Monday, August 17, 2020

Greenland's melting ice sheet has 'passed the point of no return,' scientists say, dooming it to disappear

Ice melted during a heat wave in Kangerlussuaq, Greenland on August 1, 2019.
Caspar Haarloev from "Into the Ice" documentary via Reuters

From BusinessInsider by Morgan McFall-Johnsen

Rising temperatures have driven Greenland's glaciers past a critical tipping point, where snowfall can no longer replenish melting ice.

  • Greenland's ice sheet may have passed a point of no return, setting it on an irreversible path to disappearance, according to researchers at Ohio State University.
  • Snowfall can no longer replenish the ice lost as Greenland's glaciers retreat, so it will keep melting and cause catastrophic sea-level rise, even if global temperatures stop rising.
  • The climate crisis could bring about other tipping points in the Arctic and the Amazon, but there may still be time to avoid those.
Greenland's ice sheet may have hit a tipping point that sets it on an irreversible path to completely disappearing.

Snowfall that normally replenishes Greenland's glaciers each year can no longer keep up with the pace of ice melt, according to researchers at Ohio State University.
That means that the Greenland ice sheet — the world's second-largest ice body — would continue to lose ice even if global temperatures stop rising.

 The Brückner and Heim glaciers in southeast Greenland.
Greenland is the second largest ice cap in the world after the Antarctic.
Jeremy Harbeck / NASA / AFP

 Heim glacier in the GeoGarage platform (DGA Denmark nautical arster chart)

In their study, published Thursday in the journal Nature, the scientists reviewed 40 years of monthly satellite data from more than 200 large glaciers that are draining into the ocean across Greenland.

"What we've found is that the ice that's discharging into the ocean is far surpassing the snow that's accumulating on the surface of the ice sheet," Michalea King, the study's lead author and researcher at Ohio State University's Byrd Polar and Climate Research Center, said in a press release.

Complete melting of the Greenland ice sheet could raise sea levels 23 feet by the year 3000.
If that happens, the ocean would swallow coastal cities across the globe.
Greenland's ice is already the world's largest single contributor to sea-level rise.
In just the next 80 years, its current melt rate would add another 2.75 inches to global sea levels, according to a study published in December.

Satellite image shows meltwater ponding on the surface of the ice sheet in northwest Greenland near the sheet’s edge on Monday, July 30, 2019.
While the heat wave broke in Western Europe after a few days, extreme temperatures shifted north and caused massive ice melts in Greenland and the Arctic.NASA via Associated Press

"Glacier retreat has knocked the dynamics of the whole ice sheet into a constant state of loss," Ian Howat, a glaciologist and co-author on the paper, said in the release.
"Even if the climate were to stay the same or even get a little colder, the ice sheet would still be losing mass."

But this is just one of many climate-change tipping points that human activity might bring about.
There is still time to avoid irreversible pathways to other calamities.

There are more points of no return

The amount of ice Greenland loses each year has steadily increased in the last two decades.
Before 2000, the researchers found, the ice sheet had an equal chance of gaining or losing mass each year.
But in the climate of the last 20 years, it will only gain mass one in every 100 years, the researchers found.

Greenland dumped an unprecedented amount of ice and water into the ocean during the summer of 2019, when a heat wave from Europe washed over the island.
The ice sheet lost 55 billion tons of water over five days — enough to cover the state of Florida in almost five inches of water.

Ice melt formed whitewaters in Kangerlussuaq, Greenland on August 1, 2019. 
Caspar Haarloev from "Into the Ice" documentary via Reuters

Melt brings about more melt, as water pooling across the ice sheet absorbs more sunlight and further heats everything around it.
That's why tipping points like Greenland's accelerate ice loss so much.

Rising global temperatures and certain human activities can bring about tipping points in other parts of the world, too.

In the Arctic, ice melt is exposing permafrost — frozen soil that releases powerful greenhouse gases when it thaws.
If warming thaws enough permafrost, the gases released will trap heat faster than humans' fossil-fuel emissions.

In the Amazon rainforest, humans have been cutting and burning trees for years, allowing moisture to escape the ecosystem.
Enough deforestation could trigger a process called "dieback," in which the rainforest would dry up, burn, and become a savanna-like landscape, releasing up to 140 billion tons of carbon into the atmosphere.
Last year, leading rainforest scientists warned that the Amazon is "teetering on the edge" of that threshold.

  In this aerial view melting ice forms a lake on free-floating ice jammed into the Ilulissat Icefjord during unseasonably warm weather on July 30, 2019 near Ilulissat, Greenland.

Still, scientists say that switching to less carbon-intensive forms of energy, like solar power, and reducing unsustainable logging and mining can help us avoid those disasters.

Even for the Greenland ice sheet, the future holds more tipping points — degrees of collapse that will accelerate the glaciers' melt even more.
Limiting global warming could delay those tipping points and give the world more time to prepare.

"We've passed the point of no return, but there's obviously more to come," Howat told CNN.
"Rather than being a single tipping point in which we've gone from a happy ice sheet to a rapidly collapsing ice sheet, it's more of a staircase where we've fallen off the first step but there's many more steps to go down into the pit."

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