An assessment of current policy scenarios over the 21st century and the reduced plausibility of high-emissions pathways

The literature on current policy scenarios has become increasingly robust in recent years, with a growing consensus that the central estimate of 21st century warming is now likely below 3C. This reflects progress on both clean energy technologies and climate policies that has reduced the plausibility of high-emissions pathways, as well as a recognition that the higher end of emissions scenarios was never intended to represent the most likely no policy baseline outcome. However, it is difficult to fully preclude warming of 4C or more under a current policy world if there are continued positive emissions after 2100 or if carbon cycle feedbacks and climate sensitivity are on the high end of current estimates in the literature. Current policy scenarios are a useful benchmark for assessing climate impacts and the effects of further mitigation, but should not be seen as either a ceiling or a floor on future warming outcomes.