2012 was not the hottest year on record, but the direction we're heading is pretty clearly a bad one.
Whew! We did it! We didn't have another warmest-year-on-record!
Just kidding. 2012 might not have been the warmest year on record (in fact it was the ninth) but that is no reason not to panic (and, for that matter, it *was* the warmest on record for the continental U.S. by far). The path we're on may not be perfectly direct, but there's no question which way we're heading. All of the 10 warmest years on record have happened in the past decade and a half.
Beginning in the late 19th century, there's enough data from around the world to construct maps of average annual temperatures for different regions. When you put all that data together (and treat the 30-year period from 1951 to 1980 as a baseline), you get the above picture of a steadily warming planet, with years before the baseline a degree or two (Celsius) below, and then more recent years shading heavily red -- a degree or two above. (Also, it should be noted that the climate change's effects are not equally distributed around the globe -- some spots, such as regions of Antarctica, are actually a bit cooler. But that does not in some magical way cancel out the warming elsewhere, nor is cooling itself not a problem. This is a climate system badly destablized, and uneven and countervailing phenomena are not indications to the contrary.)
Overall, the average temperature last year was 58.3 degrees Fahrenheit -- one degree warmer than it was during the years when the baseline was established and 1.4 degrees more than in 1880. Back then, the amount of carbon dioxide in the atmosphere was 285 parts per million. Today it is over 390, and rising steadily. According to scientists, anything exceeding 350 ppm (*at most*) is a threat to the environment in which "civilization developed and to which life on Earth is adapted."
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