A large iceberg with areas of open water nearby. Photo: NASA/Linette Boisvert

Without significant near-term cuts to greenhouse gas emissions, all of the ice in Greenland could be lost within the next millennium, a new study finds.

Why it matters: The Greenland Ice Sheet is the second-largest ice sheet in the world, containing enough water to raise global sea levels by 23 feet if it were to melt completely. While a 1,000-year timeframe sounds extremely long, it is unusually speedy in geologic time, and the resultant sea level rise would drown many coastal megacities long before the year 3000.

  • In fact, the study shows that melting at the present rate could contribute between 19 to 63 inches to global sea level rise within the next two centuries alone — greater than previous estimates, according to NASA, which helped sponsor the new research.

What they did: For the study, published in Science Advances, researchers used an open source computer model that captures how outlet glaciers, large rivers of ice ending in the sea, will respond to various amounts of climate warming.

  • They investigated the sources and magnitude of uncertainty in projections of Greenland ice loss by running their the model 500 times out to the year 3000 for each of three possible future climate scenarios, each time adjusting key land, ice, ocean and atmospheric variables to test their effects on ice melt rate.

What they found: The study found that Greenland will likely become ice-free within 1,000 years unless greenhouse gas emissions are substantially cut. Here are the results for the three specific emissions scenarios they examined:

  • Under a scenario consistent with achieving the Paris climate agreement's temperature targets, Greenland could lose between 8 to 25% of its mass, the study found, contributing to between 0.59–to 1.88 meters, or 1.93 to 6.16 feet, of sea level rise.
  • Under an emissions pathway that features modest emissions reductions, the ice sheet would lose between 26 to 57% of its mass, the study shows, yielding between 1.86 to 4.17 meters, or 6.10 to 13.6 feet, of sea level rise.
  • And if the world were to continue on a roughly business as usual emissions course, then Greenland could lose between 72 and 100% of its mass by the year 3000, adding between 5.23 to 7.28 meters, or 17.1 to 23.88 feet, of sea level rise.

Between the lines: The study points to the risk of an escalating sea level rise crisis throughout the next several centuries unless carbon dioxide emissions from fossil fuel burning, deforestation and other sources are slashed in the near term.

  • Once set in motion, the melting of the Greenland and Antarctic Ice Sheets will stay in motion for a long period, meaning that waiting to cut emissions would lock in many more meters of sea level rise.
  • The study refers to this phenomenon as the "committed sea level rise," with ice melt continuing well beyond when global average surface temperatures are stabilized.
  • Such findings are consistent with other studies that have shown ice sheets taking centuries to millennia to stabilize following an initial pulse of rapid global warming.

But, but, but: The study is based on computer modeling that takes into account prescribed, but imperfect, scenarios of greenhouse gas emissions. It's possible that future emissions will turn out quite differently, and that the models used are missing important features that help regulate the Greenland Ice Sheet.

  • However, the study notes that the uncertainties may actually underplay global temperature increases.
  • The research does not incorporate the newest data on how ocean warming is affecting glacial melt along Greenland's coasts. Josh Willis, who leads a NASA program examining the ocean-ice melt connection, tells Axios that his team's findings show this study's melt projections may need to be increased.
  • "I think it's likely we will find that the ocean has a bigger impact than was accounted for in this study," Willis, who was not involved in the new study, said via email. 

What they're saying: "While sea-level rise in the next decades may be considered small by some people, the next decades will determine the mid and long-term future of our planet. It will not only affect our children but many generations down the road," study lead author Andy Aschwanden tells Axios in an email.

Go deeper: Rising sea levels could cost the U.S. trillions

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Senate Majority Leader Mitch McConnell talks to reporters on Capitol Hill last Thursday. Photo: Chip Somodevilla/Getty Images

With President Trump planning to nominate his third Supreme Court justice nominee this week, key Republican senators are indicating their stance on replacing the late Justice Ruth Bader Ginsburg with less than 50 days until Election Day.

The state of play: Senate Majority Leader Mitch McConnell (Ky.) has vowed that "Trump’s nominee will receive a vote on the floor of the United States Senate." Two GOP senators — Sen. Lisa Murkowski (R-Alaska) and Sen. Susan Collins (R-Maine) — have said they oppose holding a vote before the election, meaning that two more defections would force McConnell to delay until at least the lame-duck session of Congress.

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Biden to Senate GOP after RBG passing: "Please follow your conscience"

Joe Biden made a direct appeal to Senate Republicans in a speech addressing the passing of Supreme Court Justice Ruth Bader Ginsburg, urging them to "cool the flames that have been engulfing our country" by waiting to confirm her replacement until after the election.

The state of play: Senate Majority Leader Mitch McConnell said soon after the news of Ginsburg's death that President Trump's nominee would get a vote on the Senate floor.