I'm passing on this response from Sebastian, see below.
I disagree with Albert over the significance of volcanism in initiating and terminating glacial periods. I discussed the possibility with several people at the colloquium. They pointed out that the glacial and interglacial periods of the Ice Ages fit well with the Milankovitch cycles. A fourier analysis of the temperature over hundreds of thousands of years shows peaks at the required frequencies. However, the temperature and sea level fluctuations suddenly flattened out after the last interglacial and Younger Dryas period, and the Earth system has been pretty stable for the past 8000 years or so [1][2]. This is now thought to be due to mankind's activities - growth of agriculture, methane from rice and cattle, etc. [3] Note, from [1], that "the prevailing theory holds that the Younger Dryas was caused by a significant reduction or shutdown of the N Atlantic thermohaline circulation in response to a sudden influx of fresh water from Lake Agassiz and deglaciation in North America". Such a pulse of water may possibly have caused a sea level rise of the type that Albert and his "First Nations" talk about. This possibility is discussed here [4]. Cheers from Chiswick, John [1] http://en.wikipedia.org/wiki/File:Epica-vostok-grip-40kyr.png [2] http://dx.doi.org/10.1016%2Fj.epsl.2008.01.032 [3] http://en.wikipedia.org/wiki/William_Ruddiman [4] http://www.giss.nasa.gov/research/briefs/gornitz_09/ ---- [Forwarded from Sebastian Watt] Hi John, I'll try to give a quick reply on my views of the ideas you've referred to. Peter Ward's suggestions relate to the ability of the atmosphere to react with SO2, form aerosols and ultimately remove it from the atmosphere. He suggests that this oxidising capacity of the atmosphere can be over-ridden if sufficient SO2 is put in to the system (essentially, there are insufficient quantities of reactants to remove it), thus subsequently allowing build-up of greenhouse gases. There is a problem with quantities in such a model. SO2 represents only a small amount of the gas reacting with oxidants. It would need to be increased massively to elicit substantial changes through the mechanism outlined. Peter might argue that volcanism did increase in the past to such a degree, on timescales of a few thousand years. I would suggest that there is not evidence for increases of the magnitude he suggests. While there was some increase in volcanism at the end of the last glacial (in some regions more than others), the timing and plausible models fit with a climatic driver to the increase, and feedbacks may then potentially occur. I can't see a plausible tectonic mechanism for the opposite suggestion of such rapidly increased rates of volcanism on the pertinent timescales that might drive the climatic change. Cheers, Seb --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
