Global Science Report is a weekly feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”
I recently returned from a trip to Greenland’s Jokabshavn Glacier, which discharges more ice than any other in the Northern Hemisphere.
Our route of flight from Reykjavik traversed the ice cap from about fifty miles north of Angmassalik to the airport at Ilulissat, on Disko Bay, about one-third of the way up Greenland’s west coast. In southeastern Greenland, we flew very close to the country’s second-highest peak, Mt. Forel (11,099 feet), and in the near future I will upload a image of a nearby mountain approximately 8,000 feet high completely covered by the ice cap.
It is obvious from the air that there is very little movement over the deepest regions of the ice, and the drift patterns in the lee of some of the submerged peaks are strongly suggestive of at least some regional accumulation. There is virtually no evidence for summer melt in the southeast, while the southwest portion of the ice cap is known to melt and refreeze at the surface on an annual cycle—I saw considerable evidence for multi-year, but small, lakes in that region.
In preparation, I read just about everything I could get my hands on, including a recent very remarkable paper by Dorthe Dahl-Jenson and about 70 coauthors. Dahl-Jensen heads up the Center for Ice and Climate at the University of Copenhagen. Dahl-Jenson’s team drilled to the bottom of the ice in northwestern Greenland, providing us with the first climate history of Greenland that includes the warmest period in the last interglacial period, from about 128,000 to 122,000 years ago, known as the Eemian. That was embedded in the Sangamon Interglacial, which ran from approximately 135,000 to 95,000 years ago.
(For perspective, the last (Wisconsin) glaciation started then and lasted to (nominally) 10,800 years ago—that last date being about a blink of a geologist’s eye ago. Homo sapiens appeared in the ice age, and evidence is that proto-civilization developed while the hemisphere was glaciated.)
One of the reigning myths in climate science is that interglacial temperatures in Greenland were about five degrees (C) above modern, causing a dramatic loss of ice and raising global sea levels about 6 meters (19 feet). Ice cores from southern Greenland in fact have wood and vegetation at their lowest levels, which are younger than the Eemian.
By measuring the ratio of two isotopes of oxygen (specifically 18O to the much more common 16O) one can infer the air temperature at the time that the snow in each annual layer crystallized. This technique has been around for decades and is considered quite reliable, and it correlates well with other temperature “proxies” that Dahl-Jensen also used. Dahl-Jensen found that the average annual temperature peaked at a whopping 8 +/- 4°C (that’s 7 to 22°F!) warmer than the recent millenium in the ice core during the Eemian maximum.
And still the ice survived. In fact, the top of the ice was only a mere 130 +/- 300 meters “lower” (actually from 557 feet higher to 1411 feet lower) than today. For perspective, her entire ice core was about 8,000 feet in depth.
If, like ex-NASA employee James Hansen, you think that global warming is going to drown us all by melting almost all of Greenland “in a hundred years” (Hansen’s words), perhaps you should try another apocalypse. According to the chart shown in Dahl-Jensen’s paper, the entire 6,000-year period averaged about 6°C warmer than the last 1000 years.
The integrated heating in this region during the Eemian maximum appears therefore to be approximately 36,000 degree-years (temperature change multiplied by time).
Climate models for the future show an annual warming of about 3°C over northwestern Greenland by around 2100, or 300 degree-years. At that rate, it would take 12,000 years to just get rid of about one-eighth of the ice in this core, or about 96,000 years to lose all of it. (That’s impossible because another ice age will have intervened.)
Evidence suggests that sea levels during the Eemian were about 4-8 meters (13-26 feet) higher than today.
Prior to Dahl-Jensen’s study, it was generally accepted that the vast majority of this rise came from the loss of Greenland’s ice, but now she cautiously writes that:
Although the documentation of ice thickness at one location on the Greenland ice sheet cannot constrain the overall ice-sheet changes during the last interglacial period, the [Eemian core] data can only be reconciled with Greenland ice-sheet simulations that point to a modest contribution (2 m) to the observed 4-8 m Eemian sea level high stand…These findings strongly imply that Antarctica must have contributed significantly to the Eemian sea level rise.
Whew! Thus does one revolutionary paper shoot pretty much the entire global warming sea-level catastrophe—the one worth being concerned about—through the heart. Antarctica is so cold that it is projected to gain ice in the coming century, as slightly increased precipitation—which may have recently been detected—falls as more snow, which compacts into more ice.
This puts any sea-level crisis out in the hundreds-of-years realm, at least, and probably far beyond our current era of burning hydrocarbons for energy and heat. In other words, forever.
As for Greenland, I have some bad news about the Jakobshavn Glacier. Its 30 X 6 mile (spectacular) Ilulissat Icefjord is going to be much less spectacular very soon, and I’ll also wager that the quick retreat of the glacier is literally grinding to a halt.
Better go to Ilulissat soon—in the next year or two—to see what was outside my hotel window (live webcam here). The spectacular nature of the fjord is a result of the massive icebergs—some a half-mile wide or so—that break off (calve) from the glacier, float down the fjord for a year or two, and then get stuck in the terminal moraine (laid down during the last glacial maximum, probably from circa 1600, when the Little Ice Age wiped out the Greenland Norse), where the fjord empties out into the ocean.
Unfortunately, the Jakobshavn Glacier has now retreated largely to its grounding line, with the exception of about 20% of the north end of the face—and that part doesn’t have far to go. In other words, it is largely no longer a calving tidewater glacier, and it is quite obvious from the air that the big bergs are getting much fewer and further between as the glacier moves further onto land. (Don’t forget to buy a helicopter ticket on Air Greenland—it’s worth it!)
When glaciers turn from tidewater to grounded, their recession rates usually slow dramatically (or, in some cases, they stop). This has probably started to happen.
So get your tickets for next summer (or later this summer) now, before the big bergs are gone.
And, before you go, don’t forget to read up—you just might come across some revolutionary good news.
Reference:
Dahl-Jensen, D., et al., 2013. Eemian interglacial reconstructed from a Greenland folded ice core. Nature 489, doi: 10.1038/nature11789.