Climate: UNEP compares pathways after a 1.5°C overshoot
· BehindLines newsroom
A climate report presented on 21 October by the United Nations Environment Programme examines how to limit an overshoot of 1.5°C and then return towards that threshold. Its press release describes its lowest possible overshoot scenario, a conditional pathway with warming peaking at 1.7–1.8°C around the middle of the century and roughly a one-in-two chance of returning to 1.5°C or below in 2100.
These figures refer to global warming relative to pre-industrial times. They describe neither a city's temperature nor a weather forecast for a particular day. The scenario considers a return after an overshoot; it does not announce that the threshold would be respected without interruption.
In its 21 October analysis, S&P Global reports the emissions reductions needed for that pathway: 18% in 2030, 45% in 2035 and 69% in 2040, each measured against 2025 levels. These percentages are reductions to be achieved, rather than decreases already observed. They concern all greenhouse gases and do not measure carbon dioxide alone.
UNEP distinguishes this pathway from the one that would result from full implementation of current national commitments. Those commitments would lead to reductions of 5–8% in 2030 and 11–15% in 2035, again relative to 2025. The comparison therefore concerns scenarios with a shared baseline, rather than promises that have already been fulfilled.
S&P Global highlights another condition: the removal and permanent storage of around 320 gigatonnes of CO2 over the century. Its account recalls the technical and socioeconomic uncertainties surrounding that operation. Removing carbon from the atmosphere and avoiding emissions are different actions, which the scenario combines.
The value of these projections lies in distinguishing possible outcomes, commitments and the conditions for achieving them. The report provides pathways for comparison; it does not guarantee that they will be implemented.