Tuesday January 24, 2017

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REGIONAL JOURNALISM, GLOBAL PERSPECTIVE.

Climate
Ice, ice data

Chilling outlook

Sea-ice conditions right now are ripe for this year to set a record minimum extent

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When it comes to looking ahead at how sea ice is going to fare during the summer melting season, scientists study two factors closely: climactic, which includes things like temperature, cloud cover and atmospheric conditions; and the initial state of the ice.

Because the former cannot be forecast with accuracy beyond more than a few days, predictions for sea-ice extent and volume at the end of the summer melting season are little more than guesswork.

Still, considering the latter factor alone can give scientists an idea of how much it will take to melt existing ice. This summer, according to scientists with AWI, a German polar-research outfit, it will not take much.

SEE VIDEO: Why thickness matters (at end of article)

Marcel Nicolaus, an AWI physicist, told a news conference in Vienna today, that this year's record-low winter maximum extent appears to have set the conditions for sea ice to reach a record minimum this summer as well.

Using data gathered over the past five years by CryoSat-2, a European satellite, and by using buoys placed on ice floes, Mr Nicolaus and Stefan Hendricks, also of AWI, conclude that the thickness of sea-ice at the end of the winter growth season was similar to the conditions seen at the same point in 2012, when the current record minimum was set.

Thickness is important because it gives an idea of how resilient ice is to sun, waves and other factors that cause it to melt or to be broken up and carried with ocean currents into the North Atlantic. It is generally considered to give a better, if harder to obtain, indicator of the state of sea-ice.

“The way it looks to us right now,” Mr Hendricks told The Arctic Journal in advance of today’s announcement, “is that a lot of sea ice melted in 2015, even though the extent didn’t set a record minimum last summer. This has given us one of the conditions that can lead to a record minimum this year.”

SEE RELATED: Annual sea-ice maximum comes early, sets record low

Last year’s summer minimum was the fourth-lowest extent on record. All summer long, the area covered by sea ice followed a similar pattern to the 2012 record year, and with an abnormally early start to the melting season many were convinced 2015 was heading for a new low.

Even though it did not break the record for extent, sea-ice thickness appears to have suffered considerably, and, according to Mr Hendricks, perhaps even more than scientists had been aware of.

The pair point to sea ice north of Alaska as one example of the decline. Typically, such ice has a thickness of 1.5m at this time of year. Measurements taken this spring indicate that it may now be less than a metre.

“Ice that thin isn’t going to hold up for long under the summer sun, or to a storm,” Mr Hendricks says.

SEE RELATED: Documenting the decline

Other scientists not involved with today’s announcement agree that 2016 got off to a bad start, but given the crucial role weather plays, they say it is still too early to say anything about how sea-ice will develop this summer.

“We are starting from a low point, but there is still a chance 2016 could be a normal year if we have the correct weather conditions,” says one scientist. “Either way, it is going to be a very intriguing year.”

Axel Schweiger, the head of the Polar Science Center, at the University of Washington, says that whether we set a new low or not is less important than the long-term trend.

“Year-to-year changes in sea-ice volumes and extent can vary considerably, and how ice fares one year is little indication of how it will do the next,” he says.

SEE RELATED: Giving a little help from above

Both he and Mr Hendricks agree that the trend is towards warmer temperatures and increasing ice-loss.

The decline of multi-year ice, often as old as ten years, Mr Hendricks explains, is a sign of this.

“We had relatively cold winters in 2013 and 2014, but we’d need to have five or ten cold years in a row if we were to see any improvement in multi-year ice. And that’s not realistic.”

Photo: Stefan Hendricks/AWI