Roundup: U.S. declares 2015 Earth's hottest year by largest margin

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.

NO SURPRISE

The announcements didn't come as a surprise, with 10 out of the 12 months last year being the warmest for their respective months on record. Only January was the second warmest January on record and April third warmest.

"You can see that we broke the record each month for the warmest month on record, except for two months," Thomas Karl, director of NOAA's National Centers for Environmental Information, told reporters during a media teleconference. "That's the first time we've seen that."

Besides, the five highest monthly departures from average for any month on record all occurred last year.

Overall, record warmth was seen around the world in 2015, including Central America, the northern half of South America, parts of northern, southern, and eastern Europe stretching into western Asia, a large section of east central Siberia and regions of eastern and southern Africa.

MORE RECORDS

The natural El Nino event, which warms the tropical Pacific Ocean, might be partly to blame for the 2015 heat record.

Karl, however, said 2015 would have likely been a record even without El Nino. "But El Nino pushed it way over the top," he added.

Gavin Schmidt, director of NASA's Goddard Institute for Space Studies, attributed 2015's temperatures largely to "the cumulative effect" of the long-term warming trend of our Earth, which is mainly caused by the emission of greenhouse gases from human activities into the atmosphere.

"The reason why this is such a warm record year is because of the long-term underlying trend," Schmidt told reporters at the same teleconference. "There is no evidence that long-term trend has slowed, paused, or hiatused at any point in the last few decades."

Since the El Nino will continue into this spring, he predicted that 2016 would be again "an exceptionally warm year and perhaps even another record."

Including the year 2015, 15 of the 16 warmest years on record have occurred during the 21st century, with the exception of 1998, which currently tied with 2009 as the sixth warmest year on record, both reports said.

CALL FOR ACTION

Astrid Caldas, a climate scientist at the Union of Concerned Scientists, said the long-term warming trend should be reversed if the world is to keep global warming below two degrees Celsius, the goal of the international climate agreement struck in Paris last December and the number that scientists believe will avoid irreversible changes to Earth's systems.

"This new record highlights how critical it was to get an agreement in Paris and the importance of countries not only following through on their commitments, but going further," Caldas said in a statement.

"A massive ramp-up of renewable- and low-carbon- energy will be essential to stay within two degrees Celsius of warming and avoid new records being set," she said.

Democratic presidential candidate Senator Bernie Sanders also sought the opportunity to urge movement away from fossil fuels.

"The debate is over," Sanders said in a statement. "Sixteen of the last 18 years have been the hottest ever recorded. Climate change is real and is caused by human activity."

"This planet and its people are in trouble. Unless we get our act together, we will see in years to come more droughts, more floods and more extreme weather disturbances," he said. Endit