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Causes of Climate Change and the Role of the Sun

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Do changes in the Sun affect the Earth’s climate? Variations in the Earth’s orbit clearly have a major effect, controlling diurnal and seasonal cycles as well as the onset of ice ages, but what about the impact of intrinsic variability within the Sun? Observations of sunspots date back to at least the 2nd century BC, and so have speculations that sunspot numbers are related to weather, although many such claims were statistically dubious. Nowadays, the need to distinguish natural from anthropogenic causes of changes in climate has placed new emphasis on quantifying and understanding any such relationship. Another consideration in the past was the lack of evidence of any measureable variation in the Sun’s energy output. The advent of satellite measurements of solar irradiance, however, together with the collation of well-calibrated records of atmospheric and oceanographic parameters, have enabled considerable progress to be made in establishing evidence of solar-climate links on a range of timescales. Our research shows that when the Sun is more active the atmosphere responds by a warming of the stratosphere in low latitudes but that the predominant signal in the lower atmosphere appears in mid-latitudes. Associated with this the jet streams weaken and move polewards, along with the mid-latitude storm-tracks. We have found that an important factor driving this response is the absorption of solar UV radiation in the stratosphere and we have been able to identify a mechanism for dynamical coupling between the stratosphere and the atmosphere below.Over the past few years some satellite measurements have suggested that variations at UV wavelengths are larger than previously understood. I will discuss the implications of these spectral variations for the stratosphere and describe how measurements of stratospheric ozone might be used synergistically with those of solar spectral irradiance to improve knowledge of the variations in both.

This talk is part of the Stokes Society, Pembroke College series.

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