Weather

The extent of sea ice in the Arctic region has dropped sharply in the last few months.

Only in April, Arctic sea ice had staged an impressive recovery and was close to the 1979-2012 average, reaching levels not seen in April for over 10 years.

But yesterday, the National Snow and Ice data centre reported that the extent of Arctic sea ice shrank to 1.58 million square miles, breaking the previous record set in the summer of 2007, based on satellite data which was first gathered in 1979.



Usually the minimum ice extent is not reached until September, suggesting that further ice loss is likely.

Including this year, the six lowest ice extents in the satellite record have occurred in the last six years.



And most scientists, whilst accepting that some of the decline in sea ice is likely to be down to natural factors such as prevailing weather conditions and natural ocean cycles, believe a substantial proportion is down to man-made influences such as global warming due to higher greenhouse gases in the atmosphere.

The big worry is that continued melting sea ice would cause serious feedback mechanisms to kick-in.

Firstly with less sea ice to reflect incoming solar radiation back into space, the sea will warm more quickly than would otherwise be the case, speeding up global warming.

And secondly, natural methane trapped under the sea-bed by permafrost could be released. Methane is a much more powerful greenhouse gas than carbon dioxide, and would also accelerate global warming.

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  • Comment number 71. Posted by greensand

    on 4 Sept 2012 17:30

    @66. newdwr54 wrote:

    "i don't see anything suspicious about this."

    Neither do I! Never did, I actually accept what CRU said:-

    "I know there were delays in getting it updated, as it's now all done jointly with the Met Office."

    Nothing suspicious quite an acceptable statement.

    The introduction of HadCRUT4 being the reason for the delays is purely supposition on your behalf, I happy to accept the CRU statement until they say differently

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  • Comment number 70. Posted by buythermals

    on 4 Sept 2012 16:48

    What about 1922?
    http://wattsupwiththat.com/2008/03/16/you-ask-i-provide-november-2nd-1922-arctic-ocean-getting-warm-seals-vanish-and-icebergs-melt/

    What about 1817?
    http://wattsupwiththat.com/2009/07/28/statement-on-arctic-climate-change-from-the-president-of-the-royal-society/

    It doesn't fit the 'unprecendented' meme so can safely be ignored. :)

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  • Comment number 69. Posted by QuaesoVeritas

    on 4 Sept 2012 16:42

    #68. - newdwr54 wrote:
    "In short: why would CRU (or MO) make a fuss about updating and publicising a data set they've effectively already admitted they know is flawed? That's all it boils down to, as far as I can see."
    There is a difference between not "urgently" updating their dataset and not updating it for 4 months. It hasn't been replaced by HadCRUT4 yet and it remains the only official MO/CRU global temperature dataset.
    In fact, by not updating it in a reasonably timely manner, they are drawing more attention to it's flaws than would otherwise be the case.
    If HadCRUT4 is so "great", why hasn't it been updated beyond December 2010 yet?

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  • Comment number 68. Posted by newdwr54

    on 4 Sept 2012 16:22

    65. QuaesoVeritas wrote:

    "But is there any evidence to suggest this is anything other than coincidence?"

    I'd say it's probably *not* a coincidence.

    Why would CRU urgently update their online HadCRUT3 dataset when they've already de facto admitted that it contains data that is 'wrong', i.e. that is not homogenized using the latest information and that has been independently re-analysed producing different results? It also contains less spatial coverage than CRU now currently has available to it.

    It's not as if they've hidden the HadCRUT3 data. They still make it available, as you know, and it's still published (admittedly obscurely) on a monthly basis by the MO.

    In short: why would CRU (or MO) make a fuss about updating and publicising a data set they've effectively already admitted they know is flawed? That's all it boils down to, as far as I can see.

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  • Comment number 67. Posted by QuaesoVeritas

    on 4 Sept 2012 16:19

    #66. - newdwr54 wrote:
    "i don't see anything suspicious about this."
    I wasn't suggesting anything suspicious, but I wouldn't be surprised if HadCRUT3 hadn't been *informally* been given a lower priority.
    I think it is more likely to be lack of resources.

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  • Comment number 66. Posted by newdwr54

    on 4 Sept 2012 16:12

    GS,

    I know the MO is updating HadCRUT3 since, as you point out, it is the only metric currently available. However, referring to my comments to QV above, CRU has been very lax in updating its official HadCRUT3 website since March, when the latest HadCRUT4 was issued.

    In the Jones et al. paper published by CRU in March it is made clear that HadCRUT4 is effectively the CRU's latest and best attempt at a global dataset. It effectively replaces HadCRUT3; as HadCRUT3 replaced HadCRUT2.

    Therefore I can understand why CRU is not rushing to update its HadCRUT3 database every month (the MO do this anyway). In this sense, HadCRUT3 is no longer the current, or 'valid' (though that's probably a poor word choice on my part) CRU 'gold standard'.

    i don't see anything suspicious about this.

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  • Comment number 65. Posted by QuaesoVeritas

    on 4 Sept 2012 15:52

    #62. - newdwr54 wrote:
    "Since the HadCRUT4 data were released in March, CRU has not updated its HadCRUT3 data on the official site on a regular basis. Hopefully HadCRUT4 updates will commence shortly and both will run in conjunction for a time."

    But is there any evidence to suggest this is anything other than coincidence?
    I will ask the person who replied directly to my recent e-mail directly.

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  • Comment number 64. Posted by greensand

    on 4 Sept 2012 15:32

    Correction to last para in 63 above:-

    should reda ..."nothing to do with HadCRUT4"...

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  • Comment number 63. Posted by greensand

    on 4 Sept 2012 15:28

    @59. newdwr54 wrote:

    "As far as I know the reason HadCRUT3 has not been updated regularly is because it is no longer considered by CRU to be a 'valid' data set."

    Nah DW there is no evidence of that. The UKMO is still updating HadCRUT3, as confirmed by the correspondence posted by QV, and now after prompting so is CRU. Also the MO is still making and reporting their Decadal Forecasts against HadCRUT3.

    Eventually HadCRUT4 will appear until then the only metric being updated by the MO is HadCRUT3.

    The lack of updating of HadCRUT3 since March until now is nothing to do with HadCRUT3 as you probably correctly posit - "Hopefully HadCRUT4 updates will commence shortly and both will run in conjunction for a time."

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  • Comment number 62. Posted by newdwr54

    on 4 Sept 2012 15:00

    60. QuaesoVeritas wrote:

    "In all of my enquiries with the MO and CRU regarding the late update of HadCRUT3 figures, they have never stated they are not updating the figures because they consider HadCRUT3 to be invalid."

    Yes, 'invalid' was a bad choice of word. HadCRUT3 is obviously valid as it stands, i.e. it does what it says on the tin.

    However, as Jones et al. (2012) state in their abstract, the new CRUTEM4 database reflects updated and re-analysed data and includes new additional data (particularly from the Russian Arctic). This causes it to differ substantially from CRUTEM3, which contributes the land portion of HadCRUT3 temperatures. http://www.agu.org/pubs/crossref/2012/2011JD017139.shtml

    As such, HadCRUT4 is clearly seen as an 'update' on HadCRUT3 (as HadCRUT3 was an update on HadCRUT2, etc). Therefore HadCRUT3 is no longer 'valid' in the sense that it is not considered to be the latest or best CRU representation of changes in the global surface temperature; not in the sense that it is 'wrong', as my terminology may have implied earlier.

    Since the HadCRUT4 data were released in March, CRU has not updated its HadCRUT3 data on the official site on a regular basis. Hopefully HadCRUT4 updates will commence shortly and both will run in conjunction for a time.

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