Mr. Castles and Mr. Henderson have criticized the Special Report on Emissions Scenarios (SRES) and other aspects of IPCC assessments. It is claimed that the methodology is “technically unsound” because market exchange rates (MER) are used instead of purchasing power parities (PPP) and that the scenarios themselves are flawed because the GDP growth in the developing regions is too high. The response is: The IPCC SRES reviews existing literature, most of which is MER based, including that from the World Bank, IEA and USDoE. Scenarios of GDP growth are typically expressed as MER (the preferred measure for GDP growth, as opposed to PPP which is a preferred measure for assessing differences in economic welfare). IPCC scenarios did include PPP-based scenarios, which Mr. Castles and Mr. Henderson have conveniently ignored. Contrary to what Mr. Castles and Mr. Henderson claim, IPCC scenarios are consistent with historical data, including that from 1990 to 2000, and with the most recent near term (up to 2020) projections of other agencies. Long-term emissions are based on multiple, interdependent driving forces, and not just economic growth. Mr. Castles and Mr. Henderson need to look beyond GDP. The IPCC scenarios provided information for only four world regions, and not for specific countries. Mr. Castles' and Mr. Henderson's critique is not of IPCC scenarios but of ongoing unpublished work in progress that is not part of SRES. We therefore show that Mr. Castles and Mr. Henderson have focused on constructing a “problem” that does not exist. SRES scenarios are sound and the IPCC has responded seriously and conscientiously. We detail our response below in nine sections. After an introduction (Section 1), we outline the SRES methodology for measuring economic output (Section 2). Section 3 compares SRES to long-historical economic development and provides five responses to the critics. Section 4 addresses the issue of country-level economic projections even if not part of SRES. Sections 5, 6 and 7 validate the SRES scenarios by comparing them with recent trends for economic and CO2 emission growth, as well as more recent scenarios available in the literature. Section 8 refutes the argument that lower economic growth in developing countries would lower GHG emissions correspondingly. Section 9 concludes.
This paper provides an overview of new emission mitigation scenarios that lead to stabilization of atmospheric CO 2 concentrations, presented in this Special Issue. All of these scenarios use as their baselines the new IPCC scenarios published in the IPCC Special Report on Emission Scenarios (SRES), which quantify a wide range of future worlds. This means the new mitigation and stabilization scenarios are based on a range of future development paths that have fundamental implications for future emissions reduction strategies. Here, we refer to these new scenarios as "Post-SRES" mitigation scenarios. In addition to providing an overview of these new scenarios, this paper also assesses the implications that emerge from a range of alternative development baselines for technology and policy measures for reducing future emissions and stabilizing atmospheric CO 2 concentrations. Nine modeling teams have participated in this joint effort to quantify a wide range of mitigation and stabilization scenarios. The nine modeling approaches involve different methodologies, data, regional aggregations and other salient characteristics. This pluralism of approaches and alternative baselines serves to cover some of the uncertainties embedded across a range of different mitigation and stabilization strategies. At the same time, several common trends and characteristics can be observed across the set of Post-SRES scenarios. First, the different baseline "worlds" described in the SRES scenarios require different technology/policy measures to stabilize atmospheric CO 2 concentrations at the same level. Second, no one single measure will be sufficient for the timely development, adoption and diffusion of mitigation options to achieve stabilization. Third, the level of technology/policy measures in the beginning of the 21st century that would be needed to achieve stabilization would be significantly affected by the choice of development path over next one hundred years. And finally, several "robust policy options" across the different worlds are identified for achieving stabilizations.
This article presents a set of 30 greenhouse gas (GHG) emissions scenarios developed by six modeling teams. The scenarios describe trajectories up to 2100 by four world regions. Today the distribution of both income and GHG emissions is very unbalanced between various world regions. Furthermore, the relative importance of individual gases and sources of emission differ from region to region. A feature shared by all scenarios is higher growth rates of population, income and GHG emissions in the current developing countries (DEV) than in industrialized countries (IND). Today the DEV regions account for about 46% of all emissions, but by 2100 no less they contribute 67-76% of the global total. By that same year the total income generated in the DEV regions reaches 58-71 % from only 16% in 1990. As a result of these two developments, GHG emissions per unit of income converge over time. Carbon emitted from fossil fuel use remains the primary source of GHG emissions over the next century: by 2100 CO, makes up 70 to 80% of total GHG emissions. The role of sulfur warrants special attention. Contrary to many earlier studies, all scenarios presented here assum e that sulfur emissions are controlled in all regions sooner or later. and to various degrees. As sulfur plays a role in cooling of the atmosphere through formation of sulfate aerosols. a local effect, this abatement constitutes a relative local warming effect. The decrease of sulfur emissions is already observed the IND regions. and is expected also in ASIA after an initial rise.
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