Earth's Climate System: The Sun
It may seem odd to include our nearby star in a discussion of Earth's climate system, but without solar radiation nothing much would happen here—no atmosphere, no climate, no humans.
The Sun as a star; blackbody radiation; Wien's Law, etc. (forthcoming link to presentation)
Solar radiation as driver of climate system; energy equilibria at top of atmosphere, land surface, etc. (forthcoming link to presentation)
Solar radiation DOES vary; could these variations be a cause of modern warming? Many technical papers address this question, and the consensus is....probably. But how much of the warming? Most climatologists, and the IPCC documents, consider the solar factor to be minor—particularly for the warming since 1975. Unfortunately for widespread understanding, the content is challenging, the typical language used is quite technical, and few gifted communicators seem to have risen from the ranks of the solar/climate nexus. A short podcast excerpt (minutes 3 to 10 of this file), hosted by me, summarizes some of these ideas more accessibly, but simplifies or bypasses many ideas.
Is Climate Sensitive to Solar Variability? Scarfetta and West (S&W), authors of this 2008 Opinion, make the startling statement that "the Sun could account for as much as 69% of the increase in Earth's average temperature." S&W have published their technical reports in peer-reviewed journals such as AGU and GRL, but this Physics Today piece is by far the most digestible for non-specialists.
Duffy and colleagues' 2009 rebuttal of the Scarfetta and West opinion notes that S&W's hypothesis conflicts with recent data and paleoclimatic records, and also includes clear, effective graphics.
Is the Sun Causing Global Warming? at the Skeptical Scientist documents a scientific consensus (including Scafetta!) that the Sun isn't a major player, particular since the 1970s.
This summary of the impact of solar variability is well-written, includes effective graphics, and affirms the subordinate role of the Sun (and cosmic rays, an even further-out factor).
RealClimate, a climate blog run by professional climatologists, has often weighed in to counter claims of solar influence in this set of posts over the years.