Is it possible to limit global warming to no more than 1.5°C? A letter

This study explores the feasibility of limiting increases in global temperature to 1.5°C above pre-industrial levels. A probabilistic simple climate model is used to identify emissions paths that offer at least a 50% chance of achieving this goal. We conclude that it is more likely than not that warming would exceed 1.5°C, at least temporarily, under plausible mitigation scenarios. We have identified three criteria of emissions paths that could meet the 1.5°C goal with a temporary overshoot of no more than 50 years: early and strong reductions in emissions, with global emissions peaking in 2015 and falling to at most 44-48 GtCO 2e in 2020; rapid reductions in annual global emissions after 2020 (of at least 3-4% per year); very low annual global emissions by 2100 (less than 2-4 GtCO 2e) and falling to zero (or below) in the 22nd century. The feasibility of these characteristics is uncertain. We conclude that the proposed date of review of the 1.5°C goal, set at 2015, may be too late to achieve the necessary scaling up of emissions cuts to achieve this goal. © 2012 Crown Copyright.