For the last 30 years, earth scientists have been warning that Greenland was nearing a tipping point into complete disintegration. Now authors of a new study published in Nature “Dynamic ice loss from the Greenland Ice Sheet driven by sustained glacier retreat” has claimed that, even if the climate now reverted to the levels where it was stable a few decades ago, that would probably still happen.
The paper is pretty impenetrable (I had to read it several times despite having a degree in earth sciences). But there is a human readable summary at CNN “Greenland’s ice sheet has melted to a point of no return, according to new study“.
Greenland’s ice sheet has melted to a point of no return, and efforts to slow global warming will not stop it from disintegrating. That’s according to a new study by researchers at Ohio State University.
“The ice sheet is now in this new dynamic state, where even if we went back to a climate that was more like what we had 20 or 30 years ago, we would still be pretty quickly losing mass,” Ian Howat, co-author of the study and a professor at Ohio State University, said.CNN “Greenland’s ice sheet has melted to a point of no return, according to new study“
Most of the mass loss over the past few decades has been around the coast where relatively warmer seawater can nibble at the edge of the glaciers. They’re retreating.
The study also found that the ice sheet is retreating in rapid bursts, leading to a sudden and unpredictable rise in sea levels, making it difficult to prepare for the effects.
The study used four decades of satellite data to measure changes in Greenland’s ice sheet. The authors found that after 2000, the ice sheet shrank so rapidly that replenishing snowfall would not keep up with the rate of melting from parts of the glacier newly exposed to warmer ocean water, even if climate change were reversed.
Entire coasts of ice are retreating at once due to climate change, Howat said, adding that all 200 glaciers that make up the Greenland ice sheet have been observed retreating within the same episode.
Even though the retreat of the Greenland Ice sheet likely cannot be reversed, it’s just the first in a series of tipping points. If climate change continues at this rate, the rate of melting will get much worse.
“We’ve passed the point of no return but there’s obviously more to come,” Howat said. “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.”CNN “Greenland’s ice sheet has melted to a point of no return, according to new study“
This study clearly shows that the coastal loss over the last 4 decades has been the biggest contributor over that time period, presumably mostly from the retreat of the glaciers and calving at the ice / seawater interface. It has increased in rate significantly over the last two decades to the point that the current IPCC worst case is now the observed case.
However that isn’t the whole story, and in a lot of ways that isn’t the most worrying factor. When you look just over the last decade in Greenland, another factor shows up as being more of a worry in the furture. Melting due to surface conditions on top of the ice sheets.
The surface ice rot that has become evident over the last decade that helps to speed up the movement of ice at the coastal regions. This was particularly evident in 2016. There is a graphic example including a photo that was written about the quite warm 2016 season.
From a helicopter clattering over Greenland’s interior on a bright July day, the ice sheet below tells a tale of disintegration. Long, roughly parallel cracks score the surface, formed by water and pressure; impossibly blue lakes of meltwater fill depressions; and veiny networks of azure streams meander west, flowing to the edge of the ice sheet and eventually out to sea.Science: “The great Greenland meltdown“
In Greenland, the great melt is on. The decline of Greenland’s ice sheet is a familiar story, but until recently, massive calving glaciers that carry ice from the interior and crumble into the sea got most of the attention. Between 2000 and 2008, such “dynamic” changes accounted for about as much mass loss as surface melting and shifts in snowfall. But the balance tipped dramatically between 2011 and 2014, when satellite data and modeling suggested that 70% of the annual 269 billion tons of snow and ice shed by Greenland was lost through surface melt, not calving. The accelerating surface melt has doubled Greenland’s contribution to global sea level rise since 1992–2011, to 0.74 mm per year. “Nobody expected the ice sheet to lose so much mass so quickly,” says geophysicist Isabella Velicogna of the University of California, Irvine. “Things are happening a lot faster than we expected.”
It’s urgent to figure out why, and how the melting might evolve in the future, because Greenland holds the equivalent of more than 7 m of sea level rise in its thick mantle of ice. Glaciologists were already fully occupied trying to track and forecast the surge in glacial calving. Now, they are striving to understand the complex feedbacks that are speeding up surface melting.
Although the Arctic is warming twice as fast as the rest of the world, high temperatures alone can’t explain the precipitous erosion of Greenland’s ice. Unseasonably warm summers appear to be abetted by microbes and algae that grow on the increasingly wet surface of the ice sheet, producing pigments that boost the ice’s absorption of solar energy. Soot and dust that blow from lower latitudes and darken the ice also appear to be playing a role, as are changes in weather patterns that increasingly steer warm, moist air over the vulnerable ice.Science: “The great Greenland meltdown“
While the water volumes themselves are of note for ocean levels, they are probably less important that their function as a lubricant for glaciers.
Unlike the loss of sea ice mass in both polar regions, this ice on Greenland and Antarctica mostly isn’t floating on water. The main effect of sea ice area reducing is to reduce the reflection of light and therefore energy back into space. It makes little direct difference to sea levels.
But the melt or calving off glaciers of ice that is on land will contribute directly to sea level rise. The reason why both of these factors, calving and surface melt, are important to understand.
But the net loss from Greenland is steadily accelerating sea level rises. Until 2000 Greenland, on average, accumulated as much mass as it shed. In the two decades of this century, it has been falling behind, creating sea water as a result.
Crumbling glaciers and torrents of melt-water slicing through Greenland’s ice block—as thick as ten Eiffel Towers end-to-end—were the single biggest source of global sea level rise in 2019 and accounted for 40 percent of the total, researchers reported in the journal Communications Earth & Environment.
Last year’s loss of mass was at least 15 percent above the previous record in 2012, but even more alarming are the long-term trends, they said.
“2019 and the four other record-loss years have all occurred in the last decade,” lead author Ingo Sasgen, a glaciologist at the Helmholtze Centre for Polar and Marine Research in Germany, told AFP.
The ice sheet is now tracking the worst-case global warming scenario of the UN’s climate science advisory panel, the IPCC, noted Andrew Shepherd, director of the Centre for Polar Observation and Modelling at the University of Leeds.
“This means we need to prepare for an extra ten centimetres or so of global sea level rise by 2100 from Greenland alone,” said Shepherd, who was not involved in the study.PhysOrg “Sea level rise quickens as Greenland ice sheet sheds record amount”
Greenland is bad enough. But the West Antarctica Ice Sheet in many ways is in a more precarious state than Greenland. There is more ice to add to sea levels, and much of the ice sheet there is grounded on land that is below sea level.
Intruding relatively warmer water has been melting ice at the grounding lines, the area where the floating ice shelf meets the part resting on bedrock, and hence affects the ice shelf stability and flow rates. The ice streams have been increasing in speed markedly, and the grounding lines are moving inland faster.
Even a more modest rise of a couple of metres would redraw the world’s coastlines and render land occupied today by hundreds of millions of people uninhabitable.PhysOrg “Sea level rise quickens as Greenland ice sheet sheds record amount”
Personally I’m less worried about people. They will move when sea water starts flooding their homes and sewer systems. It is likely to be a series of events over quite long periods of time as humans measure time. However the effects on the highly productive food growing regions near to coastlines and rivers over time is more worrisome. Sea level rises often are more expressed in ground waters and rivers becoming more saline, which have obvious agricultural implications.
My guess is that the IPCC is going to have to change what its old worst case scenario is to make it the current scenario. God knows what the worst case scenario will then look like.