NBC - It'll be a few more days before it's official, but 2015 will go down in the record books as the warmest year since those books were first kept 135 years ago.
In parts of the U.S., this year will be remembered for unusually warm weather when the season typically brings snow and ice. On much of the East Coast, December has felt like spring, complete with early blooming flowers and sprouting daffodils.
But the warming trend also has brought more extreme weather in other parts of the country, with severe storms causing tornadoes across the Midwest and snowstorms in Texas and New Mexico.
Read more at CNBC.com: Scenes from the severe holiday storms
Last month brought the highest monthly temperature, according to the National Oceanic and Atmospheric Administration, with the average global surface temperature running 1.7 degrees Fahrenheit (1.0 degrees Celsius) warmer than the 135-year average.
The difference was even greater in the northern hemisphere, where much of the developed world lives. Despite those who reject mainstream climate science, the majority of the world's climate scientists attribute the warming trend to increased man-made carbon dioxide.
"Global climate is changing and this is apparent across the United States in a wide range of observations," according to the third U.S. National Climate Assessment. "The global warming of the past 50 years is primarily due to human activities, predominantly the burning of fossil fuels."
The trend over the last 135 years is clear, with average global temperatures rising every decade. More recently, the impact has been felt in more severe weather events with costly — and deadly — results. Since 1980, the number of extreme weather events bringing economic losses of more than $1 billion each has been rising, according to a NOAA report.