Comments 1 to 6:

1. Agnostic at 10:15 AM on 7 January, 2013
   Interesting comment about IPCC authors of the soon to be published 5AR – that they would prefer to be conservative in their reporting, findings and conclusions rather than accurate. Probably explains why they conclude that the Arctic Ocean could be ice-free in summer by the end of the century.
   
   The problem of course is that such seemingly wrong assertions on Arctic sea ice cast doubt on other conclusions reported by the IPCC.
2. bibasir at 10:36 AM on 7 January, 2013
   How about "where it is and where it's going."
3. JasonB at 14:12 PM on 7 January, 2013
   Agnostic:
   
   One of the sad things about this "debate" is how "conservative" is taken to mean "assume things won't be bad unless proven otherwise", or "err on the side of optimism despite evidence to the contrary" — the opposite approach to that normally taken in risk management.
   
   A doctor notices something suspicious. Which is the more conservative stance?
   
   1. "Let's get some tests done to make sure it's nothing serious."
   
   2. "Let's assume it's OK until you start showing signs of serious illness."
   
   Given the almost ludicrous extent to which the IPCC underestimated the rate of Arctic sea ice loss in the last report,
   
   
   
   it's appalling that they have apparently been bullied into updating it to the meek claim that "A seasonally ice-free Arctic Ocean within the next 50 years is a very distinct possibility".
   
   Here we have a doctor looking at someone already showing signs of serious illness and still thinking "conservative" means "Let's not break the bad news because they might still get better"...
4. desertphile at 15:46 PM on 7 January, 2013
   I am not a math wizard, but just fitting a simple curve function on the observed data it looks closer to seasonally free of sea ice closer to year 2022, conservatively. William M. Connolley might yet lose his wager.
5. mercpl at 20:51 PM on 7 January, 2013
   The PIOMAS volume graphs are quite scary. I actually took the last PIOMAS graph and gave it to a few friends and changed the x-y axes to represent some stupid made-up values like vampire movie gross ticket sales, they all predicted a zero of about 2015-2020. Then I showed them that they were really predicting Arctic sea-ice volume.
   
   http://psc.apl.washington.edu/wordpress/research/projects/arctic-sea-ice-volume-anomaly/
6. CBDunkerson at 22:37 PM on 7 January, 2013
   The truly sick thing with the IPCC 50 year estimate for the 'distinct possibility of seasonally ice-free' is that, if the observed trends continue, then there is a 'distinct possibility' that in 50 years the Arctic Ocean will be ice-free year round.
   
   If the PIOMAS data is charted by total volume rather than anomaly you get;
   
   
   
   Note that the Winter maximum values have decreased from ~33 to ~22... almost as much as the ~17 to ~3 decrease in Summer minimum values. If we take that Winter maximum decline as a flat rate then it'd be about 65 more years before it hit zero... but the decline is visibly accelerating and thus 50 years is in the ballpark.
   
   Of course, there have been arguments for a long time that the declines in the Summer minimum will level off (any time now)... and the whole 'months with no sunlight' thing would certainly argue for there being some kind of floor on how low the Winter maximum can go without a profound change in climate.
   
   The large 'ice islands' which break off land ice areas will prevent a true zero sea-ice volume until Greenland has largely melted out, but we will almost certainly see a 'near zero' ice volume before 2020 if the PIOMAS results are accurate. After that we should start seeing just how warm Arctic waters get with no ice cover and be able to start making better projections for what is going to happen to the Winter maximums.

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