Climate and paleoclimate: What we can learn about solar luminosity variations

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:(1) 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.(2) 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.(3) There are considerable uncertainties in the record of past climates.(4) 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.

The Sharp Rise of Δ14Cca. 800 cal BC: Possible Causes, Related Climatic Teleconnections and the Impact on Human Environments

“…How could a relatively small reduction in solar activity induce the relatively large change in global climate inferred for 2650 BP? Answering this question involves a considerable degree of speculation, since the effect of solar variability on the Holocene climate is still controversial (e.g., Wigley 1981;Roederer 1995). In any case, to provide an answer, it is necessary to look at the effect of solar variations on the atmosphere.…”

The faint young sun‐climate paradox: Continental influences

“…Following the early work of Sagan and Mullen [1972], most of these investigations have exclusively considered an enhanced greenhouse effect due to some postulated change in the composition of the earth's atmosphere. The recent consensus [Owen et al, 1979;Henderson-Sellers and Schwartz, 1980;Wigley, 1981;Walker et al, 1981 ] seems to favor the greenhouse effect due to a larger abundance of carbon dioxide in the early atmosphere. While this may be an entirely reasonable solution, consideration should be given as to whether it is the complete solution.…”