AGW Observer

Observations of anthropogenic global warming

New research from last week 4/2012

Posted by Ari Jokimäki on January 30, 2012

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

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

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

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

Photo: Tiina Oinas


Analysis of European parapatric hares and climate change

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

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

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


Wet forest soils are important source for methane in Europe

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

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

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


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

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

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

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


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

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

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

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


Precipitation expected to decline in subtropics due to poleward shifts

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

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

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


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

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

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

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


Hemispheric shift in atmospheric radiocarbon

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

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

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


Fossil fuel emissions are the strongest contributor to atmospheric radiocarbon trends

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

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

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


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

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

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

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


Look out, squirrels are getting bigger!

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

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

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

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