Keeping warming within the 2 °C limit after Copenhagen

The object of the United Nations Climate Change Conference in Copenhagen in December 2009 was to reach an agreement on a new international legal architecture for addressing anthropogenic climate change post-2012. It failed in this endeavour, producing a political agreement in the form of the Copenhagen Accord. The Accord sets an ambitious goal of holding the increase in the global average surface temperature to below 2 °C. This paper describes 45 CO2-only mitigation scenarios that provide an indication of what would need to be done to stay within the 2 °C limit if the international climate negotiations stay on their current path. The results suggest that if developed countries adopt a combined target for 2020 of ≤20% below 1990 levels, global CO2 emissions would probably have to be reduced by ≥5%/yr, and possibly ≥10%/yr, post-2030 (after a decade transitional period) in order to keep warming to 2 °C. If aggressive abatement commitments for 2020 are not forthcoming from all the major emitting countries, the likelihood of warming being kept within the 2 °C limit is diminutive.