The research, conducted by scientists from the University of Bristol and the University of Innsbruck, provides a sobering projection of how glaciers could evolve over the next five centuries in scenarios where the world overshoots and later returns to the 1.5°C target set by the Paris Agreement.
It is the first study to simulate glacier changes as far ahead as the year 2500 under such "overshoot" conditions — where global temperatures climb to as much as 3°C above pre-industrial levels before declining again.
"Our findings clearly show that a world that exceeds 1.5°C of warming, even temporarily, leads to significantly greater glacier loss," said Dr. Fabien Maussion, co-author and Associate Professor in Polar Environmental Change. "People often ask whether glaciers will return if we reduce emissions. Sadly, this research shows they won't — not in our lifetimes or those of our children."
Overshooting 1.5°C Has Long-Term Impacts
2024 was officially the hottest year on record, and for the first time, global temperatures exceeded the 1.5°C threshold within a calendar year. Though this milestone is based on short-term data — and the Paris Agreement refers to long-term averages — the trajectory remains troubling. The UN World Meteorological Organization recently warned there is now a near 50% chance that at least one year between 2024 and 2028 will exceed the 1.5°C average target.
To explore the long-term implications of overshooting that limit, scientists modelled a scenario where global temperatures rise to 3°C by around 2150 before gradually dropping back to 1.5°C by 2300 and stabilising at that level through 2500.
Even in this best-case recovery scenario, glaciers lose substantially more mass than if the 1.5°C threshold had never been breached. The study projects up to 16% more ice loss by 2200 and 11% more by 2500 compared to a no-overshoot pathway — in addition to the 35% of glacier mass already expected to vanish even if the planet stays below 1.5°C.
Since 2000, melting glaciers have already contributed nearly 2 centimetres to global sea level rise, making them the second biggest driver after ocean thermal expansion.
Alpine Glaciers Could Take 500 Years to Regrow
Dr. Lilian Schuster, lead author of the study published in Nature Climate Change, said that while recovery is technically possible, the timescales involved are measured in centuries or even millennia. "Our models show that large polar glaciers would require hundreds, if not thousands, of years to recover from a 3°C overshoot," she said.
Though the study didn't assess the polar ice sheets directly, it found that smaller glaciers — like those in the Alps, Himalayas and Tropical Andes — may start to regrow by around 2500 if global temperatures decline and stabilise. However, such a timeline puts recovery well beyond the reach of current and future generations.
Melting in these mountainous regions also disrupts water availability downstream. In some areas, if glaciers do begin to regrow post-peak warming, water runoff could drop below even the levels projected for a steady 1.5°C world — a phenomenon the researchers call "trough water."
"About half of the glacier-fed basins we studied will likely face this type of water shortage beyond 2100," Schuster explained. "Understanding the magnitude and duration of these impacts will be key for future water resource management."
‘Irreversible' Change and a Call to Action
The results underscore the long-term damage that even temporary delays in climate action can inflict. "Overshooting 1.5°C, even for a short period, commits us to centuries of glacier loss," said Dr. Maussion. "Much of the damage becomes locked in. Cooling the planet again won't simply reverse the decline."
As global policies continue to fall short of what's needed — current trajectories suggest a rise of around 3°C — the research adds further urgency to reduce emissions as quickly and deeply as possible.
"The longer we wait to act, the more we shift the burden of irreversible climate impacts onto future generations," Maussion concluded.