Federal climate scientists announced Wednesday that 2015 was the hottest year on record, simultaneously heating up another round in the global-warming debate as climate skeptics quickly challenged the findings.
Even as the East Coast braced for a mammoth snowstorm, the National Oceanic Atmospheric Administration and NASA found that last year’s globally averaged temperature hit a 136-year high, driven by an unusually strong El Nino weather pattern combined with carbon dioxide emissions.
Scientists at NOAA found that the average 2015 temperature of 58.62 degrees Fahrenheit passed the record-breaking 2014 average by a record margin of 0.29 degrees, or 1.62 degrees above the 20th century average.
The numbers were slightly different at NASA, which uses another measurement; NASA analysts estimated that 2015 was 0.23 degrees warmer than 2014 and 1.6 degrees higher than last century’s average.
“This trend will continue; it will continue because we understand why it’s happening,” Gavin Schmidt, director of the NASA Goddard Institute of Space Studies, told the Associated Press. “It’s happening because the dominant force is carbon dioxide.”
Climate-change activists said Wednesday the new numbers only underscore the importance of honoring the national pledges in the global climate accord reached by President Obama and other world leaders in Paris last month.
But while climate-change groups responded by doubling down on calls to reduce CO2 emissions, climate skeptics challenged the agency methodology and noted that the results were actually cooler than climate-model projections.
“2015 Was Not Even Close to the Hottest Year on Record,” said James Taylor, Heartland Institute senior fellow for environment policy, in a Wednesday op-ed for Forbes.
He argued that satellite temperatures show 1998 was the warmest year on record since 1979, and noted that the 136 years of record-keeping fail to take into account other indicators showing “temperatures have been warmer than today for most of the past several thousand years.”
Skeptics also argued that climate models show that last year’s temperatures should have been even higher, given the El Nino factor.
“Yes, 2015 was warm. It ‘smashed’ the previous record because of a strong El Nino,” said Chip Knappenberger, assistant director of the libertarian Cato Institute*, in an email.
“Yet, despite breaking the old global temperatures ‘by far,’ the observations only approached the climate model projections for the temperature of an ‘average’ year for 2015,” he said. “In other words, climate models continue to run too hot.”
He referred to the discrepancy between climate models and actual temperatures as “lukewarming.”
Roger Pielke Jr., environmental studies professor at the University of Colorado Boulder, said that there were fewer extreme weather events despite the warm temperatures. Climate-change groups have argued that global warming contribute to hurricanes and other weather-related disasters.
“It’d be great if just one journalist (any!) would note that 2015 — warmest year ever — also had the lowest catastrophe losses in a generation,” Mr. Pielke said on Twitter.
Meanwhile, Vermont Sen. Bernard Sanders, who’s running for the Democratic presidential nomination, declared that “the debate is over.”
“Fourteen of the last 16 years have been the hottest ever recorded,” Mr. Sanders said in a statement. “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.”
* Correction: In the original story, Mr. Knappenberger’s affiliation was incorrectly given.