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Abstract As carbon dioxide and other greenhouse gases accumulate in the atmosphere and contribute to rising global temperatures, it is important to examine how derivative changes in climate may affect natural and managed ecosystems. In this series of papers, we study the impacts of climate change on agriculture, water resources and natural ecosystems in the conterminous United States using twelve scenarios derived from General Circulation Model (GCM) projections to drive biophysical impact models. These scenarios are described in this paper. The scenarios are first put into the context of recent work on climate-change by the IPCC for the 21st century and span two levels of global-mean temperature change and three sets of spatial patterns of change derived from GCM results. In addition, the effect of either the presence or absence of a CO2 fertilization effect on vegetation is examined by using two levels of atmospheric CO2 concentration as a proxy variable. Results from three GCM experiments were used to produce different regional patterns of climate change. The three regional patterns for the conterminous United States range from: an increase in temperature above the global-mean level along with a significant decline in precipitation; temperature increases in line with the global-mean with an average increase in precipitation; and, with a sulfate aerosol effect added to in the same model, temperature increases that are lower than the global-mean. The resulting set of scenarios span a wide range of potential climate changes and allows examination of the relative importance of global-mean temperature change, regional climate patterns, aerosol cooling, and CO2 fertilization effects. [ABSTRACT FROM AUTHOR]

Abstract As carbon dioxide and other greenhouse gasses accumulate in the atmosphere and contribute to rising global temperatures, it is important to examine how a changing climate may affect natural and managed ecosystems. In this series of papers, we study the impacts of climate change on agriculture, water resources and natural ecosystems in the General Circulation Model (GCM)-derived climate change projections, described in Part 1, to drive the crop production and water resource models EPIC (Erosion Productivity Impact Calculator) and HUMUS (Hydrologic Unit Model of the United States). These models are described and validated in this paper using historical crop yields and streamflow data in the conterminous United States in order to establish their ability to accurately simulate historical crop and water conditions and their capability to simulate crop and water response to the extreme climate conditions predicted by GCMs. EPIC simulated grain and forage crop yields are compared with historical crop yields from the US Department of Agriculture (USDA) and with yields from agricultural experiments. EPIC crop yields correspond more closely with USDA historical county yields than with the higher yields from intensively managed agricultural experiments. The HUMUS model was validated by comparing the simulated water yield from each hydrologic basin with estimates of natural streamflow made by the US Geological Survey. This comparison shows that the model is able to reproduce significant observed relationships and capture major trends in water resources timing and distribution across the country. [ABSTRACT FROM AUTHOR]

This paper examines the subject of hydrologic variability and its changes in two separate integrations of a coupled ocean-atmosphere general circulation model developed at the Geophysical Fluid Dynamics Laboratory/NOAA assuming a 1% per year increase to a doubling and quadrupling of CO, respectively. Changes in time mean state and variability of precipitation, runoff and soil moisture are evaluated using monthly and seasonal mean data derived from these integrations. Various statistical tests are then performed on the resulting time mean and variability changes. The patterns of hydrologic change for these three quantities are similar to those obtained from previous studies. In northern middle to higher latitudes for the time means, the changes include increases in monthly mean precipitation, increases in monthly mean runoff during the fall, winter and spring seasons and decreases of monthly mean soil moisture during summer. Many of these changes are found to be statistically significant at the 5% significance level for both the time mean and variability especially for the results where CO is quadrupled such as monthly mean precipitation. Significant changes also include increases of runoff variability during spring, winter and spring and increases of soil moisture variability during the summer season. These results support statements made in previous IPCC reports that increasing greenhouse gases can lead to more severe and frequent floods and droughts depending upon season and latitude. This study also indicates that the approaches to equilibrium of these two integrations, and the resulting hydrologic changes, take place over time scales of hundreds of years in agreement with several previous investigations. [ABSTRACT FROM AUTHOR]

The economics of CO2 capture and storage in relation to the possibility of leakage of CO2 from geological reservoirs once this greenhouse gas has been stored artificially underground will be among the main determinants of whether CCS can significantly contribute to a deep cut in global CO2 emissions. This paper presents an analysis of the economic and climatic implications of the large-scale use of CCS for reaching a stringent climate change control target, when geological CO2 leakage is accounted for. The natural scientific uncertainties regarding the rates of possible leakage of CO2 from geological reservoirs are likely to remain large for a long time to come. We present a qualitative description, a concise analytical inspection, as well as a more detailed integrated assessment model, proffering insight into the economics of geological CO2 storage and leakage. Our model represents three main CO2 emission reduction options: energy savings, a carbon to non-carbon energy transition and the use of CCS. We find CCS to remain a valuable option even with CO2 leakage of a few percent per year, well above the maximum seepage rates that we think are likely from a geo-scientific point of view. [ABSTRACT FROM AUTHOR]

This paper assesses regional abatement action and costs for two scenarios in which atmospheric greenhouse gas concentrations stabilise at 450 and 550 ppm CO2-equivalent. It evaluates two allocation schemes: Multi-Stage and Contraction & Convergence. It was found that abatement costs as percentages of GDP vary significantly by region, with high costs for the Middle East and the former Soviet Union, medium costs for the OECD regions and low costs or even gains for (other) developing regions. In addition to the abatement costs they incur, fossil-fuel-exporting regions are also likely to be affected by losses of coal and oil exports while the former Soviet Union and South America could experience increased bio-energy exports. Especially in the former Soviet Union and Asia, non-CO2 abatement options are important in the short term in reducing their emissions. Carbon capture and storage, energy efficiency improvements, bio-energy use and the use of renewables dominate reductions in the long term in all regions. It was found that the regional costs are influenced more by the assumed stabilisation level and baseline scenario than by the allocation regimes explored or the assumptions for different technologies. [ABSTRACT FROM AUTHOR]

The economic benefits of a multi-gas approach to climate change mitigation are clear. However, there is still a debate on how to make the trade-off between different greenhouse gases (GHGs). The trade-off debate has mainly centered on the use of Global Warming Potentials (GWPs), governing the trade-off under the Kyoto Protocol, with results showing that the cost-effective valuation of short-lived GHGs, like methane (CH4), should be lower than its current GWP value if the ultimate aim is to stabilize the anthropogenic temperature change. However, contrary to this, there have also been proposals that early mitigation mainly should be targeted on short-lived GHGs. In this paper we analyze the cost-effective trade-off between a short-lived GHG, CH4, and a long-lived GHG, carbon dioxide (CO2), when a temperature target is to be met, taking into consideration the current uncertainty of the climate sensitivity as well as the likelihood that this will be reduced in the future. The analysis is carried out using an integrated climate and economic model (MiMiC) and the results from this model are explored and explained using a simplified analytical economic model. The main finding is that the introduction of uncertainty and learning about the climate sensitivity increases the near-term cost-effective valuation of CH4 relative to CO2. The larger the uncertainty span, the higher the valuation of the shortlived gas. For an uncertainty span of ±1°C around an expected climate sensitivity of 3°C, CH4 is cost-effectively valued 6.8 times as high as CO2 in year 2005. This is almost twice as high as the valuation in a deterministic case, but still significantly lower than its GWP100 value. [ABSTRACT FROM AUTHOR]

This paper examines different concepts of a 'warming commitment' which is often used in various ways to describe or imply that a certain level of warming is irrevocably committed to over time frames such as the next 50 to 100 years, or longer. We review and quantify four different concepts, namely (1) a 'constant emission warming commitment', (2) a 'present forcing warming commitment', (3) a 'zero emission (geophysical) warming commitment' and (4) a 'feasible scenario warming commitment'. While a 'feasible scenario warming commitment' is probably the most relevant one for policy making, it depends centrally on key assumptions as to the technical, economic and political feasibility of future greenhouse gas emission reductions. This issue is of direct policy relevance when one considers that the 2002 global mean temperatures were 0.8 ± 0.2°C above the pre-industrial (1861-1890) mean and the European Union has a stated goal of limiting warming to 2°C above the pre-industrial mean: What is the risk that we are committed to overshoot 2°C? Using a simple climate model (MAGICC) for probabilistic computations based on the conventional IPCC uncertainty range for climate sensitivity (1.5 to 4.5 °C), we found that (1) a constant emission scenario is virtually certain to overshoot 2°C with a central estimate of 2.0°C by 2100 (4.2°C by 2400). (2) For the present radiative forcing levels it seems unlikely that 2°C are overshoot. (central warming estimate 1.1 °C by 2100 and 1.2°C by 2400 with ∼10% probability of overshooting 2°C). However, the risk of overshooting is increasing rapidly if radiative forcing is stabilized much above 400 ppm CO2 equivalence (1.95 W/m²) in the long-term. (3) From a geophysical point of view, if all human-induced emissions were ceased tomorrow, it seems 'exceptionally unlikely' that 2°C will be overshoot (central estimate: 0.7°C by 2100; 0.4°C by 2400). (4) Assuming future emissions according to the lower end of published mitigation scenarios (350 ppm CO2eq to 450 ppm CO2eq) provides the central temperature projections are 1.5 to 2.1 °C by 2100 (1.5 to 2.0°C by 2400) with a risk of overshooting 2°C between 10 and 50% by 2100 and 1-32% in equilibrium. Furthermore, we quantify the 'avoidable warming' to be 0.16-0.26°C for every 100 GtC of avoided CO2 emissions - based on a range of published mitigation scenarios. [ABSTRACT FROM AUTHOR]

The greenhouse gas emissions scenarios published by the IPCC in the Special Report on Emission Scenarios (SRES) continue to serve as a primary basis for assessing future climate change and possible response strategies. These scenarios were developed between 1996 and 1999 and sufficient time has now passed to make it worth examining their consistency with more recent data and projections. The comparison performed in this paper includes population, GDP, energy use, and emissions of CO2, non-CO2 gases and sulfur. We find the SRES scenarios to be largely consistent with historical data for the 1990-2000 period and with recent projections. Exceptions to this general observation include (1) in the long-term, relatively high population growth assumptions in some regions, particularly in the A2 scenario; (2) in the medium-term, relatively high economic growth assumptions in the LAM (Latin America, Africa and Middle East) region in the A1 scenario; (3) in the short-term, CO2 emissions projections in Al that are somewhat higher than the range of current scenarios; and (4) substantially higher sulfur emissions in some scenarios than in historical data and recent projections. In conclusion, given the relatively small inconsistencies for use as global scenarios there seems to be no immediate need for a large-scale IPCC-led update of the SRES scenarios that is solely based on the SRES scenario performance vis-a-vis data for the 1990-2000 period and/or more recent projections. Based on reported findings, individual research teams could make, and in some cases already have made, useful updates of the scenarios. [ABSTRACT FROM AUTHOR]

The Paris Climate Agreement sets out an aggressive goal of limiting global average warming to well below 2 °C. As a first step, virtually all countries have put forth greenhouse gas emission reduction pledges in the form of nationally determined contributions, or NDCs, for the 2030 timeframe. Our analysis looks beyond the NDCs to explore potential post-2030 regional emissions reduction participation and ambition. For each scenario, we examine the implications for global emissions and long-term temperature. We then evaluate the regional consequences for energy systems and ensuing costs. We conclude by reflecting on the additional global abatement costs of tightening temperature goals. Overall, this study provides a multidimensional characterization of the scale of regional effort supporting climate outcomes, details important to decision-makers as they consider mid-century emissions targets, and long-run climate objectives. [ABSTRACT FROM AUTHOR]

China has embarked on an ambitious pathway for establishing a national carbon market in the next 5-10 years. In this study, we analyze the distributional aspects of a Chinese emissions-trading scheme from ethical, economic, and stated-preference perspectives. We focus on the role of emissions permit allocation and first show how specific equity principles can be incorporated into the design of potential allocation schemes. We then assess the economic and distributional impacts of those allocation schemes using a computable general equilibrium model with regional detail for the Chinese economy. Finally, we conduct a survey among Chinese climate-policy experts on the basis of the simulated model impacts. The survey participants indicate a relative preference for allocation schemes that put less emissions-reduction burden on the western provinces, a medium burden on the central provinces, and a high burden on the eastern provinces. Most participants show strong support for allocating emissions permits based on consumption-based emissions responsibilities. [ABSTRACT FROM AUTHOR]

While it has been recognized that actions reducing greenhouse gas (GHG) emissions can have significant positive and negative impacts on human health through reductions in ambient fine particulate matter (PM) concentrations, these impacts are rarely taken into account when analyzing specific policies. This study presents a new framework for estimating the change in health outcomes resulting from implementation of specific carbon dioxide (CO) reduction activities, allowing comparison of different sectors and options for climate mitigation activities. Our estimates suggest that in the year 2020, the reductions in adverse health outcomes from lessened exposure to PM would yield economic benefits in the range of $6 to $30 billion (in 2008 USD), depending on the specific activity. This equates to between $40 and $198 per metric ton of CO in health benefits. Specific climate interventions will vary in the health co-benefits they provide as well as in potential harms that may result from their implementation. Rigorous assessment of these health impacts is essential for guiding policy decisions as efforts to reduce GHG emissions increase in scope and intensity. [ABSTRACT FROM AUTHOR]

Here we present two new metrics used for comparing climate impacts of emissions of different climate forcers: the Global Sea level rise Potential (GSP) and the Integrated Global Sea level rise Potential (IGSP). The GSP represents the Sea Level Rise (SLR) at a given time horizon due to an emission pulse of a forcer; the IGSP is similar but represents the time integrated SLR up to a given point in time. The GSP and IGSP are presented relative to the SLR caused by a comparable emission pulse of carbon dioxide. The metrics are assessed using an Upwelling-Diffusion Energy Balance Model (UDEBM). We focus primarily on the thermosteric part of SLR, denoted GSP. All of the examined climate forcers - even black carbon, a very Short-Lived Climate Forcer (SLCF) - have considerable influence on the thermosteric SLR on the century time scale. For a given time horizon and forcer, GSP lies in between the corresponding metric values obtained using Global Warming Potential (GWP) and Global Temperature change Potential (GTP), whereas IGSP ends up in the opposite end to GTP in the spectrum of compared metrics. GSP and IGSP are more sensitive for SLCFs than for the long-lived Greenhouse Gases (GHGs) to changes in the parameterization of the model (under the time horizons considered here). We also use a Semi-Empirical (SE) model to estimate the full SLR, and corresponding GSP and IGSP, as alternatives to the thermosteric approach. For SLCFs, GSP is greater than GSP for all time horizons considered, while the opposite holds for long-lived GHGs such as SF. [ABSTRACT FROM AUTHOR]

Minimizing the future impacts of climate change requires reducing the greenhouse gas (GHG) load in the atmosphere. Anthropogenic emissions include many types of GHG's as well as particulates such as black carbon and sulfate aerosols, each of which has a different effect on the atmosphere, and a different atmospheric lifetime. Several recent studies have advocated for the importance of short timescales when comparing the climate impact of different climate pollutants, placing a high relative value on short-lived pollutants, such as methane (CH) and black carbon (BC) versus carbon dioxide (CO). These studies have generated confusion over how to value changes in temperature that occur over short versus long timescales. We show the temperature changes that result from exchanging CO for CH using a variety of commonly suggested metrics to illustrate the trade-offs involved in potential carbon trading mechanisms that place a high value on CH emissions. Reducing CH emissions today would lead to a climate cooling of approximately ~0.5 °C, but this value will not change greatly if we delay reducing CH emissions by years or decades. This is not true for CO, for which the climate is influenced by cumulative emissions. Any delay in reducing CO emissions is likely to lead to higher cumulative emissions, and more warming. The exact warming resulting from this delay depends on the trajectory of future CO emissions but using one business-as usual-projection we estimate an increase of 3/4 °C for every 15-year delay in CO mitigation. Overvaluing the influence of CH emissions on climate could easily result in our 'locking' the earth into a warmer temperature trajectory, one that is temporarily masked by the short-term cooling effects of the CH reductions, but then persists for many generations. [ABSTRACT FROM AUTHOR]

Perennial crops are among the most valuable of California's diverse agricultural products. They are also potentially the most influenced by information on future climate, since individual plants are commonly grown for more than 30 years. This study evaluated the impacts of future climate changes on the 20 most valuable perennial crops in California, using a combination of statistical crop models and downscaled climate model projections. County records on crop harvests and weather from 1980 to 2005 were used to evaluate the influence of weather on yields, with a series of cross-validation and sensitivity tests used to evaluate the robustness of perceived effects. In the end, only four models appear to have a clear weather response based on historical data, with another four presenting significant but less robust relationships. Projecting impacts of climate trends to 2050 using historical relationships reveals that cherries are the only crop unambiguously threatened by warming, with no crops clearly benefiting from warming. Another robust result is that almond yields will be harmed by winter warming, although this effect may be counteracted by beneficial warming in spring and summer. Overall, the study has advanced understanding of climate impacts on California agriculture and has highlighted the importance of measuring and tracking uncertainties due to the difficulty of uncovering crop-climate relationships. [ABSTRACT FROM AUTHOR]

To clarify the link between existing infrastructure legacy and the 2°C target, we extend the work of Davis et al. (Science 329:1330-1333, ) by introducing non-CO greenhouse gases and the inertia in transportation-needs drivers. We conclude that climate policies able to maintain climate change below 2°C cannot disregard existing infrastructure. [ABSTRACT FROM AUTHOR]

The United Nations Framework Convention on Climate Change (UNFCCC ) calls for stabilization of atmospheric greenhouse gas (GHG) concentrations at a level that would prevent dangerous anthropogenic interference with the climate system. We use three global energy system models to investigate the technological and economic attainability of meeting CO2 concentration targets below current levels. Our scenario studies reveal that while energy portfolios from a broad range of energy technologies are needed to attain low concentrations, negative emission technologies—e.g., biomass energy with carbon capture and storage (BECCS)—significantly enhances the possibility to meet low concentration targets (at around 350 ppm CO2). [ABSTRACT FROM AUTHOR]

The author reflects on the need of the Intergovernmental Panel on Climate Change (IPCC) to develop new emissions metrics to calculate CO2-equivalent emissions. He comments on IPCC's use of the Global Warming Potentials (GWP) as an established method for comparing the climate effects of various greenhouse gases. He cites several alternatives to GWP including the "price ratios" suggested by Manne and Richels and the Temperature Proxy Index (TEMP) proposed by Tanaka and colleagues.

The integrated assessment models (IAMs) that economists use to analyze the expected costs and benefits of climate policies frequently suggest that the “optimal” policy is to go slowly and to do relatively little in the near term to reduce greenhouse gas emissions. We trace this finding to the contestable assumptions and limitations of IAMs. For example, they typically discount future impacts from climate change at relatively high rates. This practice may be appropriate for short-term financial decisions but its extension to intergenerational environmental issues rests on several empirically and philosophically controversial hypotheses. IAMs also assign monetary values to the benefits of climate mitigation on the basis of incomplete information and sometimes speculative judgments concerning the monetary worth of human lives and ecosystems, while downplaying scientific uncertainty about the extent of expected damages. In addition, IAMs may exaggerate mitigation costs by failing to reflect the socially determined, path-dependent nature of technical change and ignoring the potential savings from reduced energy utilization and other opportunities for innovation. A better approach to climate policy, drawing on recent research on the economics of uncertainty, would reframe the problem as buying insurance against catastrophic, low-probability events. Policy decisions should be based on a judgment concerning the maximum tolerable increase in temperature and/or carbon dioxide levels given the state of scientific understanding. The appropriate role for economists would then be to determine the least-cost global strategy to achieve that target. While this remains a demanding and complex problem, it is far more tractable and epistemically defensible than the cost-benefit comparisons attempted by most IAMs. [ABSTRACT FROM AUTHOR]

Several economic reviews demonstrate the substantial costs related to climate change and consequently call for early action. These reviews, however, have been limited to measuring ‘objective’ risks and expected material damage related to climate change. The ‘subjective’ perceived risk of climate change and society’s willingness to pay (WTP) to avoid these risks are expected to provide an important additional motivation for direct action. We investigate whether and why air travel passengers—an increasingly important source of greenhouse gas emissions—are supportive of measures that increase the cost of their travel based on the polluter pays principle and compensate the damage caused by their flight. Compared to the results of the few previous studies that have elicited WTP estimates for climate policy more generally, our results appear to be at the lower end of the scale, while a comparison to estimates of the social cost of carbon shows that the average WTP estimate in this study is close to the estimated marginal damage cost. Although significant differences are found between travellers from Europe, North America, Asia and the rest of the world, we show that there exists a substantial demand for climate change mitigation action. The positive risk premium over and above the expected property damage cost assessments should be accounted for more explicitly in economic reviews as it will add to the burden of proof of direct action. Measurements of passenger WTP will help policy makers to design effective financial instruments aimed at discouraging climate-unfriendly travel activities as well as to generate funds for the measures directed at climate change mitigation and adaptation. Based on stated WTP by travellers to offset their greenhouse gas emissions, funds in the order of magnitude of €23 billion could be generated annually to finance climate change mitigation activities. [ABSTRACT FROM AUTHOR]

Rises in surface air temperature (SAT) in response to increasing concentrations of greenhouse gases (GHGs) are expected to he amplified in northern high latitudes, with warming most pronounced over the Arctic Ocean owing to the loss of sea ice. Observations document recent warming, but an enhanced Arctic Ocean signal is not readily evident. This disparity, combined with varying model projections of SAT change, and large variability in observed SAT over the 20th century, may lead one to question the concept of Arctic amplification. Disparity is greatly reduced, however, if one compares observed trajectories to near-future simulations (2010-2029), rather than to the doubled-CO2 or late 21st century conditions that are typically cited. These near-future simulations document a preconditioning phase of Arctic amplification, characterized by the initial retreat and thinning of sea ice, with imprints of low-frequency variability. Observations show these same basic features, but with SATs over the Arctic Ocean still largely constrained by the insulating effects of the ice cover and thermal inertia of the upper ocean. Given the general consistency with model projections, we are likely near the threshold when absorption of solar radiation during summer limits ice growth the following autumn and winter, initiating a feedback leading to a substantial increase in Arctic Ocean SATs. [ABSTRACT FROM AUTHOR]

So far, climate change mitigation pathways focus mostly on CO2 and a limited number of climate targets. Comprehensive studies of emission implications have been hindered by the absence of a flexible method to generate multi-gas emissions pathways, user-definable in shape and the climate target. The presented method 'Equal Quantile Walk' (EQW) is intended to fill this gap, building upon and complementing existing multi-gas emission scenarios. The EQW method generates new mitigation pathways by 'walking along equal quantile paths' of the emission distributions derived from existing multi-gas IPCC baseline and stabilization scenarios. Considered emissions include those of CO2 and all other major radiative forcing agents (greenhouse gases, ozone precursors and sulphur aerosols). Sample EQW pathways are derived for stabilization at 350 ppm to 750 ppm CO2 concentrations and compared to WRE profiles. Furthermore, the ability of the method to analyze emission implications in a probabilistic multi-gas framework is demonstrated. The probability of overshooting a 2°C climate target is derived by using different sets of EQW radiative forcing peaking pathways. If the probability shall not be increased above 30%, it seems necessary to peak CO2 equivalence concentrations around 475 ppm and return to lower levels after peaking (below 400 ppm). EQW emissions pathways can be applied in studies relating to Article 2 of the UNFCCC, for the analysis of climate impacts, adaptation and emission control implications associated with certain climate targets. See www.simcap.org for EQW-software and data. [ABSTRACT FROM AUTHOR]

Methane is, after carbon dioxide, the most important anthropogenic greenhouse gas. Governments plan to abate methane emissions. A crude set of estimates of reduction costs is included in FUND, an integrated assessment model of climate change. In a cost-benefit analysis, methane emission reduction is found to be instrumental in controlling the optimal rate of climate change. In a cost-effectiveness analysis, methane emission reduction largely replaces carbon dioxide emission reduction. Methane emission reduction reinforces the case for international cooperation in climate policy, but complicates the efficient allocation of emission reduction efforts. Methane emission reduction at the short run does not help to achieve the ultimate objective of the Framework Convention on Climate Change. [ABSTRACT FROM AUTHOR]

Presents a study which estimated the greenhouse externality to childbearing from the increased carbon dioxide abatement costs. Nature of the greenhouse externality to childbearing; Definition of externalities to childbearing; Discussion of results.

Focuses on the greenhouse gas abatement cost and benefit projections of emission reduction through 2100. Effect of the emission of greenhouse gases into the atmosphere; Estimated damages caused by carbon dioxide doubling; Analysis of abatement costs.