Hi David, I disagree with your estimation of 12 years and suggest 5 years is more likely and could even be optimistic, at least for September sea ice decline to below the 10% mark.
The PIOMAS graph, updated to end June 2011 here [1], made me think that 2016 was the most likely date, fitting a curve rather a straight line because of positive feedback. This is confirmed by Ron Larson from his analysis, see earlier in thread. You have to work out what the y-axis anomaly represents. When we get to -14 thousand km-3, which is a gnat's whisker below the line across the bottom of the graph, I estimate that we'd have less than 10% of ice volume left in September. Unfortunately [1] does not give you the vital data as to what the total sea ice volume is that they are measuring anomaly against! However, you can see that this year is almost as down on 2007 as 2007 was on the 1979-2010 average. If we assume that September 2007 was 40% down on the 1979-2010 average (which was true for the area), the 2011 could be almost 80% down. We only need to reach 90% down to have 10% sea ice volume left, that Ron talks about as being a critically low level. That makes the 2016 date seem quite reasonable, if not optimistic! Peter Wadhams points out that the sea ice thickness is decreasing faster than the sea ice extent. These trends are of course masked by much wind and weather variability from year to year, which affects ice flow, not just direct melting. This explains why one can have had relatively little change in the minimum sea ice extent since September 2007, although the volume has been declining. 64 trillion dollar question* If geoengineering is to have a good chance to save the Arctic sea ice, then it needs to be deployed quickly, building up to maximum strength by summer 2013. By then the Arctic annually-averaged radiative forcing of the "albedo flip" (as ice/snow reflection of sunlight turns to sea/land absorption of sunlight) may exceed 10 Watts per square metre [2]. Could a combination of SRM methods, with deployment ramped up as fast as possible, have a chance to exceed 10 W/m-2 of negative forcing in the Arctic by summer 2013, in order to halt Arctic warming and save the Arctic sea ice? Note that cloud brightening and other SRM methods could contribute to negative forcing by cooling the water flowing into the Arctic, especially the currents from the North Atlantic. So cooling does not have to be directly of the Arctic itself. Cheers from Chiswick, John * P.S. It's a 64 trillion dollar question if you consider that losing the sea ice could have repercussions affecting the total global GDP, which is around that value. [1] http://psc.apl.washington.edu/wordpress/research/projects/arctic-sea-ice-volume-anomaly/ [2] http://www.mail-archive.com/[email protected]/msg00660.html [geo] Re: Geoengineering - cloud effects John Nissen Wed, 10 Dec 2008 13:42:10 -0800 --- On Wed, Jul 20, 2011 at 5:50 PM, David Appell <[email protected]>wrote: > By my estimation of PIOMASS data, September sea-ice could be gone in > about 12 years: > > http://davidappell.blogspot.com/2011/07/arctic-ice-is-at-record-low.html > > > David > -- > David Appell, independent science journalist > e: [email protected] > w: http://www.davidappell.com > m: St. Helens, OR > > > > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/geoengineering?hl=en. > > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
