Mountain glaciers face centuries of irreversible loss if warming surpasses 1.5°C

Mountain glaciers are already vanishing worldwide – and if global warming hits 3°C, even briefly, their recovery will be beyond reach for generations.

That’s the stark message from a modeling study led by the University of Bristol and the University of Innsbruck. The modeling simulations through 2500 show that overshooting 1.5°C melts more ice and locks in higher seas than staying below it.

What if we go too far

Earth’s thermometer is edging dangerously close to the Paris ceiling. In 2023, average surface temperatures topped 1.5°C for the first full calendar year, and current policies are steering us toward roughly 3°C of warming by late-century.

Engineers and economists often suggest that massive deployment of carbon-capture technology could, eventually, pull the planet back down to safer temperatures. But what happens to frozen water stored in glaciers during that hot detour?

“Current climate policies are putting the Earth on a path close to 3°C,” said corresponding author Fabien Maussion, a scientist at the University of Bristol. “It’s clear that such a world is far worse for glaciers than one where the 1.5°C limit is held.”

“We aimed to discover whether glaciers can recover if the planet cools again. It’s a question many people ask – will glaciers regrow in our lifetime, or that of our children? Our findings indicate sadly not.”

Two futures, centuries apart

The researchers compared two temperature pathways. The first stabilizes at 1.5°C by mid-century and stays there.

The second allows warming to climb to about 3°C around 2150, then decline – through aggressive negative-emissions programs – to 1.5 °C by 2300, where it holds steady.

In the overshoot world, mountain glaciers lose an additional 16 percent of their present ice by 2200 and 11 percent more by 2500. That’s on top of the roughly 35 percent already expected to melt even if the 1.5°C threshold is never crossed.

Every kilogram of this lost ice becomes meltwater that eventually reaches the ocean, lifting global sea levels further.

A 500-year forecast

The Bristol team and partners used an open-source glacier model that simulates every mountain glacier outside Greenland and Antarctica – more than 200,000 of them – based on local topography, historic mass-balance data, and climatic inputs.

For future conditions they tapped a set of overshoot projections supplied by the University of Bern. Modeling through 2500 shows most ice sheets don’t recover, even after global temperatures drop.

“Our models show it would take many centuries, if not millennia, for the large polar glaciers to recover from a 3°C overshoot,” said lead author Lilian Schuster from the University of Innsbruck.

“For smaller glaciers such as those in the Alps, the Himalayas and the Tropical Andes, recovery won’t be seen by the next generations but is possible by 2500.”

When mountain glaciers stop giving

When glaciers shrink, they first enter a peak-water phase, dumping extra runoff that downstream farms and cities often depend upon during summer dry spells. But once the ice reservoir drains past a tipping point, annual flow diminishes.

If cooling eventually allows regrowth, glaciers begin storing water again, exacerbating the low-flow period – a phenomenon the authors dub “trough water.”

“If glaciers regrow, they start storing water again as ice – and that means less water flows downstream. We call this effect ‘trough water,’ in contrast to peak water. We found that roughly half of the basins we studied will experience some form of trough water beyond 2100,” Schuster said.

The study covers basins from the Andes to the Himalayas, many of which already face seasonal water stress.

Extra inches – permanent consequences

The extra 11-16 percent slice of lost ice above a no-overshoot future locks in several additional centimeters of sea-level rise.

That margin may sound small, but it compounds with thermal expansion and ice-sheet losses, raising storm-surge risk for hundreds of millions of coastal residents.

Overshoot also harms mountain ecosystems: glacier forefields shift upslope, cold-water habitats shrink, and culturally significant landscapes disappear. Tourism economies tied to iconic glaciers could struggle, even if late-century cooling stabilizes temperatures.

Irreversible glacier loss

The overshoot scenario mirrors a “late net-zero” world in which society continues burning fossil fuels well into the 2100s, counting on large-scale carbon capture later.

But the glacier model shows that waiting carries irreversible costs. Maussion noted that overshooting 1.5°C, even temporarily, locks in glacier loss for centuries.

“Our study shows that much of this damage cannot simply be undone – even if temperatures later return to safer levels. The longer we delay emissions cuts, the more we burden future generations with irreversible change.”

Mountain glaciers need swift action

The findings are part of the EU-funded PROVIDE project, which assesses overshoot risks across water, agriculture, and biodiversity.

They bolster the case for immediate, deep emissions reductions rather than banking on future technological rescues. For regions reliant on glacier melt, planners may need to prepare for both short-term flood hazards and long-term water scarcity.

While advanced carbon-removal techniques remain essential for achieving net-zero, some parts of Earth’s cryosphere respond more slowly. The study shows that mountain glaciers, in particular, may not recover even if temperatures later drop.

In essence, once the ice is gone, it will not return within any timeframe that can protect current societies or ecosystems.

The study is published in the journal Nature Climate Change.

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