The Sciences

Our ice is disappearing

Bad AstronomyBy Phil PlaitJan 21, 2010 9:49 PM


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If you are a normal person trying to figure out who is right and who is wrong on an issue, it can be pretty confusing. When it comes to things like global warming, there are folks out there who twist, distort, and spin the facts so grievously that it's hard to tell the difference between what they are doing and outright lying. And when one of them does it, a slew of others pick it up, making the chorus of nonsense self-reinforcing, muddying the waters even more. We saw this happen with the CRU emails that were hacked -- a situation which was nowhere near as important as so many trumped them up to be -- and of course we will see it again and again. To help staunch that, there are two points about global warming I've recently come across that I want to make sure are very clear. 1) Some global warming denialists obfuscate what's going on with Antarctica, saying the ice there is actually growing, not melting. That is patently false. Where it really matters, Antarctic ice is melting.

As you can see by this NASA graphic from the linked page, Antarctica loses over 100 billion tons of ice per year, the equivalent of about a hundred cubic kilometers (more than 20 cubic miles) of ice. That number is hard to grasp, but it's the equivalent to the volume of a mountain about 14,000 feet high -- or, if you prefer, it's like saying that one Colorado Rocky Mountain's worth of ice disappears every year. Just in Antarctica alone. You may note that the line fitted to the points in that graph is changing its slope, getting steeper with time. I wouldn't extrapolate that too much, but if true, it means the loss rate is accelerating. 2) The IPCC report in 2007 was a landmark analysis of the current GW situation. It has been attacked repeatedly by denialists, of course. As it happens, in one part of the report they said that Himalayan glaciers may melt away completely by 2035. This turns out to have been based on a report that was not peer-reviewed, and most likely incorrect. However, this does not mean the entire report is wrong, and it certainly doesn't even mean that Himalayan glaciers are fine! Quite the opposite, in fact. A new study of Himalayan ice using satellite data shows that the ice is disappearing, and from 2003 to 2009 shrank at a rate of 47 billion tons per year. I'll be careful to note that the uncertainty in this measurement is about 25% (12 Gt/year) and has a short baseline in time, but even considering that, the loss of Himalayan ice is definitely large and almost certainly increasing -- perhaps twice as rapidly now as it was in the past 40 years before the study. This is supported by a ground-based study of over 600 glaciers being monitored by Chinese scientists, which showed that between 1980 and 1995, 90% of those glaciers were retreating, and in the period of 1995 - 2005, 95% retreated. In other words, the vast majority of the glaciers studied were losing ice, and in more recent years the number of glaciers losing ice increased. This is all consistent with global loss rates of ice: it's disappearing faster now than it was in previous decades.

Get a good look at Himalayan glaciers while you still can. Expect to hear the antiglobal warming crowd crowing over this, and the media misreporting this to sow more doubt about global warming. But the important point to remember is this: the Himalayan ice really is shrinking, and the same thing is happening in Antarctica. Global warming is real. It's also getting worse. You can shout, you can scream until you're red in the face, and you can deny the facts all you want. But facts are pesky: they exist whether you believe in them or not.

My thanks to expert glaciologists Drs. Lonnie Thompson and C. K . Shum for taking time to explain the Himalayan studies to me and for providing me with the numbers from the ground studies.

Glacier image from mckaysavage's Flickr stream licensed under creative comons.

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