Reason #232: Heat Waves

Every year, the National Oceanic and Atmospheric Association, in conjunction with scientists from 47 other countries, publishes a "State of the Climate" report, assessing the previous year's weather and noting any unusual incidents and trends.

Though it makes a point of being as apolitical as possible and does not blame climate change for conditions that are not conclusively known to have been caused by climate change, this year's report finally broke down and added a new section detailing the wide range of conditions that seem to be climate-change-related.

Among the noteworthy evidence:

• 2011 was one of the fifteen warmest years on record (from the last hundred years or so).
• Carbon dioxide levels in the atmosphere have reached 390 parts per million, the highest ever recorded.
• Major droughts like the one in Texas last year are now twenty times more likely than they were fifty years ago.
• Abnormally warm Novembers like the one England experienced last year are now sixty-two times more likely than fifty years ago.

 The report focuses on comparisons--twenty times more likely, sixty-two times more likely--thanks to what's called event attribution science. Like I mentioned at the top, it's very hard to point to climate change as the absolute cause of any one event, so the best researchers can do is point out the degree of improbability associated with the event, and track the evolution of that improbability.

For the record, the overall odds of last year's heat pattern happening randomly are one in 1.6 million.