Solar Variation

Solar variation is the change in the amount of radiation emitted by the Sun (see Solar radiation) and in its spectral distribution over years to millennia. These variations have periodic components, the main one being the approximately 11-year solar cycle (or sunspot cycle). The changes also have aperiodic fluctuations. In recent decades, solar activity has been measured by satellites, while before it was estimated using 'proxy' variables. Scientists studying climate change are interested in understanding the effects of variations in the total and spectral solar irradiance on Earth and its climate.

Variations in total solar irradiance were too small to detect with technology available before the satellite era, although the small fraction in ultra-violet light has recently been found to vary significantly more than previously thought over the course of a solar cycle. Total solar output is now measured to vary (over the last three 11-year sunspot cycles) by approximately 0.1%, or about 1.3 Watts per square meter (W/m2) peak-to-trough from solar maximum to solar minimum during the 11-year sunspot cycle. The amount of solar radiation received at the outer surface of Earth's atmosphere averages 1366 W/m2. There are no direct measurements of the longer-term variation, and interpretations of proxy measures of variations differ. The intensity of solar radiation reaching Earth has been relatively constant through the last 2000 years, with variations estimated at around 0.1-0.2%. Solar variation, together with volcanic activity are hypothesized to have contributed to climate change, for example during the Maunder Minimum. However, changes in solar brightness are too weak to explain recent climate change.

Read more about Solar Variation:  History of Study Into Solar Variations, Solar Activity and Irradiance Measurement, Solar Interactions With Earth, Other Effects Due To Solar Variation, Solar Variation and Climate

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Global Warming Controversy - Mainstream Scientific Position, and Challenges To It - Solar Variation
... global warming others attribute global warming to natural variation ocean currents increased solar activity or cosmic rays ... The consensus position is that solar radiation may have increased by 0.12 W/m² since 1750, compared to 1.6 W/m² for the net anthropogenic forcing ... in radiative forcing of the two major natural factors (solar variation and volcanic aerosols) is estimated to be negative for the past two, and possibly the past four, decades" ...
Effects of The Solar Cycle - Effects On Earth - Terrestrial Climate
... Both long-term and short-term variations in solar activity are hypothesized to affect global climate, but it has proven extremely challenging to directly quantify the link between solar variation and the ... Later research has concentrated more on correlating solar activity with global temperature ... that there may also be regional climate impacts due to the solar cycle ...
Nir Shaviv - Solar Variation
... Shaviv’s solar hypothesis has been disputed by Mike Lockwood and Claus Froehlich in an analysis of the sun’s output over the last 25 years ... Secondly, Shaviv argues that short term variations in radiative forcing are damped by the oceans, leading to a lag between changes in solar output and the effect on global temperatures ... was weaker than the 1990 maximum, increasing solar activity during previous decades was still having a warming effect, not unlike the lag between noon and the ...
Solar Variation and Climate - Historical Perspective
... The study of cycles was generally popular through the first half of the century ... Governments had collected a lot of weather data to play with and inevitably people found correlations between sun spot cycles and select weather patterns ...

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