Warm temperatures on the East Coast in December and drought-fueled heat in the West pushed the nation's average temperature to its second-highest level in 120 years. That's how long average temperature records have been kept.
The National Oceanic and Atmospheric Administration says the average temperature in 2015, collected from the contiguous 48 states, hit 54.4 degrees.
"That's about 2.4 degrees warmer than the 20th century average," said Deke Arndt, a NOAA climate researcher.
The average temperature includes day and night temperatures across the entire year and is one degree below the overall record set in 2012.
Arndt said the high average is not enough to prove climate change is happening but it is further evidence the planet is getting warmer.
"There's no doubt that the U.S. has really warmed up in the last two or three decades. This is kind of an exclamation point on the end of that signal," Arndt said.
California's drought was one of 10 severe weather events in the nation that caused more than $1 billion in damages last year.
Arndt said extreme weather will increase as average temperatures climb.
