Glacier Futures in a 1.5°C Post-Overshoot World: Irreversible Risks of Delayed Climate Action

Surpassing 1.5 °C of global warming, even temporarily, could cause irreversible loss of glacier mass and water runoff that would persist for centuries, according to a groundbreaking study by Lilian Schuster et al., published in Nature Climate Change (2024). 

The study reveals a stark reality: even if global temperatures return below 1.5 °C after peaking at 3.0 °C, global glaciers will still lose 11% more mass by 2500 than if warming had been limited without overshoot. This mass loss fuels sea-level rise and permanently alters water availability in glacier-dependent regions. 

A key finding is the concept of “trough water”, a long-lasting drop in glacier runoff that occurs when glaciers begin to regrow after peak warming. This means that in some regions there could be less water available during the cooling phase than under stable, warmer conditions. This phenomenon poses serious concerns for areas like Central Asia, the Alps, and parts of South America, where many communities depend on glacier-fed rivers. 

These changes will affect both global sea levels and local water security, impacting agricultural yields and food security, increasing flooding and further spread water-borne and infectious diseases. Furthermore, the research suggests that relying on long-term carbon dioxide removal is risky, given physical feedback and nonlinear glacier responses. 

The study underscores a critical message: overshoot matters. Once global temperatures rise, glacier systems don’t easily recover, even with subsequent cooling. Delayed action could lead to complex and unforeseen outcomes, including local disputes over reduced water during cooling. 

The world after an overshoot will be fundamentally different from the one before it. 

Feature image: Global glacier mass loss and sea level rise projections. Credit: Schuster, 2025. 

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