1. 2016 was hot everywhere.
2016 was the hottest year ever measured, following 2014 and 2015, which also set records as the hottest year ever. Modern temperature records begin in 1879, meaning all three of those years were warmer than any year in the previous 135 years.
According to a new study in Geophysical Research Letters, also published on Thursday, the chances of this kind of three-year warmest-ever streak happening without some kind of human-caused global warming less than 0.03 percent. When global warming is taken into account, the chances of it happening swell to between 30 and 50 percent.
2016 was hot thanks to a combination of two factors: long-term global warming, caused by human emissions; and an especially monster El Niño, which warms temperatures across much of the world. These combined to push temperatures to a new level: 2016 was the first year that the global average temperature was 1 degree Celsius warmer than the years in the late 19th century. The Paris Agreement on climate change and a long history of climate treaties seek to keep global temperatures from rising by 2 degrees Celsius.
The atmosphere had the highest concentration of carbon dioxide ever recorded: 402.9 parts per million. This is the highest value recorded since logs began 58 years ago. Scientists—who have also pieced together the long-term composition of the atmosphere from bubbles stuck in ice cores—argue it may be the highest concentration of CO2 in the air in 800,000 years.
2. 2016 was hot and costly in North America.
The United States also had its second-hottest year on record in 2016. Every state had an above-average spring temperature, summer temperature, and autumn temperature.
There were 15 major weather or climate-related disasters in the United States, including—in a new record—four inland floods that weren’t caused by a tropical storm. These events directly cost Americans $46 billion, the second highest amount (in inflation-adjusted dollars) since records began in 1980.
Canada also had its most expensive natural disaster ever—the wildfire near Fort McMurray, Alberta—which burned more than 2,200 square miles of land and cost $3 billion in U.S. dollars.
3. The seas kept rising in 2016.
The global average sea level also reached its highest level ever, and “sunny-day flooding” got particularly bad in the American Southeast.
As it exists today, sea-level rise is caused by melted ice from mountain glaciers and from “thermal expansion”—that is, the water expands as it gets hotter. 2016 was the 37th consecutive year that mountain glaciers receded, and the sea-surface temperature was the warmest ever recorded. By the end of the century, most sea-level rise will probably come from the melted polar ice caps—like the Greenland ice sheet, which reached a new record low in 2016.