U.S. heat over the past 12 months: a one in half-a-million event [View all]

[phantom power]

The U.S. record for hottest 12-month period fell for the second straight month in May. The June 2011 - May 2012 temperatures smashed the previous record by a startling 0.4°F, which is a huge margin to break a record by for a 1-year period. The past twelve months have featured America's 2nd warmest summer, 4th warmest winter, and warmest spring on record. Thirty-two states were record warm for the 12-month period, and an additional ten states were top ten warm. Each of the 12 months from June 2011 through May 2012 ranked among the warmest third of their historical distribution for the first time in the 1895-present record. According to NCDC, the odds of this occurring randomly during any particular month are 1 in 531,441. Thus, we should only see one more 12-month period so warm between now and 46,298 AD--assuming the climate is staying the same as during the past 118 years. The unusual warmth was due, in part, to a La Niña event in the Pacific that altered jet stream patterns, keeping the polar jet stream much farther to the north than usual. However, it is highly unlikely that the extremity of the heat during the past 12 months could have occurred without a warming climate. Some critics have claimed that recent record warm temperatures measured in the U.S. are due to poor siting of a number of measurement stations. Even if true (and the best science we have says that these stations were actually reporting temperatures that were too cool), there is no way that measurement errors can account for the huge margin by which U.S. temperature records have been crushed during the past 12-month, 5-month, and 3-month periods.

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2115



Figure 2. Three of the top ten warmest 12-month periods in the contiguous U.S. since 1895 have occurred since April 2011. Image credit: NOAA/NCDC.