Warmest 12-month periods for the contiguous United States, 1895-2012. Credit: National Climatic Data Center.
Although September by itself was only 23rd warmest such month on record (tied with 1980), the unusual warmth from January through August virtually guarantees that 2012 as a whole will be the warmest since modern recordkeeping began. According to the National Climatic Data Center (NCDC), October through December would need to rank among the top 10 percent coldest such periods on record to thwart the warm temperature record. (Globally, however, 2012 is not expected to rank as the warmest year, as the January to August period ranked ninth on the list.)
