Jakobshavn Glacier is Greenland's fastest-thinning glacier.

  • Greenland's fastest-thinning glacier has stopped retreating for the first time in 20 years, NASA found.
  • Jakobshavn Glacier grew 100 feet in height between 2016 and 2017.
  • Researchers suspect the change was brought about by colder water temperatures, causing the glacier to melt more slowly.
  • Temperatures in the North Atlantic Ocean oscillate between warm and cold every five to 20 years.

A glacier in Greenland that has been rapidly thinning for the past two decades has stopped retreating, and started to thicken again, a report from researchers at NASA has found.

Jakobshavn Glacier has been the fastest thinning glacier in Greenland for around 20 years, but is now thickening once again.

"Jakobshavn is now flowing more slowly, thickening, and advancing toward the ocean instead of retreating farther inland," NASA said.

"The glacier is still adding to global sea level rise - it continues to lose more ice to the ocean than it gains from snow accumulation - but at a slower rate."

Scientists suspect that the rate of shrinkage has slowed because a current brought colder water to the North Atlantic Ocean. The temperature of the water that flows into the glacier's fjords can affect how fast the ice caps melt.

Ala Khazendar, who authored the report, told NASA News that the result was unexpected.

"At first we didn't believe it. We had pretty much assumed that Jakobshavn would just keep going on as it had over the last 20 years," she said. "However, the Oceans Melting Greenland mission has recorded cold water near Jakobshavn for three years in a row."

In 2016, water temperatures in the region reached their lowest level since the late 1980's, most probably because of a climate pattern called the North Atlantic Oscillation (NAO). The NAO causes the Atlantic Ocean to switch between warm and cold every five to 20 years.

The cold water halted the melting process, and set off a dramatic change: Jakobshavn grew 100 feet in height between 2016 and 2017.

But the thickening of the glacier is almost guaranteed to be temporary. As the climate pattern progresses and the water heats up again, the glacier will start to lose ice faster again.

This could have dire consequences for coastal cities. Jakobshavn drains about 7% of Greenland's ice sheet, meaning that it has a huge impact on global sea levels.

If all of Greenland's ice sheet were to melt, which would take centuries, sea levels could rise enough to submerge the southern tip of Florida.

While global warming has increased the melting of ice around the world, NASA's study showed that other factors can play a role.

"For example, the shape of the bed under a glacier is very important, but it is not destiny. We've shown that ocean temperatures can be just as important."

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