Earth's persistent record 2016 heat is now dancing near levels that a world agreement is trying to avoid, U.S. federal scientists said.

The National Oceanic and Atmospheric Administration said Tuesday that globally , June was the 14th straight record hot month, with Earth averaging 16.4 C (61.52 F). That is 0.9 degrees Celsius (1.62 degrees F) warmer than average and a shade above the record set in 2015. The last month Earth wasn't record hot was April 2015.

Scientists said records keep falling because of a combination of man-made global warming and the natural El Nino, a periodic warming of the Pacific that changes weather worldwide and heats the globe. But El Nino ended a couple months ago and the record heat — and record melting of Arctic sea ice — has stuck around.

What's really got federal scientists' attention is the record warm first half of 2016, which comes after two record hot years.

NOAA said the first half of 2016 was 0.2 degrees Celsius (0.36 degrees F) warmer than last year's record.

Paris Agreement limit hit

NASA chief climate scientist Gavin Schmidt said the first six months of the year were not just the warmest on record, by far, but 1.3 degrees Celsius (2.3 degrees F) warmer than the last two decades of the 19th century. But more importantly, he said 2016 so far is about 1.5 degrees Celsius ( 2.7 degrees) warmer than pre-industrial times.

That 1.5 degrees Celsius mark is key. A December 2015 international pact to control global warming set a goal of avoiding 1.5 degrees Celsius warming above pre-industrial levels. And the agreement says if Earth can't limit global warming to 1.5 degrees, at least it should limit it to 2 degrees (3.6 degrees Fahrenheit) above pre-industrial levels.

Because El Nino is a factor — Schmidt figured about 40 per cent of the reason 2016 is hotter than 2015 is due to El Nino — 2017 will likely be a bit cooler than 2016. When scientists look at long-term warming since pre-industrial times they don't look at one year, but it's still a pretty noticeable threshold, Schmidt said.

"It's fair to say we are dancing with those lower targets," Schmidt said.

99% chance of record

Schmidt and NOAA climate scientist Jake Crouch said 2016 will likely be the hottest year on record for a third consecutive year. Schmidt said his statistical calculations put the chance of 2016 being record hot at 99 per cent.

Temperature records go back to 1880.

Chunks of sea ice, melt ponds and open water are all seen in this image captured over the Chukchi Sea on Saturday, July 16, 2016. NASA scientists said the warming has caused an extreme melting of Arctic sea ice for the beginning of 2016. (Operation IceBridge/Goddard/NASA)

NASA scientists said the warming has caused an extreme melting of Arctic sea ice for the beginning of 2016. Usually Arctic sea ice peaks in the winter and reaches its lowest point in September.

But so far five of the first six months of 2016 set record low averages, said NASA sea ice scientist Walt Meier. Sea ice measurements go back to 1979.