The Massachusetts Institute of Technology (MIT) Integrated Global System Model is used to make probabilistic projections of climate change from 1861 to 2100. Since the model's first projections were published in 2003, substantial improvements have been made to the model, and improved estimates of the probability distributions of uncertain input parameters have become available. The new projections are considerably warmer than the 2003 projections; for example, the median surface warming in 2091-2100 is 5.18C compared to 2.48C in the earlier study. Many changes contribute to the stronger warming; among the more important ones are taking into account the cooling in the second half of the twentieth century due to volcanic eruptions for input parameter estimation and a more sophisticated method for projecting gross domestic product (GDP) growth, which eliminated many low-emission scenarios.However, if recently published data, suggesting stronger twentieth-century ocean warming, are used to determine the input climate parameters, the median projected warming at the end of the twenty-first century is only 4.18C. Nevertheless, all ensembles of the simulations discussed here produce a much smaller probability of warming less than 2.48C than implied by the lower bound of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) projected likely range for the A1FI scenario, which has forcing very similar to the median projection in this study. The probability distribution for the surface warming produced by this analysis is more symmetric than the distribution assumed by the IPCC because of a different feedback between the

A discussion of the opportunities and challenges involved mitigating greenhouse gas emissions from passenger travel. In the nineteenth century, horse transportation consumed vast amounts of land for hay production, and the intense traffic and ankle-deep manure created miserable living conditions in urban centers. The introduction of the horseless carriage solved many of these problems but has created others. Today another revolution in transportation seems overdue. Transportation consumes two-thirds of the world's petroleum and has become the largest contributor to global environmental change. Most of this increase in scale can be attributed to the strong desire for personal mobility that comes with economic growth. InTransportation in a Climate-Constrained World, the authors present the first integrated assessment of the factors affecting greenhouse gas (GHG) emissions from passenger transportation. They examine such topics as past and future travel demand; the influence of personal and business choices on passenger travel's climate impact; technologies and alternative fuels that may become available to mitigate GHG emissions from passenger transport; and policies that would promote a more sustainable transportation system. And most important, taking into account all of these options are taken together, they consider how to achieve a sustainable transportation system in the next thirty to fifty years.

The Kyoto Protocol allows reductions in emissions of several 'greenhouse' gases to be credited against a CO 2-equivalent emissions limit, calculated using 'global warming potential' indices for each gas. Using an integrated global-systems model, it is shown that a multi-gas control strategy could greatly reduce the costs of fulfilling the Kyoto Protocol compared with a CO 2-only strategy. Extending the Kyoto Protocol to 2100 without more severe emissions reductions shows little difference between the two strategies in climate and ecosystem effects. Under a more stringent emissions policy, the use of global warming potentials as applied in the Kyoto Protocol leads to considerably more mitigation of climate change for multi-gas strategies than for the-supposedly equivalent-CO 2-only control, thus emphasizing the limits of global warming potentials as a tool for political decisions. Many trace atmospheric constituents affect the radiative budget of the atmosphere. The Kyoto Protocol includes carbon dioxide (CO 2), methane (CH 4), nitrous oxide (N 2 O), perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), and sulphur hexafluoride (SF 6) (

Change combines cutting-edge scientific research with independent policy analysis to provide a solid foundation for the public and private decisions needed to mitigate and adapt to unavoidable global environmental changes. Being data-driven, the Joint Program uses extensive Earth system and economic data and models to produce quantitative analysis and predictions of the risks of climate change and the challenges of limiting human influence on the environmentessential knowledge for the international dialogue toward a global response to climate change.To this end, the Joint Program brings together an interdisciplinary group from two established MIT research centers: the Center for Global Change Science (CGCS) and the Center for Energy and Environmental Policy Research (CEEPR). These two centers-along with collaborators from the Marine Biology Laboratory (MBL) at Woods Hole and short-and long-term visitors-provide the united vision needed to solve global challenges.At the heart of much of the program's work lies MIT's Integrated Global System Model. Through this integrated model, the program seeks to discover new interactions among natural and human climate system components; objectively assess uncertainty in economic and climate projections; critically and quantitatively analyze environmental management and policy proposals; understand complex connections among the many forces that will shape our future; and improve methods to model, monitor and verify greenhouse gas emissions and climatic impacts.This reprint is intended to communicate research results and improve public understanding of global environment and energy challenges, thereby contributing to informed debate about climate change and the economic and social implications of policy alternatives. Given uncertainty in long-term carbon reduction goals, how much non-carbon generation should be developed in the near-term? This research investigates the optimal balance between the risk of overinvesting in non-carbon sources that are ultimately not needed and the risk of underinvesting in non-carbon sources and subsequently needing to reduce carbon emissions dramatically. We employ a novel framework that incorporates a computable general equilibrium (CGE) model of the U.S. into a two-stage stochastic approximate dynamic program (ADP) focused on decisions in the electric power sector. We solve the model using an ADP algorithm that is computationally tractable while exploring the decisions and sampling the uncertain carbon limits from continuous distributions.The results of the model demonstrate that an optimal hedge is in the direction of more non-carbon investment in the near-term, in the range of 20-30% of new generation. We also demonstrate that the optimal share of non-carbon generation is increasing in the variance of the uncertainty about the long-term carbon targets, and that with greater uncertainty in the future policy regime, a balanced portfolio of non-carbon, natural gas, and coal generation is desirable.