In a powerful testament to the warming of the planet, two leading US science agencies jointly declared 2016 the hottest year on record, surpassing the previous record set last year - which itself had topped a mark set in 2014.

The pronouncement comes just before US President-elect Donald Trump, who has tweeted that global warming is a hoax, takes office after a campaign in which he threatened to pull the US out of an international agreement to fight climate change.

Trump has since said he has an open mind about the Paris climate accord, even as he has nominated to various Cabinet posts a slate of men who have raised questions about the extent to which human activity is responsible for rising temperatures around the world.

Scientists have been far less guarded, noting the striking reality that global temperatures have set a record three years in a row.

Advertisement

"We don't expect record years every year, but the ongoing long-term warming trend is clear," said Gavin Schmidt, who directs Nasa's Goddard Institute of Space Studies, in a statement accompanying the government temperature report.

Nasa announced the record jointly with the National Oceanic and Atmospheric Administration.

Last year's warmth was manifested across the planet, from the warm tropical ocean waters off the coast of northeastern Australia that contribute to the widespread death of coral in the Great Barrier Reef, to the Arctic, where melting sea ice hit regular monthly record lows and overall temperatures were the highest on record, at least from January through September of 2016.

In a catalogue of some of the extremes the planet witnessed during the year, the Noaa noted the megafire that engulfed Fort McMurray, in Alberta, Canada, at the beginning of May, a conflagration that came relatively early in the year for bushfires.

That event was consistent with a warming climate, as well as with the role of El Nino, although scientists are reluctant to formally say that climate change has played a role in an individual event without conducting extensive analysis.

Extreme high temperatures were seen from India - where the city of Phalodi recorded temperatures of 51C in May, a new national record - to Iran, where a temperature of 53C was recorded in Delhoran on July 22.

For the contiguous US, 2016 was merely the second warmest year on record, but for Alaska, it was the warmest yet recorded, underscoring once again the sharpness of Arctic warmth, in particular.

Last year's warmth was partly enhanced by a strong weather pattern known as El Nino, triggered by unusually warm waters in the Pacific. But the scientists underscore that the event is hardly the only cause.

For example, 1998 was also, at the time, the warmest year on record, thanks in part to a strong El Nino - but the 2016 planetary temperature now far surpasses that year, meaning other factors probably contributed to the temperature's rise.

"This El Nino might have contributed about a quarter or a third" of the record in 2016, said Deke Arndt, chief of the global monitoring branch at Noaa's National Centres for Environmental Information.

Scientists said the three-year rise in temperatures increases the urgency to battle climate change. "2016 is a wake-up call in many ways," said Jonathan Overpeck, a climate scientist at the University of Arizona. "Climate change is real, it is caused by humans and it is serious."