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New Ice Age Theory
amigoro writes "Most believe that the ice ages are the result of subtle changes in Earth's orbit, known as the Milankovitch cycles. According to one scientist, that is not the case. Robert Ehrlich of George Mason University in Fairfax, Virginia, has developed a model which hypothesizes a dimmer switch inside the sun that causes its brightness to rise and fall on timescales of around 100,000 or 41,000 years, exactly the same period as between ice ages on Earth. The main problem with Milankovitch cycles is that they can't explain how the ice ages go from 100,000 year cycle to 41,000 year cycle. The cycles predicted by Ehlrich's model line up with the observations."
"The climate depends more on atmospheric composition than on any variation in the sun or even our proximity to it. That's why venus is hotter than mercury."
That's less "difference in atmospheric composition" and more "has an atmosphere or not."
Yeah, it definitely could be a combination of all manners of cycles. That's the thing about climate shifts- there are so many variables interacting, that some interact in very different ways. I wrote a summary paper a few years ago for a seminar about a theory of frequency modulation of the Milankovitch cycles to help solve some of the classic Milankovitch "problems". Here's a link for it: http://www.sciencemag.org/cgi/content/abstract/285 /5427/564. Looking at the followup research, Dr. Rial has done both frequency modulation to see what he can do with the three main Milankovitch cycles (that being orbital eccentricity (changing in how "oval" the Earth's orbit is, every 100,000 and 400,000 years), planetary precession (changing the location of the seasons, so that the Northern Hemisphere winter moves from January to January over the course of 21,000 years) and the planet's obliquity (changes in the tilt of the earth from 22.5 degrees to 24.5 degrees, over a course of 41,000 years).
Through this frequency modulation, he was able to produce a signal very close the delta-O 18 ratios found for the Vostok core in Antartica. His theory also was able to "demodulate" the Vostok core to get peaks at 41kyr (kyr = 1000 years), 100kyr, and 21kyr as predicted by the classic Milankovitch cycles.
While these solar fluctuations may exist (and I'm not an astronomer, just a meteorology/atmospheric science/climatology PhD student) I'd prefer to firm them up before they replace the classical orbital mechanisms that we know exist. Whether they cause the Ice Ages or not, they are present in the orbital path.
Yes, the Himalayas are the youngest mountain ranges on earth, but the timescale is still way too long to explain the occurence of ice-age cycles.
We actually did a simulation using a coupled GCM to remove the Tibetan pleateau all together, to see its influence. The result was that some aspects of the current climate system, for example the Asian monsoon, or the western Pacific warm pool has weakened dramatically. The jet stream did change dramatically, but that alone was not enough to trigger a continental ice sheet.
We then changed the orbital parameters to see which impact is greater. The result was that a slight change in orbital parameters is far efficient in changing the northern hemispheric surface temperature in the order of 7-8 degC.
So the parent is correct in some respect. I guess he just didn't bother to explain in detail.