Earth’s average surface temperature in 2017 placed as the second or third highest on record, according to new analyses by NASA and the National Oceanic and Atmospheric Administration (NOAA).
NASA’s analysis, released yesterday during a press conference, showed that 2017 is the second-hottest year on record and that the average global temperature rose 0.9°C (1.6°F) above the 1951–1980 average. The size of the temperature increase was calculated from thousands of measurements from more than 6,000 weather stations, ship- and buoy-based observations of sea surface temperatures, and measurements across Antarctic research stations.
An analysis from NOAA, released during the same press conference, produced similar results: According to NOAA’s models, 2017 ranked as the third-warmest year on record. Specifically, NOAA scientists found that temperatures rose 0.84°C (1.5°F) above the 20th century average (1901–2000).
“Despite colder than average temperatures in any one part of the world, temperatures over the planet as a whole continue the rapid warming trend we’ve seen over the last 40 years,” said Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies in New York City, at the press conference.
The World Meteorological Organization (WMO) also released a 2017 climate report yesterday, which also placed last year among the top three warmest years on record. According to WMO’s figure for 2017, the world’s average surface temperature has risen 1.1°C since preindustrial times. 2016 remains the warmest year on their record, with temperatures reaching 1.2°C above the preindustrial era.
Atmosphere to Ocean
At the press conference, Deke Arndt, a chief of the monitoring branch at NOAA’s National Centers for Environmental Information, described warming trends in different layers of the Earth system. He explained that temperatures in the middle troposphere, between 3,000 and 10,000 meters (where most commercial jets fly), ranked third or fourth warmest on record, depending on which group assembled the data. The upper ocean, which scientists know captures much of the excess energy trapped in the atmosphere, also reached its largest heat content on record in 2017, Arndt said.
The Warming North
In the Arctic, which warms at a faster rate than the rest of the globe, minimum sea ice extent continued to fall in 2017, the newly released analyses show. Similar results were highlighted in December, when NOAA released its annual Arctic Report Card. In that report, scientists concluded that the mean Arctic temperature rose 1.6°C in 2017 the (second-highest average after 2016), and in March 2017, observed the lowest maximum sea ice extent on record.
Observations of Arctic conditions in 2017 “confirm that the Arctic shows no signs of returning to the reliably frozen state that it was in just a decade ago,” said Jeremy Mathis, director of NOAA’s Arctic Research Program, when the report card was unveiled.
At play here is a key feedback mechanism, Arndt noted. Sea ice, with its bright white surface, reflects solar energy back into the atmosphere, helping to cool surface temperatures. But when sea ice melts, it exposes the darker surface of the underlying water, which absorbs solar energy. And the more that sea ice melts, the more energy is absorbed—a positive feedback mechanism of accelerating warming and ice loss, he said.
Some warmer than average temperatures can be attributed to a global climate phenomenon called the El Niño–Southern Oscillation, or ENSO. Two distinct temperature and weather trends make up ENSO. One is El Niño, in which the tropical Pacific Ocean warms; the other is La Niña, in which it cools. El Niño and La Niña can bring anomalously cool or warm, or dry or wet, conditions to different regions of the world. On small timescales, the El Niño effect can amplify warming signals.
Spanning all of 2015 and the first third of 2016, for example, warming from an extreme El Niño fed into overall observed warming. However, Schmidt stressed that even when scientists statistically remove the effects of El Niño and La Niña from the record, 2017 is still one of the warmest years on record. The WMO’s analysis, similarly, showed that 2017 was the warmest year without an El Niño What’s more, studies have shown that as more greenhouse gases are released, extreme El Niños could become more frequent.
—JoAnna Wendel (@JoAnnaScience), Staff Writer