Glaciers could take centuries to recover from climate change overshoot

The impact of melting glaciers will be felt for centuries – even if global warming is reversed.

At the current rate of warming, global temperatures in 2100 are set to be around 2.7ºC higheropens in a new window than they were at the beginning of the twentieth century. If this happens, it’s predicted that the mass of glaciers will drop by around a third, with the vast majority of small glaciers vanishing altogether.

While it is possible for glaciers to regrow, new research has dampened hopes that it could happen any time soon. A study published in the journal Nature Climate Change suggests that the large polar glaciers that hold most of the world’s fresh water will still be melting in 2500 and only stabilise after thousands of years.

The findings also add to previous research that shows overshooting the 1.5ºC climate target will lock in changes that cannot easily be reversed. Even if temperatures can be returned to 1.5ºC in the future, global glaciers will lose an additional 11% of their mass than if the threshold had never been breached.

Dr Fabien Maussionopens in a new window, who co-authored the research, says that any scenario with this overshoot is “far worse for glaciers than one where the 1.5°C limit is held”.

“Overshooting 1.5°C, even temporarily, locks in glacier loss for centuries,” Fabien says. “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.”

How is climate change affecting glaciers?

There are more than 215,000 glaciers around the world, which collectively hold more than 2% of the entire world’s water. These icy landscapes are an important habitat in their own right, supporting organisms like ice algae, ice worms and many other species.

As the Earth’s largest store of freshwateropens in a new window, holding around 70% of the entire planet’s supply, glaciers also support many other ecosystems. Their meltwater is vital for alpine habitats, while also feeding rivers that support biodiversity far from mountains.

While a certain amount of melting is a natural part of a glacier’s life, the rate has been increasing significantly in recent years. Glacial losses have increased by more than a third in the past decadeopens in a new window as global temperatures have reached new highs.

Even if global warming was to stop today, at around 1.3ºC above pre-industrial levels, the excess heat already means that the world’s glaciers will lose around 30% of their mass by 2500 – causing sea levels to rise by about nine centimetres and inundate low lying regions of the world.

While limiting warming to 1.5ºC is seen as the ‘least-bad’ option for climate change, it will still be devastating for glaciers. As most are relatively small, half of all the world’s glaciers are expected to melt completely by 2100opens in a new window even if this threshold isn’t breached.

It’s increasingly likely, however, that average temperature levels will rise even higher as global greenhouse gas emissions hit new heights. It’s estimated more than 70% of all glaciers will be lost if temperatures rise by 3ºC, likely causing many specialised alpine species to become extinctopens in a new window.

Glaciers and climate overshoots

In the face of rising temperatures, technologies that remove planet-warming greenhouse gases from the atmosphere have been touted as a way of reversing the impacts of climate change. It’s suggested that this could allow global temperatures to be returned to 1.5ºC if the threshold is breached.

Such technologies, however, are not yet rolled out at the scale that would be needed to reduce global temperatures. Furthermore, they’re seen by some as a justification to continue extracting and using fossil fuels, rather than making the emissions cuts needed to halt global warming.

As an overshoot of the 1.5ºC threshold becomes more likely, the researchers wanted to investigate how glaciers would respond to such a scenario. They modelled what would happen if global warming hit 3ºC by the middle of the twenty-second century, and then dropped back to 1.5ºC by 2300.

They found that, as the planet overshoots 1.5ºC, glaciers will lose an additional 16% of their mass than if this limit had never been breached. As temperatures cool again, the refreezing of smaller glaciers, mainly in the Alps, Himalayas and Tropical Andes, would reduce this to 11%. Larger glaciers are likely to continue melting.

While the refreezing of these glaciers is good for the planet as a whole, it means that less meltwater will be available to feed alpine habitats and rivers. Dr Lilian Schusteropens in a new window, the lead author of the study, describes this effect as “trough water”.

“We found that roughly half of the basins we studied will experience some form of trough water beyond 2100,” Lilian says. “It’s too early to say how much impact this will have, but our study is a first step toward understanding the many and complex consequences of climate overshoots for glacier-fed water systems and sea-level rise.”

The study adds to the mounting pile of evidence that cutting emissions sooner rather than later is the cheapest, most effective and least damaging way to halt our planet’s rising temperatures.