No Existing Climate Policy Prevents Further Warming

No Existing Climate Policy Prevents Further Warming

Proceedings National Academy of Sciences
October 7, 2008  vol. 105  no. 40

Temperature increase of 21st century mitigation scenarios
D. P. Van Vuurena, et al

ABSTRACT

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 CO2 concentrations, radiative forcing, and temperature increase for these new scenarios using two reduced-complexity climate models. These scenarios result in temperatureincrease of 0.5- 4.4°C over 1990 levels or 0.3-3.4°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 1.4C (with a range of 0.5-2.8C) 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.

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