Future warming will depend strongly on the cumulative CO2 emissions released through to the end of this century. A finite quota of cumulative CO2 emissions, no more than 1,200 Gt CO2, is needed from 2015 onwards to stabilize climate below a global average of 2 °C above pre-industrial conditions by 2100 with a likelihood of 66%. This corresponds to about 30 years at current emissions levels. However, during the past decade, emissions from fossil fuel combustion and cement production have increased substantially to 36.1 ± 1.8 Gt CO2 yr-1 in 2013, projected to reach 37.0 ± 1.8 Gt CO2 yr-1 in 2014 (ref. 3), 65% above their 1990 level. Staying within the 2 °C limit in a costeffective way will require strong mitigation action across all sectors, with greater effort needed the longer mitigation is delayed.