That makes the longest such streak in the 137 years the record has existed.
"The globally averaged temperature over land and ocean surfaces for May 2016 was the highest for the month of May in the NOAA global temperature dataset record, which dates back to 1880," the agency said in a statement.
The powerful but waning El Nino weather phenomenon -- which tends to warm equatorial waters in the Pacific -- may have contributed to this year's record, climate scientists said, but doesn't explain all of it.
"The state of the climate so far this year gives us much cause for alarm," World Climate Research Program director David Carlson director said.
"The super El Nino is only partly to blame. Abnormal is the new normal."
May's combined average temperature came to 1.57 degrees Fahrenheit (0.87 Celsius) above the 20th-century average for the month of 58.6 degrees Fahrenheit (14.8 Celsius).
That was 0.04 degrees Fahrenheit (0.02 Celsius) above the previous record for May, which was set last year.
May 2016 tied with June and August 2015 as the 12th-highest monthly temperature increase on record, NOAA said.
May's record temperatures were accompanied by other extreme weather events, including heavy rainfall in Europe and the southern United States.
Overall, 13 of the 15 monthly high-temperature records have taken place since February 2015, it added.
Experts say global warming is contributing to a growing number of environmental disasters around the world, from the bleaching of the Great Barrier Reef to the wildfires raging across Canada.
Last year marked the hottest on record so far, beating 2014, which previously held the title.
With 13 months in a row now setting records for heat, 2016 -- although not quite half over yet -- is on track to be another scorching year.
The temperature across global land and ocean surfaces from January through May reached 1.94 degrees Fahrenheit (1.08 Celsius) above the 20th century average of 55.5 degrees Fahrenheit (13 Celsius), making it the highest for January-May on record, surpassing the previous record set last year by 0.43 degrees Fahrenheit (0.24 Celsius).
The World Bank said last month that the global community is not prepared for a swift increase in climate change-related natural disasters -- such as floods and droughts -- which will put 1.3 billion people at risk by 2050.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)
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