Esa's Cryosat sees Arctic sea-ice volume bounce back

Arctic sea ice thickness - late Oct 2013

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The bounce back in the extent of sea ice in the Arctic this summer was reflected also in the volume of ice.

Data from Europe's Cryosat spacecraft suggests there were almost 9,000 cu km of ice at the end of this year's melt season.

This is close to 50% more than in the corresponding period in 2012.

It is a rare piece of good news for a region that has witnessed a rapid decline in both area cover and thickness in recent years.

But scientists caution against reading too much into one year's "recovery".

"Although the recovery of Arctic sea ice is certainly welcome news, it has to be considered against the backdrop of changes that have occurred over the last few decades," said Prof Andy Shepherd of University College London, UK.

"It's estimated that there were around 20,000 cu km of Arctic sea ice each October in the early 1980s, and so today's minimum still ranks among the lowest of the past 30 years," he told BBC News.

Cryosat is the European Space Agency's (Esa) dedicated polar monitoring platform.

It has a sophisticated radar system that allows scientists to work out the thickness of the ice floes covering the Arctic Ocean.

In the three years following its launch, the spacecraft saw a steady decline in autumn ice volume, with a record low of 6,000 cubic km being recorded in late October 2012.

But after a sharply colder summer this year, the autumn volume number has gone up.

Measurements taken in the same three weeks in October found the floes to contain just shy of 9,000 cu km.

Ice breaker Thicker ice has been retained in the Arctic

Part of this stronger performance can be put down to the greater retention of older ice.

This is evident particularly around the Canadian archipelago and North Greenland, where there is much more two-year-old and three-year-old ice than in previous years.

"One of the things we'd noticed in our data was that the volume of ice year-to-year was not varying anything like as much as the ice extent - at least for the years 2010, 2011 and 2012," explained Rachel Tilling from the UK's Nerc Centre for Polar Observation and Modelling (CPOM).

"This is why we're really quite surprised by what we've seen in 2013.

"We didn't expect the greater ice extent left at the end of the summer melt to be reflected in the volume.

"But it has been. And the reason is related to the amount of multi-year ice in the Arctic."

Dr Don Perovich is a sea-ice expert at Dartmouth College, US.

He said Cryosat's data tallied with observations made by other spacecraft.

"In previous summers, some of the [multi-year ice] migrated over to the Alaska and Siberia areas where it melted. But this past summer, it stayed in place because of a change in wind patterns. And so there'll likely be more multi-year ice next year than there was this year," he told BBC News.

Satellite altimetry: How to measure sea-ice volume

Infographic (BBC)
  • Cryosat's radar has the resolution to see the Arctic's floes and leads
  • Some 7/8 of the ice tends to sit below the waterline - the draft
  • The aim is to measure the freeboard - the ice part above the waterline
  • Knowing this 1/8th figure allows Cryosat to work out sea-ice thickness
  • The thickness multiplied by the area of ice cover produces a volume

The minimum ice extent in the Arctic this summer was recorded as 5.10 million sq km. Again, this was a figure almost 50% larger than the all-time satellite-low mark achieved 12 months previously - when floes were reduced to just 3.41 million sq km by mid-September.

Area/extent is easier to measure, but scientists regard thickness/volume to be the best metric with which to judge the health of the ice pack, which is why Cryosat's unique data-set is so important.

For a while, it was uncertain whether the European satellite would get any autumn measurements this year.

The spacecraft suffered a major fault in its onboard power system at the beginning of October, and all science activity was halted.

But engineers managed to switch the satellite over to a back-up system and normal operations were resumed on 11 October.

"We lost the side 'A' of the power subsystem we believe for good, although we still have hope to be able to use part of it in the future in case we experience another issue," said Esa Cryosat mission manager Dr Tommaso Parrinello.

"Since 2 October, we have been operating on the redundant chain, but all other subsystems are still being operated on their prime chain 'A'. Therefore, the science instruments and the quality of data have not been affected."

The new Cryosat study was presented here in San Francisco to the American Geophysical Union (AGU) Fall Meeting, where the annual Arctic Report Card was also released.

Thickness comparison The observations show clearly that more thick ice (red/yellow) has been retained this year and follow me on Twitter: @BBCAmos


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  • rate this

    Comment number 39.

    For those interested, David Ericson and Goesta Wollin predicted back in the '60's that if the N polar ice melted the area, now a cold desert, might become much more humid with more snow and much thicker permanent ice cover and that this, together with concomitant ocean dynamics changes might be the main trigger for N hemisphere glaciations.

  • rate this

    Comment number 38.

    Someone still believes the myriad computer models which say we are heading towards catastrophic warming? I don't think one of them had made a true prediction yet.

    A true prediction would be science. Shouting "yah boo sucks deniers" isn't.

  • rate this

    Comment number 37.

    Annual variations do not prove anything one way or another. You need to look at long term trends. This idea is well illustrated by football results. A couple of weeks ago Sunderland beat Manchester City. But the long term trend is that Sunderland are likely to get relegated and Manchester City will finish in the top four.

  • rate this

    Comment number 36.

    Sounds like the the satellite designers, engineers and the scientific teams analysing the data are skating on thick ice.

    Unfortunately we will need to wait another few years to get an indication of whether this is going to continue or a reverse happens and the global warming camp leaps upon it.

  • rate this

    Comment number 35.

    The experts on the climate are all out in force to let us know how wrong everyone else is and how right they are. Tell me guys, if you're all so knowledgeable why are you spending your Monday morning preaching to people on the internet and not out there doing something? Oh wait, that's right, you're Google parrots.

  • rate this

    Comment number 34.

    Don´t get too excited or believe we are turning a corner; one swallow does not summer make. The general trend is still towards Global Warming.

  • rate this

    Comment number 33.

    One year for one item is statistically insignificant.

    It's trends over decades that are important.

  • rate this

    Comment number 32.

    Silly article. Anyone with an understanding of statistics should know that you can't make valid extrapolations from isolated pieces of data. You have to look at data over thousands of years to make valid deductions and data trends, because of standard deviation.

  • rate this

    Comment number 31.

    In the days of the Roman empire, wine was grown all the way up to the Scottish border.

    Yes, the climate is changing. It always is. But why the huge panic?

  • rate this

    Comment number 30.

  • rate this

    Comment number 29.

    Man made global warming is a total scam to give the global elite an excuse to raise taxes and give them more power over the masses. Thousands of "independent" scientists claim that man made global warming is non existent or highly over stated. The BBC and the Guardian have promoted this scam at every opportunity. Do your own research people and question everything.

  • rate this

    Comment number 28.

    We've been "monitoring" these facts and figures for 100 years or so

    Just how long has the earth existed in it's current form?

    We predict death doom and destruction if a few years figures vary yet over millions of years we have seen far more dramatic changes - none of them "man made"

    If the earth were a business, these "experts" would be accused quite rightly of micro management


  • rate this

    Comment number 27.

    Ah a seasonal variation in the 'weather'...attracting the usual collection of 'climate' experts:)

  • rate this

    Comment number 26.

    For all the cynics, please remember that Cryostat is only one source of information. Geologists have thourands of years worth of data. Ice cores, dendrochronolgy, etc. The Geological Society issued an appendix this month. Gaps in data have been plugged. The outlook does not change from their original 2010 report, it just becomes stronger.

  • rate this

    Comment number 25.

    @ 10 Sadlerorchit

    There are over 1 million years of arctic and antarctic climate records from ice cores, which granted, may not be as accurate as the varved sediment records from Northern Scandanavia, but rest assured the many months I spent looking at the 6500 years of THOSE records for my master thesis make me believe that the scientists are well enough informed to make recommendations.

  • rate this

    Comment number 24.

    19. MrNormal
    How typical that the first comments here are from the scientifically illiterate GW deniers. This is just seasonal variation which has nothing to do with the long-term trend.
    I'd agree if I didn't think you'd be saying the opposite if we'd had an unusually heavy melt this year. I get thoroughly sick of one off events "proving" anything.

  • rate this

    Comment number 23.

    It's perfectly NORMAL for the thickness and amount of ice to vary. We have different methods of measuring it these days and I don't think anyone really knows what to expect. Just don't hold your breath.

  • rate this

    Comment number 22.

    Important, welcome -- though not yet a trend. Comparing to 1980s levels is of course crucial. Keep the focus because maybe all the efforts and concerns are finally yielding however small yet precious incremental gains… Let's amplify what we are all doing right!

  • rate this

    Comment number 21.

    'This is close to 50% more than in the corresponding period in 2012.' - can we see a refund on those pesky green taxes? If not a refund, then a reduction?..

    So the hippies in the green paty & liberals, what excuses will they use now to make sure we all wear hemp and hug trees? They really don't have a cluw.

  • rate this

    Comment number 20.

    Why is this subject registered for comment? There is nothing to say about one years data - like the man says you can't read anything into 'one year's recovery'


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