In La Paz, Bolivia, a city with a population of roughly two million, as much as 27 per cent of the water supply comes from glacial melt. It’s one of many communities around the world that rely on seasonal meltwater to feed its rivers and provide fresh water for drinking and crop irrigation. While it’s normal for some ice to melt, rising temperatures caused by climate change are precipitating significant glacial retreat. To make matters worse, a new study suggests that we’ve been overestimating how much water our glaciers hold.
Until now, calculating the amount of ice contained in the world’s glaciers has required a lot of guesswork – the logistical and political challenges of gaining access to these remote areas has made monitoring them difficult. In all, in situ measurements of ice thickness exist for only around two per cent of the world’s glaciers, and even this research is often incomplete.
A key piece of missing information, explains Romain Millan, a geophysicist at the Institute of Environmental Geosciences in Grenoble, France, and the study’s lead author, is data on the ice velocity of glaciers worldwide. ‘We usually think of glaciers as non-moving ice bodies,’ says Millan, ‘but in fact, glaciers naturally move under their own weight.’ As more ice accumulates above, the ice below it melts and deforms, causing it to slowly flow downhill ‘a bit like thick syrup’. How rapidly a glacier moves depends on the thickness of its ice. Turning that around, data on how rapidly a glacier moves can help scientists to better estimate its volume.
By analysing more than 800,000 high-resolution satellite images taken between 2017 and 2018, the researchers were able to track the flow of ice in each location, allowing them to make much more accurate calculations than had previously been possible. ‘We knew that this would make a big difference,’ says Millan, explaining that the results showed a lot of regional variation but that, overall, the study revealed many glaciers are shallower than anticipated.
Two notable differences in freshwater availability are in the Himalaya, where there is 37 per cent more ice than was thought, and in the tropical Andes of South America, where there is 27 per cent less ice than had previously been estimated – a potential cause for concern for the mountain communities nearby. Millan stresses that there’s still a lot of uncertainty in these regions, where measurements remain sparse but the local people are often highly dependent on freshwater resources. However, the data taken from the satellite images, which is publicly available, has already sparked new projects that he hopes will lead to ever more accurate results. ‘Getting this data set was a huge piece of work that has now unlocked a lot of new possibilities for research,’ he says.