WASHINGTON - Blistering heat blanketed the Earth in 2015 like never before, making it by far the hottest year by the widest margin on record, and reflecting a continued long-term warming trend in global climate change.

Last year was the planet's warmest since modern record keeping began in 1880, boosted by a long-term build-up of greenhouse gases and a

strong El Nino warming the Pacific Ocean, two major U.S. government agencies said Wednesday.

"Climate change is the challenge of our generation," Charles Bolden, head of the U.S. space agency NASA, said in a statement. "It is a key data point that should make policy makers stand up and take notice -- now is the time to act on climate."

LARGEST MARGIN

A report by NASA showed that globally-averaged temperatures in 2015 shattered the previous mark set in 2014 by 0.13 degrees Celsius, noting that only once before, in 1998, has the new record been greater than the old record by this much.

The U.S. National Oceanic and Atmospheric Administration (NOAA), which used much of the same raw temperature data, but different analyzing methods, put 2015's average temperature at 14.80 degrees Celsius, which was 0.90 degrees Celsius above the 20th century average.

"This was the highest among all 136 years in the 1880-2015 record, surpassing the previous record set last year by 0.16 degrees Celsius and marking the fourth time a global temperature record has been set this century," the NOAA report wrote.

"This is also the largest margin by which the annual global temperature record has been broken," it said.