Second, what I am seeing in these arguments is a very dangerous practice called "cherry picking"; selectively picking out data that support your argument and ignoring contrary evidence. It certainly looks interesting that Earth, Mars, Jupiter, Triton, and Pluto are warming, and if that’s all you heard then it seems logical to think maybe the Sun is the cause. But they aren’t the only objects in the solar system. What about Mercury, Venus, Saturn, Uranus… and if you include Triton to support your case, you’d better also take a good look at the nearly 100 other sizable moons in the solar system. Are they warming too?
I have heard nothing about them in these arguments, and I suspect it’s because there’s not much to say. If they are not warming, then deniers won’t mention them, and scientists won’t report it because there is nothing to report ("News flash: Phobos still the same temperature!" is unlikely to get into Planetary Science journals). However, I can’t say that with conviction, because the absence of evidence is not evidence of absence. Any planetary scientists reading this blog entry, please contact me. I’m interested in hearing more.
Mars: To start, is Mars even warming globally at all? Perhaps not — it might be a local effect. And if it is global, there already is an idea of why that might be happening: it would be due to periodic changes in its orbit, called Milankovitch cycles. The Earth has them too, and they do affect our climate. And the guy who is proposing that the Sun is warming Mars doesn’t think CO2 is a greenhouse gas. I think his science is a little suspect. His reasoning is certainly specious– he says if Mars and Earth are both warming, it must be due to the Sun. As I point out above, that is clearly not necessarily the case. Even if this martian warming turns out to be true, it may just be a natural effect of the shape of the orbit of Mars.
Of course it’s possible. There are links to the Sun’s behavior and Earth’s climate (look up the Maunder minimum for some interesting reading), and it would be foolish to simply deny this. However, this is a vastly complex and difficult system to understand, and simply claiming "Yes it’s due to the Sun" or "No it’s not due to the Sun" is certainly naive.
5) There are political and ideological ramifications of global warming, and a lot of people — politicians, in fact — have a lot at stake and are known to twist science to meet their needs.
With all of these facts lined up, it’s clear that the one thing we need to do is be very, very careful when someone comes in and makes a broad, sweeping statement about global warming’s cause, especially when they have ulterior motives for saying what they do. This may sound like an ad hominem, but we have seen, over and over, how science gets abused these past few years by those in power. A jaundiced eye is critical in science, and a little skepticism — or in this case, a lot — is a good thing.