Sunday, January 10, 2010

Milankovitch Update: "Moderate Cooling"

Several chaotic variables determine the amount of solar energy impacting the earth. One variable, called Milanković theory, relates variations in eccentricityaxial tilt (also called obliquity), and precession of the Earth's orbit to climatic patterns on Earth, as shown in the charts below covering different time scales:

and see prior post on the cause of ice ages
What is the present status of the earth's orbit (insolation) in relation to the past and what do the next 2000 years portend? For some perspective, the mean insolation of the past 1 million years (at summer solstice, 65N latitude) is 495.08 W/m^2, and the present day isolation is 480.08. This is 3% below the mean of the past 1 million years (graph below)

The last time insolation was this low was about 20,000 years ago, just before thawing of the last ice age. Insolation peaked again 11,000 years ago and has declined since then.

Insolation is now bottoming for the next 2 millenia at a relatively "cold" level, but short of the lows associated with the peak of past ice ages.   

Solar Insolation Computer Codes for Windows
Press release today on another paper relating Milankovitch cycles to global climate change.

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