Glaciers are formations of densely packed ice that cover much of Greenland and Antarctica, as well as mountain ranges around the world. Some of them formed more than 10,000 years ago when the last glacial period—the tail end of the most recent Ice Age—ended. Some alpine (mountain) glaciers are sources of freshwater, and, in some regions, provide substantial amounts of the water people consume. Glaciers form and grow when snowfall is heavy enough to compress into solid ice, and can even flow downhill at a very slow pace.
But glaciers are threatened by the rise in global temperatures due to human activity, through melting or sublimation (ice going directly from solid to vapor without becoming liquid first) and because they aren't being replenished at their usual rates. This has many profound consequences, some of which feed back into the general problem of climate change.
Where glaciers are melting into the ocean, they contribute to sea-level rise. Drastic loss of ice also decreases Earth's albedo, the amount of light the planet reflects back into space, which increases global temperatures even more. And alpine glacial melting affects the water cycle for entire regions, impacting our water supply.
To track the problem, the World Glacier Monitoring Service (WGMS) compiled data from 1919 to 2019 in its Fluctuations of Glaciers Database from a variety of scientific sources and researchers in over 30 countries.
While the database was originally established to understand ice ages of Earth's past, today WGMS draws on decades of observations to understand the present and future of glaciers under climate change.
Stacker took the February 2019 edition of the database and picked 40 glaciers for which WGMS has at least 30 years of ongoing measurements, using the Fluctuations of Glaciers Database to estimate the accumulated mass loss over the time of observation. Unfortunately, that means many extremely important glaciers in the Southern Hemisphere and Central Asia are not included due to the lack of long-term observations.
This story uses a standard glacier measurement: the mass balance, which is the total loss of ice from a glacier in a given period of time, written in terms of the "millimeter water equivalent" or mm w.e. In plain terms, 1 kilogram of water spreads out over a square meter to the depth of 1 millimeter, so mm w.e. provides both the mass of the ice loss and an estimate of how much of the glacier is gone.
It's important to note that all these measurements involve absolute ice loss, without regard to the original size of the glacier. That means some glaciers might seem less affected, but because they started off smaller, their decline is all the more drastic.