A new study published in Nature by 30 scientists analyzes future scenarios where global temperatures temporarily exceed the 1.5°C limit set by the Paris Agreement, and then fall again through efforts to reduce emissions. The researchers caution that even a temporary overshoot could have irreversible consequences, and stress the need for rapid, near-term emissions reductions to mitigate climate risks.
The study, backed by the European Innovation Fund HORIZON2020, is the result of a three-and-a-half-year project examining ‘overshoot’ scenarios—where temperatures rise above 1.5°C but eventually drop after achieving net-negative CO2 emissions.
Although it may be possible to reverse global temperature rise after exceeding 1.5°C, the researchers warn that some climate impacts, such as rising sea levels, will be irreversible.
According to Dr. Carl-Friedrich Schleussner, head of the integrated climate impacts group at the International Institute of Applied Systems Analysis and scientific advisor at Climate Analytics, who led the study, the findings disprove the idea that overshooting 1.5°C will lead to the same climate outcomes as if more ambitious actions were taken earlier to avoid exceeding that threshold.
“Only by doing much more in this critical decade to reduce emissions and keep peak temperatures as low as possible can we limit climate damage,” Schleussner emphasized.
How Long and How High We Let Temperatures Rise Matters
The study by scientists highlights the benefits of reversing temperature increases through achieving global net-negative emissions. If global warming is reversed, it could reduce sea level rise by 40cm by the year 2300, compared to a scenario where temperatures are merely stabilized.
“Warming will continue until we reach net zero emissions,” said co-author Prof. Joeri Rogelj, professor of climate science and policy at Imperial College London. “The sooner we reach net zero, the lower the peak warming and the smaller the risks of irreversible impacts.”
Rogelj also stressed the importance of countries submitting ambitious new emissions reduction targets (known as Nationally Determined Contributions or NDCs) ahead of next year’s climate summit in Brazil.
Carbon Removal Capacity is Key to Managing Future Risks
The scientists further emphasize that, while it may still be possible to limit warming to 1.5°C in the long run, it is crucial to prepare for higher warming outcomes in case the climate system responds more severely than expected.
Achieving this requires combining deep emissions reductions with large-scale, environmentally sustainable carbon removal technologies. The researchers estimate that hundreds of gigatonnes of carbon removal may be necessary to prevent catastrophic warming.
“There’s no way to rule out the need for significant net negative emissions, so we must minimize residual emissions now,” added Gaurav Ganti, a research analyst at Climate Analytics and co-author of the study. “We cannot waste carbon removal on offsetting emissions that we could avoid in the first place.”
Dr. Schleussner concluded, “Our work underscores the urgency for governments to act now in reducing emissions. The race to net zero should be seen as a sprint, not a marathon.”
