The decade ending in 2020 was the hottest in recorded history, with temperatures higher than any other period in at least two millennia and possibly much longer. The main culprit behind the extreme warming, atmospheric carbon dioxide, has reached a level not seen in at least 3 million years. The last seven years are now the warmest since measurement began in the 19th century. In five major temperature datasets updated on Thursday, 2020 finished in a statistical tie with 2016 as the hottest year on record, coming in about 1.2° Celsius hotter than the 19th century. Four of the five research centers showed 2020 slightly cooler than 2016, but within the uncertainty window. The year 2019 is a very close third. “That’s the global average,” said Ahira Sánchez-Lugo, a physical scientist at the U.S. National Oceanic and Atmospheric Administration’s National Centers for Environmental Information, one of the scientific groups reporting new annual temperature data. “There are some regions that are warming a lot faster.” One degree may sound small, she added, but “a small change in the global temperature average can lead to big changes when it comes to extreme weather. We're already seeing that.” Heatwaves, wildfires, more intense storms, and changes in rain and snow all point to a world already facing heightened danger. With each passing year, scientists grow more confident in attributing many of these weather anomalies to the heat trapped in the atmosphere and oceans. “When the ingredients for a hurricane come together, we’re seeing that these hurricanes are intensifying a lot faster,” Sánchez-Lugo said. “They’re moving slower, and the precipitation rates associated with these hurricanes are increasing as well.” The record-high temperatures of 2016 had temporary help from El Niño, the naturally occurring Pacific Ocean phenomenon that raises thermometers. That wasn’t the case for 2020, which not only lacked the irregular warming trend but also featured an appearance from El Niño’s cooling counterpart, La Niña, beginning in August. January through November each ranked among the top four warmest occurrences of that month; December came in as the eighth warmest, helping lower the annual average.