A friend of mine recently drew my attention to last year's March 2 episode of the Prickly City comic strip, which you can view here. (Incidentally, it appears that this website, GoComics, lets you subscribe to a variety of strips, all of which will appear on your own personalized comics page every day, which is good to know.) Prickly City is drawn from a conservative viewpoint — not that there's anything wrong with that — and this particular episode reflects an unfortunately commonplace misunderstanding, especially on the right, about global warming.
(Prickly City is credited to and was created by Chicago Tribune editorial cartoonist Scott Stantis, but for several year now it has been drawn by Eric Allie. I'm not sure who does the writing. Possibly they both contribute, as they seem to have similar political views.)
In brief, this episode shows Carmen, the strip's conservative protagonist, saying across a series of panels, "The Earth has been molten ... a solid sheet of ice ... bouncing between ice ages ... Isn't climate change kind of what Earth does?" To which her liberal friend Winslow (a coyote pup) replies with a dismissive gesture and the exclamation "Lunatic!"
Winslow's response really ought to be something more on the order of "Good grief! Didn't they cover this in school?" Then again, Prickly City takes a negative view of schools as well. (Did you know, for example, that truancy laws are a conspiracy on the part of teachers' unions to get more money? See this strip.)
OK, I admit that my suggestion wouldn't make for a very good punchline, but the original isn't particularly funny either. Anyway, my main gripe isn't so much with the comic as the lamentable fact that even at this late date a lot of people are likely not to realize what's wrong with the underlying assumptions here.
Yes, the Earth's climate has varied a lot over its history, but that's hardly reassuring given that the results have sometimes been pretty unpleasant and even catastrophic. Moreover, while the Earth has experienced periods of warming in the past (coming out of ice ages, for example), the rate of warming over the past few decades has been extraordinarily rapid, about 10 or 20 times as fast as change coming out of the last ice age, for example.
(One quibble in passing: It's possible that the Earth was frozen over one or more times, most recently as a glaciation roughly 650 million years ago, but that's uncertain. For a summary of the evidence for and against the hypothesis, see Wikipedia's "Snowball Earth" article.)
Another difference is the current level and complexity of modern human civilization. Humans have faced global and localized climate change in the past, sometimes leading to serious disruptions of agriculture, the depopulation of whole regions, mass migrations, and even the collapse of cultures, if only in the affected areas. Today there are vastly more of us, global climate change by definition isn't just a local problem, and comparable events would be proportionally far worse.
Fortunately, while past major climate change resulted from events beyond our control, such as variations in the Earth's orbit or gigantic meteorite strikes, this time the main cause is human activity, which means that we can do something about it. We've waited too long to prevent it entirely (for one thing, it's already happening, and we don't have a time machine), but we can still limit how bad it will be.
For more on the notion that past climate change means we can ignore the present global warming, see these links from the Royal Society (the original national science academy), the Skeptical Science website, Grist, and Weather Underground (a meteorology website, not the group from the 60s!).
Also, if you haven't yet read it, you might want to take a look at this previous post on research by former climate-change doubter Richard Muller and his team, some of it funded by fossil-fuel interests. See also this page on the Skeptical Science website about the overwhelming number of scientists and scientific organizations who agree that the evidence clearly does point to human-caused climate change and that it's past time to do something to mitigate it. (You can also find my earlier posts about climate change here if you're interested.)
(Updated 2015 June 7 to add some additional links, fix typos, and try to improve my writing.)