Posts Tagged ‘Greenland’
|In this week’s issue of Science: Greenland ice loss is accelerating, and now we know why
Saturday, November 14th, 2009
Greenland and Antarctica are two places that climate scientists are studying intensely because of the potential for significant sea level rise were they to melt. Over the past 20 years, scientists have used a variety of methods to track ice loss, and they have found that Greenland has been losing ice more rapidly over the past decade than it had in the 1990s. In fact, since 2004, ice loss has accelerated to such a high level that Greenland is now losing about 270 billion tons of ice per year. Greenland’s contribution to sea level rise has been about 0.13-0.74 mm/yr, or about 4-23% of global sea level rise observed from 1993-2005.
In this week’s issue1,2 of Science (subscription required), Michiel van den Broeke and colleagues used a couple of methods to confirm that this acceleration of ice loss is real and to understand why it’s happening.
The extent of ice in a glacier is like a bank account, but instead of money, we’re keeping track of ice. When inflows (precipitation = snow) exceed outflows (mostly due to melting and runoff), the ice sheet gets bigger, just like a bank account grows when deposits exceed withdrawals. We say that there is a positive surface mass balance. When outflows exceed inflows, then the ice sheet shrinks, and we say there is a negative surface mass balance.
They found that before 1996, Greenland’s ice sheet had a positive mass balance (getting bigger) because precipitation exceeded runoff. Between 1996-2004, precipitation and runoff both increased, and since these roughly cancel out one another, the ice sheet didn’t change much. However, after 2004, precipitation stopped increasing while runoff continued to rise exponentially. Mass balance has been negative for about five years now, with a cumulative mass loss of almost one trillion tons of ice in that span. Amazing.
The next big question, therefore, is what’s causing precipitation to change? Will it go back up, thereby reversing the ice loss, or will it remain the same or decrease, causing loss to continue accelerating? Nobody knows at this point.
1van den Broeke (2009) Partitioning recent Greenland mass loss. Science 326:984
2Bowdoin people can access the article here.
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Photo credit: http://www.flickr.com/photos/chrissy575/ / CC BY-NC 2.0
Tags: Greenland
Posted in climate change science, polar ice, sea level rise | 2 Comments »
In this week’s issue of Nature: Ice sheets thinning
Thursday, October 15th, 2009
Most people are aware that the loss of ice from land masses like Greenland and Antarctica have the potential to raise sea level. One of the current concerns about polar ice loss is that as sea level rises, ice loss is accelerating.How does this work? Much of the ice along the margins of these land masses is what we call “grounded” –it physically stuck on the rough land lying under the coastal ocean. Imagine a block of ice sitting on a dinner plate, which, in turn, is sitting on something rough like a carpet. If you tilt up one end of the plate just a bit, gravity causes the ice to slide off until it hits the carpet, where it gets stuck. Most of the ice block remains on the plate but a bit is wedged (grounded) into the carpet. This is what basically happens to many of the glaciers flowing off the Greenland and Antarctic land masses.
Here’s the bad news:
Tags: Antarctica, climate warming, Greenland, ice, sea level
Posted in climate change science, polar ice, sea level rise | 1 Comment »
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