Copenhagen pledges don’t add up

The general consensus on last December’s UN climate change summit in Copenhagen seems to be that the event was a political farce, and failed to meet its original objectives. That may be so, but the bleary-eyed summit participants did at the very last moment succeed in cobbling together a document that contains a number of atmospheric carbon emissions-reduction pledges, with a stated aim of keeping global warming to below 2°C.

Do the pledges add up? Not according to a team of climatologists led by Joeri Rogelj and Malte Meinhausen at the Potsdam Institute for Climate Impact Research. Published tomorrow in the journal Nature, the scientists’ calculations show that if you take into account various loopholes in the global carbon emissions regime, the Copenhagen pledges are nowhere near enough to keep global warming to below 2°C.

Most UN member states will only meet their carbon emissions targets if there is a binding international agreement in place. There is no such treaty. Also, many states will likely be given extra emissions allowances as a result of land-use change, such as the planting of forests, and these will exceed actual emissions savings.

The Potsdam researchers estimate that annual carbon emissions will reach 47.9–53.6 gigatonnes of CO2 equivalent by 2020. This is between 10 and 20% higher than current levels, and more than the 40–44 gigatonnes required to restrict global warming to the desired two degree level. Even if emissions are halved by 2050, the scientists say there is still a 50% chance that global warming will exceed 2°C by the end of this century.

Further reading: Rogelj et al., “Copenhagen Accord pledges are paltry”, Nature 464, 1126 (2010)