The internationally agreed goal of limiting global temperature rise to 2℃ is still achievable, but may be slipping out of reach, according to research published online in Nature Climate Change this week.

At the United Nations climate conference in Copenhagen in 2009, countries recognized that global average temperature rise should be limited to 2℃ above pre-industrial levels. To achieve this goal, decision-makers need to know how much global emissions need to be cut to keep temperatures below the 2℃ threshold, and whether it is technically and economically feasible to make such cuts.

In the most comprehensive assessment of these factors so far, which extends and confirms earlier work by the United Nations Environment Programme, Joeri Rogelj and colleagues re-analyse ‘feasible’ emission scenarios from the literature to see whether they limit warming to ‘safe’ levels. They find that to have a ‘likely’ (greater than 66%) chance of keeping temperature rise below 2℃, global emissions will probably need to peak before 2020, fall to about 44 gigatonnes of carbon dioxide equivalent in 2020, then keep falling — a pathway that will be very challenging to achieve.