Throughout 2017, extreme weather events reached epic proportions: In January, the Arctic and Australia suffered serious heat waves that melted ice caps and cut power to 40,000 homes. By February, droughts dried out Somalia and lasted the full year. And from August through December, the United States faced hurricane after hurricane after hurricane, as well as forest fires and mudslides out West.

This year of record-breaking disasters had experts wondering whether the rising global temperature played a role. As a part of their annual look at global temperature trends, NASA revealed that 2017 was the second hottest year on record, while the National Oceanic and Atmospheric Administration (NOAA) reported 2017 as the third hottest year.

“Warmth is pervasive across the planet,” Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, told reporters via a press conference Thursday. “The planet is warming remarkably uniformly.”

Why NASA and NOAA rank 2017 differently: The difference comes from how each organization analyzes global temperatures. NASA climate scientists took surface temperature measurements from 6,300 weather stations, at an Antarctic research station and by ship and buoy for sea surface temperatures. They then compared these readings to data collected between 1951 to 1980, which the researchers used as an average.

NOAA scientists gathered similar temperature data, but their average time period encompassed all of the 1900s. The averages differ, but the results aren’t too far off. Based on their results, the last three years are the warmest in either record.

What they found: NASA and NOAA estimated that 2017’s temperature was between 1.51 to 1.6 degrees Fahrenheit above the averages calculated by each group.

“There is year-to-year variability, but the long-term trends are very clear — especially since the mid-20th century,” said Deke Arndt, chief of the global monitoring branch at NOAA’s National Centers for Environmental Information (NCEI).

Schmidt said 2017 was the warmest year without an El Nino event, which was the case for 2014, 2015 and 2016. El Nino warms the Pacific Ocean and changes weather patterns, sometimes causing short-term variations in the average global temperature. This phenomenon ruled a good part of 2015 through early 2016 and is likely the reason why these two years were warmer than 2017.



NASA and NOAA released 2017’s global temperature data. Here are thermal images of Earth from 1860 to 2017, showing a rapid warming of the planet. Video by NASA

Why it matters: Arndt said the global climate system is complex, and the effects of El Nino mess with this system to a certain degree. But none of this explains the overall temperature rise scientists have witnessed since the 19th century.

“The additional energy that’s trapped by greenhouse gases kind of manifests and expresses itself in different ways throughout the climate system and especially from year to year,” Arndt said.

What’s to come: These scientists worry that the extreme weather events seen in 2017 will only get worse as the planet heats up.

Recently, the NCEI’s Billion-Dollar Weather and Climate report showed that 2017 had 16 natural disasters in the U.S. alone, which spawned a new record of more than $306 billion in damages. Each event exceeded $1 billion, and together resulted in 362 deaths.

The total cost of disasters in 2017 around the world amounts to $330 billion, reports Munich Re of Germany, a reinsurance organization. These costs were second only to 2011, when an earthquake and tsunami hit Japan and raised global repair costs up to $354 billion (in today’s dollars).

As of right now, NASA and NOAA can’t concretely predict what 2018 will have in store in terms of extreme weather. But Schmidt said it’s clear that the years to come will get hotter and extreme weather will get harder to manage.