Temperature increase of 21st century mitigation scenarios.

Estimates of 21st Century global-mean surface temperature increase have generally been based on scenarios that do not include climate policies. Newly developed multigas mitigation scenarios, based on a wide range of modeling approaches and socioeconomic assumptions, now allow the assessment of possible impacts of climate policies on projected warming ranges. This article assesses the atmospheric CO(2) concentrations, radiative forcing, and temperature increase for these new scenarios using two reduced-complexity climate models. These scenarios result in temperature increase of 0.5-4.4 degrees C over 1990 levels or 0.3-3.4 degrees C less than the no-policy cases. The range results from differences in the assumed stringency of climate policy and uncertainty in our understanding of the climate system. Notably, an average minimum warming of approximately 1.4 degrees C (with a full range of 0.5-2.8 degrees C) remains for even the most stringent stabilization scenarios analyzed here. This value is substantially above previously estimated committed warming based on climate system inertia alone. The results show that, although ambitious mitigation efforts can significantly reduce global warming, adaptation measures will be needed in addition to mitigation to reduce the impact of the residual warming.

Strengthening the Montreal protocol: does it cool down the greenhouse?

Strengthening of the Montreal Protocol is recently being negotiated in London in 1990 in order to achieve further reductions of the regulated CFCs and to include possibly more substances. In this article the implications of different policies with respect to control of ozone depleting substances for climate change are analysed, including the proposed substitution by HCFCs and HFCs, carbon tetrachloride and methylchloroform. A special halocarbon module was developed within the framework of RIVM's Integrated Model to Assess the Greenhouse Effect (IMAGE). IMAGE is a parameterized science based policy model and has been developed to give policy agencies a concise overview of the quantitative aspects of the greenhouse problem, to evaluate various policy options concerning climate change and to serve as a means of communication. It is concluded, from simulations with the halocarbon module, that it is of primary importance to achieve a further reduction of the regulated CFCs compared to the Montreal Protocol with compliance by as many countries as possible. From the perspective of the greenhouse effect the inclusion of longer lived halocarbons, such as carbon tetrachloride and HCFC-22 in the protocol comes second. The application of methylchloroform, halons and HCFCs and HFCs with lower global warming potentials (GWPs) than HCFC-22 contributes only marginally to the greenhouse effect in comparison with the much more important greenhouse gases carbon dioxide, methane, ozone and nitrous oxide. Especially if further growth of the total production of HCFCs after complete replacement of the present CFCs can be avoided by using these alternatives with a lower GWP, these substances could therefore be tolerated in a transition period, from the perspective of global warming.