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Is it true that solar activity has a very close correlation with global temperatures? Is it true that cloud activity has a close but inverse relationship with global temperatures?
James
Professor Mitchell: Direct measurements of solar activity have only been made since 1978, so all longer-term solar series make use of surrogate data, mainly based on some aspect of the sunspot cycle. There is some disagreement between the different series, but most show a good correlation with changes in global mean temperature up to about 1960, and for one time series (solar cycle length) to about 1980. Since then, satellite measurements show no discernible trend (up or down) in solar intensity, but global mean temperatures have continued to increase. Ignoring, for the sake of argument, the difficulties in determining cloud amount from satellites (e.g. in high latitudes it is difficult to distinguish between low cloud and snow) there are suggestions that there have been periods of correlation between cloud amount and one measure of solar activity, cosmic rays, but these have been of limited length, and not sustained.
The mechanism by which cosmic rays might affect climate is as yet speculative and unquantified. Cosmic rays reaching the earth are modulated by solar activity and produce ions (electrically charged particles) in the atmosphere, and recent laboratory experiment suggest ions can under the right conditions lead to increases in cloudiness. There is no compelling evidence that this affect is large enough or acts on the right type of cloud to produce the required effect.
The bottom line is, even if cosmic rays have a detectable effect on climate, measured solar activity over the last few decades has changed little, and so cannot explain the continued warming trend. In contrast, increases in carbon dioxide is well measured, its warming effect is well quantified, it explains most of the recent warming and increases are likely to continue into the foreseeable future.
The bottom line is, even if cosmic rays have a detectable effect on climate, measured solar activity over the last few decades has changed little, and so cannot explain the continued warming trend. In contrast, increases in carbon dioxide is well measured, its warming effect is well quantified, it explains most of the recent warming and increases are likely to continue into the foreseeable future.
