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Arctic summer melt - which records are being broken?

  • 21 Aug 2012, 14:50
  • Carbon Brief staff

Every year, sea ice in the Arctic grows and shrinks with the seasons. But it's also affected by other things like the weather, which play a large role in explaining changes from year to year. This means that although Arctic sea ice is in long-term decline, that decline isn't uniform.

In 2007, the sea ice reached a record low - and since then a lot of attention has been paid to the summer melt season. The Arctic gets its fair share of misleading reporting, and with such a lot of coverage in the run up to the September sea ice minimum it can get confusing. To address this, we'll be regularly pulling together key points from the best coverage on Arctic summer melting.

Here are the links for Tuesday 21st August

In anticipation of sea ice minimum headlines, it's worth noting there are a number of ways to take measurements of Arctic sea ice - we can look at sea ice extent, area and volume.

Sea ice area is the ocean surface area that is covered in ice, as measured by satellites. A more frequently used term however is sea ice extent - which looks at the area which is covered by some amount of ice, usually at least 15 per cent. This measurement therefore captures some open water between ice floes.

Sea ice volume takes into account how thick the ice is as well as the area it covers. That's important because thinner ice is more vulnerable to change due to weather conditions. While the long term warming trend can explain thinning, variable weather conditions help explain how we can have record lows some years and not others.

A number of institutions record these measurements, using  different techniques to compute the data collected by satellites. Since there are many different data sets around, some - say for sea ice area - might be broken while others might not.

Getting this into context is important - as of yesterday, some institutions reported new record low for sea ice area since satellites began, well before September when the minimum is usually reached. Records held by the Arctic Regional Ocean Observing System ( ROOS) also indicate this to be the case.

But it will perhaps be more interesting to see if the record low for sea ice volume is broken over the coming weeks, given that stormy conditions at the start of August this year may have sizably affected ice which is becoming increasingly thin over the long term. This however remains to be seen.

Ted Scambos, of the National Snow and Ice Data Centre (NSIDC) which measures sea ice extent, reported yesterday that melting is likely to exceed the previous record while the sea ice is still retreating, and that a new ice extent daily record "would be likely by the end of August".

Whether the sea ice reaches a new record low or not this year is almost beside the point however. If we want to try and look at the impacts climate change is having in the Arctic, it's the long term trend which matters. And the long term trend is one of continuing decline:

 

PIOMAS Ice Volume Anomaly


Fig. 1: Arctic sea ice volume anomaly from
PIOMAS 1979-2012. Shaded areas show one and two SD from the trend.

NSIDC July Ice Extent

Fig. 2: Arctic sea ice extent (July) from NSIDC - 1979-2012

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