Irreversible glacier change and trough water for centuries after overshooting 1.5 °C

This study explores the long-term impacts of temporarily exceeding the 1.5 °C global warming threshold on the world’s glaciers. Using simulations from the Open Global Glacier Model and GFDL-ESM2M Earth System Model, it examines glacier mass loss and runoff under both temperature stabilization and overshoot scenarios through the year 2500. The research introduces the concept of “trough water”—a period of reduced glacier runoff following regrowth after an overshoot—highlighting risks to water security in glacier-dependent regions. The work is motivated by growing concerns over climate tipping points and the irreversibility of glacier loss even if global temperatures later decline.

The results show that exceeding 1.5 °C, even temporarily, causes irreversible glacier mass loss and higher sea-level rise that persists for centuries. Under a 3.0 °C overshoot scenario, glaciers lose 11% more mass globally by 2500 than under a steady 1.5 °C warming. In key basins like the Indus and Rapel, glacier runoff is significantly reduced during dry seasons for up to 300 years, threatening water availability. These findings underscore the urgency of limiting peak warming through immediate emissions reductions.