WASHINGTON: Another month, another global heat record smashed.

The National Oceanic and Atmospheric Administration on Tuesday said August's temperature of 61.74 degrees (16.52 Celsius) was .09 degrees (.05 Celsius) warmer than the old August record set last year, and was the 16th consecutive month of record-breaking heat. NOAA monitoring chief Deke Arndt said it was also the hottest summer, with 2016 on pace to smash last year's record for the hottest year.

August 2016 was also 1.66 degrees (0.92 Celsius) warmer than the 20th-century average. It was the fifth hottest month of any kind recorded, going back to 1880. Six of the 17 hottest months on record have been the summer months of 2015 and 2016.

The June-through-August summer was 2.18 degrees (1.21 Celsius) warmer than the 20th-century average and beat the old summer heat record, set last year, by one-fifth of a degree (0.11 Celsius), NOAA said.

"The needle has been shoved all the way over into the red by greenhouse gases," Arndt said.

NOAA's announcement came on a day when 375 members of the National Academy of Sciences, including Stephen Hawking and 30 Nobel laureates, released an open letter urging American leaders not to pull out of an international agreement to curb global warming.

Organiser and MIT climate scientist Kerry Emanuel said the scientists wrote the letter in response to the Republican party platform that rejects the Paris climate agreement reached last December. The letter said presidential nominee Donald Trump's advocacy of withdrawing from that agreement would "send a clear signal to the rest of the world: The United States does not care about the global problem of human-caused climate change."

Pulling out of the Paris accord, Emanuel said, "will accelerate our head-long plunge into a riskier and riskier climate."

"Everywhere we look we see signs that the climate really is changing," Emanuel said. "We're getting wake-up calls more frequently and we really have to do something about this."