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Chris Mooney @chriscmooney
, 14 tweets, 3 min read Read on Twitter
1. In 2016, standing atop Petermann glacier in far northwestern Greenland, I saw meltwater everywhere. Some of it was dramatic and dynamic, like this
2. In other places it was frozen and still, like this.
3. But there was definitely a sense that it was a problem – that the rivers, gullies, lakes, puddles, and everything in between atop this glacier were a sign of its unhealth.
4. Mostly the water was fleeting, moving, changing – it didn’t seem like it was a permanent record of anything. Yet that’s what scientists have just shown in a study I just wrote about this morning…
5. Meltwater in Greenland doesn’t automatically make its way to the sea – in many cases, it sits around and refreezes again. Then, it exists as a dense ice layer within the snow and firn that its itself a marker of a melt event.
6. So scientists from Dartmouth and several other institutions withdrew a series of ice cores from West Greenland and showed that there are more of these melt layers in the last two decades or so than there were in prior years.
7. It's honesty a pretty straightforward demonstration -- that is, once you've taken snowmobiles at multiple points across Greenland, extracted cores, gotten them back to be analyzed somehow, and so on.
8. In one case, the scientists were able to compare recent years with an ice core record that showed conditions in Greenland dating all the way back to 1547 – and still, the most recent decades had more refrozen meltwater than anything in that record.
9. Ergo – Greenland is melting more than it has in at least 450 years. But maybe a lot more than that, as there are other strands of evidence that can be used to infer Greenland’s temperatures going back further in time.
10. [You'll recall that all of this matters because Greenland is the largest single contributor to sea level rise at the moment, the world's second largest ice sheet, and contains 20 or more feet of potential sea level rise.]
11. This isn’t the first study to tell us Greenland is melting fast – far from it. But it does give a sense of the abnormality and strength of the perturbation. It gives us context.
12. At present, with current melt rates, Greenland is giving up an average of 286 billion tons of ice per year in correspondence with a temperature rise of about 2 degrees F. 286 billion tons is the better part of a millimeter of sea level rise per year.
13. The real question is how high this number can go and how much the rate of sea level rise can correspondingly increase – and, whether or not the change will be steady and linear.
14. The end #thread
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