Even if humanity succeeds in slowing global temperature rise after temporarily exceeding the Paris climate target and bringing it back below 1.5°C in the long term, the world’s glaciers will continue to shrink for centuries, or even millenia.
Humanity is still clinging to the hope that the effects and damage caused by global warming can one day be reversed. But new research shows that this hope is misleading.
An international research team, led by the University of Bristol and the University of Innsbruck, reports in Nature Climate Change (published on May 19) that mountain glaciers worldwide would continue to melt for centuries, even if global temperatures drop back below the 1.5°C limit after exceeding it.
In such so-called “overshoot” scenarios, glaciers lose significantly more mass than in a world where warming never exceeds the threshold set by the Paris Agreement.
“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,” says Dr. Fabien Maussion, Associate Professor of Polar Environmental Change at the University of Bristol and corresponding author of the study, in a university press release.
“Current climate policies are putting the Earth on a path close to 3°C. It’s clear that such a world is far worse for glaciers than one where the 1.5°C limit is held.”
Dr. Fabien Maussion, University of Bristol
Long-term projection through the year 2500
To investigate the long-term consequences of temporarily exceeding the 1.5°C limit, the research team simulated the development of mountain glaciers worldwide up to the year 2500 for the first time – excluding the large ice sheets in the Arctic and Antarctic
The basis was a so-called overshoot scenario, in which the global average temperature first rises by up to 3 °C above pre-industrial levels by 2150, before gradually declining by 2300 and stabilizing at +1.5 °C.
The results show that an additional 16 percent of glacier ice mass would be lost by 2200, and a further 11 percent by 2500 – on top of the approximately 35 percent already considered certain to be lost even if the 1.5°C target is met. The meltwater released will ultimately flow into the oceans, contributing to global sea level rise.
The study was published just one day before another paper in which scientists warn of the irreversible retreat of the ice sheets in Greenland and Antarctica once the 1.5°C limit is exceeded, as polarjournal.net reported yesterday.
After the 1.5°C mark was exceeded for the first time last year, it is now highly likely that the limits set out in the Paris Climate Agreement will not be met.
Polar glaciers particularly affected
Not all glaciers respond to climate change in the same way. In particular, glaciers in high-latitude regions such as Svalbard, Alaska, the Russian Arctic, the edges of Greenland, and on sub-Antarctic and Antarctic islands – which together account for around two-thirds of global glacier mass – react slowly to temperature changes due to their relatively flat topography.
Even if the climate cools again in the coming centuries, ice loss in these regions will continue until at least 2500, with no signs of regeneration.
“Our models show it would take many centuries, if not millennia, for the large polar mountain glaciers to recover from a 3°C overshoot. For smaller glaciers such as those in the Alps, the Himalaya and the Tropical Andes, recovery won’t be seen by the next generations but is possible by 2500,” says Dr. Lilian Schuster, researcher at the University of Innsbruck and lead author of the study.
In other regions, such as Iceland or the Canadian Arctic, there are hardly any differences between the scenarios – either because there is little ice left or because regional climate conditions under overshoot and stabilization differ very little.
Impacts on water supply
Glacier retreat could be particularly dramatic in regions where meltwater is vital. According to Dr. Schuster, a subsequent cooling of the global climate could have paradoxical consequences in some areas: if glaciers begin to grow again, they will once again store water as ice and release correspondingly less meltwater. For river catchment areas that are heavily dependent on glacier meltwater, this could lead to long-term water shortages.
This development harbors potential for conflict: while global efforts aim to stabilize temperatures and reduce emissions, local interests in a reliable water supply could increasingly come into conflict with these climate goals in the future.
“The world after an overshoot will be different from the world before the overshoot.”
The authors emphasize that subsequent emission reductions and carbon capture and storage will not be sufficient to reverse the processes described.
“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,” says Dr. Maussion.