Greenland Ice Sheet

A paper published in Nature Communications Earth & Environment using over 30 years worth of satellite data finds that the Greenland Ice Sheet experienced an increase in melting at the start of the century that was "sufficient to effectively shift the ice sheet to a state of persistent mass loss".

The implication is that the ice sheet may have passed the point of no return.

The researchers found that, throughout the 1980s and 90s, snow gained through accumulation and ice melted or calved from glaciers were mostly in balance, keeping the ice sheet intact.

Before 2000, the ice sheet would have about the same chance to gain or lose mass each year. In the current climate, the ice sheet will gain mass in only one out of every 100 years.

Co-author Ian Howat:

Glacier retreat has knocked the dynamics of the whole ice sheet into a constant state of loss. Even if we were to stabilize at current temperatures, the ice will continue to disintegrate more quickly than if we hadn't messed with the climate to begin with.

Update (September 4):  A study published in Nature Climate Change finds that ice sheets are melting at a rate matching worst-case scenarios from previous forecasts.

Melting of ice in Greenland has pushed the world’s oceans up by 10.6mm since the sheets were first monitored by satellite in the 1990s, while Antarctic ice has contributed a further 7.2mm. The latest measurements show the world’s seas are now rising by 4mm each year.

Melting ice now contributes more to sea level rise than thermal expansion.

Update (July 23, 2023):  A rediscovered ice core includes frozen soil from Northwest Greenland. 

As scientists started to sieve it to separate out the sediment, they were surprised to see twigs, mosses, leaves and seeds.

[They] calculated that the sediment was deposited in an ice-free environment roughly 416,000 years ago.

This doesn't bode well. 

Levels of carbon dioxide in the atmosphere are 1.5 times higher now than they were 400,000 years ago, and global temperatures keep climbing.

If Greenland's ice sheet saw rapid melting during a period of moderate warming, it "may be more sensitive to human-caused climate change than previously understood – and will be vulnerable to irreversible, rapid melting in coming centuries," the study authors said in a statement.