hottest year
Outlet glacier Hoffellsjökull as seen in Vatnajökulsþjóðgarður National Park in southeast Iceland. Due to climate change, Hoffellsjökull glacier has retreated a considerable distance and a deep glacial lake is rapidly developing in the depression left behind. Courtesy:avadgartner

As record months piled up, it became clear a while ago that 2015 was going to be the hottest year on record. Now the final numbers are coming in—and like the official times from a race between me and Usain Bolt, they’re hardly a surprise.

Just as La Niñas hold down the global average temperature because of the cool ocean water rising to the surface in the eastern equatorial Pacific, El Niño conversely pushed the average temperature up. And 2015 saw a doozy of an El Niño that rivaled the monsters of 1997 and 1982. As the long-term trend of global warming continues, El Niño years are likely to be your record-setters.

By coloring individual months as El Niño (red) or La Niña (blue) conditions, you can see that El Niño years tend to rise above the warming trend.
By coloring individual months as El Niño (red) or La Niña (blue) conditions, you can see that El Niño years tend to rise above the warming trend.  NOAA/NASA

The US saw the second-warmest year on record for the Lower 48 (2012 is still tops), and the third wettest year as Oklahoma and Texas set records. California, however, had its 13th-driest year, with the promise of El Niño rains yet to deliver. The UK had its sixth-wettest year on record, but not quite as warm—15 years have been warmer.

NOAA, NASA, and the UK Met Office agree: 2015 was the warmest year on record. And by the way, data lacking any of the adjustments sometimes maligned by climate contrarians tell the same story. NOAA/NASA
NOAA, NASA, and the UK Met Office agree: 2015 was the warmest year on record. And by the way, data lacking any of the adjustments sometimes maligned by climate contrarians tell the same story. NOAA/NASA

But globally, 2015 beat out 2014 to set the record for temperature by a country mile. It set the record in every dataset, including those run by NOAA, NASA, and the UK Met Office. The Berkeley Earth team has been reluctant to award a top ranking in the past, wary of overlapping error bars, but its release stated that “2015 set the record with 99.996 percent confidence.” Preliminary data has it on top in the Japanese Meteorological Agency dataset, as well.

2015 was the warmest year on record by far. NOAA/NASA
2015 was the warmest year on record by far. NOAA/NASA

NASA’s dataset puts 2015 at 0.87°C (1.57°F) above the 1951-1980 average it uses as zero. NOAA’s estimate is basically identical, at 0.90°C above the 20th century average it uses as its baseline. NOAA, NASA, the UK Met Office, and Berkeley Earth all noted that 2015 was the first year to clear °C above the temperature of the late 1800s.

If 2015 put the fear in you and you resolved not to let 2016 set a new record, I’ve got bad news for you. The current El Niño is forecast to peak this winter and weaken through the spring, but that equatorial warmth takes a few months to move poleward. Given that outlook, the UK Met Office’s annual forecast anticipates an even warmer 2016.

Much has been made in recent public discourse about a supposed “pause” in global warming since 1998—the last potent El Niño peak. It was always a cherry-pick easily countered by longer-term analysis, but 2015 should officially put paid to that claim. In a few years, we may be hearing politicians talk about “no warming since 2016,” instead.

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