New laser measurements can help pinpoint how and when the world’s vast stores of ice will vanish.
From the frozen crags of the Andes and Rockies to country-sized ice sheets covering Greenland and Antarctica, global warming is melting the world’s ice at a dizzying rate. In the last five years, mountain glaciers have unexpectedly disintegrated and collapsed, including a pair of deadly ice avalanches in Tibet. In Alaska, a quarter-mile section of the Flat Creek glacier broke away and oozed down the valley, mowing down 400-year-old trees.
This ice loss is worrying for many reasons. Modern humans evolved on a planet where ice has been a crucial regulator, reflecting some of the sun’s heat back to space, and storing huge amounts of moisture—about 69 percent of the world’s freshwater is stored in glaciers and ice sheets. Slow melting and replenishment were in balance for 10,000 years or so, until human-caused global warming disrupted the cycle.
The meltdown is having impacts across the planet. As ice melts off Greenland and Antarctica their gravitational mass decreases, sending the water surging toward the equator, where sea level rising two or three times as fast as the global average is already swamping islands. A study published April 30 in the journal Science helps show from where the water is coming, and exactly which processes are causing it.
The loss of mountain glaciers is disconcerting for cities and farming areas in the Western United States and other areas that rely on slow-melting mountain ice. Alpine towns that have faced giant avalanches of ice, mud, rocks and snow are also anxious and in South America, mountain towns are threatened by sudden floods from collapsing glaciers.
How Fast Will it Melt?
Knowing how fast global warming will speed up the melting is crucial for people trying to plan future water supplies for cities and farms, or for when they might have to abandon low-lying coastal areas and islands. The new study uses data from NASA’s ICESat ( Ice, Cloud, and Land Elevation Satellite) missions to make increasingly accurate calculations of how much ice melted off Greenland and Antarctica from 2003 to 2019, as human-caused warming really kicked into high gear. The study calculated that Greenland lost about 200 gigatons per year during the study period and Antarctica about 118 gigatons annually, together raising sea level by 0.55 inches.
The laser sensors can peer into the steep ice canyons along the edges of Greenland and Antarctica, said NASA scientist Alex Gardner, a co-author of the new paper.
“The numbers are quite consistent between different sensors,” Gardner said. “People are really starting to converge on what the central estimates are and we have increasing confidence in those numbers.”
Flying 310 miles high at 3.4 miles per second, ICESat measures a grid of the entire Earth every three months, sending trillions of photons down to the surface.
“They bounce photons off the surface like they’re ping pong balls and maybe 12 bounce back to the telescope,” Gardner said. “From that, they can measure the height of the ice down to a distance of a few centimeters. It’s unprecedented. It’s helping us understand, what are the processes that are leading to those changes, adding spatial details and insights into what’s happening and why.”
That includes the vast frozen expanse of East Antarctica, long thought to be a bastion of stable ice. “Our thinking on that is quickly evolving,” Gardner said. “For the most part, East Antarctica still seems fairly stable,” but there are signs that warmer water incursions could make some of the ice vulnerable to irreversible retreat.”
Source: Insideclimate News