Why is Greenland covered in ice?

Aug 27, 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

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User comments : 12

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Alizee
Aug 27, 2008
This comment has been removed by a moderator.
ripley60
4.4 / 5 (12) Aug 27, 2008
This article points to a more truthful dialog about the debate over climate change. Unlike "Alizee" above, I can't draw a black and white conclusion over the absolute cause and effect of "global warming." As a scientist, it is obvious that human activity impacts our environment. But so does a major volcanic eruption or meteor strike. I think it is imperative that scientist remain completely objected and not study such an important issue through a biased lens. Blaming industry or capitalism for global warming, while beating the war drum, only divide's the people who must work together. Doing so would truly be "political science."
MikeB
3.4 / 5 (12) Aug 27, 2008
"Using state-of-the-art computer climate and ice-sheet models,"...

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.
kivahut
3.9 / 5 (11) Aug 28, 2008
I still can't understand why everyone is so upset about global warming. I think warmer weather is nice. When Greenland is free from ice, maybe I'll consider vacationing there. Until then, I'm going to the tropics.
Alizee
Aug 28, 2008
This comment has been removed by a moderator.
Phaze
3.9 / 5 (11) Aug 28, 2008
global warming is irrelevant. things change. it will be nice when transforming the earth is a norm.
locations of "perfection" will change. it will bring growth to mankind
superhuman
3.8 / 5 (11) Aug 28, 2008
"Using state-of-the-art computer climate and ice-sheet models,"...

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.


Yeah, state of the art in climate modeling leaves much to be desired.
Soylent
3 / 5 (9) Aug 28, 2008
"Using state-of-the-art computer climate and ice-sheet models,"...

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.


Weather is not climate.
ShadowRam
3 / 5 (7) Aug 28, 2008
Everyone is so worried about CO2.. what about the 2x molecules of water you put in the atmosphere when you burn most hydrocarbons?
deatopmg
2.7 / 5 (7) Aug 28, 2008
I still can't understand why everyone is so upset about global warming. I think warmer weather is nice.
It means more dry weather, which destabilizes the natural ecosystems (food supplies). Anyway, our industry is adopted to existing situation. Every change is expensive here.

..while beating the war drum..
I'm not beating the war drum, but the true is, the exhausting of fossil fuel sources makes the geopolitical situation less stable.


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.
MikeB
3 / 5 (6) Aug 28, 2008
Weather is not climate. And pennies aren't dollars either, but you ain't gonna be able to count your dollars if you don't figure out your pennies.
Weather is what climate is made of.
kiwiiano
2.3 / 5 (3) Sep 02, 2008
Everyone is so worried about CO2.. what about the 2x molecules of water you put in the atmosphere when you burn most hydrocarbons?

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.
themotie
3 / 5 (2) Sep 04, 2008
MikeB:

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.
themotie
3 / 5 (2) Sep 05, 2008
I'll add that the meteorologists (the researchers, that is, not neccessarily the TV weathermen and -women) use to say that climate is what you can predict, weather is what you get.