Last year was the earth's hottest in 136 years of record-keeping, NASA and the National Oceanic and Atmospheric Administration announced Wednesday.
In two separate analyses, the agencies agreed that 2015 was a record-breaker. NASA found that 2015 was 1.8 degrees Fahrenheit warmer than the late 19th century, while NOAA found 2015 was 1.62 degrees Fahrenheit warmer than the 20th century average.
"Globally averaged temperatures in 2015 shattered the previous mark set in 2014 by 0.23 degrees Fahrenheit (0.13 Celsius)," NASA reported. "Only once before, in 1998, has the new record been greater than the old record by this much."
The previous hottest year, 2014, had an average global temperature of 58.24 degrees Fahrenheit. That was already 1.24 degrees above the 20th century average.
"Climate change is the challenge of our generation, and NASA's vital work on this important issue affects every person on Earth," NASA Administrator Charles Bolden said in a statement. "Today's announcement not only underscores how critical NASA's Earth observation program is, it is a key data point that should make policy makers stand up and take notice -- now is the time to act on climate."
The heat in 2015 can be attributed to both global warming caused by humans and the winter's powerful El Niño event, the World Meteorological Organization said in November. It noted record-high levels of greenhouse gases in the Northern hemisphere last year.
"This new high temperature record confirms our previous interpretation that the pause was temporary and that global warming has not slowed," Richard Muller, scientific director of Berkeley Earth, said in a statement. (The "pause" was the dozen-plus years before 2014 when global temperatures basically held steady.)
"The decades-long rise due to greenhouse gas emission is now clearly continuing," added Robert Rohde, the lead scientist on the Berkeley Earth study.
Democratic presidential candidate Sen. Bernie Sanders (I-Vt.) used the news to urge movement away from fossil fuels.
"The debate is over," Sanders said. "Fourteen of the last 16 years have been the hottest ever recorded. Climate change is real and is caused by human activity. This planet and its people are in trouble. Unless we get our act together, we will see in years to come more droughts, more floods and more extreme weather disturbances."
While 2015 was a record-breaking year for the planet, it was only the second-hottest year on record for the U.S., which NOAA reported earlier this month saw an average 54.4 degrees F last year. That was 2.4 degrees above the country's 20th century average, but 0.9 degrees under the record 55.3 degree average for 2012.
Experts have been estimating for months that last year would prove to be the world's hottest in over a century. After a NASA report found that this past October was the first month to surpass the 20th century's average temperature by more than 1 degree Celsius, Gavin Schmidt, director of the agency's Goddard Institute for Space Studies, tweeted there was now a 99.9 percent chance that 2015 would be crowned the hottest year on record.
The severe heat was palpable around the planet. In May, 120-degree days in India melted New Delhi's asphalt and killed around 2,500 people, making it the fifth-deadliest heat wave on record. The next month, temperatures as high as 113 degrees killed at least 1,200 people in Pakistan and sent more than 65,000 heatstroke patients to hospitals.
The heat also broke records across Europe in June and July, when triple-digit temperatures settled on Spain, Portugal, France, the United Kingdom, Germany and Poland.
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