What about global warming being caused by the sun?
Some scientists have theorized that increases in solar output are responsible for a significant portion of the observed global warming. For instance, Scafetta & West (2006) estimated that 25-35% of the global warming in the 1980-2000 period was attributable to solar variability. Other scientists disagree, finding no evidence of global warming due to solar activity changes since the 1940s. Since any increase in solar radiation would heat both the lower and upper atmosphere, the observed drop in upper atmospheric temperatures in the past 30 years argues against a large portion of the observed greenhouse effect being caused by solar variability. The observed cooling of the upper atmosphere in recent decades is strong evidence that the warming at Earth’s surface is due to human-emitted greenhouse gases. It should also give us additional confidence in the climate models, since they predicted that this upper atmospheric cooling would occur.