On Feb 5, 1:52 pm, Robert Indigo Ellison <[email protected]> wrote: > Dear Alistair,... >> will the jump be to a cooler state or to a >> warmer state? > > I don't know - I am inclined to think that cooling is more likely - > simply because we at a Quaternary warm extreme. What factors are > implicated in a switch from warm to cold? Not known with any > certainty.
PETM -- only good paleo case of an already warm environment pushed by a sudden increase in CO2 at a rate comparable to the present rate of change. What happened? Temperature spiked up, starting from that already very warm level. Warm to cold? well enough established; biogeochemical cycling--in each paleo episode the biology is dramatically different, because evolution has been working away during the interim. -------- Nature. 2000 Sep 14;407(6801):171-4. Termination of global warmth at the Palaeocene/Eocene boundary through productivity feedback. Bains S, Norris RD, Corfield RM, Faul KL. Department of Earth Sciences, University of Oxford, UK. [email protected] Comment in: * Nature. 2000 Sep 14;407(6801):143-4. The onset of the Palaeocene/Eocene thermal maximum (about 55 Myr ago) was marked by global surface temperatures warming by 5-7 degrees C over approximately 30,000 yr (ref. 1), probably because of enhanced mantle outgassing and the pulsed release of approximately 1,500 gigatonnes of methane carbon from decomposing gas-hydrate reservoirs. The aftermath of this rapid, intense and global warming event may be the best example in the geological record of the response of the Earth to high atmospheric carbon dioxide concentrations and high temperatures. This response has been suggested to include an intensified flux of organic carbon from the ocean surface to the deep ocean and its subsequent burial through biogeochemical feedback mechanisms. Here we present firm evidence for this view from two ocean drilling cores, which record the largest accumulation rates of biogenic barium--indicative of export palaeoproductivity--at times of maximum global temperatures and peak excursion values of delta13C. The unusually rapid return of delta13C to values similar to those before the methane release and the apparent coupling of the accumulation rates of biogenic barium to temperature, suggests that the enhanced deposition of organic matter to the deep sea may have efficiently cooled this greenhouse climate by the rapid removal of excess carbon dioxide from the atmosphere. -------- Look at the change from oceanic organisms living primarily on shallow continental shelf habitats, to the more recent development of planktonic organisms capable of thriving far from shore, the coccolithophores. Once they evolved and became widespread, the carbon could be rapidly turned into carbonate and aragonite and deposited as sediment, giving us the White Cliffs of Dover and similar vast beds of chalk -- 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
