For three years in a row, Earth breaks heat record

For the third year running, Earth’s thermostat broke a new record: 2016 was the warmest year since record-keeping began in 1880.

Spurred by climate change and heat from a monster El Niño, the global average surface temperature last year was 0.94 degrees Celsius (1.69 degrees Fahrenheit) higher than the 20th century average of 13.9° C (57° F). That slightly edges out the previous titleholder, 2015, by 0.04 degrees C (SN: 2/20/16, p. 13). Eight months during 2016 set new all-time highs, including July, which was Earth’s warmest month on record, scientists from the National Oceanic and Atmospheric Administration and NASA reported January 18.

This is only the second time that the annual temperature record has been broken three years in a row, Deke Arndt, chief of the monitoring branch of NOAA’s National Centers for Environmental Information in Asheville, N.C., said in a news conference. The previous trio — 1939 through 1941 — don’t rank within the top 30 warmest years on record, he noted.

Last year’s heat helped set other records as well. As of January 17, for instance, global sea ice extent is at its paltriest point in potentially thousands of years, according to data from the National Snow and Ice Data Center and sea ice reconstructions.

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Melt down

High temperatures caused global sea ice coverage in 2016 to reach its smallest extent on record, new observations show. Colored lines trace yearly sea ice extent since 1978. The gray-shaded region shows two standard deviations from the average daily sea ice extent.

WIPNEUS

Source: NSIDC

Greenhouse gases released by human activities such as fossil fuel burning have cranked Earth’s thermostat over the last few decades by trapping heat that would otherwise escape into space. All 16 years of the 21st century rank among the 17 warmest on record.

Humankind’s fossil fuel habit isn’t solely to blame for 2016’s sweltering heat, says Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research in Boulder, Colo. The 2015–2016 El Niño, among the three strongest on record, raised global temperatures by releasing pent-up heat from the ocean into the atmosphere (SN Online: 6/9/16).

Within a decade or so, as global warming continues, 2016’s heat will be par for the course even during non-El Niño years, Trenberth predicts. “The temperature record is like going up a staircase, and now with 2015 and 2016, we’ve seemed to go up another step,” he says. “We’ll maybe oscillate around this higher level for a few years, but I don’t think we’ll ever go back to the values we’ve seen in previous years.”