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Probabilistic cost estimates for climate change mitigation
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For more than a decade, the target of keeping global warming below 2 6C has been a key focus of the international climate debate1. In response, the scientific community has published a number of scenario studies that estimate the costs of achieving such a target 2–5. Producing these estimates remains a challenge, particularly because of relatively well known, but poorly quantified, uncertainties, and owing to limited integration of scientific knowledge across disciplines6. The integrated assessment community, on the one hand, has extensively assessed the influence of technological and socio-economic uncertainties on low-carbon scenarios and asso- ciated costs2–4,7. The climate modelling community, on the other hand, has spent years improving its understanding of the geo- physical response of the Earth system to emissions of greenhouse gases8–12. This geophysical response remains a key uncertainty in the cost of mitigation scenarios but has been integrated with assess- ments of other uncertainties in only a rudimentary manner, that is, for equilibrium conditions6,13. Here we bridge this gap between the two research communities by generating distributions of the costs associated with limiting transient global temperature increase to below specific values, taking into account uncertainties in four factors: geophysical, technological, social and political. We find that political choices that delay mitigation have the largest effect on the cost–risk distribution, followed by geophysical uncertainties, social factors influencing future energy demand and, lastly, technological uncertainties surrounding the availability of greenhouse gas miti- gation options. Our information on temperature risk and mitigation costs provides crucial information for policy-making, because it clarifies the relative importance of mitigation costs, energy demand and the timing of global action in reducing the risk of exceeding a global temperature increase of 2 6C, or other limits such as 3 6C or 1.5 6C, across a wide range of scenarios.
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Project Bog Turtle
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Project Bog Turtle, established in 1995, is a conservation initiative of the North Carolina Herpetological Society. Tom Thorp (Three Lakes Nature Center and Aquarium, Richmond, VA) is currently the chair and is assisted by Ann B. Somers (UNC-Greensboro, Greensboro, NC). The original project was originated in the late 1970s by Dennis Herman as a continuation of a bog turtle distribution survey, initiated by Robert T. Zappalorti (Herpetological Associates, Inc.), in southwestern North Carolina and expanded to include other southern states to locate new sites and populations of bog turtles. Most of the work, however, was conducted in North Carolina. The project involved population density studies in several sites and a captive propagation and head-start program at the Atlanta Zoological Park (now Zoo Atlanta). It was evident, as the project progressed, that additional personnel and assistance from various state, federal, and private agencies would be needed.
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Projected climate-induced faunal change in the Western Hemisphere
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Climate change is predicted to be one of the greatest drivers of ecological change in the coming century. Increases in temperature over the last century have clearly been linked to shifts in species distributions. Given the magnitude of projected future climatic changes, we can expect even larger range shifts in the coming century. These changes will, in turn, alter ecological communities and the functioning of ecosystems. Despite the seriousness of predicted climate change, the uncertainty in climate-change projections makes it difficult for conservation managers and planners to proactively respond to climate stresses. To address one aspect of this uncertainty, we identified predictions of faunal change for which a high level of consensus was exhibited by different climate models. Specifically, we assessed the potential effects of 30 coupled atmosphere–ocean general circulation model (AOGCM) future-climate simulations on the geographic ranges of 2954 species of birds, mammals, and amphibians in the Western Hemisphere. Eighty percent of the climate projections based on a relatively low greenhouse-gas emissions scenario result in the local loss of at least 10% of the vertebrate fauna over much of North and South America. The largest changes in fauna are predicted for the tundra, Central America, and the Andes Mountains where, assuming no dispersal constraints, specific areas are likely to experience over 90% turnover, so that faunal distributions in the future will bear little resemblance to those of today.
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Projected increase in continental runoff due to plant responses to increasing carbon dioxide
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In addition to influencing climatic conditions directly through radiative forcing, increasing carbon dioxide concentration in- fluences the climate system through its effects on plant physi- ology1. Plant stomata generally open less widely under increased carbon dioxide concentration2, which reduces transpiration1,3–6 and thus leaves more water at the land surface7. This driver of change in the climate system, which we term ‘physiological for- cing’, has been detected in observational records of increasing average continental runoff over the twentieth century8. Here we use an ensemble of experiments with a global climate model that includes a vegetation component to assess the contribution of physiological forcing to future changes in continental runoff, in the context of uncertainties in future precipitation. We find that the physiological effect of doubled carbon dioxide concentrations on plant transpiration increases simulated global mean runoff by 6 per cent relative to pre-industrial levels; an increase that is com- parable to that simulated in response to radiatively forced climate change (11 6 6 per cent). Assessments of the effect of increasing carbon dioxide concentrations on the hydrological cycle that only consider radiative forcing9–11 will therefore tend to underestimate future increases in runoff and overestimate decreases. This sug- gests that freshwater resources may be less limited than previously assumed under scenarios of future global warming, although there is still an increased risk of drought. Moreover, our results high- light that the practice of assessing the climate-forcing potential of all greenhouse gases in terms of their radiative forcing potential relative to carbon dioxide does not accurately reflect the relative effects of different greenhouse gases on freshwater resources.
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Projecting Global Land-Use Change and Its Effect on Ecosystem Service Provision and Biodiversity with Simple Modelsf
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Projections of declining surface-water availability for the southwestern United States
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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 1–4. Over southwest North America, models project a steady drop in precipitation minus evapotranspiration, P − E, the net flux of water at the land surface5–7, leading to, for example, a decline in Colorado River flow8–11. This would cause widespread and important social and ecological consequences12–14. Here, using new simulations from the Coupled Model Intercomparison Project Five, to be assessed in Intergovernmental Panel on Climate Change As- sessment 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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Projections of Future Drought in the Continental United States and Mexico
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Using the Palmer drought severity index, the ability of 19 state-of-the-art climate models to reproduce observed
statistics of drought over North America is examined. It is found that correction of substantial biases in
the models’ surface air temperature and precipitation fields is necessary. However, even after a bias correction,
there are significant differences in the models’ ability to reproduce observations. Using metrics based on the
ability to reproduce observed temporal and spatial patterns of drought, the relationship between model performance
in simulating present-day drought characteristics and their differences in projections of future drought
changes is investigated. It is found that all models project increases in future drought frequency and severity.
However, using the metrics presented here to increase confidence in the multimodel projection is complicated
by a correlation between models’ drought metric skill and climate sensitivity. The effect of this sampling error
can be removed by changing how the projection is presented, from a projection based on a specific time interval
to a projection based on a specified temperature change. This modified class of projections has reduced
intermodel uncertainty and could be suitable for a wide range of climate change impacts projections.
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