Hi John, Current theory is that glacial/interglacial phasing is related to the amount of solar insolation around 60-70 degrees north (where there is a lot of land surface, covered in snow) especially around May (when spring melt is strongest)
Basically we think that the ice/snow albedo feedback is predominant on these timescales. Amount of solar radiation at 650 N depends on astronomical characteristics of the earth's orbit round the sun....tilt, eccentricity, and the precession of the equinoxes, together known as the Milankovich cycles. This phasing determines GMST, with CO2 levels lagging temperature by several hundred years, but adding additional positive feedback on the temperature. Interglacials stop when insolation in high northern latitudes in spring falls to low levels allowing greater snow and ice cover. Regards, Colin ----- Original Message ----- From: John Nissen To: geoengineering Cc: [EMAIL PROTECTED] ; Davies, John Sent: Thursday, October 09, 2008 11:21 PM Subject: [geo] What stopped global warming before? Hi all, Through the Ice Ages, temperatures rose sharply during interglacial periods, but peaked at around the temperature we have today. This temperature seemed to have been a natural limit. What was the thermostat mechanism that stopped temperatures going higher? Here are some possible theories: 1. Meltwater turned off the Gulf Stream, allowing the Arctic sea ice to grow, cooling the Arctic region with positive feedback on this cooling sufficient to make the global temperature fall sharply. 2. Despite greenhouse warming from water vapour (a positive feedback on global warming), cloud cover increased, with cloud brightening from the fiercer storms at sea (resulting from the global warming). This extra albedo was sufficient to offset the water vapour greenhouse effect and cool the Gulf Stream, allowing Arctic sea ice to grow. 3. Sea level rise caused pressure on coastal magma chambers, thus increasing volcanic activity, which had an immediate cooling effect, through fine dust and aerosols in the stratosphere. This again could have allowed Arctic sea ice to grow. 4. Any others? In each case, grow-back of the Arctic sea may have been crucial to get an amplification of an initial cooling. If so, the Arctic sea ice has been essential to the Earth's thermostat control. But today we are seeing this thermostat breaking in front of our eyes. That is a powerful argument for geoengineering to save the Arctic sea ice. Pronto. Cheers from Chiswick, John --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
