Hi all, I have been away from geoengineering debates for some time as I was busy, first, with the non-scientific job I was still holding, and second, with renewable energies researches. Since the publishing of "21 unusual renewable energies for the 21st century", co-written with Renaud, I am in the process of being recruited as a full-time researcher - first, half-time from now to the summer. I hope that in the long run it will give me more time for your forum.
I've got two questions about Arctic. First, of course there is this very large albedo positive feedback; but don't you think that there'd be a less emphasized negative feedback which would always prevent the core of the sea ice sheet from fully disappearing, not only at the end of summer but all year long, as the result of a cumulative process? What I'm thinking of is the fact that a thick ice sheet, covered by snow, is probably a fairly good thermal insulator, so rather little heat can pass through it in the winter, and an existing ice sheet can grow only slowly in winter - of course it melts slowly in summer as long as it keeps white snow on it, so it can rather well survive. But, in winter, a completely open Arctic sea would lose heat at a rather high rate, so that it would efficiently cancel the summer albedo effect during the first winter months, and during the next ones a new ice sheet would rapidly be created, at least not too far from the pole. Do you know whether this effect is correct (maybe the dominant heat transfer is infrared emissions from the sea to the sky through the ice, so that I'm wrong?) and correctly taken into account in the models? My second question is about Greenland ice cap flowing towards the sea as the result of coastal glaciers bottom being more lubricated because of water (melted ice or snow) reaching this bottom. I still think that an adequate geoingineering control (limited actions, macroscopic impact to some effects of climate change) could be to dig some tunnels to extract this water and letting it reach the sea through other ways. In the Alps, I already knew that typically 100-km long networks of hydraulic tunnels had been dug in the 1970's to collect water to large dams such as the Mont-Cenis's one. I recently learnt that there exist tunnels under glaciers that are used as subways for ski-addicts in Tignes and Les Deux-Alpes. Do you think these are interesting references to prove the technical and economical feasibility of such action, should the Greenland ice cap be threatened in a rather short term? Best regards to all, Denis Bonnelle. -----Message d'origine----- De : [email protected] [mailto:[email protected]] De la part de Renaud-KdeR Envoyé : lundi 24 janvier 2011 16:47 À : geoengineering Objet : [geo] Albedo decline in the Arctic M. G. Flanner, K. M. Shell, M. Barlage, D. K. Perovich, M. A. Tschudi. Radiative forcing and albedo feedback from the Northern Hemisphere cryosphere between 1979 and 2008. Nature Geoscience, 2011; DOI: 10.1038/ngeo1062 Loss of Reflectivity in the Arctic Doubles Estimate of Climate Models ScienceDaily (Jan. 18, 2011) - A new analysis of the Northern Hemisphere's "albedo feedback" over a 30-year period concludes that the region's loss of reflectivity due to snow and sea ice decline is more than double what state-of-the-art climate models estimate. The findings are important, researchers say, because they suggest that Arctic warming amplified by the loss of reflectivity could be even more significant than previously thought. The study was published online this week in Nature Geoscience. It was funded primarily by the National Science Foundation, with data also culled from projects funded by NASA, the Department of Energy and others. "The cryosphere isn't cooling the Earth as much as it did 30 years ago, and climate model simulations do not reproduce this recent effect," said Karen Shell, an Oregon State University atmospheric scientist and one of the authors of the study. "Though we don't necessarily attribute this to global warming, it is interesting to note that none of the climate models used for the 2007 International Panel on Climate Change report showed a decrease of this magnitude." The cryosphere is the collective portion of the Earth's surface where water is in solid form and includes sea ice, snow, lake and river ice, glaciers, ice sheets and frozen ground. Most of these frozen areas are highly reflective, and "bounce" sunlight back into the atmosphere, keeping the Earth cooler than it would be without the cryosphere. But as temperatures warm, ice and snow melts and reflectivity decreases, noted Shell, an assistant professor in OSU's College of Oceanic and Atmospheric Sciences. "Instead of being reflected back into the atmosphere, the energy of the sun is absorbed by the Earth, which amplifies the warming," Shell said. "Scientists have known for some time that there is this amplification effect, but almost all of the climate models we examined underestimated the impact -- and they contained a pretty broad range of scenarios." As part of the study, Shell, lead author Mark Flanner of the University of Michigan, and their colleagues compared Northern Hemisphere cryosphere changes between 1979 and 2008 in 18 different climate models to changes in actual snow, ice and reflectivity measurements of the same period. They determined that mean radiative forcing -- or the amount of energy reflected into the atmosphere -- ranged from 4.6 to 2.2 watts per meter squared. During the 30-year study period, cryosphere cooling declined by 0.45 watts per meter squared. The authors attribute that decline equally to loss of snow and sea ice. "Some of the decline may be natural climate variability," Shell said. "Thirty years isn't a long enough time period to attribute this entirely to 'forcing,' or anthropogenic influence. But the loss of cooling is significant. The rate of energy being absorbed by the Earth through cryosphere decline -- instead of being reflected back to the atmosphere -- is almost 30 percent of the rate of extra energy absorption due to carbon dioxide increase between pre-industrial values and today." The "albedo" or reflectivity process is simple, scientists say, but difficult to measure on a broad scale. The reflectivity of ice and snow is obviously much greater than that of darker, unfrozen ground, or open sea water. But researchers also have discovered that variations in the snow and ice result in different albedo impacts. For example, pools of melted water on top of sea ice can have significantly less reflectivity, which in essence may speed up the warming and possibly melting of that sea ice. "While the current group of models underestimates these Northern Hemisphere cryosphere changes, new models will be released this year that will have better representations of snow and ice," Shell said. "This study will help climate modelers improve the new generation of models to better predict the rate of cryosphere and albedo decline in the future." -- 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.
