I have often pondered this question about ENSO contributions to interannual variations in global average temperature. I wonder if it has been fully addressed in the literature, hence a reference to a good paper on this would be helpful if someone has one.
Oliver mentions the ocean, and certainly this plays a part. In the eastern tropical pacific, the typical condition has the oceanic thermocline shallow enough that the trade winds driven upwelling draws cool water from below the thermocline to the surface. During El Nino, the thermocline dips and the cool sub-thermocline water is now too deep for the upwelling to draw on. Thus, we typically think of "warm water moving from the west pacific to the east pacific" during an El Nino, but I think it is more accurate to say that the eastern pacific warms while the west pacific stays about the same temperature, and the warming of the east has more to do with vertical mixing in the ocean than west-to-east mixing. So El Nino shuts down a process in the eastern pacific that under non-El Nino conditions acts to cool the atmosphere. This is certainly an important factor, but I've often wondered if this is really sufficient to explain the global-scale warm anomaly. Oliver also mentions albedo and long-wave absorption. Given that clouds impact both of these, and dramatic changes in tropical cloud patterns accompany El Nino, I've always assumed that these changes in clouds play a role in the global temperature anomaly. Alastair mentions cloud-induced warming, but the cloud albedo contributes a cooling that is comparable in magnitude to the warming from the cloud greenhouse effect, so it may not be as simple as saying there are more clouds. Someone must have looked at the changes in cloud radiative forcing during El Nino. Anyone know of the paper? Regarding "the amount of energy that can be released/soaked up by the oceans is finite": that might be true, but we're a long way from warming the deep ocean as much as it could be, and the time it takes to mix thermal anomalies through the entire depth of the ocean is millennial in scale. So by all means, changes in ocean currents that alter the rate of vertical mixing of thermal energy in the ocean can have profound impacts on the global average surface temperature. -Eric On Apr 25, 4:34 pm, oku <[EMAIL PROTECTED]> wrote: > Hi, > > I currently have a discusion with a skeptic. I am trying to get the > point across that the radiation balance of the earth can only be > influenced by the three factors 1) solar radiation, 2) albedo and 3) > absorption of long wave radiation by the atmosphere (see > here:http://ipcc-wg1.ucar.edu/wg1/FAQ/wg1_faq-1.1.html). If we have high > average temperature during El Nino, and low during La Nina periods, > then this *seems* to contradict that. I understand that in El Nino, > warm ocean water releases heat to the atmosphere, and during a La Nina > the cold ocean water soaks up that heat. Since we measure surface > temperatures and not deep ocean temperatures, there is no > contradiction. Is that correct? Would it also be correct to conclude > that long term changes in ocean currents therefore cannot change the > average temperature of the earth (disregarding feedbacks), but just > local climates, because the amount of energy that can be released/ > soaked up by the oceans is finite? (The guy I have the discussion with > seems to be a fan of William Gray) > > Thanks, > Oliver --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups Global Change ("globalchange") newsgroup. Global Change is a public, moderated venue for discussion of science, technology, economics and policy dimensions of global environmental change. Posts will be admitted to the list if and only if any moderator finds the submission to be constructive and/or interesting, on topic, and not gratuitously rude. 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/globalchange -~----------~----~----~----~------~----~------~--~---
