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2011 Literature Review Archives - Impacts and Adaptation

Amstrup, S.C., E.T. DeWeaver, D.C. Douglass, B.G. Marcot, G.M. Durner, C.M. Bitz and D.A. Bailey. 2010. Greenhouse gas mitigation can reduce sea-ice loss and increase polar bear persistence. Nature, Vol 468, p. 955-958, doi: 10.1038/nature09653. See also: Derocher, A.E. 2010. Climate Change: The prospects for polar bears. Nature, Vol 468, p. 905-906.

A new study makes the point that previously predicted declines in polar bear populations based on projected increases in global temperatures are not unavoidable. Greenhouse gas mitigation efforts that limit the increase in global mean surface air temperature to less than around 2OC above pre-industrial were found to greatly improve the likelihood that sustainable polar bear populations will exist throughout this century.

Observed declines in polar bear health, survival and population size have been linked with declines in summer sea ice (a key habitat requirement for access to prey, for mating and traveling) which have in turn been associated with increasing global surface temperatures.  Projections of Arctic sea ice loss published in 2007 by the United States Geological Survey suggested that under a moderate ‘business as usual’ greenhouse gas emission scenario (IPCC SRES A1B) two-thirds of the world’s polar bears could be lost by 2050.  Recent emissions trends suggest that without mitigation efforts there will be little divergence from the 2007 projections.  Amstrup et al use the Community Climate System Model version 3 (CCSM3) to investigate the potential for greenhouse gas (GHG) mitigation efforts to prevent the loss of sea ice habitat essential for polar bear survival.  The authors also explore the relationship between sea ice extent and temperature increases with the purpose of identifying possible tipping points (i.e. a threshold to irreversible ice loss).  If such a tipping point were surpassed future mitigation of GHG emissions would confer no benefits to polar bear populations.  Projections of important polar bear habitat features were developed based on global mean surface air temperature projections derived from five emissions scenarios.  The authors identified a linear relationship between global mean surface air temperature and sea ice habitat and no evidence for a threshold beyond which Arctic sea-ice collapses irreversibly.  The authors suggest that rapid ice losses (both in observations and simulations) are related to increased volatility of a thinning sea ice cover and can be reversed but  do caution that their results are based on a single model and that tipping points may still exist in the real world. The authors conclude that mitigation efforts (in conjunction with wildlife management efforts) that keep the global mean surface air temperature increase to <1.25oC above the 1980-1999 mean are likely to maintain sufficient sea-ice habitat for polar bears to persist at sustainable, albeit lower than present, levels throughout the century. 

Beaumont, L.J., A. Pitman, S. Perkins, N.E. Zimmerman, N.G. Yoccoz and W. Thuiller. 2011. Impacts of climate change on the world’s most exceptional ecoregions. PNAS, Vol 108, pp 2306-2311, doi: 10.1073/pnas.1007217108.

Climate model simulations indicate that by 2070 up to ~80% of the world’s most exceptional terrestrial and aquatic ecoregions will routinely experience monthly temperatures considered extreme compared to the 1961-1990 period. Twentieth century warming has been linked to changes in biological systems worldwide and these projected changes may therefore place increasing stress on these iconic ecoregions.

The ‘Global 200’ is a set of terrestrial and freshwater ecoregions identified as irreplaceable or distinct because of their biological diversity and global uniqueness (amongst other attributes).  Protection of these ecoregions would be of value to conservation efforts worldwide but the majority are threatened by habitat loss, fragmentation and degradation.  Beaumont and colleagues investigate the impacts projected climate changes may also have on a subset of these regions by exploring changes in their exposure to monthly precipitation and temperature extremes (defined as >±2 standard deviations from the 1961-1990 mean) simulated for 2070.  The authors developed ensembles of climate model simulations from 23 climate models for three emission scenarios (IPCC SRES B1, A1B and A2, with ~200 simulations each).  The results indicate that by 2030, the entire range of 12-22% of the world’s most important ecoregions may be subjected to extreme monthly temperatures and an additional 38-39% will likely be exposed over parts of their range.  By 2070, these numbers increase dramatically with 60-86% of terrestrial and 51-83% of aquatic ecoregions projected to be exposed to extreme monthly temperatures over their entire range over some part of the year.  It is generally thought that high-latitude ecosystems may be more vulnerable to climate change because projected temperature increases are greatest for these regions.  However, the absolute range of temperature variability is lower in the tropics than high-latitude regions therefore a smaller absolute temperature increase in the tropics can be more extreme in terms of deviation from the mean.  As a consequence, the authors find that tropical and subtropical ecoregions and mangroves are projected to experience extreme monthly temperatures earliest with lower temperature increases (in some cases with <1oC local warming).  Unlike temperature, projected monthly precipitation does not exceed the threshold defined as extreme (i.e. >±2 standard deviations from the 1961-1990 mean) over the 21st century for any of the ecoregions under the three emission scenarios (the authors note high variability amongst the simulations). However, changes in other properties of precipitation such as changes in daily extremes not captured in this study may impact these ecoregions.  Ultimately ecosystem response to changes in climate is a result of many factors but these results indicate that changes in temperature extremes may place increasing stress on these key ecoregions.

Biastoch, A., T. Treude, L.H. Rüpke, U. Riebesell, C. Roth, E.B. Burwicz, W. Park, M. Latif, C.W. Böning, G. Madec and K. Wallmann. 2011. Rising Artic Ocean temperatures cause gas hydrate destabilization and ocean acidification. GRL Vol 38, L08602.

A study of the stability of Arctic Ocean methane hydrates under a moderate global warming scenario shows the impact of methane release on global average surface temperatures would not be significant in the next 100 years. However, release of methane into the water above the sea floor could deplete local oxygen levels and significantly enhance seawater acidification in parts of the Arctic Ocean over this time period. 

One of the potential mechanisms for abrupt climate change relates to large and sudden releases of methane from frozen methane hydrates in the ocean floor. Those that are in shallow sediments in the Arctic Ocean are of particular interest since these are expected to be more susceptible to destabilization due to strong ongoing Arctic warming. This study by Biastoch and colleagues assesses the stability of ocean floor methane gas hydrates across the Arctic region under future global warming. The evolution of bottom water temperatures was analyzed in an ensemble of eight 100-yr long global warming experiments (1% per year increase in CO2 until CO2 doubling in ~ yr 2070 and stabilization thereafter) with a coupled climate model (KCM) using the NEMO v2.3 ocean/ice modeling framework. Projected changes to regional bottom water temperatures within the next 100 years show a highly non-uniform distribution, with the strongest impacts on shallow regions affected by Atlantic inflow from the European Nordic Seas into the Arctic Ocean. The impact of this warming on the thickness of the gas hydrate stability zone below the seafloor was evaluated and the fate of released methane estimated. Release of methane into the water column was shown to cause local oxygen depletion and to reduce pH up to 0.25 units in some parts of the Arctic Ocean bottom waters, adding to projected ocean-wide acidification caused by uptake of anthropogenic CO2. Based on their estimate of how much of the released methane would reach the atmosphere, the authors considered the impact not significant in terms of adding to global warming.  They estimate an additional average methane flux of only 162 Mt CH4 per year from melting Arctic hydrates over the next 100 years, an amount much smaller than current anthropogenic methane emissions.  Over longer time scales, there is greater potential for more significant methane releases.

Coops, N.C. and R.H. Waring. 2011. A process-based approach to estimate lodgepole pine (Pinus contorta Dougl.) distribution in the Pacific Northwest under climate change. Climatic Change, Vol 105, pp 313-328, doi: 10.1007s10584-010-9861-2.

Projections of the 21st century distribution of lodgepole pine in western North America indicate a moderate decline in its distribution by 2020 (roughly an 8% decline).  By the 2080s however climate conditions are likely to favour other species and lodgepole pine may be absent from much of western North America (occupying only 17% of its current range).

Lodgepole pine is widely distributed across western North America and plays a key role in western ecosystems.  Coops and Waring investigate the possible future distribution of this commercially important species under a changing climate.  They first develop a model of the climate factors that in part control photosynthesis and growth in lodgepole pine and therefore contribute to its current distribution.  The model was calibrated using tree species presence/absence data for 12,600 plots in Canada and the U.S. and climate data.  The important climate modifiers identified by the model include soil water storage, evaporative demand, temperature and frost; the relative importance of each modifier varied across the species range and by month.  The model was able to produce the current distribution of lodgepole pine with ~70% accuracy.  Projections of future climate (i.e. namely the variables identified as important for growth) for three thirty-year periods over the 21st century were obtained from the Canadian Climate Centre model (CGCM2) for the A2 scenario (close to the upper bound of the IPCC SRES scenarios).  These data were fed into the model yielding estimates of the future distribution of the species for three 30-year periods centred on the decades 2020 (2011-2040), 2050 (2041-2070) and 2080 (2071-2100).  The simulations indicate that by the 2020s there will be an 8% reduction in the distribution of lodgepole pine (a reduction of ~8, 000km2). By the 2080s the total area suitable for lodgepole pine is projected to be only 17% of its current distribution (a total area of only 15,000 km2) and the species is likely to be almost completely absent from Oregon, Washington and Idaho.  The projected changes in appropriate habitat occur because the area becomes too warm and too dry for lodgepole pine to compete well with other more drought-tolerant species.  The study does not consider the impacts of possible changes in disturbance such as fire and insect infestations that are likely to also accompany a warmer, drier climate.

Fung, F., A. Lopez and M. New. 2011. Water availability in a +2°C and +4°C worlds. Philosophical Transactions of the Royal Society A 369: 99-116.

The relative influence of population growth versus climate change on water stress is shown to shift when moving from +2°C to +4°C worlds. With less warming, population growth is a dominant driver of water stress whereas with greater warming the effects of climate change on the water cycle become dominant.

A recent study by U.K. researchers investigates the relative importance of population change and climate change for water stress in river basins around the world when global warming is limited to about 2°C compared to about 4°C. To do this they make use of the large number of climate simulations (for the SRES AIB emission scenario) available through the experiment and the Coupled Model Intercomparison Project Phase 3. Simulations that show an increase in global mean temperature in at least one season of 2°C and 4°C above the 1961-1990 mean some time in the 21st century (corresponding to ~ 2.5°C and ~4.5°C above pre-industrial) were used to drive a global hydrological model (MacPDM). A simple index of water stress reflecting water resources available per capita was used to identify water stressed regions. Population projections were based on medium growth scenarios from the U.N. Population Division. They found that changes in mean annual run-off in a +2°C world are generally amplified in a +4°C world; drier areas become drier and wetter areas become wetter. For all river basins except the tropical Amazon the seasonality of run-off also becomes stronger, with wet seasons becoming wetter and dry seasons drier. 71% and 74% of 112 river basins worldwide show an increase in water stress in +2°C and +4°C worlds respectively, with the stressed area generally increasing in spatial extent and magnitude of stress in the +4°C world. Consensus across ensembles was stronger for projections of water stress than for changes in mean annual run-off suggesting that for the majority of river basins, the direction of change in the water stress index is strongly dependent on projected population in the river basin. There is general agreement among ensembles that water stress will increase in all river basins in Africa, India, the eastern U.S. and Europe. However, in moving from a +2°C to +4°C world, there is a small but increasing number of basins that may experience less water stress, reflecting areas where water availability increased more than population. For a few river basins, there is no consensus about the direction of change. For these basins, the uncertainty is dominated by differences in projected mean annual run-off from different global climate models, emphasizing again the importance of including a variety of climate models for impact assessments.

Maclean, M.D. and R.J. Wilson. 2011. Recent ecological responses to climate change support predictions of high extinction risk. PNAS Vol. 108 No. 30, pp 12337–12342.

Estimates of extinction risk from studies documenting observed responses to recent climate change and from predictive studies of the impacts of future climate change converge at mean extinction probabilities, by 2100, of about 10-14%.  This result provides support to assertions that anthropogenic climate change ranks as a significant threat to global biodiversity.

The growing number of studies documenting ecological changes in response to recent climate change presents an opportunity to test whether the magnitude and nature of recent responses match predictions.  A recently published study does this, focusing on observations and predictions of extinction risk. Maclean and Wilson use a dataset of 130 observed and 188 predicted ecological responses to climate change obtained from studies appearing in major science journals from 2005 to 2009. Estimates of extinction risk for all 318 responses were derived using International Union for Conservation of Nature (IUCN) Red List Criteria (based on relationships between changes in population size and extinction probability). Various types of potential biases in the data set were accounted for, including biases related to type of climate impact studied, region of investigation and non-independence of extinction risk among taxa. After taking account of these possible biases, they found that predictive studies suggest a mean extinction probability over 90 years (out to the year 2100) of ~10% across taxa and regions while observation-based studies gave a mean extinction probability of ~14% for the same time period. Although the authors state these estimates should be treated with caution in light of the many difficulties in assessing impacts on biodiversity, the similarity in these estimates and their robustness to common sources of bias, provide confidence that realized ecological responses to climate change support predictions of future change. The authors also note that these estimates are lower than some published estimates based on the proportion of species ‘committed to extinction’ explaining that estimated extinction risk over a given time period would be expected to be lower than estimates of commitment to extinction.

Pisaric, M.F.J., J. R. Thienpont, S. V. Kokelj, H. Nesbitt, T. C. Lantz, S. Solomon and J. P. Smol. 2011. Impacts of a recent storm surge on an Arctic delta ecosystem examined in the context of the last millennium. Proceedings of the National Academy of Sciences, Vol 108(22), pp 8960-8965, doi:10.1073/pnas.1018527108.

A recent coastal inundation event that brought saltwater to parts of the Mackenzie Delta is found to be unique over the past millennia with substantial impacts observed in both terrestrial and aquatic ecosystems.  Higher sea levels combined with decreases in sea ice extent and duration are expected to increase the occurrence of these events in the future.

It is thought that the higher sea levels anticipated with projected climate warming will have large impacts on low lying coastal ecosystems.  Impacts are expected to be particularly pronounced in the Arctic because reduced sea ice extent and duration (i.e. the length of the open-water season) as well as increasingly variable storm activity are likely to increase the risk of storm surge occurrence and coastal inundation.  Pisaric and colleagues explore the impacts of a coastal inundation event associated with a recent storm surge (1999) in the Mackenzie Delta in terms of its uniqueness over the past millennium and the magnitude of its impacts.  Tree-ring growth chronologies developed from alder shrubs sampled at various distances form the coast in or near the inundated area show that the trees were able to recover form previous inundations over the past century but enhanced tree mortality is evident after the 1999 event.  Longer records of diatom (unicellular algae) assemblages were obtained from dated sediment cores extracted from two lakes (one within and one outside the inundation area).  The abundance of different types of diatom taxa through time reflects changes in lake salinity.  The authors found a dramatic shift from freshwater diatom taxa to those that thrive in brackish waters following the 1999 saltwater intrusion.  This shift was unprecedented over the past ~1000 years (the age of the lake) and there was no shift from freshwater to brackish taxa in the control lake located outside the inundation zone.  The ecological impacts (to both terrestrial and aquatic systems) of the 1999 storm surge were significant.  The authors infer that there has been no biological recovery at the lake since the intrusion and the alder shrubs indicate that terrestrial systems are still altered over a decade after the event.  They conclude that events such as this are likely to be more common around the circumpolar Arctic in the future with potentially long lasting impacts on ecosystems and coastal communities.

Wittrock, V., S.N. Kulshreshtha and E. Wheaton. 2011. Canadian prairie rural communities: their vulnerabilities and adaptive capacities to drought. Mitigation and Adaptation Strategies to Global Change 16:267-290.

An assessment of the vulnerability of Canadian communities in the Palliser Triangle to the severe drought of 2001-2002 demonstrates that where adaptation measures had been implemented in response to earlier droughts, vulnerability was lower, providing good evidence of the advantage of anticipatory adaptation.

There is a strong tendency among global climate model projections for continental interiors to become drier in summer, with an increased risk of drought, in response to continued emissions of greenhouse gases and associated climate warming. Obtaining knowledge on community vulnerabilities to drought would therefore be advantageous in planning adaptation measures. This study assessed the physical and social vulnerabilities of six communities in the Palliser Triangle region of the Canadian prairies during the 2001-2002 drought (one of the most severe droughts recorded in this region of North America). The Palliser Triangle is the driest part of the Canadian prairies yet agriculture is the main economic driver in most of the communities located there The study adopted a method for qualitative community vulnerability assessment previously described in the literature, using both environmental indicators (water availability, and climate) and socio-economic indicators (income, employment, education, demographics and infrastructure). The range of impacts from the 2001-2002 drought included declines in potable water supply, water scarcity, poor pasture for cattle, declines in cattle production and poor crop yields, and associated income losses, among other things. The assessment found that in general, communities that had implemented drought adaptation measures and strategies in response to previous droughts, were less vulnerable to the 2001-2 drought, providing good evidence of the benefits of adaptation. However, althoughaccess to a secure potable water supply was essential in buffering the community from the drought, it was not enough on its own, to reduce vulnerability sufficiently. Two of the six communities were assessed to have been ‘secure’ during the 2001-2 drought, while four communities were assessed as vulnerable, but for different reasons. Research such as this can be used to help inform community-specific adaptation planning to increase resilience to future droughts.

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