The Combination of Earth's Tilt and Eccentricity Cause Both Warming and Cooling
by Carl G. Looney
(Reno, NV, US)
Major forces affecting global climate
The really cold period of the most recent ice age started about 75 kyrs 75,000 years ago when the Earth's eccentricity was approaching the maximum, which was about 62,500 kyrs ago. At that time the Earth's tilt was near minimum. So what did this do?
The near-minimum tilt meant that more of the solar radiation was more directly on the tropic regions to create warmer ocean surfaces, which would have moved via currents to the temperate zones. The near maximum eccentricity meant that Earth's perihelion added extra heat to the tropical oceans.
The warmer waters moved to temperate latitudes while the aphelion was colder. The warmer currents, say off Western Europe, and the colder air, put a lot more water vapor in the air, where it blocked the temperate zone irradiation and the colder air precipitated out the water vapor. Tremendous amounts of water vapor are the key.
Perhaps there was a lot of flooding at first, as the geological records show (huge rounded stones that were washed dozens and hundreds of miles rather being broken and carried by moving ice. But without solar irradiation, snow pack built up.
About 12,500 years ago, there was minimum eccentricity so the Earth was nearer the Sun a aphelion and about the same at perihelion. About 20,000 years ago, the Earth was approaching this minimum so that
the Earth was relatively warmer. Also the tilt was about in the middle between minimum and maximum and headed toward maximum, so there was more solar irradiation in the temperate zones to melt glaciers. At 20,000 years ago, the ice began melting sharply (the temperatures climbed sharply and the volume of ice declined sharply). At 9,000 years ago, there was maximum tilt.
In another thousand years, the tilt will be ready to slip past the midway to minimum tilt again, and in another 12,500 years we will be slipping to more max. than min. eccentricity. At that time, we will slide rapidly at first, then see-saw up and down with a downward trend in temperature and ice buildup. These slippages past the halfway points are nonlinear: the change is gradual, say from min. to max., at first but then speeds up and makes a big jump near the halfway mark.
So we have another 10,000 years of good times except for these little 80 year and 1500 year cycles that may be colder. Right now solar activity is slowing and the ll year solar cycles are lengthening, which correlates very highly with lowering temperatures on Earth.
Barry's Response - Yes, Carl, good introductory analysis and charts of our current position with respect to the two shortest Milankovitch Cycles forcing our climate. Thank you very much.