What does overshooting 1.5C actually mean?
The world is already about 1.4C above pre-industrial temperatures on a 20-year average and is expected to cross the Paris Agreement’s 1.5C threshold within the next few years [3]. In the UN’s most optimistic scenario, warming peaks around 1.8C near mid-century, while current policies point toward about 2.6C by 2100 [3]. Returning below 1.5C would require both ending fossil-fuel use and removing carbon dioxide from the atmosphere [2][3].
Overshoot is not a harmless delay: every additional fraction of warming and every year above 1.5C increases exposure to extreme weather, sea-level rise, ecosystem loss and potentially irreversible tipping points [2][3]. Tree planting alone could reduce warming by at most about 0.1C, according to the report, leaving any return pathway dependent on deeper emissions cuts and carbon-removal technologies whose scalability remains uncertain [3].
Key insights
- The 1.5C benchmark reflects evidence that climate impacts worsen substantially at 2C compared with 1.5C [3].
- An overshoot pathway requires temperatures to rise above 1.5C temporarily and then fall through emissions elimination and net carbon removal [3].
- Risks named in the report include destabilization of the West Antarctic and Greenland ice sheets, Amazon degradation and disruption of Atlantic Ocean circulation [3].
- The gap between the best available pathway at 1.8C and current-policy projections of 2.6C shows that policy choices still strongly affect the severity of warming [3].