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On Thu, 2010-01-07 at 18:06 +0000, Simon Waters wrote: > Philip Whateley wrote: > > > > What I found interesting was the recent British Antarctic Survey Ice > > Dome C data for the last 800000 years. > > > > It shows that every inter-glaciation temperature spike for the past 500k > > years has gone to around 5degC above present. > > > > It would be interesting to know whether the predicted anthropogenic > > 2-3degC rise is in addition to the 5degC we can expect as a result of > > solar activity, or whether the 2-3deg is the net effect of solar > > activity, greenhouse gas emissions and particulate emissions reducing > > solar absorption. > > The temperature rise forecast is CO2 forced, so it is a warming that is > expected over recent historical averages including any expected changes > in climate due to additional CO2 (and methane), but I don't think there > are any substantive changes in natural climate expected over the time > scales of interest (i.e. next 100 years). > > The larger historical fluctuations as I understand it are on a much > longer time scale (100,000 year cycle). > > I don't think the fluctuations you mention are due to solar activity but > due to variations in the earth's orbit (Milankovitch cycles). > > The peak of the current interglacial was 21,000 years ago as I > understand it. Where did you get the idea it would get 5 degrees warmer > naturally, or are you meaning in 75,000 years when the cycle would repeats? > > http://stratus.astr.ucl.ac.be/textbook/chapter5_node13.html > The data from the ice core samples (available for download from http://news.bbc.co.uk/1/hi/in_depth/sci_tech/2009/copenhagen/8393855.stm) shows an interglaciation spike beginning about 19,000 years bp. The data is based on deviation from the average for 1900-2000, as zero. The data shows the the current (baseline) temperature some 3 to 5 degrees cooler than the last 4 interglaciation spikes. The data also shows some other interesting anomolies, such as CO2 peak lags temperature peak by around 30,000 to 40,000 years? Phil -- The Mailing List for the Devon & Cornwall LUG http://mailman.dclug.org.uk/listinfo/list FAQ: http://www.dcglug.org.uk/linux_adm/list-faq.html