Air force
Projected Increases in North Atlantic Tropical Cyclone Intensity from CMIP5 Models
Gabriele Villarini & Gabriel Vecchi
Journal of Climate, May 2013, Pages 3231-3240
Abstract:
Tropical cyclones - particularly intense ones - are a hazard to life and property, so an assessment of the changes in North Atlantic tropical cyclone intensity has important socioeconomic implications. In this study, the authors focus on the seasonally integrated power dissipation index (PDI) as a metric to project changes in tropical cyclone intensity. Based on a recently developed statistical model, this study examines projections in North Atlantic PDI using output from 17 state-of-the-art global climate models and three radiative forcing scenarios. Overall, the authors find that North Atlantic PDI is projected to increase with respect to the 1986-2005 period across all scenarios. The difference between the PDI projections and those of the number of North Atlantic tropical cyclones, which are not projected to increase significantly, indicates an intensification of North Atlantic tropical cyclones in response to both greenhouse gas (GHG) increases and aerosol changes over the current century. At the end of the twenty-first century, the magnitude of these increases shows a positive dependence on projected GHG forcing. The projected intensification is significantly enhanced by non-GHG (primarily aerosol) forcing in the first half of the twenty-first century.
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Projected increase in tropical cyclones near Hawaii
Hiroyuki Murakami et al.
Nature Climate Change, forthcoming
Abstract:
Projections of the potential impacts of global warming on regional tropical cyclone activity are challenging owing to multiple sources of uncertainty in model physical schemes and different assumptions for future sea surface temperatures. A key factor in projecting climate change is to derive robust signals of future changes in tropical cyclone activity across different model physical schemes and different future patterns in sea surface temperature. A suite of future warming experiments (2075-2099), using a state-of-the-art high-resolution global climate model, robustly predicts an increase in tropical cyclone frequency of occurrence around the Hawaiian Islands. A physically based empirical model analysis reveals that the substantial increase in the likelihood of tropical cyclone frequency is primarily associated with a northwestward shifting of the tropical cyclone track in the open ocean southeast of the islands. Moreover, significant and robust changes in large-scale environmental conditions strengthen in situ tropical cyclone activity in the subtropical central Pacific. These results highlight possible future increases in storm-related socio-economic and ecosystem damage for the Hawaiian Islands.
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Anatomy of Dissent: A Cultural Analysis of Climate Skepticism
Myanna Lahsen
American Behavioral Scientist, June 2013, Pages 732-753
Abstract:
Based on findings from ethnographic analysis of U.S. climate scientists, this article identifies largely unrecognized sociocultural dimensions underpinning differences in scientists' perceptions of anthropogenic climate change. It argues that culturally laden tensions among scientists have influenced some to engage with the antienvironmental movement and, as such, influence U.S. climate science politics. The tensions are rooted in broad-based and ongoing changes within U.S. science and society since the 1960s and propelled by specific scientific subgroups' negative experiences of the rise of environmentalism and of climate modeling, in particular. Attending to these and other experience-based cultural dynamics can help refine cultural theory and enhance understanding of the deeper battles of meaning that propel climate science politics.
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Quantifying the consensus on anthropogenic global warming in the scientific literature
John Cook et al.
Environmental Research Letters, April-June 2013
Abstract:
We analyze the evolution of the scientific consensus on anthropogenic global warming (AGW) in the peer-reviewed scientific literature, examining 11 944 climate abstracts from 1991-2011 matching the topics 'global climate change' or 'global warming'. We find that 66.4% of abstracts expressed no position on AGW, 32.6% endorsed AGW, 0.7% rejected AGW and 0.3% were uncertain about the cause of global warming. Among abstracts expressing a position on AGW, 97.1% endorsed the consensus position that humans are causing global warming. In a second phase of this study, we invited authors to rate their own papers. Compared to abstract ratings, a smaller percentage of self-rated papers expressed no position on AGW (35.5%). Among self-rated papers expressing a position on AGW, 97.2% endorsed the consensus. For both abstract ratings and authors' self-ratings, the percentage of endorsements among papers expressing a position on AGW marginally increased over time. Our analysis indicates that the number of papers rejecting the consensus on AGW is a vanishingly small proportion of the published research.
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A global assessment of the effects of climate policy on the impacts of climate change
N.W. Arnell et al.
Nature Climate Change, May 2013, Pages 512-519
Abstract:
This study presents the first global-scale multi-sectoral regional assessment of the magnitude and uncertainty in the impacts of climate change avoided by emissions policies. The analysis suggests that the most stringent emissions policy considered here - which gives a 50% chance of remaining below a 2 °C temperature rise target - reduces impacts by 20-65% by 2100 relative to a ‘business-as-usual' pathway which reaches 4 °C, and can delay impacts by several decades. The effects of mitigation policies vary between sectors and regions, and only a few are noticeable by 2030. The impacts avoided by 2100 are more strongly influenced by the date and level at which emissions peak than the rate of decline of emissions, with an earlier and lower emissions peak avoiding more impacts. The estimated proportion of impacts avoided at the global scale is relatively robust despite uncertainty in the spatial pattern of climate change, but the absolute amount of avoided impacts is considerably more variable and therefore uncertain.
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Kevin Anchukaitis et al.
Journal of Climate, May 2013, Pages 3001-3012
Abstract:
Northwestern North America has one of the highest rates of recent temperature increase in the world, but the putative "divergence problem" in dendroclimatology potentially limits the ability of tree-ring proxy data at high latitudes to provide long-term context for current anthropogenic change. Here, summer temperatures are reconstructed from a Picea glauca maximum latewood density (MXD) chronology that shows a stable relationship to regional temperatures and spans most of the last millennium at the Firth River in northeastern Alaska. The warmest epoch in the last nine centuries is estimated to have occurred during the late twentieth century, with average temperatures over the last 30 yr of the reconstruction developed for this study [1973-2002 in the Common Era (CE)] approximately 1.3° ± 0.4°C warmer than the long-term preindustrial mean (1100-1850 CE), a change associated with rapid increases in greenhouse gases. Prior to the late twentieth century, multidecadal temperature fluctuations covary broadly with changes in natural radiative forcing. The findings presented here emphasize that tree-ring proxies can provide reliable indicators of temperature variability even in a rapidly warming climate.
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Continental-scale temperature variability during the past two millennia
PAGES 2k Consortium
Nature Geoscience, May 2013, Pages 339-346
Abstract:
Past global climate changes had strong regional expression. To elucidate their spatio-temporal pattern, we reconstructed past temperatures for seven continental-scale regions during the past one to two millennia. The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century. At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them. There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructions show generally cold conditions between AD 1580 and 1880, punctuated in some regions by warm decades during the eighteenth century. The transition to these colder conditions occurred earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere regions. Recent warming reversed the long-term cooling; during the period AD 1971-2000, the area-weighted average reconstructed temperature was higher than any other time in nearly 1,400 years.
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Martin Hoerling et al.
Journal of Climate, May 2013, Pages 2811-2832
Abstract:
The record-setting 2011 Texas drought/heat wave is examined to identify physical processes, underlying causes, and predictability. October 2010-September 2011 was Texas's driest 12-month period on record. While the summer 2011 heat wave magnitude (2.9°C above the 1981-2010 mean) was larger than the previous record, events of similar or larger magnitude appear in preindustrial control runs of climate models. The principal factor contributing to the heat wave magnitude was a severe rainfall deficit during antecedent and concurrent seasons related to anomalous sea surface temperatures (SSTs) that included a La Niña event. Virtually all the precipitation deficits appear to be due to natural variability. About 0.6°C warming relative to the 1981-2010 mean is estimated to be attributable to human-induced climate change, with warming observed mainly in the past decade. Quantitative attribution of the overall human-induced contribution since preindustrial times is complicated by the lack of a detected century-scale temperature trend over Texas. Multiple factors altered the probability of climate extremes over Texas in 2011. Observed SST conditions increased the frequency of severe rainfall deficit events from 9% to 34% relative to 1981-2010, while anthropogenic forcing did not appreciably alter their frequency. Human-induced climate change increased the probability of a new temperature record from 3% during the 1981-2010 reference period to 6% in 2011, while the 2011 SSTs increased the probability from 4% to 23%. Forecasts initialized in May 2011 demonstrate predictive skill in anticipating much of the SST-enhanced risk for an extreme summer drought/heat wave over Texas.
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Projections of declining surface-water availability for the southwestern United States
Richard Seager et al.
Nature Climate Change, May 2013, Pages 482-486
Abstract:
Global warming driven by rising greenhouse-gas concentrations is expected to cause wet regions of the tropics and mid to high latitudes to get wetter and subtropical dry regions to get drier and expand polewards. Over southwest North America, models project a steady drop in precipitation minus evapotranspiration, P-E, the net flux of water at the land surface, leading to, for example, a decline in Colorado River flow. This would cause widespread and important social and ecological consequences. Here, using new simulations from the Coupled Model Intercomparison Project Five, to be assessed in Intergovernmental Panel on Climate Change Assessment Report Five, we extend previous work by examining changes in P, E, runoff and soil moisture by season and for three different water resource regions. Focusing on the near future, 2021-2040, the new simulations project declines in surface-water availability across the southwest that translate into reduced soil moisture and runoff in California and Nevada, the Colorado River headwaters and Texas.
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Seasonal Changes in Solar Radiation and Relative Humidity in Europe in Response to Global Warming
Kimmo Ruosteenoja & Petri Räisänen
Journal of Climate, April 2013, Pages 2467-2481
Abstract:
Future seasonal changes in surface incident solar radiation and relative humidity (RH) over Europe and adjacent ocean areas were assessed based on phase 3 of the Coupled Model Intercomparison Project (CMIP3) model ensemble. Under the A1B scenario, by 2070-99, summertime solar radiation is projected to increase by 5%-10% in central and southern Europe. In winter, radiation decreases in most of northern and eastern Europe by 5%-15%. RH drops in summer in the southern European inland by 8%-12%, whereas in winter a small increase of 2%-3% is projected for northeastern Europe. In spring, the change is an intermediate between those in the extreme seasons, while in autumn the patterns resemble summer. Over the northern Atlantic Ocean, RH increases in all seasons by 1%-2%. The intermodel agreement on the sign of all these shifts is good, and the patterns recur in the responses to the A2 and B1 scenarios. Substantial changes are already simulated to occur before the midcentury, for example, in summer RH decreases by more than 5% in the inner Balkan Peninsula. Projected changes in these two variables agree well and are also mainly consistent with precipitation responses both in the multimodel mean and in individual models. According to all indicators, southern European summers become more arid, while winters, in the north particularly, become moister and darker. The increasing radiation and declining RH exacerbate summertime drought in southern Europe, whereas excessive humidity in the north may, for example, inflict moisture damages in constructions.
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Assessment of groundwater inundation as a consequence of sea-level rise
Kolja Rotzoll & Charles Fletcher
Nature Climate Change, May 2013, Pages 477-481
Abstract:
Strong evidence on climate change underscores the need for actions to reduce the impacts of sea-level rise. Global mean sea level may rise 0.18-0.48 m by mid-century and 0.5-1.4 m by the end of the century. Besides marine inundation, it is largely unrecognized that low-lying coastal areas may also be vulnerable to groundwater inundation, which is localized coastal-plain flooding due to a rise of the groundwater table with sea level. Measurements of the coastal groundwater elevation and tidal influence in urban Honolulu, Hawaii, allow estimates of the mean water table, which was used to assess vulnerability to groundwater inundation from sea-level rise. We find that 0.6 m of potential sea-level rise causes substantial flooding, and 1 m sea-level rise inundates 10% of a 1-km wide heavily urbanized coastal zone. The flooded area including groundwater inundation is more than twice the area of marine inundation alone. This has consequences for decision-makers, resource managers and urban planners, and may be applicable to many low-lying coastal areas, especially where groundwater withdrawal is not substantial.
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How do people update? The effects of local weather fluctuations on beliefs about global warming
Tatyana Deryugina
Climatic Change, May 2013, Pages 397-416
Abstract:
Global warming has become a controversial public policy issue in spite of broad scientific consensus that it is real and that human activity is a contributing factor. It is likely that public consensus is also needed to support policies that might counteract it. It is therefore important to understand how people form and update their beliefs about climate change. Using unique survey data on beliefs about the occurrence of the effects of global warming, I estimate how local temperature fluctuations influence what individuals believe about these effects. I find that some features of the updating process are consistent with rational updating. I also test explicitly for the presence of several heuristics known to affect belief formation and find strong evidence for representativeness, some evidence for availability, and no evidence for spreading activation. I find that very short-run temperature fluctuations (1 day-2 weeks) have no effect on beliefs about the occurrence of global warming, but that longer-run fluctuations (1 month-1 year) are significant predictors of beliefs. Only respondents with a conservative political ideology are affected by temperature abnormalities.
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Renewable energy and unemployment: A general equilibrium analysis
Nicholas Rivers
Resource and Energy Economics, forthcoming
Abstract:
Using a three-sector general equilibrium model, the impact of renewable electricity support policies on the rate of equilibrium unemployment is analyzed. In a simple two-factor version of the model, the paper shows analytically that renewable electricity support policies lead to an increase in the rate of unemployment. A numerical analysis is conducted with an expanded three-factor model. In this version, most scenarios analyzed also lead to an increase in equilibrium unemployment. However, the paper identifies conditions in which renewable energy support policies can decrease the rate of equilibrium unemployment. In particular, when the elasticity of substitution between capital and labor is low, when capital is not mobile internationally, and when the labor intensity of renewable generation is high relative to conventional generation, renewable electricity support policies may reduce the rate of equilibrium unemployment. The model is parameterized to represent the US economy, such that the magnitudes of quantities can be observed. Although there is some variation in the results depending on parameters, the findings suggest in general that reducing electricity sector emissions by 10 percent through renewable electricity support policies is likely to increase the equilibrium unemployment rate by about 0.1 to 0.3 percentage points.
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Market Effects of Voluntary Climate Action by Firms: Evidence from the Chicago Climate Exchange
Will Gans & Beat Hintermann
Environmental and Resource Economics, June 2013, Pages 291-308
Abstract:
Are private voluntary environmental actions by firms a sign of mismanagement, or a profitable "win-win" replacement for regulation? Empirical evidence is decidedly mixed. In this study, we use 19 years of monthly stock price returns, from 1991 to 2009, to examine the profitability of participation in CCX, a large voluntary greenhouse gas mitigation program. After controlling for systemic market risk as well as industry-specific shocks, we find statistically significant and positive excess returns for firms that announce their decision to join CCX. In addition, the progress of proposed greenhouse gas legislation (the Waxman-Markey bill) had a positive and large impact on excess returns for CCX member firms, suggesting that a major incentive for firms to join CCX may be to prepare for future regulation. Marginal abatement costs (proxied by the carbon price), on the other hand, were unrelated to excess returns. Our results imply that voluntary approaches should play a role in combating climate change, but that relying on them alone is not enough.
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Regulatory Dealing: Technology Adoption versus Enforcement Stringency of Emission Taxes
Jessica Coria & Clara Villegas-Palacio
Contemporary Economic Policy, forthcoming
Abstract:
We analyze the role of targeted enforcement of emissions taxes when the regulator wants to minimize aggregate emissions via the adoption of new more environmentally friendly technology. The regulator wants to speed up the path of technology adoption generated by a policy of uniform enforcement (that monitors adopters and nonadopters with the same probability) by engaging in a regulatory deal where a reduced monitoring probability is granted in "exchange" for adoption of the new technology. We set up a theoretical model, characterize the circumstances in which such dealing minimizes aggregate emissions, and test our hypothesis using economic laboratory experiments. Our analytical and experimental results suggest that even though such a deal might imply an increased level of violation by adopters, such tolerance is rather an integral part of an overall enforcement strategy that minimizes aggregate emissions when the rate of adoption is endogenous.
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Energy consumption and the unexplained winter warming over northern Asia and North America
Guang Zhang, Ming Cai & Aixue Hu
Nature Climate Change, May 2013, Pages 466-470
Abstract:
The worldwide energy consumption in 2006 was close to 498 exajoules. This is equivalent to an energy convergence of 15.8 TW into the populated regions, where energy is consumed and dissipated into the atmosphere as heat. Although energy consumption is sparsely distributed over the vast Earth surface and is only about 0.3% of the total energy transport to the extratropics by atmospheric and oceanic circulations, this anthropogenic heating could disrupt the normal atmospheric circulation pattern and produce a far-reaching effect on surface air temperature. We identify the plausible climate impacts of energy consumption using a global climate model. The results show that the inclusion of energy use at 86 model grid points where it exceeds 0.4 W m-2 can lead to remote surface temperature changes by as much as 1 K in mid- and high latitudes in winter and autumn over North America and Eurasia. These regions correspond well to areas with large differences in surface temperature trends between observations and global warming simulations forced by all natural and anthropogenic forcings. We conclude that energy consumption is probably a missing forcing for the additional winter warming trends in observations.
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The Reversibility of Sea Level Rise
N. Bouttes, J.M. Gregory & J.A. Lowe
Journal of Climate, April 2013, Pages 2502-2513
Abstract:
During the last century, global climate has been warming, and projections indicate that such a warming is likely to continue over coming decades. Most of the extra heat is stored in the ocean, resulting in thermal expansion of seawater and global mean sea level rise. Previous studies have shown that after CO2 emissions cease or CO2 concentration is stabilized, global mean surface air temperature stabilizes or decreases slowly, but sea level continues to rise. Using idealized CO2 scenario simulations with a hierarchy of models including an AOGCM and a step-response model, the authors show how the evolution of thermal expansion can be interpreted in terms of the climate energy balance and the vertical profile of ocean warming. Whereas surface temperature depends on cumulative CO2 emissions, sea level rise due to thermal expansion depends on the time profile of emissions. Sea level rise is smaller for later emissions, implying that targets to limit sea level rise would need to refer to the rate of emissions, not only to the time integral. Thermal expansion is in principle reversible, but to halt or reverse it quickly requires the radiative forcing to be reduced substantially, which is possible on centennial time scales only by geoengineering. If it could be done, the results indicate that heat would leave the ocean more readily than it entered, but even if thermal expansion were returned to zero, the geographical pattern of sea level would be altered. Therefore, despite any aggressive CO2 mitigation, regional sea level change is inevitable.
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Ecological limits to terrestrial biological carbon dioxide removal
Lydia Smith & Margaret Torn
Climatic Change, May 2013, Pages 89-103
Abstract:
Terrestrial biological atmospheric carbon dioxide removal (BCDR) through bioenergy with carbon capture and storage (BECS), afforestation/reforestation, and forest and soil management is a family of proposed climate change mitigation strategies. Very high sequestration potentials for these strategies have been reported, but there has been no systematic analysis of the potential ecological limits to and environmental impacts of implementation at the scale relevant to climate change mitigation. In this analysis, we identified site-specific aspects of land, water, nutrients, and habitat that will affect local project-scale carbon sequestration and ecological impacts. Using this framework, we estimated global-scale land and resource requirements for BCDR, implemented at a rate of 1 Pg C y-1. We estimate that removing 1 Pg C y-1 via tropical afforestation would require at least 7 × 106 ha y-1 of land, 0.09 Tg y-1 of nitrogen, and 0.2 Tg y-1 of phosphorous, and would increase evapotranspiration from those lands by almost 50 %. Switchgrass BECS would require at least 2 × 108 ha of land (20 times U.S. area currently under bioethanol production) and 20 Tg y-1 of nitrogen (20 % of global fertilizer nitrogen production), consuming 4 × 1012 m3 y-1 of water. While BCDR promises some direct (climate) and ancillary (restoration, habitat protection) benefits, Pg C-scale implementation may be constrained by ecological factors, and may compromise the ultimate goals of climate change mitigation.
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Mitigation of short-lived climate pollutants slows sea-level rise
Aixue Hu et al.
Nature Climate Change, forthcoming
Abstract:
Under present growth rates of greenhouse gas and black carbon aerosol emissions, global mean temperatures can warm by as much as 2 °C from pre-industrial temperatures by about 2050. Mitigation of the four short-lived climate pollutants (SLCPs), methane, tropospheric ozone, hydrofluorocarbons and black carbon, has been shown to reduce the warming trend by about 50% by 2050. Here we focus on the potential impact of this SLCP mitigation on global sea-level rise (SLR). The temperature projections under various SLCP scenarios simulated by an energy-balance climate model are integrated with a semi-empirical SLR model, derived from past trends in temperatures and SLR, to simulate future trends in SLR. A coupled ocean-atmosphere climate model is also used to estimate SLR trends due to just the ocean thermal expansion. Our results show that SLCP mitigation can have significant effects on SLR. It can decrease the SLR rate by 24-50% and reduce the cumulative SLR by 22-42% by 2100. If the SLCP mitigation is delayed by 25 years, the warming from pre-industrial temperature exceeds 2 °C by 2050 and the impact of mitigation actions on SLR is reduced by about a third.
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A Reconciled Estimate of Glacier Contributions to Sea Level Rise: 2003 to 2009
Alex Gardner et al.
Science, 17 May 2013, Pages 852-857
Abstract:
Glaciers distinct from the Greenland and Antarctic Ice Sheets are losing large amounts of water to the world's oceans. However, estimates of their contribution to sea level rise disagree. We provide a consensus estimate by standardizing existing, and creating new, mass-budget estimates from satellite gravimetry and altimetry and from local glaciological records. In many regions, local measurements are more negative than satellite-based estimates. All regions lost mass during 2003-2009, with the largest losses from Arctic Canada, Alaska, coastal Greenland, the southern Andes, and high-mountain Asia, but there was little loss from glaciers in Antarctica. Over this period, the global mass budget was -259 ± 28 gigatons per year, equivalent to the combined loss from both ice sheets and accounting for 29 ± 13% of the observed sea level rise.
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Marco Mazzotti et al.
Climatic Change, May 2013, Pages 119-135
Abstract:
Direct Air Capture (DAC) of CO2 with chemicals, recently assessed in a dedicated study by the American Physical Society (APS), is further investigated with the aim of optimizing the design of the front-end section of its benchmark two-loop hydroxide-carbonate system. Two new correlations are developed that relate mass transfer and pressure drop to the air and liquid flow velocities in the countercurrent packed absorption column. These relationships enable an optimization to be performed over the parameters of the air contactor, specifically the velocities of air and liquid sorbent and the fraction of CO2 captured. Three structured Sulzer packings are considered: Mellapak-250Y, Mellapak-500Y, and Mellapak-CC. These differ in cost and pressure drop per unit length; Mellapak-CC is new and specifically designed for CO2 capture. Scaling laws are developed to estimate the costs of the alternative DAC systems relative to the APS benchmark, for plants capturing 1 Mt of CO2 per year from ambient air at 500 ppm CO2 concentration. The optimized avoided cost hardly differs across the three packing materials, ranging from $518/tCO2 for M-CC to $568/tCO2 for M-250Y. The $610/tCO2 avoided cost for the APS-DAC design used M-250 Y but was not optimized; thus, optimization with the same packing lowered the avoided cost of the APS system by 7 % and improved packing lowered the avoided cost by a further 9 % The overall optimization exercise confirms that capture from air with the APS benchmark system or systems with comparable avoided costs is not a competitive mitigation strategy as long as the energy system contains high-carbon power, since implementation of Carbon Capture and Storage, substitution with low-carbon power and end-use efficiency will offer lower avoided-cost strategies.
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Quantifying the benefit of early climate change mitigation in avoiding biodiversity loss
R. Warren et al.
Nature Climate Change, forthcoming
Abstract:
Climate change is expected to have significant influences on terrestrial biodiversity at all system levels, including species-level reductions in range size and abundance, especially amongst endemic species. However, little is known about how mitigation of greenhouse gas emissions could reduce biodiversity impacts, particularly amongst common and widespread species. Our global analysis of future climatic range change of common and widespread species shows that without mitigation, 57±6% of plants and 34±7% of animals are likely to lose ≥50% of their present climatic range by the 2080s. With mitigation, however, losses are reduced by 60% if emissions peak in 2016 or 40% if emissions peak in 2030. Thus, our analyses indicate that without mitigation, large range contractions can be expected even amongst common and widespread species, amounting to a substantial global reduction in biodiversity and ecosystem services by the end of this century. Prompt and stringent mitigation, on the other hand, could substantially reduce range losses and buy up to four decades for climate change adaptation.
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Recent climate and ice-sheet changes in West Antarctica compared with the past 2,000 years
Eric Steig et al.
Nature Geoscience, May 2013, Pages 372-375
Abstract:
Changes in atmospheric circulation over the past five decades have enhanced the wind-driven inflow of warm ocean water onto the Antarctic continental shelf, where it melts ice shelves from below. Atmospheric circulation changes have also caused rapid warming over the West Antarctic Ice Sheet, and contributed to declining sea-ice cover in the adjacent Amundsen-Bellingshausen seas. It is unknown whether these changes are part of a longer-term trend. Here, we use water-isotope (δ18O) data from an array of ice-core records to place recent West Antarctic climate changes in the context of the past two millennia. We find that the δ18O of West Antarctic precipitation has increased significantly in the past 50 years, in parallel with the trend in temperature, and was probably more elevated during the 1990s than at any other time during the past 200 years. However, δ18O anomalies comparable to those of recent decades occur about 1% of the time over the past 2,000 years. General circulation model simulations suggest that recent trends in δ18O and climate in West Antarctica cannot be distinguished from decadal variability that originates in the tropics. We conclude that the uncertain trajectory of tropical climate variability represents a significant source of uncertainty in projections of West Antarctic climate and ice-sheet change.
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Acceleration of snow melt in an Antarctic Peninsula ice core during the twentieth century
Nerilie Abram et al.
Nature Geoscience, May 2013, Pages 404-411
Abstract:
Over the past 50 years, warming of the Antarctic Peninsula has been accompanied by accelerating glacier mass loss and the retreat and collapse of ice shelves. A key driver of ice loss is summer melting; however, it is not usually possible to specifically reconstruct the summer conditions that are critical for determining ice melt in Antarctic. Here we reconstruct changes in ice-melt intensity and mean temperature on the northern Antarctic Peninsula since AD 1000 based on the identification of visible melt layers in the James Ross Island ice core and local mean annual temperature estimates from the deuterium content of the ice. During the past millennium, the coolest conditions and lowest melt occurred from about AD 1410 to 1460, when mean temperature was 1.6 °C lower than that of 1981-2000. Since the late 1400s, there has been a nearly tenfold increase in melt intensity from 0.5 to 4.9%. The warming has occurred in progressive phases since about AD 1460, but intensification of melt is nonlinear, and has largely occurred since the mid-twentieth century. Summer melting is now at a level that is unprecedented over the past 1,000 years. We conclude that ice on the Antarctic Peninsula is now particularly susceptible to rapid increases in melting and loss in response to relatively small increases in mean temperature.