Every Increment of Warming Above 1.5°C Increases the Risk of Crossing Tipping Points – Even if Overshoot is Temporary

Nature Communications, 1 August 2024

Current climate policies are not ambitious enough to prevent tipping points from being crossed, even if long-term temperatures return to 1.5°C by 2300, new analysis shows. The authors investigated the risk of tipping where warming temporarily overshoots 1.5°C, but global temperatures are then brought back down using negative emissions technologies. They found that the longer the 1.5°C threshold is breached, and the higher the peak temperature; the greater the risk of crossing tipping points for the West Antarctic and Greenland ice sheets, the Atlantic Meridional Overturning Circulation (AMOC), and the Amazon rainforest. Scenarios following pledged NDCs under the UNFCCC in 2020 until 2100 would lead to a 10–90% chance of tipping points being crossed (median estimate: 30%), even when subsequently designed such that temperatures return to 1.5°C after overshoot. Tipping risk was found to increase with every 0.1°C of overshoot peak temperature, and risk accelerates non-linearly for peak overshoot temperatures above 2°C. This research underscores the importance of the Paris Agreement climate objective to hold warming to ‘well below 2°C’, with as little and as brief overshoot of even 1.5°C as possible.

Full paper: https://www.nature.com/articles/s41467-024-49863-0
News Briefing: https://www.carbonbrief.org/every-0-1c-of-overshoot-above-1-5c-increases-risk-of-crossing-tipping-points/