ICE MELT: Satellite measurements reveal how rapidly Earth is losing ice.
Image: Wikimedia Commons/Mila Zinkova
For years, scientists have warned that climate change is taking its toll on Earth's ice, thawing not just the massive ice sheets of Greenland and Antarctica but mountain glaciers and ice caps from the Andes to the Alps.
But with few long-term measurements of ice outside the polar regions, getting a handle on just how fast it was melting was tricky.
Now a new study, published yesterday in the journal Nature, attempts to solve that problem by using data from NASA satellites to provide a uniform, up-to-date survey of mountain glaciers and ice caps. Calculations by researchers at the University of Colorado show the world lost 150 billion tons of non-polar ice each year from 2003 to 2010, enough to raise sea level by 0.4 millimeters per year during that time.
"People have looked at Greenland and Antarctica for several years, and there are a lot of studies on that ice," said University of Colorado glaciologist John Wahr, an author of the new research. "But there are a lot of areas covered with ice that haven't been considered at all."
Fewer than 120 of the planet's 160,000 glaciers have been monitored by researchers, and only 37 of those have been tracked for more than 30 years.
That's due in many cases to the sheer difficulty of reaching that ice and operating in harsh alpine environments. Scientists have been forced to take measurements from a handful of glaciers and extrapolate their behavior to entire glacial systems, Wahr said, making many estimates of ice loss highly uncertain.
He and his colleagues attempted to circumvent that problem by analyzing data collected by NASA's twin GRACE satellites, which orbit the Earth in tandem 16 times a day.
The probes fly about 135 miles apart -- a distance that constantly changes as GRACE-1 and GRACE-2 pass over the Earth's surface. Small changes in the planet's gravity field can push the satellites together, ever so slightly, or pull them apart. Those minute variations -- as small as 1 micron -- allow scientists to measure changes in the mass of the Earth's surface.
"With GRACE, you get really comprehensive results over an entire glacier system," Wahr said. "We see all the glacier."
385B tons of polar ice melted per year
In addition to estimating ice loss from glaciers and ice caps outside the poles, the new study calculates that the massive ice sheets in Greenland and Antarctica shed 385 billion tons of ice per year during the eight-year study period, contributing 1.06 millimeters per year to sea-level rise.
That's in line with an earlier study, published last year in Geophysical Research Letters, that used GRACE data and other observations to estimate ice loss at the poles. One of the authors of that paper, glaciologist Eric Rignot of NASA's Jet Propulsion Laboratory and the University of California, Irvine, praised the new research.
"It's a great paper," said Rignot, who was not involved in the Nature study. "It's the first time that a uniform method has been applied to all the mountain glaciers of the world so there is no regional bias, a priori."
While current observations and future climate change projections suggest that melting of polar ice will be the largest factor in future sea-level rise, Rignot said that "doesn't make mountain glaciers irrelevant," because in many areas they are important sources of water for drinking and agriculture.
But GRACE isn't perfect. Its twin probes have trouble measuring changes in smaller glacier systems, and can't zoom in on an individual glacier, limitations that Wahr readily acknowledges.
Those limitations should caution anyone against reading too much into the new study's estimates of ice loss from relatively small glacier systems, said Graham Cogley, a glaciologist at Trent University in Ontario who did not contribute to the research.
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13 Comments
Add CommentRight, keep clinging to your hope that the smoke pouring out your kitchen windows isn't matched to a fire burning inside. That's about the level of silliness you're at man. Just keep clinging to those hopes, because that's all you got.
Reply | Report Abuse | Link to thisAs long as we 'burn' to live, we will 'burn' in the end. Whether, it be wood, coal, oil, natural gas or uranium the results of all those reactions will destroy us.
Reply | Report Abuse | Link to thisDo you actually read the article??
Reply | Report Abuse | Link to thisWhich part of which model do you think has been refuted by this article?
Reply | Report Abuse | Link to thisWhat is your model? That ice won't melt when it gets warmer?
What makes you think our best information is models anyway?
Reply | Report Abuse | Link to thisThere are lots of paleologic studies which show, for instance, that under similar, or approaching conditions, the earth has been essentially ice free. What makes you think the physics of the earth today are that much different from what they have been in the past?
A little troubling about the coming gap in GRACE-like data; calibration across gaps is a pain.
Reply | Report Abuse | Link to thisBetter data is always good. Unfortunately those who DENY that more CO2 will lead to disaster for humanity do not seem to let better data get in the way of their fears. All you DENIERS keep praying to your flawed FOSSIL FUEL PROPAGANDA and what they predict---even though they have been demonstrated to be flawed...deeply flawed
Reply | Report Abuse | Link to thisFunny how you can make a case for ANYTHING by changing a few words...especially when the original speaker presents ZERO facts to back up their claims!
Pokerplyer,
Reply | Report Abuse | Link to thisAgain, what makes you think the earth system will behave differently now than it has in the past?
Let's do a little simple math.
According to this study, which you claim supports your position that there is nothing to worry about, the loss in ice mass, put into two basic categories, is:
Greenland + Antarctica loss: 385 billion tons/year
Everything else: 148 billion tons/year
Total losses: ~533 billion tons/year
The high end of prior estimates put high Asian range (including Himalaya) losses at 50 billion tons/year; this study puts them at 4 billion tons/year.
That's a big reduction for one area of the world, but does not change the fact that a lot of ice mass is being lost, and that the rate is accelerating.
Here is a slightly more technical summary of the same paper:
http://www.sciencedaily.com/releases/2012/02/120209100544.htm
and here are measurements of the acceleration of ice mass loss from Greenland and Antarctica.
"We find that during this time period the mass loss of the ice sheets is not a constant, but accelerating with time, i.e., that the GRACE observations are better represented by a quadratic trend than by a linear one, implying that the ice sheets contribution to sea level becomes larger with time."
http://citeseerx.ist.psu.edu/viewdoc/summary;jsessionid=938A77EA91CCEF23603DB338334C306F?doi=10.1.1.170.8753
Somehow you have taken the reduction in ice loss around the Himalayas to mean that ice does not melt when the world gets generally warmer. It is you who are unable to come to grips with the facts.
Have you ever considered that your comments don't last long at RealClimate and Skeptical Science because you make assertions that are contrary to readily verifiable facts?
Reply | Report Abuse | Link to thisI'm still trying to get my head around what pokerplayer is trying to get across. This study confirms we are on track for significant sea level rise this century.
Reply | Report Abuse | Link to thisYou know, repeating something over and over again does not make it true. There are models, or ensembles of models that are tracking within error bounds. Some are outside of those bounds, but those have been underestimating effects in the real world.
Reply | Report Abuse | Link to thishttp://www.skepticalscience.com/climate-models-intermediate.htm
You also are clinging to the believe that GCMs are the only way of knowing what the earth will do, and it has been pointed out to you that paleologic records of the earth under similar conditions indicate an ice-free planet is coming if BAU continues. You haven't challenged that.
You also haven't challenged the idea that ice sheet loss is accelerating (looks like on a quadratic, the right side of an upside down parabola in simple terms). So, again, where do you think that water is going to end up if not the ocean?
Please at least attempt to defend your argument.
So if you accept this research, even if you think it invalidates some models, you must accept that this study also confirms we are on track for significant sea level rise this century?
Reply | Report Abuse | Link to thisOh my God! Not a whole millimeter every ten years? Before you know it the cities will be under water. After 4000 or 5000 years this could get serious, assuming of course that the trend continues which is almost impossible to happen. It may be decreasing a millimeter per decade by then. Worry, worry, worry.
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