> > I share your stated concerns regarding the possibility of abrupt > climate change. The difference is, I think we may already be seeing > it happening as we write while you appear to be uninterested. > >
Eric The McWilliams paper is particularly difficult to translate into English. I am not sure I understand it myself. As for Atlantic currents the ‘transport index estimates the strength of the baroclinic gyre circulation in the North Atlantic, or the strength of the Gulf Stream and North Atlantic Current system. The units (Mtons s-1) are within a few percent of the volumetric unit of transport (Sverdrups = 106 m3s-1). It is calculated from the difference of the potential energy anomalies (PEA) near Bermuda and in the Labrador Basin (top two panels). The index was defined by Curry and McCartney (J. Phys. Oceanogr., 2001). The evolution of the index from 1950 through 2000 shows a circulation reducing through the low NAO period in the 1960s, then strengthening during the period of persistently high NAO over the next 25 years, reaching a peak in the mid-1990s. They found that the timing and mechanisms associated with PEA changes in each gyre varied, and were dependent on both locally and remotely-forced changes in the ocean (see paper for details).’ http://ioc-goos-oopc.org/state_of_the_ocean/sub/berm_lab_trans.php - click on full series to see index since 2000. You can click on ‘evolution of the index’ to see values since 1950 along with values of the NAO. There is also a link to the Curry and McCartney paper. ‘This analysis underscores the need to move beyond passive-response, mixed layer representations of the ocean in assessing climate variability. It suggests a system that grows sometimes large signals through the interaction of several factors: diabatic mixed layer/air– sea flux anomalies; planetary waves; intergyre exchanges of heat, salt, and mass in the thermocline and deeper layers; and perhaps baroclinic instabilities in the deep Gulf Stream system. At times these factors are additive (e.g., at the extremes of the transport index) and at other times opposing (between the transport extremes). The resultant weakened or strengthened gyre circulation can thus be more—or less—efficient at transporting heat, salt, and other climatically relevant properties from one location to another. Anomalies of circulation strength may therefore play an important role in building heat anomalies as well as moving them geographically beneath the overlying atmosphere.’ The NAO precedes the transport index by about a year – so expect further decline in transport. This is an example – by the way – of abrupt climate change on interaanual to decadal timescales. There is much better info on sea ice (and other things) from Prof Ole Humlum – a glaciologist. http://www.climate4you.com/ ‘Based on these observational data, Polyakov et al. (2003) concluded that the ‘examination of records of fast ice thickness and ice extent from four Arctic marginal seas (Kara, Laptev, East Siberian, and Chukchi) indicates that long-term trends are small and generally statistically insignificant, while trends for shorter records are not indicative of the long-term tendencies due to strong low-frequency variability in these time series, which places a strong limitation on our ability to resolve long-term trends’. The key phrase is low frequency variability – again a decadal abrupt shift – following closely from Arctic temperature and zonal SLP changes and therefore also ocean salt and heat transport and deep water formation. What does this mean for the future? Don’t look at me – I think we are on the extreme warm climate ‘strange attractor.’ Much more likely to shift to cooler mode. As much as a 10 degree cooling in a couple of months to years is possible. Cheers Robert -- 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
