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The current nationally determined contributions, pledged by the countries under the Paris Agreement, are far from limiting climate change to below 2 ∘C temperature increase by the end of the century. The necessary ratcheting up of climate policy is projected to come with a wide array of additional benefits, in particular a reduction of today's 4.5 million annual premature deaths due to poor air quality. This paper therefore addresses the question how climate policy and air pollution–related health impacts interplay until 2050 by developing a comprehensive global modeling framework along the cause and effect chain of air pollution–induced social costs. We find that ratcheting up climate policy to a 2 ∘ compliant pathway results in welfare benefits through reduced air pollution that are larger than mitigation costs, even with avoided climate change damages neglected. The regional analysis demonstrates that the 2 ∘C pathway is therefore, from a social cost perspective, a "no-regret option" in the global aggregate, but in particular for China and India due to high air quality benefits, and also for developed regions due to net negative mitigation costs. Energy and resource exporting regions, on the other hand, face higher mitigation cost than benefits. Our analysis further shows that the result of higher health benefits than mitigation costs is robust across various air pollution control scenarios. However, although climate mitigation results in substantial air pollution emission reductions overall, we find significant remaining emissions in the transport and industry sectors even in a 2 ∘C world. We therefore call for further research in how to optimally exploit climate policy and air pollution control, deriving climate change mitigation pathways that maximize co-benefits. [ABSTRACT FROM AUTHOR]

This paper compares projections over the twenty-first century of SO, BC, and OC emissions from three technologically detailed, long-term integrated assessment models. The character of the projections and the response of emissions due to a comprehensive climate policy are discussed focusing on the sectoral level. In a continuation of historical experience, aerosol and precursor emissions are increasingly decoupled from carbon dioxide emissions over the twenty-first century due to a combination of emission controls and technology shifts over time. Implementation of a comprehensive climate policy further reduces emissions, although there is significant variation in this response by sector and by model: the response has many similarities between models for the energy transformation and transportation sectors, with more diversity in the response for the building and industrial sectors. Much of these differences can be traced to specific characteristics of reference case end-use and supply-side technology deployment and emissions control assumptions, which are detailed by sector. [ABSTRACT FROM AUTHOR]

Abstract During the negotiations on the Kyoto Protocol, Brazil proposed allocating the greenhouse gas emission reductions of Annex I Parties according to the relative effect of a country’s historical emissions on global temperature increase. This paper analyses the impact of scientific uncertainties and of different options in policy implementation (policy choices) on the contribution of countries’ historical emissions to indicators of historical responsibility for climate change. The influence of policy choices was found to be at least as large as the impact of the scientific uncertainties analysed here. Building on this, the paper then proceeds to explore the implications of applying the Brazilian Proposal as a climate regime for differentiation of future commitments on the global scale combined with an income threshold for participation of the non-Annex I regions. Under stringent climate targets, such a regime leads to high emission reductions for Annex I regions by 2050, in particular for Europe and Japan. The income threshold assumptions strongly affect the Annex I reductions, even more than the impact of another burden-sharing key. A variant of the Brazilian Proposal, allocating emission reductions on the basis of cumulative emissions since 1990, would lead to a more balanced distribution of emission reductions. [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]

In integrated assessments of climate change, greenhouse-gas emissions and climate change impacts provide the linkages between the world economy and the climate system. Key climatic processes operate at the scales of centuries. This requires highly aggregated models for portraying the dynamics of the economic system. An extended Ramsey-type optimal growth model is presented as the appropriate tool to be integrated with a reduced-form climate model in the ICLIPS integrated assessment. The eleven-region model of the world economy involves exogenous population and endogenous investment dynamics with productivity progress based on a technological diffusion model. World regions are linked via intertemporal trade flows of the composite consumption/investment good, capital mobility, and emission permit trading. Coupled with the ICLIPS Climate Model, the Aggregated Economic Model can determine corridors of permitted long-term carbon emission paths or, as primarily discussed in this paper, specific cost-effective emission trajectories. The sensitivity of mitigation costs to externally specified climate change/impact constraints and to assumptions about non-CO2 greenhouse-gas emissions is also discussed. [ABSTRACT FROM AUTHOR]