*Folks, I forward this email sent to "Climate Intervention" to "Geoengineering" mostly because it is a *climate *discussion and not a *climate intervention*discussion.
Best, Ken * --------------- Hi all, We currently have "polar amplification" of temperature, such that the temperature rise is several times greater than the global average, both in the Arctic as a whole and in the West Antarctic peninsular. What is the mechanism for this amplification? The polar amplification could soon result in several degrees K temperature rise, i.e. abrupt climate change. Abrupt climate change has occurred in the past, and is occurring now in the Arctic. I suggest this is/was largely due to the positive feedback albedo effect of the Arctic sea ice, as ice melts to water. This could be sufficient to explain the polar amplification - with a small global warming signal (e.g. through the Gulf Stream) being amplified by positive feedback. This idea may be supported below, see where I marked in bold. I came across this, in: http://blogs.nature.com/climatefeedback/2007/12/agu_meeting_the_outlook_for_th_1.html [quote] That nature has surprises in store is indicated by the recent paper by Steffensen et al (Science Express 19 June, 08) - "High-Resolution Greenland Ice Core Data Show Abrupt Climate Change Happens in Few Years", documenting catastrophic temperature rises at the end of the Youngest dryas (11.7 kyr) and the Oldest dryas (14.7 kyr) when temperatures rose by several degrees over few years, as in the abstract below: Abstract: "The last two abrupt warmings at the onset of our present warm interglacial period, interrupted by the Younger Dryas cooling event, are investigated in high temporal resolution from the Greenland NGRIP ice core. The deuterium excess, a proxy of Greenland precipitation moisture source, switches mode within 1-3 years over these transitions and initiates a more gradual change (50 years) of the Greenland air temperature as recorded by water stable isotopes. The onsets of both abrupt Greenland warmings are slightly preceded by decreasing Greenland dust deposition, reflecting wetting of Asian deserts. A northern shift of the ITCZ could be the trigger of these abrupt shifts of northern hemisphere atmospheric circulation resulting in 2-4K changes in Greenland moisture source temperature from one year to the next." Whereas there was more ice at that stage (Laurentian and Fennoscandian ice sheets) than at present negates a direct comparison, the paper demonstrates an extreme instability of the ice sheets and temperatures. As CO2 levels did not rise above 300 ppm during the terminations, it would follow these changes mainly reflect ice melt feedback effects. Posted by: Dr Andrew Glikson (Earth and paleo-climate science) | August 6, 2008 03:57 AM [end quote] Abrupt temperature change was also noted in the Greenland ice core - 5 degrees in a single season - by Iain Stewart in one of his BBC TV programmes. Again, the albedo effect could be implicated. What are other possible mechanisms for polar amplification and abrupt climate change? One mechanism could involve a shift of atmospheric circulation. The above article mentions a northerly shift of the ITCZ (intertropical convergence zone [1]) - is this happening at present - and if so, what is causing it? Note that, if atmospheric CO2 does not have a direct effect on polar amplification, then emissions reduction cannot have a counter effect, to halt polar amplification. Cheers, John [1] http://www.physicalgeography.net/fundamentals/7p.html ___________________________________________________ Ken Caldeira Carnegie Institution Dept of Global Ecology 260 Panama Street, Stanford, CA 94305 USA [email protected]; [email protected] http://dge.stanford.edu/DGE/CIWDGE/labs/caldeiralab +1 650 704 7212; fax: +1 650 462 5968 --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
