Irreversible glacier change and trough water for centuries after overshooting 1.5 °C
- Hakan Sener
- Jun 4
- 3 min read
Overshooting 1.5°C leads to centuries of glacier loss and reduced water runoff, with long-term sea-level and water security risks.
A new study published by Lilian Schuster and colleagues reveals that even if humanity returns to 1.5°C after temporarily overshooting it, the damage to mountain glaciers will be irreversible for centuries. Glaciers won’t just lose more mass—they will also reduce freshwater availability during critical dry seasons, a phenomenon the authors name “trough water”.
The paper examines glacier and hydrological responses through the year 2500 using detailed modeling of over 200,000 glaciers under stabilization and overshoot scenarios. It finds that overshoot leads to up to 11% more glacier mass loss by 2500 and introduces long-term risks to water security and sea-level rise, particularly in key regions like Central Asia, South America, and the European Alps.
Key Findings: Overshoot Has Deep, Lasting Consequences
Overshooting 1.5°C Leads to Irreversible Glacier Mass Loss
In a scenario where warming peaks at 3.0°C before returning to 1.5°C, global glacier mass loss is 11% higher by 2500 than in a steady 1.5°C stabilization scenario.
This added loss contributes an extra 34 mm of sea-level rise, much of which is irreversible within centuries.
Even if warming halted today at 1.2°C, about 30% of glacier mass would still be lost by 2500.
Trough Water: A New Risk for Water Supplies
After overshoot, some glaciers begin to regrow—but that regrowth temporarily reduces runoff below historical levels.
This dip, termed “trough water”, could persist for decades or centuries, especially in arid regions that rely heavily on glacial meltwater during dry seasons.
In South America’s Rapel Basin, for example, trough water could last over 300 years, with seasonal runoff dropping by more than 50%.
Glacier Response Time and Geography Matter
Glaciers in steep mountain areas respond more quickly and can partially regrow, but still suffer long-term mass loss.
Large ice masses in high-latitude regions like Alaska and the Russian Arctic respond too slowly to recover, locking in sea-level rise.
Trough water impacts are most severe in glacier-fed basins already prone to drought—especially in Central and South Asia, the Andes, and parts of Europe.
Why Mitigation Now Matters More Than Ever
The study warns against relying on overshoot scenarios followed by technological carbon removal to fix the climate. Because glaciers respond slowly and non-linearly to temperature, even small overshoots commit the Earth to persistent glacier loss, water insecurity, and higher sea levels.
Critically, glacier runoff declines even in basins where glaciers eventually regrow, meaning that local water access suffers even as global temperatures fall. This highlights a conflict between short-term adaptation needs and long-term climate mitigation—and makes the case for limiting warming peaks rather than just long-term averages.
A Post-Overshoot World Will Be Drier, Hotter, and Less Predictable
The Schuster et al. study introduces “trough water” as a powerful concept showing that overshooting 1.5°C has consequences that won’t be undone for centuries. Even if climate goals are eventually met, glaciers—and the communities that depend on them—may still face long-term losses.
Avoiding these outcomes requires rapid and aggressive emissions reductions now, not delayed action followed by promises of future fixes. Once the peak is passed, the world’s glaciers won’t simply return to their prior states. And neither will the security they provide.
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