2015 was Earth’s hottest year on record
PARCHED EARTH The drought-stricken Molatedi Dam in South Africa in November. AP
WASHINGTON—Last year wasn’t just Earth’s hottest year on record—it also left a century of high temperature marks in the dust.
The National Oceanic Atmospheric Administration (NOAA) and Nasa announced on Wednesday that 2015 was by far the hottest year in 136 years of record keeping.
For the most part, scientists at the US agencies and elsewhere blamed man-made global warming, with a boost from El Niño, a warming of parts of the Pacific Ocean that changes weather worldwide and adds to the globe’s heat.
NOAA said 2015’s temperature was 14.79 degrees Celsius warmer than 2014, the largest jump ever over a previous record. That’s 1.62 degrees above the 20th-century average.
Nasa, which measures differently, said 2015 was 0.23 degrees warmer than the record set in 2014 and 1.6 degrees above 20th-century average.
Because of the wide margin over 2014, Nasa calculated that 2015 was a record with 94-percent certainty, more than double the certainty it had last year when announcing 2014 as a record.
NOAA put the number at above 99 percent—or “virtually certain,” said Tom Karl, director of NOAA’s National Centers for Environmental Information.
For the first time Earth is 1 degree warmer than it was in preindustrial times, NOAA and Nasa said. That’s a key milestone because world leaders have set a threshold of trying to avoid warming of 1.5 or 2 degrees above preindustrial times.
Because of the pace of rising temperatures, “we don’t have very far to go to reach 1.5,” Karl said.
Not ‘magic numbers’
But 1.5 or 2 degrees are not “magic numbers” and “we’re already seeing the impacts of global warming,” said Nasa Goddard Institute of Space Studies director Gavin Schmidt.
“This trend will continue; it will continue because we understand why it’s happening,” Schmidt said. “It’s happening because the dominant force is carbon dioxide” from burning of fossil fuels like coal, oil and gas.
Scientists started predicting a global temperature record months ago, in part because an El Niño weather pattern, one of the largest in a century, is releasing an immense amount of heat from the Pacific Ocean into the atmosphere.
But the bulk of the record-setting heat, they say, is a consequence of the long-term planetary warming caused by human emissions of greenhouse gases.
“The whole system is warming up, relentlessly,” said Gerald A. Meehl, a scientist at the National Center for Atmospheric Research in Boulder, Colorado.
Rapid global warming
It will take a few more years to know for certain, but the back-to-back records of 2014 and 2015 may have put the world back onto a trajectory of rapid global warming, after a period of relatively slow warming dating to the last powerful El Niño, in 1998.
The end of 2015 was especially remarkable in the United States, with virtually every state east of the Mississippi River having a record warm December, often accompanied by heavy rains.
A warmer atmosphere can hold more water vapor, and an intensification of rainstorms was one of the fundamental predictions made by climate scientists decades ago as a consequence of human emissions.
That prediction has come to pass, with the rains growing more intense across every region of the United States, but especially so in the East.
The term global warming is generally taken to refer to the temperature trend at the surface of the planet, and those are the figures reported by the agencies on Wednesday.
The figures were for the lower 48 United States. That land mass covers less than 2 percent of the surface of Earth, so it is not unusual to have a slight divergence between United States temperatures and those of the planet as a whole.
Annual marks
Although 2015 is now the hottest on record, it was the fourth time in 11 years that Earth broke annual marks for high temperature.
“It’s getting to the point where breaking record is the norm,” Texas Tech climate scientist Katharine Hayhoe said. “It’s almost unusual when we’re not breaking a record.”
December 2015 was the 10th month last year that set a monthly warmth record, with only January and April not hitting high marks.
“That’s the first time we’ve seen that,” NOAA’s Karl said.
In December last year, the globe was 14.79 degrees warmer than normal, beating the old record set in 2014 by more than half a degree, NOAA calculated.
Earth has broken monthly heat records 34 times since 2000. The last time a global cold month record was set was December 1916 and the coldest year on record was 1911, according to NOAA.
Strong El Niño
An added factor this year is the strong El Niño. Michael Mann of Pennsylvania State University said a strong El Niño could add about a third of a degree of warming to Earth’s temperature but that “sits upon the ramp of global warming.”
Karl and Schmidt both said 2015 would have been a record without El Niño.
“But El Niño pushed it way over the top,” Karl said.
And it’s likely to happen this year, too.
Schmidt, Karl and others said there was a better than even chance that this year will pass 2015 as the hottest year on record, thanks to El Niño.
“2015 will be difficult to beat, but you say that almost every year and you get surprised,” said Victor Gensini, a meteorology professor at the College of DuPage outside of Chicago.
Measurements from Japan, Britain and the University of California at Berkeley also show 2015 is the warmest on record. From the wires
