THEGREENGROK

Climate Update: Temperature Moderate but Skating on Thin Ice


by Bill Chameides | April 7th, 2009
posted by Erica Rowell (Editor)

Permalink | 2 comments

The big news this week was the loss of the ice bridge that helped anchor the Wilkins Ice Shelf to a neighboring island. (European Space Agency)

Winter 2009 is history. Let’s take a quick look at what the climate has been up to.

Global Temperatures

Two factors that influence the year-to-year (interannual) variations in global temperatures are the state of the Southern Ocean and the activity of the Sun. Both continue to favor cooler temperatures: the Sun, still bereft of sunspots, makes the current solar minimum the strongest on record since 1913; and La Nina, the cold phase of the El Nino-Southern Oscillation (ENSO), continues to dominate in the Southern Ocean.

These two factors no doubt contributed to global temperatures during January and February of 2009 falling below the record highs of 2007. Nevertheless, the 2009 temperatures were high; according to NASA’s Goddard Institute of Space Studies, January and February 2009 were the tenth warmest on record.

Ice Melting

The thickness of winter ice indicates that the ice is thinner than average, suggesting it will be more susceptible to thaw this coming summer. (Source: The National Snow and Ice Data Center – http://nsidc.org/arcticseaicenews/2009/040609.html)

However, while global temperatures have moderated somewhat, the largest warming trends continue to be found in the polar regions. As a result, ice continues to melt in the Arctic and Antarctic.

Sea ice in the Arctic peaked in February and now approaches its summertime melting season with thesmallest percentage of old, thick ice (i.e., ice that is more than two years old) on record. This is significant because younger, thin ice is more susceptible to melting during the warmer months. (On the positive side, the data show that over the past two years, the fraction of one- to two-year-old ice has increased, and the fraction of less than one-year-old ice has decreased slightly.)

Of course the big news this week has been the loss of the ice bridge that helped anchor the Wilkins Ice Shelf to a neighboring island. This latest event is part of a larger trendof ice shelf collapses in the Antarctic. Because ice shelves float on the ocean, their loss does not in and of itself contribute to sea level rise. But the ice shelves help support and hold back the ice sitting atop the Antarctic continent and so their loss could speed the flow of continental ice into the sea.

Bottom line: Gazing at the global thermometer is important and necessary, but it’s also important to bear in mind that there is a long-term trend at work that will ultimately determine the direction of our climate. The melting of ice in the polar regions may provide a better indication of that long-term trend.

filed under: Antarctica, Arctic, El Nino-Southern Oscillation, faculty, La Nina, temperatures
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2 Comments

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  1. Al G.
    Apr 7, 2009

    In this case I am honestly looking for enlightenment…why does the “age” of the ice matter, shouldn’t thickness be the overwhelmingly important property?

    • Bill Chameides
      Apr 15, 2009

      Al G., The age is a metric for expressing thickness. The older the ice, the thicker the ice.

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