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These cycles will have effec Patrick Kelly wrote: > > The astronomical cycles that David refers to are called Milankovitch > Cycles. > > http://www.ncdc.noaa.gov/paleo/milankovitch.html > http://en.wikipedia.org/wiki/Milankovitch_cycles > Hi Patrick & All, Nov 26, 2006 Thanks for these URLs. The top one led me to http://www.aip.org/history/climate/cycles.htm#M_52_ which contains a good account (or so it seems to me) of climatology over the years. One passage in this account has me baffled and perhaps someone can explain. The passage being "The changes in the atmosphere could also answer the old persuasive objection to Milankovitch's theory -- if the timing of ice ages was set by variations in the sunlight falling on a given hemisphere, why didn't the Southern Hemisphere get warmer as the Northern Hemisphere cooled, and vice-versa? The answer was that changes in atmospheric CO2 and methane physically linked the two hemispheres, warming or cooling the planet as a whole.(52*) " What configuration of tilt and orbital distortion could lead to one hemisphere receiving more insolation in e.g. summer than the other hemisphere would receive 6 months later ? Tilt would have to be symmetrical and even if the sun was at times not exactly at the intersection of the major and minor axis of the orbital ellipse, surely this assymetry would not flip in the space of 6 months. Yours truly, Dave Webster, Kentville
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