How much heat does the Earth receive from the sun?

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Dear Tom,
How much heat does the Earth receive from the sun? I’m told the sun’s heat drives the weather.

James Chwo,
Chicago

Dear James,
The Earth is approximately 93,000,000 miles from the sun and the sun’s energy radiates outward in all directions. The Earth, about 8,000 miles in diameter, intercepts only a tiny portion of the sun’s total energy output: only about a two-billionth.

The Earth receives energy at the rate of 5,000,000 horsepower per square mile. (One horsepower is the force required to raise 33,000 pounds one foot per minute.) But only about 70 percent of that energy makes its way down to the Earth’s surface. The other 30 percent is absorbed in the atmosphere. The energy of sunlight, converted to heat in the atmosphere and at the Earth’s surface, drives the weather.

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