Yesterday, there was record heat (101F) in Spokane and it continues on into today. (It hit 109F in Walla Walla; I hope the grape vines didn't get scorched.) And, of course, the Live Earth concerts are this weekend.
Most educated people understand that global warming is a fact, and that it is largely the result of humans' effect on the environment in the form of CO2 emissions. Those, perhaps, with a vested interest in denying that humans cause global warming (energy companies and people who make millions investing in them) have done pretty well putting forth lies that masquerade as objective science--not by disproving the science behind global warming, which is fairly uncomplicated, but by simply casting doubt and by pointing out that the Earth has always had cycles of warming and cooling. (Yes, but not to this extent, and not this rapidly.)
Anyway, if you haven't read Al Gore's "An Inconvenient Truth" (or seen the movie), I strongly urge you to do so. It explains the science very well and in very simple terms with plenty of graphics so that anybody can comprehend it. It's also humorous and not a dry text at all, actually an enjoyable (albeit scary) read.
In the meantime, here's a link to another very simple, clear explanation of how it is we know that humans are the cause of the current rapidly rising temperature of the planet.