July marked the Earth's hottest month in modern times, setting a new record for planet-wide heat that has not been seen in 137 years of record-keeping, US government scientists said Wednesday.

"The globally averaged temperature over land and ocean surfaces for July 2016 was the highest for both the month of July and for any month in the NOAA global temperature dataset record, which dates back to 1880," said the National Oceanic and Atmospheric Administration.

"This marks the 15th straight month the monthly global temperature record has been shattered, the longest such streak in the 137-year record."