Proc. Natl Acad. Sci. USA 105, 15258–15262 (2008)

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Even the most stringent of published climate mitigation measures may not avert dangerous climate change, shows a new analysis. An increase in global average surface temperature of 2 °C above pre-industrial values is generally considered to be the level of warming that could have serious impacts and, as such, is to be avoided.

Detlef van Vuuren of the Netherlands Environment Assessment Agency and colleagues assessed the possible impacts of various climate policies on twenty-first century warming using two reduced-complexity climate models and recently developed multigas mitigation scenarios. For policies that aim to stabilize atmospheric greenhouse gas concentrations at the lowest levels being proposed, there was an average warming of 1.9 °C, with a full range of 1.1–3.4 °C, above pre-industrial temperatures by 2100. They found that in the absence of climate policy, temperatures could increase 2.0–8.3 °C above pre-industrial values by the end of the century.

The authors stress that the most ambitious policies optimistically assume the global deployment of new technologies and policies over relatively short periods of time, yet still lead to considerable increases in global mean temperature. They warn that adaptation will be needed alongside mitigation to reduce the impacts of future warming.