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DCL

If you live in certain places around the country, you might have noticed that some of your summer was a tad cooler than usual. In fact, some cities indeed registered colder temperatures than average. Now, if you're a climate change skeptic, you might figure you've just borne witness to some ironclad proof that global warming is a sham.

Your logic may fall upon the following lines: Global warming means that temperatures should be rising, not sinking. It was cool out this summer. Ergo, climate change is a sham.

And if you also happened to be a prominent politician who was opposed to a climate bill and a global warming skeptic, you might write and publish a piece vociferously announcing this logic. Of course, you'd be ridiculed in the scientific community, but, of course, you wouldn't care.

To toss one more 'of course' on the growing heap: Of course, most people that have their doubts about climate change stirred by an unusually cool summer don't run around publishing their opinions in the local papers' op-ed section. They just wonder.

And you shouldn't feel stupid for wondering, either--it's a perfectly valid question to ask. But there's an explanation, and it's not that global warming "alarmists" are all worked up over nothing. It's just that climate change isn't occurring over a steady, completely predictable course--it's a gradual (for now), erratic rise in temperature that can have different effects in different regions.

As Grist's Umbra points out,

the last decades have included the hottest years on record, when you look at ocean and surface temperatures. Last year was the eighth-warmest on record; full stats are not yet in on 2009, of course, but already we know that the world's oceans set a heat record in July. All this does not seem to indicate ten years worth of cooling temperatures.

This emphasizes the importance of not relying on personal, anecdotal evidence to attempt to prove a greater, general point (which is one of the oldest, and most common fallacies in the books). If eight out of the last ten years showed increasingly warm temperatures, and the two that didn't were a bit cooler, it seems obvious what kind of a conclusion you'd still make about the general trend.

Also, it's worth noting that climate change will have different affects on temperatures in different parts of the world--hence the shift from 'global warming' to the more palatable 'global climate change.' While the first term is still correct, since the planet is on average seeing warmer and warmer temps, some regions may see wetter, and sometimes, colder weather. The basic explanation for this is that as heat increases, more water evaporates around the world, putting more vapor into the atmosphere--which can cause heavier rainfalls and worse storms, and create cooler weather patterns.

For more useful resources to help you dig a little deeper into the facts about climate change, check out these sites, each hell bent on keeping the facts straight: Real Climate, Grist, and Climate Progress. And, of course--TreeHugger.