Jay Zwally: World’s fastest glacier doubled speed in past decade

In less than a decade, the Jakobshavn Glacier in southwestern Greenland has doubled its rate of flow into the sea.

EarthSky spoke with Jay Zwally of the NASA Goddard Space Flight Center. He said:

At present the models suggest that, as Earth climate continues to warm, the Greenland ice sheet will continue to contribute more to sea level rise at a faster and faster rate.

In 2001, this glacier was already the fastest in the world. It flowed from land to sea at 7 kilometers (4 miles) per year.

By July 2010, Jakobshavn Glacier had more than doubled its rate of flow to 15 kilometers per year. The reason is thought to be meltwater underneath the glacier, lubricating the glacier bed from below and allowing the glacier to slide more rapidly toward the sea.

About 90 percent of Greenland is covered with ice, and the ice is generally very thick – up to 3 kilometers (2 miles) thick in the center. The ice grows in the center from winter snowfall, and slowly, naturally moves towards Greenland’s coasts in a process of constant flow. Some of the ice moves out into the ocean through what are called outlet glaciers. Jakobshavn Glacier is the largest outlet glacier in Greenland.

This one glacier is currently discharging about 5 percent of the ice that leaves the Greenland ice sheet. It has been said that the Jakobshavn Glacier has the potential to contribute more to sea level rise than any other single feature in the northern hemisphere.

Why Jakobshavn Glacier is flowing faster

The Jakobshavn Glacier is located in the southern half of Greenland, which is warmer than the northern part and closer to the Gulf Stream. Southern Greenland is warmer than northern Greenland, and is responding to climate change more dramatically.

For decades, where the Jakobshavn Glacier met the ocean, part of it floated. The floating part is called an ice tongue, and at the end of the ice tongue, the ice calves off into very large icebergs. It’s believed that the iceberg that sank the Titanic might have come from this glacier.

Around the mid-1990s, the ocean in this part of the world began to warm noticeably, according to scientists’ measurements. As ocean temperatures climbed, the floating part of Jakobshavn Glacier started to thin. As it got thinner, it could no longer stay in place. Over a period of about 8 years, the glacier’s floating ice tongue disappeared.

And when the floating section of the glacier went away, it allowed the ice behind it to begin flowing faster. That is why the speed at which the ice was moving toward the sea doubled in less than a decade.

Warmer ocean waters, ice melt, and rising seas

Air temperatures in the vicinity of Greenland have increased noticeably in the last 10 years. Ocean temperatures, particularly around Greenland’s southern glaciers, have also been rising. Warmer water is coming up along the southwestern coast of Greenland and attacking the floating parts of the glaciers.

During the 1990s, the amount of snow that was coming in and going out of Greenland were approximately equal. The ice sheet was in balance. At that time, Greenland did not contribute to sea level rise.

But over the last 10 years, that has changed. The Greenland ice sheet is now losing about 170 gigatons each year, according to Dr. Jay Zwally (see his video, top right). Melting Greenland ice is causing sea level to rise about half a millimeter each year, or about 15 percent of the current global sea level rise.

Scientists are using data related to Greenland’s ice melt in computer models of how ice flows and of Earth’s climate as a whole. Meanwhile, scientists can calculate that – if all the ice in Greenland melted – sea level would rise about seven meters. No one expects all of Greenland’s ice to melt, but this icy continent is likely to contribute to a significant amount to global sea level rise over the next 100 years.

November 28, 2011

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