations. Climate sensitivity increases by 23% between the first and third CO2 doublings. Increases in the positive water vapor and cloud feedbacks are partially balanced by a decrease in the positive surface albedo feedback and an increase in the negative lapse rate feedback. Feedbacks can be decomposed into a radiative flux change and a climate variable response to temperature change. The changes in water vapor and Planck feedbacks are due largely to changes in the radiative response with climate state. Higher concentrations of greenhouse gases and higher temperatures lead to more absorption and emission of longwave radiation. Changes in cloud feedbacks are dominated by the climate response to temperature change, while the lapse rate and albedo feedbacks combine elements of both. Simulations with a slab ocean model (SOM) version of the GCM are used to verify whether a SOM-GCM accurately reproduces the behavior of the fully coupled model. Although feedbacks differ in magnitude between model configurations (with differences as large as those between CO2 doublings for some feedbacks), changes in feedbacks between CO2 doublings are consistent in sign and magnitude in the SOM-GCM and the fully coupled model."
Citation: Alexandra K. Jonko and Karen M. Shell, Benjamin M. Sanderson and Gokhan Danabasoglu, Journal of Climate 2012, doi: http://dx.doi.org/10.1175/JCLI-D-12-00479.1.
Global heatwaves have increased in frequency, intensity and duration
Abstract: "Using the latest HadGHCND daily temperature dataset, global trends in observed summertime heatwaves and annually calculated warm spells for 1950–2011 are analysed via a multi-index, multi-aspect framework. Three indices that separately focus on maximum temperature (TX90pct), minimum temperature (TN90pct) and average temperature (EHF) were studied with respect to five characteristics of event intensity, frequency and duration. Despite which index is employed, increases in heatwave/warm spell intensity, frequency and duration are found. Furthermore, TX90pct and TN90pct trends are larger and exhibit more significance for warm spells, implying that non-summer events are driving annual trends over some regions. Larger increases in TN90pct aspects relative to EHF and TX90pct are also observed. While qualitative information on event trends is similar across the indices, quantitative values vary. This result highlights the importance of employing the most appropriate index when assessing the impact of sustained extreme temperature events."
Citation: Perkins, S. E., L. V. Alexander, and J. R. Nairn (2012), Increasing frequency, intensity and duration of observed global heatwaves and warm spells, Geophys. Res. Lett., 39, L20714, doi:10.1029/2012GL053361.
Fossil fuel facilities are predominant methane sources in winter over western Siberia
Abstract: "Aircraft measurements of carbon and hydrogen isotopic ratios of atmospheric CH4 (δ13CH4 and δD-CH4), with the respective precisions of 0.08‰ and 2.2‰, as well as CH4 concentration were made at 1 and 2 km altitudes over western Siberia during 2006–2009. δ13CH4 and δD-CH4 were almost always lower at lower altitudes, while the CH4 concentration was higher, implying strong sources on the ground with low isotopic values. δ13CH4 showed a clear seasonal minimum in the late summer, while seasonality of CH4 and δD-CH4 was ambiguous due to the local disturbances. By inspecting the relationships between the CH4 concentration and isotopes, we found that isotopic source signatures in the winter (December–April) are −41.2 ± 1.8 and −187 ± 18‰ for δ13CH4 and δD-CH4, respectively, and the corresponding values in the summer (June–October) are −65.0 ± 2.5 and −282 ± 25‰. These values indicate predominant CH4 emissions from fossil fuel facilities in the winter and wetlands in the summer. It was also found that the shorter-term CH4 variations are more influenced by fossil CH4 than that from wetlands. The finding presumably reflects the fact that the former is released from limited areas such as leakage from fossil fuel facilities, while the latter is released from a vast expanse of wetland. By employing a CH4 emission data set used in an atmospheric chemistry transport model, we calculated seasonal isotopic changes of CH4 sources in western Siberia and compared them to the estimates obtained in this study. The results indicated that the seasonal change in the CH4 emission data set is reasonable, at least in terms of a ratio of fossil to biogenic emissions."
Citation: Umezawa, T., T. Machida, S. Aoki, and T. Nakazawa (2012), Contributions of natural and anthropogenic sources to atmospheric methane variations over western Siberia estimated from its carbon and hydrogen isotopes, Global Biogeochem. Cycles, 26, GB4009, doi:10.1029/2011GB004232.
Clouds could help deglaciating a Snowball Earth
Abstract: "Neoproterozoic, and possibly Paleoproterozoic, glaciations represent the most extreme climate events in post-Hadean Earth, and may link closely with the evolution of the atmosphere and life. According to the Snowball Earth hypothesis, the entire ocean was covered with ice during these events for a few million years, during which time volcanic CO2 increased enough to cause deglaciation. Geochemical proxy data and model calculations suggest that the maximum CO2 was 0.01–0.1 by volume, but early climate modeling suggested that deglaciation was not possible at CO2 = 0.2. We use results from six different general circulation models (GCMs) to show that clouds could warm a Snowball enough to reduce the CO2 required for deglaciation by a factor of 10–100. Although more work is required to rigorously validate cloud schemes in Snowball-like conditions, our results suggest that Snowball deglaciation is consistent with observations."
Citation: Abbot, D. S., A. Voigt, M. Branson, R. T. Pierrehumbert, D. Pollard, G. Le Hir, and D. D. B. Koll (2012), Clouds and Snowball Earth deglaciation, Geophys. Res. Lett., 39, L20711, doi:10.1029/2012GL052861.
Abrupt shutdown of Atlantic Meridional Overturning Circulation due to global warming seems unlikely
Abstract: "The evolution of the Atlantic Meridional Overturning Circulation (MOC) in 30 models of varying complexity is examined under four distinct Representative Concentration Pathways. The models include 25 Atmosphere-Ocean General Circulation Models (AOGCMs) or Earth System Models (ESMs) that submitted simulations in support of the 5th phase of the Coupled Model Intercomparison Project (CMIP5) and 5 Earth System Models of Intermediate Complexity (EMICs). While none of the models incorporated the additional effects of ice sheet melting, they all projected very similar behaviour during the 21st century. Over this period the strength of MOC reduced by a best estimate of 22% (18%–25%; 5%–95% confidence limits) for RCP2.6, 26% (23%–30%) for RCP4.5, 29% (23%–35%) for RCP6.0 and 40% (36%–44%) for RCP8.5. Two of the models eventually realized a slow shutdown of the MOC under RCP8.5, although no model exhibited an abrupt change of the MOC. Through analysis of the freshwater flux across 30°–32°S into the Atlantic, it was found that 40% of the CMIP5 models were in a bistable regime of the MOC for the duration of their RCP integrations. The results support previous assessments that it is very unlikely that the MOC will undergo an abrupt change to an off state as a consequence of global warming."
Citation: Weaver, A. J., et al. (2012), Stability of the Atlantic meridional overturning circulation: A model intercomparison, Geophys. Res. Lett., 39, L20709, doi:10.1029/2012GL053763.
A review on adapting agriculture to climate change
Abstract: "The agricultural sector is highly vulnerable to future climate changes and climate variability, including increases in the incidence of extreme climate events. Changes in temperature and precipitation will result in changes in land and water regimes that will subsequently affect agricultural productivity. Given the gradual change of climate in the past, historically, farmers have adapted in an autonomous manner. However, with large and discrete climate change anticipated by the end of this century, planned and transformational changes will be needed. In light of these, the focus of this review is on farm-level and farmers responses to the challenges of climate change both spatially and over time. In this review of adapting agriculture to climate change, the nature, extent, and causes of climate change are analyzed and assessed. These provide the context for adapting agriculture to climate change. The review identifies the binding constraints to adaptation at the farm level. Four major priority areas are identified to relax these constraints, where new initiatives would be required, i.e., information generation and dissemination to enhance farm-level awareness, research and development (R&D) in agricultural technology, policy formulation that facilitates appropriate adaptation at the farm level, and strengthening partnerships among the relevant stakeholders. Forging partnerships among R&D providers, policy makers, extension agencies, and farmers would be at the heart of transformational adaptation to climate change at the farm level. In effecting this transformational change, sustained efforts would be needed for the attendant requirements of climate and weather forecasting and innovation, farmer’s training, and further research to improve the quality of information, invention, and application in agriculture. The investment required for these would be highly significant. The review suggests a sequenced approach through grouping research initiatives into short-term, medium-term, and long-term initiatives, with each initiative in one stage contributing to initiatives in a subsequent stage. The learning by doing inherent in such a process-oriented approach is a requirement owing to the many uncertainties associated with climate change."
Citation: Muhuddin Rajin Anwar, De Li Liu, Ian Macadam and Georgina Kelly, Theoretical and Applied Climatology, 2012, DOI: 10.1007/s00704-012-0780-1.
Ocean warming of the last century cannot be explained by natural variability
Abstract: "Of the additional energy absorbed by the Earth over the past decades, by far the largest fraction is taken up by the oceans. Yet most attribution studies focus on the surface warming, and only few have used patterns of ocean warming to attribute changes to external forcing or internal variability. Here we use the combined observed evidence from warming of the atmosphere and ocean with the latest climate model simulations to demonstrate that both the depth profiles and spatial warming patterns near the surface are very heterogeneous when resulting from internal unforced variability. In the 20th-century simulations on the other hand, the observed spatial pattern is smooth, and the warming decreases almost gradually with depth in the ocean, consistent with observations and a penetration of the surface warming to intermediate depth by diffusion and advection. We argue that such physically motivated arguments combining different lines of evidence and types of observations offer insight that is complementary to optimal fingerprint attribution methods. We conclude that the simultaneous global warming of the atmosphere and mixed layer alone is uninformative for attribution, but the magnitude of ocean heat uptake, the homogeneity of the spatial pattern as well as the distribution of warming below the mixed layer strongly argue for the 20th-century warming being largely externally forced."
Citation: Sedláček, J. and R. Knutti (2012), Evidence for external forcing on 20th-century climate from combined ocean-atmosphere warming patterns, Geophys. Res. Lett., 39, L20708, doi:10.1029/2012GL053262.
Increasing seabed temperatures make gas hydrate unstable in shallow Norwegian-Svalbard margin regions
Abstract: "The potential impact of future climate change on methane release from oceanic gas hydrates is the subject of much debate. We analyzed World Ocean Database quality controlled data on the Norwegian-Svalbard continental margin from the past 60 years to evaluate the potential effect of ocean temperature variations on continental margin gas hydrate reservoirs. Bottom water temperatures in the Norwegian-Svalbard margin were subject to significant cooling until 1980 (by ∼2°C offshore NW-Svalbard and in the Barents Sea) followed by a general bottom water temperature increase until 2010 (∼0.3°C in deep-water areas offshore NW-Svalbard and mid-Norwegian margin and ∼2°C in the shallow areas of the Barents Sea and Prins Karls Forland). Bottom water warming in the shallow outer shelf areas triggered the Gas Hydrate Stability Zone (GHSZ) retreat toward upper continental slope areas, potentially increasing methane release due to gas hydrate dissociation. GHSZ responses to temperature changes on human time scales occur exclusively in shallow water and only if near-surface gas hydrates exist. The responses are associated with a short time lag of less than 1 year. Temperatures in the bottom water column seem to be partly regulated by the North Atlantic Oscillation (NAO), with positive NAO associated with warm phases. However, cooling events in the surface water offshore NW-Svalbard might be associated with El Niño events of 1976–1977, 1986–1987 and 1997–1998 in the Pacific. Such ocean cooling, if long enough, may delay ocean temperature driven gas hydrate dissociation and potential releases of methane to the ocean."
Citation: Ferré, B., J. Mienert, and T. Feseker (2012), Ocean temperature variability for the past 60 years on the Norwegian-Svalbard margin influences gas hydrate stability on human time scales, J. Geophys. Res., 117, C10017, doi:10.1029/2012JC008300.
Other studies from last week
CLASSIC OF THE WEEK: Humphreys (1909)
Abstract: No abstract.
Citation: Humphreys, W. J., Astrophysical Journal, vol. 29, p.14, DOI: 10.1086/141615.
This is a cross-post from AGW Observer. When each paper is published, it is notified in AGW Observer Facebook page and Twitter page. At least some of these are also retweeted in Skeptical Science 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.