Why is Greenland covered in ice?
August 27th, 2008
Computer models show that while (tectonic) uplift of the Rocky Mountains may have contributed to increased ice cover on Greenland, this change was small in comparison with the ice sheet caused by a decrease in carbon dioxide. Credit: Dan Lunt, University of Bristol
There have been many reports in the media about the effects of global warming on the Greenland ice-sheet, but there is still great uncertainty as to why there is an ice-sheet there at all.
Reporting today (28 August) in the journal Nature, scientists at the University of Bristol and the University of Leeds show that only changes in atmospheric carbon dioxide are able to explain the transition from the mostly ice-free Greenland of three million years ago, to the ice-covered Greenland of today.
Understanding why the ice formed on Greenland three million years ago will help understand the possible response of the ice sheet to future climate change.
Dr Dan Lunt from the University of Bristol and funded by the British Antarctic Survey, explained: "Evidence shows that around three million years ago there was an increase in the amount of rock and debris deposited on the ocean floor around Greenland. These rocks could not have got there until icebergs started to form and could transport them, indicating that large amounts of ice on Greenland only began to form about three million years ago.
"Prior to that, Greenland was largely ice-free and probably covered in grass and forest. Furthermore, atmospheric carbon dioxide levels were relatively high. So the question we wanted to answer was why did Greenland become covered in an ice-sheet?"
There are several competing theories, ranging from changes in ocean circulation, the increasing height of the Rocky Mountains, changes in the Earth's orbit, and natural changes in atmospheric greenhouse gas concentrations. Using state-of-the-art computer climate and ice-sheet models, Lunt and colleagues decided to test which, if any, of these theories was the most credible.
While the results suggest that climatic shifts associated with changes in ocean circulation and tectonic uplift did affect the amount of ice cover, and that the ice waxed and waned with changes in the Earth's orbit, none of these changes were large enough to contribute significantly to the long-term growth of the Greenland ice sheet.
Instead, the new research suggests that the dominant cause of the Greenland glaciation was the fall from high atmospheric carbon dioxide levels to levels closer to that of pre-industrial times. Today concentrations are approaching the levels that existed while Greenland was mostly ice-free.
Dr Alan Haywood from the University of Leeds added: "So why did elevated atmospheric carbon dioxide concentrations fall to levels similar to the pre-industrial era? That is the million dollar question which researchers will no doubt be trying to answer during the next few years."
Citation: The paper: ‘Late Pliocene Greenland glaciation controlled by a decline in atmospheric CO2 levels’, by Daniel J. Lunt, Gavin L. Foster, Alan M. Haywood, and Emma J. Stone. Nature, 28 August 2008, doi:10.1038/nature07223.
Source: University of Bristol
Jul 01, 2009 |
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These models cannot predict next week's weather. They cannot be run backwards a month to show last month's weather. And yet they can predict with a very high degree of confidence what happened three million years ago.
Strange that every study shows that temperature rise preceeds CO2 rise, and yet these advanced computers don't know that.
Just another human caused global warming article.
I'm not beating the war drum, but the true is, the exhausting of fossil fuel sources makes the geopolitical situation less stable.
locations of "perfection" will change. it will bring growth to mankind
Yeah, state of the art in climate modeling leaves much to be desired.
Weather is not climate.
Where do you get more dry weather? Some places will be drier and some wetter. All in all it will add up to overall wetter because warmer bodies of water evaporate more and warmer air carries exponentially more water. When air masses, w/ the same delta temp. as today, meet more precipitation forms (look at a psychrometric chart). AND change creates real jobs not the phony ones created by government at our expense.
There is no exhausting of the fossil fuel sources. Gull island alone could be 2 million barrels/day but it has been capped and put off limits for over 30 yrs by the powers that be. ANWR and environs contains enough oil and gas to keep the uSA going for many, many 10s of yrs. The Green river oil and Baaken tar sands for many MANY 100s of yrs. All w/o taking a drop from the middle east.
Weather is what climate is made of.
The H20 will have left the atmosphere within days, weeks at most. CO2 can hang around for months or years. It's not uncommon for people to get hung up on water as a GHG. It is, but it's very dynamic. The analogue is that when the bath is overflowing, it doesn't matter how much water is in the bath, it's the input from the taps that is pouring down the stairs.
Weather is not "what climate is made of". Climate can be seen as the statistical average of weather over a long period. That you can't predict the outcome of the roll of a die doesn't invalidate statistics as a science, right? It is still perfectly possible to tell what the average die roll will be: 3,5, a roll you can't even make.
You can even calculate (using multidisciplinary science, physics and statistics in this case) what the statistical outcome of fiddling with the die's center of mass will be. But you still can't predict the outcome of one roll of the die using the same type of calculations. Calculating the result of one die roll involves so much more. Like predicting next weeks weather.