Greenland’s melting glaciers
Monday
With so many things in the news to worry about these days, it’s hard to keep in mind the most serious threat facing us, which is climate change. Scientists are now discovering that the Greenland glaciers are melting faster than predicted, which could lead to catastrophic sea level rise by the end of the century. A technical description of the melting process brings to mind Coleridge’s haunting poem “Kubla Khan.”
A March Washington Post article reported on a new study of Greenland’s glaciers, entitled Oceans Are Melting Greenland in order to give it the eye-catching acronym OMG:
Greenland is, in fact, the largest global contributor to rising seas — adding about a millimeter per year to the global ocean, NASA says — and it has 7.36 potential meters (over 24 feet) to give. The question is how fast it could lose that ice, and over five years, OMG plans to pull in enough data to give the best answer yet.
“We’ve never observed Greenland disappearing before, and that’s what OMG is about,” says Josh Willis, a researcher at NASA’s Jet Propulsion Laboratory who is the principal investigator on the mission. “We want to watch how it shrinks over the next five years, and see how we can use that information to better predict the future.”
According to the Post article, while the results are not yet it, the United Nations Intergovernmental Panel on Climate Change
said in 2013 that Greenland’s melting might at most contribute 21 centimeters to sea-level rise by 2100, with some possible addition from rapid ice collapse (this is the high-end number for what scientists call the “likely” range in a worst-case global warming scenario, to be precise).
One reason for the accelerated melting involves caves of ice into which rivers are pouring, which is what made me think of Coleridge’s poem. Here’s the technical description of a process known as “dynamic thinning”:
Dynamic thinning is, in a way, a positive feedback loop. When it gets warm enough, the surface snow and ice begin to thaw. The melt water either pools or flows in rivers along the surface, or begins flowing under the snow that covers the ice of the sheet. In the process, it flows into small cracks, enlarging them as it moves towards the bottom of the ice sheet. The amount of melt water traveling through these fissures varies greatly. Waleed Abdalati, head of NASA Goddard Space Flight Centers Cryospheric Sciences Branch, mentioned that “for the first few weeks, the melt water sounds like a peaceful stream. Soon it takes on the menacing roar of a rushing river.”
As surface melt increases, it collects into rivers that carry it to turquoise blue pools or plunge into crevasses or ice tunnels called moulins or glacier mills. Moulin…can extend downwards hundreds of meters, reaching the base of the glacier, or can flow within the glacier. Wherever the water ends up, moulins can affect both the melting rate and also the velocity of a glacier. The streams bring surface heat in the form of water down through the glacier to the bottom of the ice sheet. Once the water reaches the bottom of the glacier, it acts as lubrication for the glacier, which then gains speed as it flows downhill towards the sea. Thus, a little melting can have a large effect.
In “Kubla Khan,” the sacred river Alph springs out of a chasm, meanders five miles, and then reaches “caverns measureless to man”—at which point, the prophecies become dire:
Five miles meandering with a mazy motion
Through wood and dale the sacred river ran,
Then reached the caverns measureless to man,
And sank in tumult to a lifeless ocean;
And ’mid this tumult Kubla heard from far
Ancestral voices prophesying war!
The shadow of the dome of pleasure
Floated midway on the waves;
Where was heard the mingled measure
From the fountain and the caves.
It was a miracle of rare device,
A sunny pleasure-dome with caves of ice!
Or as Abdalati puts it, “for the first few weeks, the melt water sounds like a peaceful stream. Soon it takes on the menacing roar of a rushing river.”
Like the poet in the poem, one expects him to add, “Beware! Beware!”
The prophecies of war, meanwhile, are not coming only from climate scientists but also from the U.S. military, which predicts that world conflicts will rise as climate change disrupts the world order. Scientific American, for instance, has pointed out that a climate change-caused drought in Syria—the worst in its history—led to the war there as farmers flooded into the cities.
Meanwhile climate deniers block environmental legislation and focus on tax cuts for the wealthy, which would allow them to build more stately pleasure domes and gardens bright with sinuous rills.
Beware! Beware!