Solar irradiance, the flux of the Sun output directed toward Earth, is the main energy source for the Earth. The Sun itself varies on several timescales over billions of years - its luminosity increases as it evolves on the main sequence toward becoming a red giant. About every 11 years its sunspot activity cycles, and within just minutes flares can erupt and release massive amounts of energy. Most of the fluctuations, from tens to thousands of years, are associated with changes in the solar magnetic field. The focus of the National Research Council September 2011 workshop on solar variability and Earth climate, and of this summary report, is mainly magnetically driven variability and its possible connection with Earth climate variations in the past 10,000 years.
Even small variations in the amount or distribution of energy received at Earth can have a major influence on Earth climate when they persist for decades. However, no satellite measurements have indicated that solar output and variability have contributed in a significant way to the increase in global mean temperature in the past 50 years. Locally, however, correlations between solar activity and variations in average weather may stand out beyond the global trend, such has been argued to be the case for the El Southern Oscillation, even in the present day.
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