Climate and paleoclimate: What we can learn about solar luminosity variations |
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| Authors: | T M L Wigley |
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| Institution: | 1. Climatic Research Unit, University of East Anglia, NR4 7TJ, Norwich, England
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| Abstract: | The Earth's climate is not constant, and has experienced major changes in the past on all timescales. The causes of these changes, although still incompletely understood, vary according to the timescale considered. Some of the most important causal mechanisms include continental drift, changes in the Earth's orbital parameters, volcanic activity and solar variations. Solar variations have been invoked to explain climatic change on almost all timescales from 1 to 109 yr. Unfortunately, even though the Sun is a prime candidate for explaining many changes in past climate, the use of past climate as a proxy for solar luminosity changes is fraught with difficulty. For example: - In many cases observed changes in climate can be adequately explained without recourse to solar variations as a causal factor. In fact, on the longest timescales the Earth's climate was remarkably similar to today in spite of a considerably lower solar output.
- For most timescales of climatic change there are, as yet, no plausible theories giving similar timescale variations in solar activity, so that a vital link between cause and effect is missing.
- There are considerable uncertainties in the record of past climates.
- On short timescales many proposed solar activity-climate links have failed to stand up to rigorous statistical analysis.
This paper reviews past changes in climate and proposed causal mechanisms on timescales of from 1 to 109 yr. The evidence for solar activity-climate links is discussed with special reference to the above points. |
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