Chapter 5 - The Oceanic Heat Budget

5.9 Variations in Solar Constant

We have assumed so far that the solar constant, the output of light and heat from the sun, is steady. Recent evidence based on variability of sunspots and faculae (bright spots) shows that the output varied by ± 0.2% over centuries (Lean, Beer, and Bradley, 1995), and that this variability is correlated with changes in global mean temperature of Earth's surface of ± 0.4°C. (Figure 5.14). In addition, White and Cayan (1998) found a small 12yr, 22yr, and longer-period variations of sea-surface temperature measured by bathythermographs and ship-board thermometers over the past century. The observed response of Earth to solar variability is about that calculated from numerical models of the coupled ocean-atmosphere climate system. Many other changes in climate and weather have been attributed to solar variability. The correlations are somewhat controversial, and much more information can be found in Hoyt and Schatten's (1997) book on the subject.

Figure 5.14 Changes in solar constant (total solar irradiance) and global mean temperature of Earth’s surface over the past 400 years. Except for a period of enhanced volcanic activity in the early 19th century, surface temperature is well correlated with solar variability. From Lean, personal communication.

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