We already knew it was a blazing hot year in the United States — the heat waves, the droughts, the wildfires — but NOAA's National Climatic Data Center has made it official. All told, 2012 was the hottest year on record for the lower 48 states, shattering the previous record set in 1998 by nearly 1°F:

Annual average temperature in the continental United States. (The Washington Post)

It was mainly the Midwest and Great Plains getting hit by unusual heat, but just about every part of the mainland United States (save for the Pacific coast) saw temperatures that were well above the average over the previous three decades:

Difference from average annual temperature in 2012 compared to the 1981-2010 average. (NOAA)

Not only that, but it was also a weird year for weather. Here's NCDC's "Climate Extremes Index," measuring the portion of the United States affected by unusually wet or dry or warm or cold conditions. This was the second-most extreme year for weather on record, behind only 1988:

All this extreme weather was pricey. The United States went through 11 natural disasters last year that cost $1 billion or more, the second-most since this statistic was first kept. (That's partly due to the wild weather itself, but also partly due to the fact that the nation's population is growing and our infrastructure is becoming more costly.)

Now the big question: What does this all have to do with climate change? The mainland United States is a mere 2 percent of the Earth's surface, so it doesn't always line up with global warming trends. Note that 2012 is "only" expected to be the eighth-hottest year on record globally, although that won't be official until next week. It's not unusual to expect our tiny patch of land here to be leap far above or below global trends in any given year.

Still, a whole lot of Americans live in the mainland United States, so what happens here gets plenty of attention. And a year like last year is basically what scientists have predicted lies in store for the United States if global temperatures keep rising. This big 2009 report from the U.S. Global Change Research Program laid out some of the expected results of future warming: drought in the Great Plains, heat waves in the Northeast, more wildfires in the Southwest... In other words, a lot like 2012 — only considerably more intense.

Related: For more on this year's NOAA report, my colleagues Jason Samenow and Juliet Eilperin have detailed breakdowns.