Earth, Wind, and Fire
The Role of China in Mitigating Climate Change
Sergey Paltsev et al.
Energy Economics, forthcoming
Abstract:
We explore short- and long-term implications of several energy scenarios of China's role in efforts to mitigate global climate risk. The focus is on the impacts on China's energy system and GDP growth, and on global climate indicators such as greenhouse gas concentrations, radiative forcing, and global temperature change. We employ the MIT Integrated Global System Model (IGSM) framework and its economic component, the MIT Emissions Prediction and Policy Analysis (EPPA) model. We demonstrate that China's commitments for 2020, made during the UN climate meetings in Copenhagen and Cancun, are reachable at very modest cost. Alternative actions by China in the next 10 years do not yield any substantial changes in GHG concentrations or temperature due to inertia in the climate system. Consideration of the longer-term climate implications of the Copenhagen-type of commitments requires an assumption about policies after 2020, and the effects differ drastically depending on the case. Meeting a 2 °C target is problematic unless radical GHG emission reductions are assumed in the short-term. Participation or non-participation of China in global climate architecture can lead by 2100 to a 200-280 ppm difference in atmospheric GHG concentration, which can result in a 1.1 °C to 1.3 °C change by the end of the century. We conclude that it is essential to engage China in GHG emissions mitigation policies, and alternative actions lead to substantial differences in climate, energy, and economic outcomes. Potential channels for engaging China can be air pollution control and involvement in sectoral trading with established emissions trading systems in developed countries.
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Adaptation to Climate Change in Preindustrial Iceland
Matthew Turner et al.
American Economic Review, May 2012, Pages 250-255
Abstract:
We investigate the effect of climate change on population growth in 18th and 19th century Iceland. We find that annual temperature changes help determine the population growth rate in pre-industrial Iceland: a year 1 degree Celsius cooler than average drives down population growth rates by 1.14%. We also find that 18th and 19th century Icelanders adapt to prolonged changes in climate after 20 years. These adaptations reduce the short run effect of annual change in temperature by about 60%. Finally, a 1 degree Celsius sustained decrease in temperature decreases the steady state population by 10% to 26%.
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Michael Cragg et al.
Economic Inquiry, forthcoming
Abstract:
Over the last 5 years, the U.S. Congress has voted on several pieces of legislation intended to sharply reduce the nation's greenhouse gas emissions. Given that climate change is a world public bad, standard economic logic would predict that the United States would "free ride" and wait for other nations to reduce their emissions. Within the Congress, there are clear patterns to who votes in favor of mitigating greenhouse gas emissions. This paper presents a political economy analysis of the determinants of "pro-green" votes on such legislation. Conservatives consistently vote against such legislation. Controlling for a representative's ideology, representatives from richer districts and districts with a lower per-capita carbon dioxide footprint are more likely to vote in favor of climate change mitigation legislation. Representatives from districts where industrial emissions represent a larger share of greenhouse gas emissions are more likely to vote no.
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Rural Nevada and Climate Change: Vulnerability, Beliefs, and Risk Perception
Ahmad Saleh Safi, William James Smith & Zhnongwei Liu
Risk Analysis, forthcoming
Abstract:
In this article, we present the results of a study investigating the influence of vulnerability to climate change as a function of physical vulnerability, sensitivity, and adaptive capacity on climate change risk perception. In 2008/2009, we surveyed Nevada ranchers and farmers to assess their climate change-related beliefs, and risk perceptions, political orientations, and socioeconomic characteristics. Ranchers' and farmers' sensitivity to climate change was measured through estimating the proportion of their household income originating from highly scarce water-dependent agriculture to the total income. Adaptive capacity was measured as a combination of the Social Status Index and the Poverty Index. Utilizing water availability and use, and population distribution GIS databases; we assessed water resource vulnerability in Nevada by zip code as an indicator of physical vulnerability to climate change. We performed correlation tests and multiple regression analyses to examine the impact of vulnerability and its three distinct components on risk perception. We find that vulnerability is not a significant determinant of risk perception. Physical vulnerability alone also does not impact risk perception. Both sensitivity and adaptive capacity increase risk perception. While age is not a significant determinant of it, gender plays an important role in shaping risk perception. Yet, general beliefs such as political orientations and climate change-specific beliefs such as believing in the anthropogenic causes of climate change and connecting the locally observed impacts (in this case drought) to climate change are the most prominent determinants of risk perception.
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Climate response to zeroed emissions of greenhouse gases and aerosols
Damon Matthews & Kirsten Zickfeld
Nature Climate Change, May 2012, Pages 338-341
Abstract:
The climate response to scenarios of zero future greenhouse-gas emissions can be interpreted as the committed future warming associated with past emissions, and represents a critical benchmark against which to estimate the effect of future emissions. Recent climate-model simulations have shown that when emissions of carbon dioxide alone are eliminated, global temperature stabilizes and remains approximately constant for several centuries. Here, we show that when aerosol and other greenhouse-gas emissions are also eliminated, global temperature increases by a few tenths of a degree over about a decade, as a result of the rapid removal of present-day aerosol forcing. This initial warming is followed by a gradual cooling that returns global temperature to present-day levels after several centuries, owing to the decline in non-carbon dioxide greenhouse-gas concentrations. We show further that the magnitude of the peak temperature response to zero future emissions depends strongly on the uncertain strength of present-day aerosol forcing. Contingent on the climate and carbon-cycle sensitivities of the model used here, we show that the range of aerosol forcing that produces historical warming that is consistent with observed data, results in a warming of between 0.25 and 0.5 °C over the decade immediately following zeroed emissions.
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Moving to Higher Ground: Migration Response to Natural Disasters in the Early Twentieth Century
Leah Platt Boustan, Matthew Kahn & Paul Rhode
American Economic Review, May 2012, Pages 238-244
Abstract:
Areas differ in their propensity to experience natural disasters. Exposure to disaster risks can be reduced either through migration (i.e., self-protection) or through public infrastructure investment (e.g., building seawalls). Using migration data from the 1920s and 1930s, this paper studies how the population responded to disaster shocks in an era of minimal public investment. We find that, on net, young men move away from areas hit by tornados but are attracted to areas experiencing floods. Early efforts to protect against future flooding, especially during the New Deal era of the late 1930s, may have counteracted an individual migration response.
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Navigating the impact-innovation double hurdle: The case of a climate change research fund
Fiona Lettice et al.
Research Policy, July 2012, Pages 1048-1057
Abstract:
This paper analyses how the funding for research grants was allocated from a specific research fund which aimed to support innovative research projects with the potential to have research impact by reducing carbon emissions. The fund received a total of 106 proposals, of which 27 were successful at obtaining financial support. Our aims were to test which factors influenced the funding decision and to discover whether or not and to what extent the fund met its intended objectives through the allocation of monies. The allocation process and its outcomes were analysed using correlation, logistical and linear regression to test our research hypotheses. Using this research funding process as a single study, we found that trying to clear the impact-innovation double hurdle in a single funding initiative ultimately compromises both goals. This paper therefore contributes to our understanding of innovation management within the context of carbon emission reduction and explains which factors influenced success in securing research monies through the funding process.
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Investment and employment from large-scale photovoltaics up to 2050
Wolf Grossmann et al.
Empirica, May 2012, Pages 165-189
Abstract:
Investments in renewable energy were at US$211 billion in 2010 and developing economies overtook developed ones for the first time in terms of new financial investments in renewable energy. Photovoltaics for generation of electricity from sunlight has the highest growth rate among the competing forms of renewable energy and has now begun to achieve grid parity in some regions. If these trends of investments continue, solar energy will play a major economic role. We analyze these developments and assess the ensuing amounts of investment and employment for a range of sizes of the sector of solar energy. We find that by 2050 electricity from photovoltaics could cover up to 90% of total global energy demand, with a then global capital investment in our main scenario in photovoltaic manufacturing capacity at 500 billion US$2010 by around 2030 and 1,500 billion by 2050. Employment in photovoltaic manufacturing is predicted to rise to 6 million by 2050. Sensitivity analysis with respect to the core parameters of assumptions is supplied.
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Identifying climatic analogs for Wisconsin under 21st-century climate-change scenarios
Samuel Veloz et al.
Climatic Change, June 2012, Pages 1037-1058
Abstract:
There is a deep disconnect between scientific and public concern about climate change. One reason is that global climate change is a fairly abstract concept with little perceived relevance, so a key challenge is to translate climate-change projections into locally concrete examples of potential impacts. Here we use climate analog analyses as an alternative method for identifying and communicating climate-change impacts. Our analysis uses multiple downscaled general circulation models for the state of Wisconsin, at 0.1 decimal degree resolution, and identifies contemporary locations in North America that are the most similar to the projected future climates for Wisconsin. We assess the uncertainties inherent in climate-change projections among greenhouse gas emission scenarios, time windows (mid-21st century vs. late 21st-century) and different combinations of climate variables. For all future scenarios and simulations, contemporary climatic analogs within North America were found for Wisconsin's future climate. Closest analogs are primarily 200-500 km to the south-southwest of their Wisconsin reference location. Temperature has the largest effect on choice of climatic analog, but precipitation is the greatest source of uncertainty. Under the higher-end emission scenarios, the contemporary climatic analogs for Wisconsin's end-21st-century climates are almost entirely outside the state. Climate-analog analyses offer a place-based means of assessing climate impacts that is complementary to the species-based approaches of species distributional models, and carries no assumptions about the characterization and conservatism of species niches. The analog method is simple and flexible, and can be readily extended to other regions and other environmental variables.
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Ocean Salinities Reveal Strong Global Water Cycle Intensification During 1950 to 2000
Paul Durack, Susan Wijffels & Richard Matear
Science, 27 April 2012, Pages 455-458
Abstract:
Fundamental thermodynamics and climate models suggest that dry regions will become drier and wet regions will become wetter in response to warming. Efforts to detect this long-term response in sparse surface observations of rainfall and evaporation remain ambiguous. We show that ocean salinity patterns express an identifiable fingerprint of an intensifying water cycle. Our 50-year observed global surface salinity changes, combined with changes from global climate models, present robust evidence of an intensified global water cycle at a rate of 8 ± 5% per degree of surface warming. This rate is double the response projected by current-generation climate models and suggests that a substantial (16 to 24%) intensification of the global water cycle will occur in a future 2° to 3° warmer world.
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Climatic effects of 1950-2050 changes in US anthropogenic aerosols - Part 2: Climate response
E.M. Leibensperger et al.
Atmospheric Chemistry and Physics, April 2012, Pages 3349-3362
Abstract:
We investigate the climate response to changing US anthropogenic aerosol sources over the 1950-2050 period by using the NASA GISS general circulation model (GCM) and comparing to observed US temperature trends. Time-dependent aerosol distributions are generated from the GEOS-Chem chemical transport model applied to historical emission inventories and future projections. Radiative forcing from US anthropogenic aerosols peaked in 1970-1990 and has strongly declined since due to air quality regulations. We find that the regional radiative forcing from US anthropogenic aerosols elicits a strong regional climate response, cooling the central and eastern US by 0.5-1.0 °C on average during 1970-1990, with the strongest effects on maximum daytime temperatures in summer and autumn. Aerosol cooling reflects comparable contributions from direct and indirect (cloud-mediated) radiative effects. Absorbing aerosol (mainly black carbon) has negligible warming effect. Aerosol cooling reduces surface evaporation and thus decreases precipitation along the US east coast, but also increases the southerly flow of moisture from the Gulf of Mexico resulting in increased cloud cover and precipitation in the central US. Observations over the eastern US show a lack of warming in 1960-1980 followed by very rapid warming since, which we reproduce in the GCM and attribute to trends in US anthropogenic aerosol sources. Present US aerosol concentrations are sufficiently low that future air quality improvements are projected to cause little further warming in the US (0.1 °C over 2010-2050). We find that most of the warming from aerosol source controls in the US has already been realized over the 1980-2010 period.
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Evolution of the global virtual water trade network
Carole Dalin et al.
Proceedings of the National Academy of Sciences, 17 April 2012, Pages 5989-5994
Abstract:
Global freshwater resources are under increasing pressure from economic development, population growth, and climate change. The international trade of water-intensive products (e.g., agricultural commodities) or virtual water trade has been suggested as a way to save water globally. We focus on the virtual water trade network associated with international food trade built with annual trade data and annual modeled virtual water content. The evolution of this network from 1986 to 2007 is analyzed and linked to trade policies, socioeconomic circumstances, and agricultural efficiency. We find that the number of trade connections and the volume of water associated with global food trade more than doubled in 22 years. Despite this growth, constant organizational features were observed in the network. However, both regional and national virtual water trade patterns significantly changed. Indeed, Asia increased its virtual water imports by more than 170%, switching from North America to South America as its main partner, whereas North America oriented to a growing intraregional trade. A dramatic rise in China's virtual water imports is associated with its increased soy imports after a domestic policy shift in 2000. Significantly, this shift has led the global soy market to save water on a global scale, but it also relies on expanding soy production in Brazil, which contributes to deforestation in the Amazon. We find that the international food trade has led to enhanced savings in global water resources over time, indicating its growing efficiency in terms of global water use.
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Calvin Lee Kwan
Energy Policy, forthcoming
Abstract:
This study used ZIP code level data from the 2000 US Census to investigate the influence of local environmental, social, economic and political variables on the distribution of residential solar PV arrays across the United States. Current locations of residential solar PVs were documented using data from the National Renewable Energy Laboratory's Open PV project. A zero-inflated negative binomial reression model was run to evaluate the influence of selected variables. Using the same model, predicted residential solar PV shares were generated and illustrated using GIS software. The results of the model indicate solar insolation, cost of electricity and amount of available financial incentives are important factors influencing adoption of residential solar PV arrays. Results also indicate the Southwestern region of the United States and the state of Florida are currently underperforming in terms of number of housing units with solar PV installations.
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The impacts of population change on carbon emissions in China during 1978-2008
Qin Zhu & Xizhe Peng
Environmental Impact Assessment Review, September 2012, Pages 1-8
Abstract:
This study examines the impacts of population size, population structure, and consumption level on carbon emissions in China from 1978 to 2008. To this end, we expanded the stochastic impacts by regression on population, affluence, and technology model and used the ridge regression method, which overcomes the negative influences of multicollinearity among independent variables under acceptable bias. Results reveal that changes in consumption level and population structure were the major impact factors, not changes in population size. Consumption level and carbon emissions were highly correlated. In terms of population structure, urbanization, population age, and household size had distinct effects on carbon emissions. Urbanization increased carbon emissions, while the effect of age acted primarily through the expansion of the labor force and consequent overall economic growth. Shrinking household size increased residential consumption, resulting in higher carbon emissions. Households, rather than individuals, are a more reasonable explanation for the demographic impact on carbon emissions. Potential social policies for low carbon development are also discussed.
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Redistributional Effects of the National Flood Insurance Program
Okmyung Bin, John Bishop & Carolyn Kousky
Public Finance Review, May 2012, Pages 360-380
Abstract:
This study examines the redistributional effects of the National Flood Insurance Program (NFIP) using a national database of premium, coverage, and claim payments at the county level between 1980 and 2006. Measuring progressivity as the departure from per capita county income proportionality, the authors find that NFIP premiums are typically proportional if the time horizon is extended beyond a single year, while claim payments are moderately progressive over all time horizons studied. The net effect of the NFIP program, defined as indemnity payments net of premiums, indicates that NFIP is proportional or at most mildly progressive, while the effect is modest. In sum, the authors find no evidence that the NFIP disproportionally advantages richer counties.
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Policy Tenure Under the U.S. National Flood Insurance Program (NFIP)
Erwann Michel-Kerjan, Sabine Lemoyne de Forges & Howard Kunreuther
Risk Analysis, April 2012, Pages 644-658
Abstract:
In the United States, insurance against flood hazard (inland flooding or storm surge from hurricanes) has been provided mainly through the National Flood Insurance Program (NFIP) since 1968. The NFIP covers $1.23 trillion of assets today. This article provides the first analysis of flood insurance tenure ever undertaken: that is, the number of years that people keep their flood insurance policy before letting it lapse. Our analysis of the entire portfolio of the NFIP over the period 2001-2009 reveals that the median tenure of new policies during that time is between two and four years; it is also relatively stable over time and levels of flood hazard. Prior flood experience can affect tenure: people who have experienced small flood claims tend to hold onto their insurance longer; people who have experienced large flood claims tend to let their insurance lapse sooner. To overcome the policy and governance challenges posed by homeowners' inadequate insurance coverage, we discuss policy recommendations that include for banks and government-sponsored enterprises (GSEs) strengthening their requirements and the introduction of multiyear flood insurance contracts attached to the property, both of which are likely to provide more coverage stability and encourage investments in risk-reduction measures.
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Kax and kol: Collapse and resilience in lowland Maya civilization
Nicholas Dunning, Timothy Beach & Sheryl Luzzadder-Beach
Proceedings of the National Academy of Sciences, 6 March 2012, Pages 3652-3657
Abstract:
Episodes of population loss and cultural change, including the famous Classic Collapse, punctuated the long course of Maya civilization. In many cases, these downturns in the fortunes of individual sites and entire regions included significant environmental components such as droughts or anthropogenic environmental degradation. Some afflicted areas remained depopulated for long periods, whereas others recovered more quickly. We examine the dynamics of growth and decline in several areas in the Maya Lowlands in terms of both environmental and cultural resilience and with a focus on downturns that occurred in the Terminal Preclassic (second century Common Era) and Terminal Classic (9th and 10th centuries CE) periods. This examination of available data indicates that the elevated interior areas of the Yucatán Peninsula were more susceptible to system collapse and less suitable for resilient recovery than adjacent lower-lying areas.
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Richard VanCuren
Climatic Change, June 2012, Pages 1071-1083
Abstract:
Exploiting surface albedo change has been proposed as a form of geoengineering to reduce the heating effect of anthropogenic increases in greenhouse gases (GHGs). Recent modeling experiments have projected significant negative radiative forcing from large-scale implementation of albedo reduction technologies ("cool" roofs and pavements). This paper complements such model studies with measurement-based calculations of the direct radiation balance impacts of replacement of conventional roofing with "cool" roof materials in California. This analysis uses, as a case study, the required changes to commercial buildings embodied in California's building energy efficiency regulations, representing a total of 4300 ha of roof area distributed over 16 climate zones. The estimated statewide mean radiative forcing per 0.01 increase in albedo (here labeled RF01) is -1.38 W/m2. The resulting unit-roof-area mean annual radiative forcing impact of this regulation is -44.2 W/m2. This forcing is computed to counteract the positive radiative forcing of ambient atmospheric CO2 at a rate of about 41 kg for each square meter of roof. Aggregated over the 4300 ha of cool roof estimated built in the first decade after adoption of the State regulation, this is comparable to removing about 1.76 million metric tons (MMT) of CO2 from the atmosphere. The point radiation data used in this study also provide perspective on the spatial variability of cool roof radiative forcing in California, with individual climate zone effectiveness ranging from -37 to -59 W/m2 of roof. These "bottom-up" calculations validate the estimates reported for published "top down" modeling, highlight the large spatial diversity of the effects of albedo change within even a limited geographical area, and offer a potential methodology for regulatory agencies to account for the climate effects of "cool" roofing in addition to its well-known energy efficiency benefits.
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Widespread Climate Change in the Himalayas and Associated Changes in Local Ecosystems
Uttam Babu Shrestha, Shiva Gautam & Kamaljit Bawa
PLoS ONE, May 2012
Background: Climate change in the Himalayas, a biodiversity hotspot, home of many sacred landscapes, and the source of eight largest rivers of Asia, is likely to impact the well-being of ~20% of humanity. However, despite the extraordinary environmental, cultural, and socio-economic importance of the Himalayas, and despite their rapidly increasing ecological degradation, not much is known about actual changes in the two most critical climatic variables: temperature and rainfall. Nor do we know how changes in these parameters might impact the ecosystems including vegetation phenology.
Methodology/Principal Findings: By analyzing temperature and rainfall data, and NDVI (Normalized Difference Vegetation Index) values from remotely sensed imagery, we report significant changes in temperature, rainfall, and vegetation phenology across the Himalayas between 1982 and 2006. The average annual mean temperature during the 25 year period has increased by 1.5°C with an average increase of 0.06°C yr-1. The average annual precipitation has increased by 163 mm or 6.52 mmyr-1. Since changes in temperature and precipitation are immediately manifested as changes in phenology of local ecosystems, we examined phenological changes in all major ecoregions. The average start of the growing season (SOS) seems to have advanced by 4.7 days or 0.19 days yr-1 and the length of growing season (LOS) appears to have advanced by 4.7 days or 0.19 days yr-1, but there has been no change in the end of the growing season (EOS). There is considerable spatial and seasonal variation in changes in climate and phenological parameters.
Conclusions/Significance: This is the first time that large scale climatic and phenological changes at the landscape level have been documented for the Himalayas. The rate of warming in the Himalayas is greater than the global average, confirming that the Himalayas are among the regions most vulnerable to climate change.
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Dispersal will limit ability of mammals to track climate change in the Western Hemisphere
Carrie Schloss, Tristan Nuñez & Joshua Lawler
Proceedings of the National Academy of Sciences, forthcoming
Abstract:
As they have in response to past climatic changes, many species will shift their distributions in response to modern climate change. However, due to the unprecedented rapidity of projected climatic changes, some species may not be able to move their ranges fast enough to track shifts in suitable climates and associated habitats. Here, we investigate the ability of 493 mammals to keep pace with projected climatic changes in the Western Hemisphere. We modeled the velocities at which species will likely need to move to keep pace with projected changes in suitable climates. We compared these velocities with the velocities at which species are able to move as a function of dispersal distances and dispersal frequencies. Across the Western Hemisphere, on average, 9.2% of mammals at a given location will likely be unable to keep pace with climate change. In some places, up to 39% of mammals may be unable to track shifts in suitable climates. Eighty-seven percent of mammalian species are expected to experience reductions in range size and 20% of these range reductions will likely be due to limited dispersal abilities as opposed to reductions in the area of suitable climate. Because climate change will likely outpace the response capacity of many mammals, mammalian vulnerability to climate change may be more extensive than previously anticipated.
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Warming experiments underpredict plant phenological responses to climate change
E.M. Wolkovich et al.
Nature, forthcoming
Abstract:
Warming experiments are increasingly relied on to estimate plant responses to global climate change. For experiments to provide meaningful predictions of future responses, they should reflect the empirical record of responses to temperature variability and recent warming, including advances in the timing of flowering and leafing. We compared phenology (the timing of recurring life history events) in observational studies and warming experiments spanning four continents and 1,634 plant species using a common measure of temperature sensitivity (change in days per degree Celsius). We show that warming experiments underpredict advances in the timing of flowering and leafing by 8.5-fold and 4.0-fold, respectively, compared with long-term observations. For species that were common to both study types, the experimental results did not match the observational data in sign or magnitude. The observational data also showed that species that flower earliest in the spring have the highest temperature sensitivities, but this trend was not reflected in the experimental data. These significant mismatches seem to be unrelated to the study length or to the degree of manipulated warming in experiments. The discrepancy between experiments and observations, however, could arise from complex interactions among multiple drivers in the observational data, or it could arise from remediable artefacts in the experiments that result in lower irradiance and drier soils, thus dampening the phenological responses to manipulated warming. Our results introduce uncertainty into ecosystem models that are informed solely by experiments and suggest that responses to climate change that are predicted using such models should be re-evaluated.
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Why are there so few fish in the sea?
Greta Carrete Vega & John Wiens
Proceedings of the Royal Society: Biological Sciences, 22 June 2012, Pages 2323-2329
Abstract:
The most dramatic gradient in global biodiversity is between marine and terrestrial environments. Terrestrial environments contain approximately 75-85% of all estimated species, but occupy only 30 per cent of the Earth's surface (and only approx. 1-10% by volume), whereas marine environments occupy a larger area and volume, but have a smaller fraction of Earth's estimated diversity. Many hypotheses have been proposed to explain this disparity, but there have been few large-scale quantitative tests. Here, we analyse patterns of diversity in actinopterygian (ray-finned) fishes, the most species-rich clade of marine vertebrates, containing 96 per cent of fish species. Despite the much greater area and productivity of marine environments, actinopterygian richness is similar in freshwater and marine habitats (15 150 versus 14 740 species). Net diversification rates (speciation-extinction) are similar in predominantly freshwater and saltwater clades. Both habitats are dominated by two hyperdiverse but relatively recent clades (Ostariophysi and Percomorpha). Remarkably, trait reconstructions (for both living and fossil taxa) suggest that all extant marine actinopterygians were derived from a freshwater ancestor, indicating a role for ancient extinction in explaining low marine richness. Finally, by analysing an entirely aquatic group, we are able to better sort among potential hypotheses for explaining the paradoxically low diversity of marine environments.
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Analysis of climate policy targets under uncertainty
Mort Webster et al.
Climatic Change, June 2012, Pages 569-583
Abstract:
Although policymaking in response to the climate change threat is essentially a challenge of risk management, most studies of the relation of emissions targets to desired climate outcomes are either deterministic or subject to a limited representation of the underlying uncertainties. Monte Carlo simulation, applied to the MIT Integrated Global System Model (an integrated economic and earth system model of intermediate complexity), is used to analyze the uncertain outcomes that flow from a set of century-scale emissions paths developed originally for a study by the U.S. Climate Change Science Program. The resulting uncertainty in temperature change and other impacts under these targets is used to illustrate three insights not obtainable from deterministic analyses: that the reduction of extreme temperature changes under emissions constraints is greater than the reduction in the median reduction; that the incremental gain from tighter constraints is not linear and depends on the target to be avoided; and that comparing median results across models can greatly understate the uncertainty in any single model.