Examining the data beyond the traditional calendar year, the latest 12-month period (May 2014–April 2015) ties with the record set last month (April 2014–March 2015) as the warmest 12-month period among all months in the 136-year period of record, as shown in the table below. In fact, this record was set several times over the past year, and nine of the ten warmest 12-month periods have occurred within the past two years (September 1997–August 1998 ties as eighth warmest). Nine of these ten 12-month periods also comprise months in two overlapping years. Only the full calendar year of 2014 is among the ten warmest 12-month periods (ties for sixth warmest).
Our 2015 count looks like this:
April was tied for the fourth hottest April on record;
March was the hottest March on record;
February was the second hottest February on record;
January was the second hottest January on record.
So far, 2015 has one hottest month, two second hottest months, and one fourth hottest month ever recorded.
For the last 12 months, the tally is:
April 2015 was tied for the fourth hottest April ever recorded;
March 2015 was the hottest March ever recorded;
February 2015 was the second hottest February ever recorded;
January 2015 was the second hottest January ever recorded;
December 2014 was the hottest December ever recorded;
November 2014 was the 7th hottest November ever recorded;
October 2014 was the hottest October ever recorded;
September 2014 was the hottest September ever recorded;
August 2014 was the hottest August ever recorded;
July 2014 was the fourth hottest July ever recorded;
June 2014 was the hottest June ever recorded;
May 2014 was the hottest May ever recorded;
So, let's see what the score is for the last 12 months: one 7th hottest month, two 4th hottest months, two 2nd hottest months and seven hottest months ever.
Nine of the last twelve months were either the hottest or second hottest ever recorded.
The last 12 months ties the record for the hottest 12-month period ever recorded. Nine of the ten hottest 12-month periods have occurred in the last two years.