The revised
estimate reduces global sea level rise by 3 inches if all glaciers were to
melt. But it raises concern for some communities that rely on seasonal melt
from glaciers to feed rivers and irrigate crops. If glaciers contain less ice,
water will run out sooner than expected. While some
ice naturally melts throughout the year, rising temperatures due to climate
change are speeding up glacier retreat. Between 2000 and 2019, these rivers of
ice lost roughly 5.4 trillion tonnes. Countries
are already struggling with disappearing glaciers. Peru is investing in desalination
to make up for declining freshwater. And Chile hopes to create artificial
glaciers in its mountains. But,
"we've had quite a poor understanding of how much ice is actually stored
in glaciers," said lead study author Romain Millan, a glaciologist at
Université Grenoble Alpes. Past analyses, for example, double-counted glaciers
along the peripheries of the Greenland and Antarctic ice sheets, overestimating
ice volume. The Nature
Geoscience study assessed how quickly glaciers were moving across the landscape,
or their velocity. Such measurements allow scientists to more accurately
measure volume, as the way glaciers flow indicates where ice is thick or thin.
But collecting this information has been limited by technology. High-resolution
satellites deployed in recent years, however, allowed for the first analysis of
how 98 percent of the world's glaciers are moving, "from small glaciers in
the Andes up to massive glaciers in Svalbard and Patagonia," said Millan. The work
analyzed more than 800,000 pairs of images of glaciers taken between 2017 and
2018, and found that many were shallower than previously assessed. Scientists
now estimate there is 20 percent less glacial ice present with the potential to
melt into the ocean and raise sea levels. Currently, glaciers are responsible
for 1 mm of annual sea level rise, or 30 percent of the yearly increase. "This
is one of the first really impressive results coming out" from satellite
advances, said Daniel Farinotti, a glaciologist at ETH Zurich not involved in
the research. Millan and
his colleagues also found that Asia's Himalayas contain 37 percent more ice
than previously estimated, while South America’s Andean glaciers contain
roughly 27 percent less ice. Already, Peru's glaciers have lost 40 percent of
their surface area since the 1970s. "This
will put more pressure on freshwater in the Andes," he said. "On the
contrary, water will be more secure in the Himalayas."