May 9, 2023 - Energy & Environment

Greenland glacier discovery shows sea level projections are too low

A picture of meltwater flowing on top Petermann Glacier in northwestern Greenland in 2016.

A 30-mile-long meltwater river runs through Petermann Glacier in August 2016. Photo: Whitney Shefte/The Washington Post via Getty Images.

Scientists may be significantly underestimating the amount of melting yet to come from glaciers that end in the sea, according to a new study.

Why it matters: The study reveals that seawater is intruding deep into northwest Greenland's Petermann Glacier, thinning the ice from below.

  • Petermann acts like a doorstop, holding back vast quantities of land-based ice. As the glacier thins, inland ice moves faster into the ocean, raising global sea levels.
  • If all that inland ice were to melt, it would raise global sea levels by about 1.6 feet, the study found.

Zoom in: The researchers used satellite radar data from three different spacecraft constellations to obtain precise readings of the glacier's height and vertical motion.

  • They found that seawater, which is slightly above freezing there, is moving inland along the grounding line, which is where the glacier transitions from resting on bedrock to a floating ice shelf.
  • Most computer models used to project ice melt from marine-terminating glaciers like Petermann assume that little to no melting occurs at the grounding line, study coauthor Eric Rignot of NASA's Jet Propulsion Laboratory and University of California, Irvine told Axios via email.

Threat level: The glacier is rising and falling with the tides, as water flushes underneath it and penetrates more than a mile inland multiple times per day, the study found.

  • This finding surprised Rignot, particularly how far inland the relatively warm ocean waters are moving.
  • "This implies that the glacier is hugely sensitive to the temperature of the water," Rignot said.
  • Seawater has even carved a 670-foot-tall cavity underneath the ice, further weakening the glacier's ability to hold ice in place.

Between the lines: Rignot said the findings may help explain why computer models have trouble accurately depicting the pace of recent glacier retreat, as well as historical glacier melt events during Earth's history.

What they're saying: The study has big implications for what may happen at marine-terminating glaciers elsewhere in Greenland as well as in Antarctica, the study notes.

  • It suggests that current sea level projections are too low.
  • "We have reasons to believe that the current [sea level rise] projections are too low, not too high. They could be as much two times too low."
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