ThinkProgress has a good article about how global warming is causing the recent outbreaks of extreme weather. The article is worth reading in full,  and also includes this video, which does a pretty good job explaining things:

You know, my Republican friends often say: “What global warming? It’s nice and cool outside right now.” That’s why the term “climate change” was introduced; because “climate” is basically an averaging of what the weather is doing. So, global warming does not mean it will henceforth be warmer than previously all day, every day, but rather that the average trend is towards warming.

And moreover, slight changes in averages can have a major ripple effect throughout the whole system.

Well, I’m not a scientist, but the video features people who are. They explain everything pretty well.

(Hat Tip to Private Buffoon.)