Well, that would be one way to stop global warming. O_O
Theoretically, the chance of a cataclysmic eruption is low. But these are the same monkeys who think the Earth is always slow because it is big. It isn't likely to erupt, but it could. The fact that Yellowstone has been fidgeting for a couple decades makes me uneasy.
The fact that humans have been drilling, dumping, and generally tampering with the environment also means that things can change -- like, say, the 4000% increase in earthquakes in Oklahoma. It's kind of like playing Jenga; you move one thing and the whole tower collapses. Only we're standing on the tower, and if it collapses, we all die.