2015 was really hot

Global warming and a “super” strong El Niño drove temperatures to new heights

el nino

A strong El Niño and global warming made 2015 into the hottest year on record, scientists report. (Areas colored blue were cooler than the 20th-century average; red areas were warmer.)


Things are definitely heating up. Spurred by global warming, 2015 smashed records. It is by far Earth’s hottest year since record-keeping began in 1880. Contributing to that record heat: what scientists are calling a “super El Niño.”

El Niño is a naturally occurring worldwide weather disruption caused by unusually warm seawater piling up in the eastern Pacific. One tends to develop every three to five years.

Temperatures across Earth’s surface were, on average, 0.90 degrees Celsius (1.6 degrees Fahrenheit) warmer than the 20th century average of 13.9 °C (57.0 °F). The National Oceanic and Atmospheric Administration and NASA reported the finding in a joint January 20 announcement.

The 2015 temps were well above the previous record set one year earlier. In 2014, temperatures were 0.74 degrees (1.3 degrees Fahrenheit) above average. The difference between the two years is the largest margin by which an annual temperature record has ever been broken.

What’s more, there’s little room for doubt that the new record is real. NOAA reported more than 99 percent confidence that 2015 was in fact the hottest year on record (considering gaps in weather data). When 2014 had nabbed the old title, scientists had just 48 percent confidence.

“2015 was the warmest year because it was warm throughout the year,” says Gavin Schmidt. He directs NASA’s Goddard Institute for Space Studies in New York City. Ten months of 2015 set all-time records. And December proved the biggest record-breaker. That’s when temperatures reached 1.11 degrees C (2 degrees F) higher than the 20th century average for that month. “It was picking up that El Niño assist in the last three months,” Schmidt said. Yet even without the boost, he adds, “this still would have been the warmest year on record.”

An armada of weather stations, buoys and ships now measures temperatures across the globe. The data they provide have shown that for 39 straight years, Earth’s year average temperature has been above the 20th century average. Heat-trapping greenhouse gases in the atmosphere largely contributed to that long-term rise in surface temperatures. Last year, however, got an additional boost from the ongoing El Niño.

The current El Niño is among the strongest ever recorded. It contributed as much as 0.15 degree C (0.27 degree F) to the new record, estimates Kevin Trenberth. He is a climate scientist at the National Center for Atmospheric Research in Boulder, Colo.

Similar El Niños contributed to high temperatures in earlier record-setting years, such as 1998. That year is now tied for the sixth-hottest. During non-El Niño years, heat builds up under the surface of the Pacific Ocean.

Strong El Niño events often precede global cooling, however. That often happens when conditions trigger the arrival of El Niño’s meteorological sibling: La Niña. The rise and fall of temperatures around the 1997-to-1998 El Niño contributed to a perceived slowdown in global warming.

El Niños usually contribute the most heat during their second years. However, that might not be true this time. The current El Niño kicked off last March. It may have done most of its warming early, Trenberth says. That’s partly because the event almost began in 2014. It then wavered. It finally peaked in strength in November 2015. Most events peak in December. If the current El Niño is mostly tapped out, 2015’s heat record might stand for a while, Trenberth predicts. NOAA and NASA, however, predict a bit more than a 50 percent chance that 2016 will be hotter still.

Power Words

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atmosphere   The envelope of gases surrounding Earth or another planet.

average    (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.

buoy  A floating device anchored to the bottom of a body of water. A buoy may mark channels, warn of dangers or carry instruments to measure the environment.

El Niño Extended periods when the surface water around the equator in the eastern and central Pacific warms.  Scientists declare the arrival of an El Niño when that water warms by at least 0.4 degree Celsius (0.72 degree Fahrenheit) above average for five or more months in a row. El Niños can bring heavy rainfall and flooding to the West Coast of South America. Meanwhile, Australia and Southeast Asia may face a drought and high risk of wildfires. In North America, scientists have linked the arrival of El Niños to unusual weather events — including ice storms, droughts and mudslides.

global warming The gradual increase in the overall temperature of Earth’s atmosphere due to the greenhouse effect. This effect is caused by increased levels of carbon dioxide, chlorofluorocarbons and other gases in the air, many of them released by human activity.

La Niña Extended periods when the surface water around the equator in the eastern Pacific cools for long stretches of time. Scientists will announce the arrival of a La Niña (lah NEEN yah) when the average temperature there drops by at least 0.4° C (0.72° degree F). Impacts on global weather during a La Niña tend to be the reverse of those triggered by an El Niño: Now, Central and South America may face severe droughts while Australia floods.

National Aeronautics and Space Administration, or NASA  Created in 1958, this U.S. agency has become a leader in space research and in stimulating public interest in space exploration. It was through NASA that the United States sent people into orbit and ultimately to the moon. It has also sent research craft to study planets and other celestial objects in our solar system.

National Oceanic and Atmospheric Administration, or NOAA     A science agency of the U.S. Department of Commerce. Initially established in 1807 under another name (The Survey of the Coast), this agency focuses on understanding and preserving ocean resources, including fisheries, protecting marine mammals (from seals to whales), studying the seafloor and probing the upper atmosphere.

weather  Conditions in the atmosphere at a localized place and a particular time. It is usually described in terms of particular features, such as air pressure, humidity, moisture, any precipitation (rain, snow or ice), temperature and wind speed. Weather constitutes the actual conditions that occur at any time and place. It’s different from climate, which is a description of the conditions that tend to occur in some general region during a particular month or season.

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