Greenland Ice Sheet Already Reached Tipping Point 20 Years Ago

Greenland Ice Sheet

The Greenland ice sheet likely lies above an ancient tundra landscape with its own complex topography. Credit: Michalea King

At the turn of the 21st century, unbeknownst to the world, the Greenland ice sheet likely entered a state of sustained mass loss that will persist for the foreseeable future, according to a new study. Though the finding has raised concern over the future of the ice sheet, scientists emphasize that reducing emissions remains critical.

The study, which looked at 40 years of satellite data, was released on August 13, 2020, in Communications Earth & Environment. Second in size only to the Antarctic ice sheets, the Greenland ice sheet covers nearly 80 percent of the vast island. It contains the equivalent of about 24 feet of global mean sea level rise and, due to its accelerated retreat, is considered the largest single contributor to rising sea levels worldwide.

While the ice sheet’s decline has been well-documented over the past two decades, this latest study, led by Michalea King of the Byrd Polar and Climate Research Center, found that widespread glacier retreat helped push the ice sheet from a balanced to an imbalanced state. This work suggests that even if the oceans and atmosphere were to stop warming today, the ice sheet will continue to lose more ice than it will gain.

Research Team Greenland Ice Sheet

Members of the research team place equipment atop the ice sheet. Credit: Michalea King

In the decades leading up to the turn of the century, the ice sheet was in a state of relative equilibrium. The ice lost in a given year would be replenished by wintertime snowfall, and the sheet maintained a near-constant mass. But beginning around the year 2000, ice discharged through outlet glaciers—channels that flow outward to the sea—started to outpace annual snowfall that, in a balanced year, would replenish lost ice. The authors sifted through 40 years of satellite data, tracking outlet glacier velocity, thickness, and calving front position over time to determine the rate of ice loss. The shift they found represents a tipping point that is unlikely to be reversible in the near future. King told GlacierHub, “It’s like a gear change… we’ve accelerated the drainage at the edge of the ice sheet, and now… we expect mass loss to be the new norm for the ice sheet in the near future.”

Ian Howat, director of the Byrd Polar and Climate Research Center and co-author of the paper, explained to GlacierHub that the dynamics of ice loss through outlet glaciers can be likened to the functioning of a dam. “Those glaciers act just like a spillway on a dam,” he said. “The more you open the spillway… the faster the reservoir gets drawn down.” The study suggests that longer-term thinning throughout the 20th century—likely due to warming oceans—led up to a mass retreat event in the early 2000s. The result was a “step-increase” in the rate of discharge through outlet glaciers; before 2000, 420 gigatons of ice were discharged annually. In the years following, the rate increased to 480 gigatons of ice discharged annually. A gigaton is equal to one billion metric tons, roughly the mass of all land mammals (excluding humans) on Earth. “When all of these glaciers retreated at once, it was enough to significantly increase the rate at which ice flows into the ocean. It’s like the spillway on the dam was opened up,” Howat said.

The ice loss shown above has resulted in about 0.8 millimeters per year of sea level rise. Credit: NASA

According to King, the significance of this new rate of discharge is that “consistently, more ice is being lost through the flow of these glaciers than is being gained by snow accumulation.” Returning to a balanced state would require an extra 60 gigatons per year of snowfall or reduced melting. Yet under essentially all climate change scenarios, the opposite is expected.

The findings of this study—along with others that document the decline of the Greenland ice sheet—spell worrying news for sea level rise trajectories. Marco Tedesco, research professor of marine geology and geophysics at the Lamont-Doherty Earth Observatory, explained to GlacierHub that the Greenland ice sheet has been, and will increasingly be, a major contributor to rising sea levels. The two primary causes of sea level rise are thermal expansion—ocean water expands as it warms—and the melting of land-based ice. With sea level rise projected to submerge land home to 150 million people permanently below the high tide line (and that estimate assumes stability of the Antarctic ice sheet), Greenland finds itself in the spotlight. “In terms of direct contribution,” Tedesco said, “Greenland is actually the largest contributor now, with about 20 to 25 percent of sea level rise due to Greenland.” Moreover, the percentage of contribution could increase to 30 or 40 percent by the end of the century, according to Tedesco.

Coastal Waters of Greenland

Coastal waters of Greenland from above. Credit: Michalea King

Another study on the Greenland ice sheet, coauthored by Tedesco, made international headlines recently, concluding that 2019 was a year of record ice loss. According to scientists, the ice lost in 2019 was double the yearly average since 2003. Ian Joughin, a glaciologist at the University of Washington’s Polar Science Center, connected the dots between these two major studies. “Nobody really, 20 years ago, was expecting glaciers to speed up as rapidly as what we’ve seen,” he told GlacierHub. In terms of annual loss of ice, “people think of it as melting, but it’s basically the balance between how much snow falls each year, and how much icebergs calve off and how much melting actually occurs on the ice sheet itself.” Ultimately, neither melting nor ice discharge alone can explain the changing ice sheet. They are, rather, two processes in a complex dynamic, which glaciologists are racing to understand using a combination of field work, remote sensing, and modeling.

Rapid international action is needed to limit global warming to 1.5˚C, which would allow more time for adaptation to rising sea levels. Addressing recent headlines declaring that the ice sheet has reached the point of no return, a statement that has since been discussed within the scientific community, Howat said, “I think it’s very important to emphasize that this loss of the ice sheet is not irreversible. We’ve witnessed a step-change that is unlikely to be reversible in the near future, but we still have a long way to go and we still have a lot of say in how quickly the ice sheet will continue to retreat.”

Reference: “Dynamic ice loss from the Greenland Ice Sheet driven by sustained glacier retreat” by Michalea D. King, Ian M. Howat, Salvatore G. Candela, Myoung J. Noh, Seongsu Jeong, Brice P. Y. Noël, Michiel R. van den Broeke, Bert Wouters and Adelaide Negrete, 13 August 2020, Communications Earth & Environment.
DOI: 10.1038/s43247-020-0001-2

23 Comments on "Greenland Ice Sheet Already Reached Tipping Point 20 Years Ago"

  1. It is generally thought that the Greenland Ice Sheet has been present for at least 18 million years, despite it having been much warmer at times in the past than what it currently is!

    What is 40 years of observations compared to 18 million? If the outlet glaciers recede to where they are no longer being influenced by the ‘warm’ ocean waters, it is reasonable that the rate of loss will decrease significantly. That is, extrapolations from the current rate are not justified! “Tipping Points” imply a condition from which there is no possible recovery. In 4.5 billion years, the Earth has NEVER experienced a Tipping Point, which is why the climate has always changed and will continue to do so. Even the end of the last great glaciation was episodic, as evidenced by numerous parallel terminal moraines in western US alpine glaciers. Linear extrapolations are a naive assumption. However, using a linear extrapolation of current rates as an upper-bound, it would take about 10,000 years for all the ice to melt. By then, we may well be into another glaciation. In any event, we probably would have run out of fossil fuels and unless we have mastered controlled thermonuclear fusion, the human population (if even still around) will be much smaller. “Much ado about nothing!”

    • Torbjörn Larsson | September 8, 2020 at 12:08 pm | Reply

      “It is generally thought that the Greenland Ice Sheet has been present for at least 18 million years, despite it having been much warmer at times in the past than what it currently is!”

      What would be the significance here, since we observe the ice loss?

      And that – not the arguable claim that this observation is not considered one of a tipping point, an open question – is important.

      • The significance is that an unstated assumption is that a tipping point involves a a physical state from which there is no possible recovery, and that is because the present circumstances can be extrapolated linearly forward in time. The longer view, 18 million years, demonstrates that there have been no tipping points, and that growth and retreat are episodic, possibly periodic, and that linear extrapolation is not justified.

  2. What happened during the medieval warm period? For nearly 400 years it was a lot warmer than it is now: where did the ice recede to at that time?

  3. Peer Reviewed Greenland Ice records for the last 10000 years.

    It’s also ironic that during the so called arctic ice loss, polar bears are late leaving the ice due to lower melting.

    Nice try though…

  4. “Peer Reviewed Greenland Ice records for the last 10000 years”
    The graph shown ends in 1855 and does not include any of the recent human-driven warming.

  5. The viking named greenland b/c it was green allowing farming so this was not caused by co2 but was natural climatic varia tion

    • Torbjörn Larsson | September 8, 2020 at 12:12 pm | Reply

      That was regional variation, yes. It didn’t change the melt much.

      This is a consequence of global warming – with global sea level increase.

      • You would have us believe that the surface temperatures in Greenland were higher than today but that it didn’t affect melting? What’s wrong with this picture?

        Sea level rise is, at best, increasing the melt rate for those glaciers that have outlets to the sea. SLR doesn’t impact the interior.

  6. Damien Jeremy Weir | September 7, 2020 at 6:03 am | Reply

    Then let us not ask each other ‘does the ice melt and rising temperatures equal X or Y?, but rather shall we continue to burn fossil fuels and do nothing to change the damage this has already created?

  7. We’re still coming out of an ice age. This land was once green with forests and vegetation. It was green…. instead of scare tactics the left are always wet for how about wondering what ancient stuff we will find and learn? To me, that’s more interesting than your leftist fear tactics.

    • Torbjörn Larsson | September 8, 2020 at 12:18 pm | Reply

      No, we came out of a glaciation period 10,,000 years ago.

      And ~ 10,000 climate scientists comes from all parts of politics, but agree on their objective work. Only in US has a public political “left/right” phony discussion started.

      This is not about that, but about the rapid change in man made global warming and the social, economical and global natural consequences, which are dire. If facts are “fear tactics”, you are easily scared as well as opting for a conspiracy theory before fact.

      • More specifically, we are in an ‘interglacial.’ We won’t know whether we have reached peak warming until after the event. From the end of the last glacial, to the peak of the interglacial, the trend is for increasing temperatures. You are making statements that are not verifiable. I’m beginning to think that you don’t understand the things you are writing about.

  8. It seems to me these scientists could have saved a lot of time if, instead of carrying out their painstaking analytical study of the facts of the situation, they had simply googled stuff like all these experts commenting here.

  9. If they don’t start spraying for climate modification soon, the warming will begin to get worse at an increasing rate, since the carbon dioxide we have already put in the atmosphere will stay there for centuries, constantly making the planet hotter and hotter. Constantly adding to the carbon dioxide in the atmosphere is extremely dangerous because it stays there so long.
    Should a positive feedback loop of methane release get going, it might make much of this planet too hot for human survival. It might start getting released from the permafrost and sea bed faster than it can be destroyed, raising the temperature at the surface FAST!

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