Does the 0.1 percent change in irradiance affect Earths climate much?
Solar irradiance changes are likely connected to dynamic aspects of climate—things like the coupling of the atmosphere and ocean—El Niño being one example—or aspects of atmospheric circulation, such as the Hadley cells that dominate in the tropics. But we’ve done a great deal of modeling, and the sun doesn’t explain the global warming that’s occurred over the last century. We think changes in irradiance account for about 10 percent global warming at most. Of course, there are also longer cycles that may have an impact on climate, but our understanding of them is limited. There is disagreement about whether the last three cycles have gotten successively brighter. Has that been resolved? No, it hasn’t. The best understanding is that irradiance cycles have been about the same in the last three cycles, but one group reports an increasing trend whereas another group says that current levels are now the lowest of the entire 30-year record. I believe these differences are due to instrumental
