Mass loss from Greenland ice accelerates

Konrad Steffen: Greenland’s contribution to sea level rise is increasing

UPDATE 10/25/10: I’ve revised this story to clarify some important points, based on more information from Konrad Steffen, director of the Cooperative Institute for Research in Environmental Sciences. The previous version suggested that 2 to 3 meters of sea level rise was possible as a result of the kind of ice dynamics that the Jakobshavn Glacier in Greenland has been undergoing, and that more northerly Greenland glaciers could begin to experience. It was not clear in the original version that this degree of sea level rise would require Antarctica to respond more quickly than it has been, not just Greenland, and that it would probably take on the order centuries, not decades.

Today, a new report warns that Asian megacities like Bangkok are at increasing risk from flooding due to rising sea level in an increasingly warmer world.

And on Tuesday, NOAA issued its “Arctic Report Card” for 2010, which found, among other things, that ice in Greenland is melting faster now than ever before, helping to increase the rate of sea level rise.

With these reports as context (and as a ‘news peg’), I’d like to share what we learned during our weekly CEJ seminar yesterday from Konrad Steffen, a climate scientist who has made huge contributions to our understanding of the behavior of Greenland’s ice sheets. Steffen is director of the Cooperative Institute for Research in Environmental Sciences here in Boulder. His comments bear directly on the new sea level report and what the NOAA Arctic report card said about Greenland.

“We already know that 2010 is the second warmest year on record,” at least so far, Steffen notes. But in Greenland, it has been the very warmest. (With Greenland instrumental records going back to 1750.)

At what he calls “Swiss Camp,” his research station on the Greenland ice sheet (at about 1,000 meters elevation and 70 degrees North), Steffen and his colleagues have observed a seesawing pattern of temperature change, with the variability explained by such factors as volcanic eruptions and the North Atlantic Oscillation.

But over the long term, there has been a clear warming trend of about 2 degrees C per decade, with a total warming at Swiss Camp of 4 degrees C since 1991.

Warming temperatures in Greenland have been expanding the area of the ice sheet that is subject to melting during the summer. Up until this year, 2007 saw the widest area of melt on record. Steffen is still analyzing the data for this year, but it looks like 2010 did indeed see a record amount of melt. (The authors of the Greenland report card have found the same thing.)

Overall, the total area of Greenland subjected to melting has increased 65 percent since 1979.

Data from NASA’s orbiting ICESat show that inland, the Greenland ice sheet is actually gaining in elevation by about 2 centimeters per year. It sounds counterintuitive, but it actually makes sense.

As the atmosphere above Greenland warms, it can hold more moisture. And that means there has been more snowfall. Snow that falls above the elevation where melting occurs simply accumulates year by year and compresses into ice. So in these regions, the ice sheet is thickening — as a result of global warming.

But along the coasts, the elevation of the ice has decreased by tens of meters — and in some places, by up to 50 meters, according to Steffen. Thus, ice loss along the coasts is outpacing any growth inland.

One of the best place to see this ice loss is the Jakobshavn Glacier on the western coast of Greenland. “The locals used to call it the ‘Dead Glacier,’ because it never moved,” Steffen says. “But in 2001, that glacier suddenly became very active.”

It is now flowing from into the sea at the extraordinary speed of 14 kilometers per year. “If you stand there, you can see the ice moving,” Steffen says. And you also can hear it. “It sounds like a train going by.”

The glacier is helping to move massive amounts of ice out to sea, where it contributes to sea level rise.

Globally, the oceans are now rising at about 3.3 millimeters per year. Last decade, the rate was 1.7 millimeters per year. “So it has roughly doubled in the last decade,” Steffen says. And Greenland’s contribution to this sea level rise has risen from about 20 percent to 30 percent between 2004 and the present.

“It’s a huge change,” Steffen says.

Between 2003 and 2007, NASA’s Grace satellite showed that it was mostly eastern Greenland that was losing ice. But now, ice loss is steadily moving up the west coast, and considerably farther north than the Jakobshavn Glacier.

“All these glaciers are moving faster into the ocean,” Steffen says.

As glaciers farther north lose more and more ice, the implications are significant. The water locked up in the ice lost to the sea every day in summer from the Jakobshavn Glacier alone is equal to the amount of water used by New York City in an entire year. But the glaciers to the north potentially could discharge at a rate 10 times that amount, according to Steffen.

If those glaciers speed up enough, they have the potential to “drain most of northern Greenland in decades or a century,” Steffen says. That’s a wide range of uncertainty, to be sure. And it reflects gaps in scientists’ understanding of the ice dynamics. More about that in a minute. But first, based on what scientists know now, what can we expect in the way of sea level rise in coming decades?

The last IPCC report, published in 2007, said we could get up to 1 meter of rise by 2100. That would be the result of ice loss not just in Greenland, of course, but also Antarctica, as well as melting of mountain glaciers, and thermal expansion of sea water. But this prediction did not include growing understanding of ice dynamics in Greenland. As a result, sea level rise by 2100 could be higher than the IPCC’s most recent prediction.

But even 1 meter of sea level rise would pose “a major challenge,” Steffen says. To offer one example, with a storm surge from a hurricane, New York City could actually be looking at 1.5 meters of water sloshing ashore. And that could flood a good portion of the city.

With ice dynamics factored in, including accelerating coastal glaciers, what might we expect? Scientists do not have adequate physical models of the processes to give a reliable estimate, according to Steffen. But he estimates that if the northern Greenland glaciers accelerate, an additional 0.5 meters of sea level rise would be feasible.

Sea level could go even higher if Antarctica were to begin responding to warming more quickly than has been observed so far. Two or even three meters may be possible, but Steffen says this would likely unfold over a long period of time — on the order of centuries, not decades.

But since physical models of ice behavior cannot yet accurately reproduce the kind of rapid ice dynamics that Jakobshavn Glacier has been undergoing, an eventual 2 to 3 meters of rise may be plausible, but the likelihood of this happening is just not known.

These caveats are important to keep in mind. So is something else: “Our coastal societies developed in a time of stable sea level,” he says. But now, sea level is rising — and at an increasing rate. “That’s why this is scary.”

The new report on the risk to coastal cities highlights the risks millions of people, particularly those living in developing nations, are now facing from sea level rise. Titled ”Climate Risks and Adaptation in Asian Coastal Megacities,” it examines how Bangkok, Ho Chi Minh City, and Manila, might be impacted by rising seas under a range of different climate change scenarios through to 2050. It is a collaborative effort by the Asian Development Bank, the Japan International Cooperation Agency, and the World Bank.

From a World Bank press release:

The report finds that costs from major flooding events on infrastructure and the economy could run into the billions of dollars, with urban poor populations likely to be the hardest hit. It concludes that all three cities need to take targeted, city-specific and cutting edge approaches to meet these challenges.

Bangkok, Ho Chi Minh City, and Manila all have populations close to or over 10 million. Two are capital cities and all three are centers of national and regional economic growth contributing substantially to the GDP of the respective countries. As coastal megacities, all face increased climate-related risks such as rising sea levels and an increased frequency of extreme weather events. While commendable measures to counteract flooding have already been taken by these cities, much more needs to be done, the report argues.