Poster's note : This paper suggests a new tipping element in the climate system. It would seem logical for geoengineering researchers to consider how geoengineering may be able to avoid it, and whether or not there's a direct interaction between the tipping point and proposed geoengineering techniques. It would be embarrassing if a miracle climate solution triggered a permanent, negative and unforeseen change in the climate system!
http://www.clim-past.net/8/1323/2012/cp-8-1323-2012.html Abstract. Understanding the behavior of the global climate system during extremely warm periods is one of the major themes of paleoclimatology. Proxy data demonstrate that the equator-to-pole temperature gradient was much lower during the mid-Cretaceous "supergreenhouse" period than at present, implying larger meridional heat transport by atmospheric and/or oceanic circulation. However, reconstructions of atmospheric circulation during the Cretaceous have been hampered by a lack of appropriate datasets based on reliable proxies. Desert distribution directly reflects the position of the subtropical high-pressure belt, and the prevailing surface-wind pattern preserved in desert deposits reveals the exact position of its divergence axis, which marks the poleward margin of the Hadley circulation. We reconstructed temporal changes in the latitude of the subtropical high-pressure belt and its divergence axis during the Cretaceous based on spatio-temporal changes in the latitudinal distribution of deserts and prevailing surface-wind patterns in the Asian interior. We found a poleward shift in the subtropical high-pressure belt during the early and late Cretaceous, suggesting a poleward expansion of the Hadley circulation. In contrast, an equatorward shift of the belt was found during the mid-Cretaceous "supergreenhouse" period, suggesting drastic shrinking of the Hadley circulation. These results, in conjunction with recent observations, suggest the existence of a threshold in atmospheric CO2 level and/or global temperature, beyond which the Hadley circulation shrinks drastically. Citation: Hasegawa, H., Tada, R., Jiang, X., Suganuma, Y., Imsamut, S., Charusiri, P., Ichinnorov, N., and Khand, Y.: Drastic shrinking of the Hadley circulation during the mid-Cretaceous Supergreenhouse, Clim. Past, 8, 1323-1337, doi:10.5194/cp-8-1323-2012, 2012. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/groups/opt_out.
