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Who is afraid of melting ice sheets?

Posted by feww on April 18, 2009

Based on its outdated “one-dimensional” model, the U.N. Climate Panel has reported that seas could rise by 18-59 cm  (7-24 inches) by 2100. The model also excludes the threat from highly probable scenarios in which ice sheets in Antarctica and Greenland could melt at exponential rates.

Ian Allison, head of  the Australian Antarctic Division’s Ice, Ocean, Atmosphere and Climate program was asked by Reuters the following question: How great is the threat from melting ice sheets?

Allison who is a researcher within the Antarctic Climate and Ecosystems Cooperative Research Center, and who has been involved in Antarctic science for more than 4 decades, responded as follows.

HOW GREAT IS THE THREAT FROM ICE SHEETS MELTING?

I think it is now unequivocal that warming of the world is occurring and I think the last IPCC (Intergovernmental Panel on Climate Change) conclusively showed that a major cause of warming is greenhouse gas emissions from mankind.

We now know that the ice sheets are contributing to sea level rise and for the Arctic, at least, this is because the warming of this region is much greater than in other places on Earth.

We also know that glaciers in mountain areas are undergoing a very rapid retreat and they’re a major contributor of sea level rise, too.

WHICH IS OF MORE CONCERN? GREENLAND OR WEST ANTARCTICA?

Greenland is of more concern because of the warming of the Arctic. Greenland is at lower latitude than much of Antarctica and we’ve seen the direct effect of the melting.

We still don’t understand many things about the dynamic response of the ice sheets but we do see direct melt exceeding snowfall in Greenland.

This might not mean a runaway effect but it does mean Greenland is contributing to sea level rise and will continue to add to sea levels at the present temperatures for many hundreds of years.”

EXPLAIN THE THREAT FROM WEST ANTARCTICA

Ice shelves and floating ice tongues can buttress the flow of grounded ice from the interior of the ice sheets. We’ve seen examples in both Greenland and Antarctica of floating ice disappearing, and the ice that sits on the land then flowing more quickly into the ocean.

“In addition, the West Antarctic may be inherently unstable. The West Antarctic forms what is called the marine ice shelf. The ice is resting on bedrock but that bedrock is below sea level. It’s like if you load too many ice cubes in your gin and tonic, the bottom one touches the bottom of the glass even though it’s well below the water level.

Where the bedrock under a marine ice sheet slopes down toward the interior, such as under parts of West Antarctica, the ice sheet may be unstable. If it thins, it will start to float at the edges, becoming an ice shelf.

For a bedrock that slopes backwards and becomes deeper further in, continued retreat of the grounded ice sheet may proceed very rapidly. A small retreat could in theory destabilize the entire West Antarctica ice sheet, leading to rapid disintegration.

WHAT ARE THE MAIN GAPS IN OUR KNOWLEDGE?

There two areas. One, we need to improve our mathematical models of ice streams, ice sheets and ice shelves to be able to better project future changes. We also need more detailed measurements of how deep the bedrock is under the ice sheets to use in the models.

The other major gap in our understanding is what is happening at the bed of the ice sheets; how they react with liquid water at the base, what role water may have in sliding processes and the role of gravels and slurry at the base.

We now know there is a lot of liquid water under the ice sheets. But we don’t really know how changes in this may affect the ice flow. Knowing what’s under the ice sheets we really need to measure that with radar systems.

WHAT ARE YOUR MAIN MESSAGES TO POLICY MAKERS?

The main thing is monitoring what’s actually happening with sea level rise and the ice sheets. We’ve now got tools that can do that, we can improve those and make sure they keep going, particularly satellite-based systems.

We need better predictive tools to know just what is likely in the next 100 years. I don’t think we should be rushing into building up coastal defenses until we know what we could be defending against. So our biggest requirement is to be able to refine our projections for what may happen in the future. (Edited by David fox).

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2 Responses to “Who is afraid of melting ice sheets?”

  1. […] Who is afraid of melting ice sheets? […]

  2. terres said

    Permafrost melting a growing climate threat
    Tue Jun 30, 2009 5:03pm EDT

    SINGAPORE (Reuters) – The amount of carbon locked away in frozen soils in the far Northern Hemisphere is double previous estimates and rapid melting could accelerate global warming, a study released on Wednesday says.

    Large areas of northern Russia, Canada, Nordic countries and the U.S. state of Alaska have deep layers of frozen soil near the surface called permafrost.

    Global warming has already triggered rapid melting of the permafrost in some areas, releasing powerful greenhouse gases carbon dioxide and methane.

    As the world gets warmer, more of these gases are predicted to be released and could trigger a tipping point in which huge amounts of the gases flood the atmosphere, rapidly driving up temperatures, scientists say.

    “Massive amounts of carbon stored in frozen soils at high latitudes are increasingly vulnerable to exposure to the atmosphere,” said Pep Canadell, executive director of the Global Carbon Project at Australia’s state-funded Commonwealth Scientific and Industrial Research Organization.

    “The research shows that the amount of carbon stored in soils surrounding the North Pole has been hugely underestimated.”

    The study is published in the latest issue of Global Biogeochemical Cycle.

    Canadell said a four-year study of the latest research on permafrost, data from new drilling projects as well as the release of previously unpublished data from the Russian Academy of Sciences had led to a rethink of carbon levels.

    “Projections show that almost all near-surface permafrost will disappear by the end of this century exposing large carbon stores to decomposition and release of greenhouse gases,” he said in a statement.

    He said if only 10 per cent of the permafrost melted, this could lead to the release of an additional 80 parts per million of carbon dioxide equivalent into the atmosphere. This would equate to about 0.7 degrees Celsius of global warming.

    According to the U.N. Climate Panel, average temperatures have already risen by about 0.7 deg C since the late nineteenth century and are forecast to rise another 1.8 to 4 deg C by 2100, Scientists say a rapidly warming planet will trigger more intense storms and droughts, rising seas and melting ice caps.

    Canadell said that on a recent trip to northern China, the permafrost at its southern limit had all but disappeared over the past 20 years.

    Locals had told him the permafrost was once 20 cm below the surface and now it was several meters down, he told Reuters from Canberra, Australia.

    In the statement, he said computer models showed global warming could trigger an irreversible process of thawing.

    For example, heat generated from increased microbial activity in the soil could lead to sustained and long-term emissions of carbon dioxide and methane.

    In addition, lakes formed as permafrost thaws would draw heat to deeper layers and bring methane trapped in pockets below to the surface.

    (Reporting by David Fogarty; Editing by Jerry Norton)
    © Thomson Reuters 2009 All rights reserved

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