Global warming was hot news this year, literally.

Perhaps the most unavoidable climate story of 2012 was the warmth that gripped much of the United States, and to a lesser degree, the planet, throughout the entire year. Heat waves brought "spring in March" to parts of the country, and broke all-time high-temperature records in a number of places. This, inevitably, led to a discussion of global warming and the degree to which it contributes to some types of extreme weather, in this case heat waves.

In fact, prominent climate scientist James Hansen, of NASA's Goddard Institute for Space Studies, and colleagues published research saying recent heat waves "were a consequence of global warming, because their likelihood in the absence of global warming was exceedingly small." Some other climate scientists, however, disagreed about the degree to which heat waves can be attributed to climate change.

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