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Abstract:

Some recent high-profile publications have suggested that immediately reducing emissions of methane, black carbon and other short-lived climate pollutants (SLCPs) may contribute substantially towards the goal of limiting global warming to 2C above pre-industrial levels. Although this literature acknowledges that action on long-lived climate pollutants (LLCPs) such as CO 2 is also required, it is not always appreciated that SLCP emissions in any given decade only have a significant impact on peak temperature under circumstances in which CO 2 emissions are falling. Immediate action on SLCPs might potentially 'buy time' for adaptation by reducing near-term warming; however early SLCP reductions, compared with reductions in a future decade, do not buy time to delay reductions in CO 2. © 2013 Macmillan Publishers Limited. All rights reserved.

Abstract:

The ratio of warming to cumulative emissions of carbon dioxide has been shown to be approximately independent of time and emissions scenarios and directly relates emissions to temperature. It is therefore a potentially important tool for climate mitigation policy. The transient climate response to cumulative carbon emissions (TCRE), defined as the ratio of global-mean warming to cumulative emissions at CO2 doubling in a 1%yr-1 CO2 increase experiment, ranges from 0.8 to 2.4K EgC-1 in 15 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5)-a somewhat broader range than that found in a previous generation of carbon-climate models. Using newly available simulations and a new observational temperature dataset to 2010, TCREis estimated from observations by dividing an observationally constrained estimate of CO2-attributable warming by an estimate of cumulative carbon emissions to date, yielding an observationally constrained 5%-95% range of 0.7-2.0K EgC-1. © 2013 American Meteorological Society.