Climate Number: Two Watts per Square Meter
The amount of solar energy Earth receives varies according to the “11-year solar cycle,” which corresponds to a cycle in the frequency and distribution of sunspots on the sun’s surface. The difference in solar energy between high and low points of the solar cycle is about two watts per square meter. About 35 percent of the variation in Earth’s climate since 1600 can be explained directly by shifts in solar forcing. Indirect effects of solar variation are also important and can have pronounced regional effects on climate. For example, the behavior of the El Niño-Southern Oscillation (ENSO), the system of winds and ocean currents that affects temperature distributions in the tropical Pacific Ocean, is believed to be influenced by solar activity. Temperature distributions in the tropical Pacific in turn have noticeable impacts on weather throughout the world, including the strength of the Indian Monsoon; the position of the Northern Hemisphere storm tracks that bring winter and spring precipitation to the United States; and the intensity of the dry season in the Amazon Basin.
For Comparison: The total amount of solar irradiance that reaches Earth varies by two watts per square meter, from 1365 watts per square meter at a low points in the solar cycle to around 1367 watts per square meter at high points – about a 0.1 percent variation. The noticeable effects of the solar cycle, despite the relatively nominal absolute change in solar radiation, illustrate the non-linear nature of Earth’s climate: small changes in certain variables can have large impacts, particularly at regional scales.
Seasons: Winter, Spring, Summer, Fall
Source: Wasco, C and Sharma, A. “Effect of solar variability on atmospheric moisture storage.” Geophysical Research Letters 36 (2009): L03703.
