UPDATE (Dec 17, 2014): Since this article was published, June 2014, August 2014, September 2014, and October 2014 have also set records for monthly average temperatures. This streak may put 2014 on track to be Earth's hottest year on record. 

Both NASA and NOAA have ranked last month as the planet’s hottest May since records began in 1880. NOAA’s National Climate Data Center (NCDC) published this finding as part of their monthly State of the Climate report. The report’s global analysis also noted that March through May 2014 was the second hottest March–May period worldwide.

In the contiguous United States, last month was only the 32^nd hottest May on record, although above average temperatures occurred on the East and West Coasts. Persistent drought continued to affect about 37% of the contiguous United States, helping to fuel large wildfires in the western part of the country.

• NASA’s temperature data and map with caveat
• NOAA’s State of the Climate report for May: global | national
• NOAA's recently released State of the Climate report for 2013: global | national | highlights
• Information from the Centers for Disease Control and Prevention (CDC) on preventing the health effects of extreme heat 

​