Tag Archives: Changes in the Velocity Structure of the Greenland Ice Sheet

On “Changes in the Velocity Structure of the Greenland Ice Sheet”

A couple days ago, scientists at the University of Texas at Austin’s Institute for Geophysics published the first map of Greenland ice movement over time, and compared the current rates of ice movement to the historical trend.

Image shows three color-coded maps of Greenland. The first shows the average rate of ice movement over the last 9,000 years with a deep blue vein of almost no movement that runs down the center (roughly) of Greenland with branches towards the edges where Greenland's geology results in slow ice movement. The blue "core" is surrounded by blue-greens fading to yellows and reds at the edges of the island, with some white. This may be where there's not sufficient data to determine average movement speeds (the ice there is probably too recent). The second image is the present-day status of ice movement on Greenland. The deep blue sections are much broader, covering more of Greenland, with a similar (at a glance) distribution of greens and yellows, but much more red around the edges of Greenland, and none of the "no-data" white. The third image shows the difference in movement speed across the parts of Greenland for which we have data going back 9,000 years. In this image, the spectrum is red (meaning faster) to white (neutral) to blue (slower movement than the historical average). Much of Greenland that is colored shows blue, indicating that over all, the ice sheets are moving more slowly now than their average speed over the last 9,000 years. The areas that where white/uncoded in the first image are also uncoded here. The only red is around the edges, near the uncoded areas where the ice is currently moving much faster, based on more recent measurements.

Greenland’s average ice speed over the last nine thousand years (left), its current speed (center) and the difference between them (right). Blues (negative values) signify lower speeds today as compared to the nine-thousand-year average.

Their basic finding is that the current rate of Greenland ice movement is slower than the average rate of the last 9,000 years. This is basically due to differences in Earth’s atmosphere over time:

During the last glacial period, higher rates of atmospheric dust deposition produced softer ice, which flowed more readily than cleaner ice. During most of the Holocene, though, atmospheric dust concentrations were lower, and the less-dusty ice that formed was stiffer, meaning it did not flow or thin so rapidly. Thus, the thickening seen today in the central regions of Greenland is partly a response to changes in ice rheology that occurred thousands of years ago.

Presumably this dust disparity doesn’t include the late 19th century leading into the 20th and 21st centuries.

If you want to look more into the research, you can go to the Science Daily article, or the research report in Science (which is behind a paywall).

This research – like a lot of climate research – can be a bit confusing to non-scientists. If you’ve paid attention to what sundry news sources have had to say about climate change and Greenland ice, you’ve probably gotten the impression that it’s not only melting, it’s also sliding into the ocean faster every year. That’s the impression I had, and it’s the impression the authors of this research had too:

“Like many others, I had in mind the ongoing dramatic retreat and speedup along the edges of the ice sheet, so I’d assumed that the interior was faster now too. But it wasn’t,”

Based on my experience in climate science communication, at some point the community of climate deniers will seize on this (with glee) as “part of a growing collection of evidence that things aren’t actually as the ‘warmists’ would have us believe”. And, to be honest, most advocates for climate action will probably ignore these findings, for the most part, because at first glance it seems like the deniers might have a point.

The problem is that we’re really good at taking “first glances” and really bad at getting the right impression from them, and as with much of science, this merits deeper discussion.

First of all, while the interior of Greenland is moving more slowly than it used to, the outer edges are moving much, much more quickly than they used to, and contributing to sea level rise. It is expected that as the edges of the Greenland ice sheet crumble into the ocean, and as temperatures continue to rise, the interior of the Greenland ice sheet will probably speed up again.

And that brings us to the second point. People of all stripes have a tendency to focus on research that supports the views they already hold, while discounting or ignoring anything that might challenge their beliefs. While they are not alone in doing this, the climate denial movement is particularly adept at it. They will take isolated bits and pieces, behave as though those bits and pieces are all of climate science.

The reality is that as long as greenhouse gas levels continue to rise, the planet’s temperature will also rise. That’s basic thermodynamics. If you increase the insulation around something, without reducing the amount of incoming heat, then it would be physically impossible for it not to warm.

The Earth’s temperature will continue to rise (and that includes both ocean and atmospheric temperatures) because we are continuing to add greenhouse gasses to the climate system. The rise in temperature has already led to rising sea levels and melting ice around the world, including Greenland. Higher temperatures will mean more melting. Again, that’s basic thermodynamics. This research shows that the changes in temperature and greenhouse gasses are not the only factors at work, and that’s good to know; but in the end, these data do not call the laws of thermodynamics into question.

There’s one more thing to mention about the deniers. A large part of their “case” rests on the notion that the scientific establishment is, in fact, suppressing or ignoring any evidence that might challenge the mainstream understanding of Earth’s climate. It’s a seductive message (there’s a reason there are so many conspiracy theorists out there), but one that is without merit. This is a clear example of a scientist going into his research with an expected finding (he thought he’d find accelerating ice movement), getting a result that was the opposite of what he expected, and reporting on it anyway, because for a majority of scientists, that’s just what you do.

Dishonesty is a factor in all human endeavors, and there are many examples of scientists fudging the numbers. It is important to note, however, that those lies are found out, usually by scientists, and that over time the record is corrected. The field of climate science is almost 200 years old, and for a majority of that time, we’ve known the thermal properties of CO2 and other greenhouse gases. We’ve also known that increasing those gases will cause Earth’s temperature to rise. Unless someone manages to produce and support research that undermines those basic facts, there is NO reason to think that Earth’s temperature will do anything other than rise, and keep on rising as long as our greenhouse gas emissions maintain a themal imbalance.

I’ll let Pippa get the last word on this –

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