Sentences with phrase «precessional cycle»
The phrase "precessional cycle" refers to the slow wobble or rotation of the Earth's axis over a period of time. It takes about 26,000 years for the axis to complete one full circle. This cycle affects the position of the North Star and causes changes in the Earth's climate and seasons over long periods. Full definition
So the occurrence of deep freshwater lakes would have forced expanding hominin populations both northwards and southwards generate a pumping effect pushing them out of East Africa towards the Ethiopian highlands and the Sinai Peninsula or into Southern Africa with each successive precessional cycle.
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Should that trend due to the 24 k year precessional cycle be discounted in your view?
Raymo and Paillard have a good story about the 100KYr cycle arising from the modulation of the precessional cycle by the changes in the Earth's orbital eccentricity, coupled with some glacial dynamical effects which «rectify» the high frequency precessional signal.
The main changes in radiative forcing from the precessional cycle are in the latitudinal and seasonal distribution, not in the global mean, which is why the nature of the response can be expected to be different from doubling CO2.
From 60S to 30N the Earth is 80 % oceans and the winter solar is a a peak in this portion of the precessional cycle.