The real debate over global warming comes down to whether 2017 was the second- or third-hottest year ever recorded.
On Thursday, NASA released an analysis that found average global temperatures last year were 1.62 degrees Fahrenheit warmer than the mean between 1951 and 1980. In a companion report, the National Oceanic and Atmospheric Administration (NOAA) found, using a different methodology, that surface temperatures were 1.51 degrees Fahrenheit above the 20th-century average, ranking the year third warmest behind 2016 and 2015.
Yet scientists at both federal agencies reached the same grave conclusion: The Earth is heating up. The five warmest years on record have all occurred since 2010.
Unlike in 2016 — the hottest year on record — the 2017 temperature has nothing to do with El Niño, the Pacific Ocean patterns that can cause record-setting warm weather.
“It’s perhaps a little bit easier to clarify these things when there isn’t an El Niño involved, but the planet is warming regardless of what’s going on in the tropical Pacific,” Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, said in a call with reporters.
The two sets of findings confirmed the rapid warming of the Arctic, and retreat of sea ice near the poles. Warming trends were strongest in the Arctic, as visualized in a map from 2013 to 2017, where average temperatures climbed 4 degrees Fahrenheit over NASA’s baseline from 1951 to 1980. Arctic sea ice covered about 4.01 million square miles, marking the second-smallest average since 1979, NOAA found. That’s about 90,000 more miles of ice than the record low set in 2016.
In Antarctica, where the Delaware-sized ice sheet Larsen C broke off last summer, sea ice fell to a record low of 4.11 square miles, roughly 154,000 square miles smaller than the previous record set in 1986, according to NOAA.
Climate change skeptics have long pointed to El Niño and the Pacific cooling event, La Niña, to seed doubt over the reality of long-term warming trends. In September, the Trump administration ― which has repeatedly dismissed climate change as a problem amid a massive push to cut back pollution regulations ― launched a climate satellite and, in the news release, listed “natural climate patterns,” such as El Niño and La Niña, as the main concern for the project.
The Trump administration has advised some agencies to avoid the term climate change, and removed references to it from federal websites. But no political appointees weighed in on the reports released Thursday, the researchers said.
“The analysis we conducted this year was done in the exact same way, with the exact same amount of rigor, we have in the years I’ve been in this position, and this is my ninth year,” Deke Arndt, chief of the monitoring section at NOAA’s National Centers for Environmental Information, told reporters.
But the evidence is clear. Average temperatures have climbed significantly over the past century, as greenhouse gas emissions from burning fossil fuels, deforestation and industrialized farming enshrouded the world in record amounts.
Last year was the United States’ costliest year ever for billion-dollar natural disasters, as 16 major climate- and weather-related catastrophes caused a record $306.2 billion in damages and killed at least 362 people.
Schmidt declined to comment on White House policies on climate change. But he said there’s little doubt about the source of the warming over the past six decades.
“Basically all of the warming in the last 60 years is attributable to human activities, and carbon dioxide emissions are the No. 1 component of that,” he said.