Most of the Hottest Years Were in Past Decade2012 was a notable year on many fronts, and that includes the weather. According to the National Oceanic and Atmospheric Administration (NOAA), last year was the hottest year on record for the contiguous U.S. and it also had the second most extreme weather on record (they're looking at droughts, wildfires, hurricanes, storms, etc). The average temperature for 2012 was 55.3°F (12.9° Celsius), 3.2°F above the 20th century average, and 1.0°F above 1998, the previous warmest year. This might not sound like much to those who haven't looked into the field much, but you have to think about how much energy it takes to warm up our planet's atmosphere by this much, which is a lot of extra energy that is being retained.
It was also a very dry year: "The average precipitation total for the contiguous U.S. for 2012 was 26.57 inches, 2.57 inches below average, making it the 15th driest year on record for the nation. At its peak in July, the drought of 2012 engulfed 61 percent of the nation with the Mountain West, Great Plains, and Midwest experiencing the most intense drought conditions. The dry conditions proved ideal for wildfires in the West, charring 9.2 million acres — the third highest on record."
The U.S. Climate Extremes Index indicated that 2012 was the second most extreme year on record for the nation. The index, which evaluates extremes in temperature and precipitation, as well as landfalling tropical cyclones, was nearly twice the average value and second only to 1998. To date, 2012 has seen 11 disasters that have reached the $1 billion threshold in losses, to include Sandy, Isaac, and tornado outbreaks experienced in the Great Plains, Texas and Southeast/Ohio Valley. (source)
Individual weather events can't be linked directly to climate change, but when you start to have lots and lots of weather events, you can see a clear trend that is going in the wrong direction...
“The heat we saw in the U.S. is consistent with what we expect in a warming world,” Deke Arndt, chief of the climate monitoring branch at the center, said on a conference call. “It’s a huge exclamation point on the end of several decades.”