Is the sun causing global warming?

Evidence of warming on Mars and other bodies in the solar system has led to the claim that it is the sun, rather than human activity, that is driving global warming on Earth. The alternative, Republican presidential candidate Fred Thompson suggests, is to believe that "Mars and Jupiter, non signatories to the Kyoto Treaty, are actually inhabited by alien SUV-driving industrialists who run their air-conditioning at 60 degrees and refuse to recycle."

But scientists say that solar radiation output has actually been declining in recent years, and attribute warming on Mars to other factors.