Record high temperatures were set in 2016 on nearly every continent. No land areas were cooler than average for the year.
The record warmth was "80-90% because of the long-term trend and 10% because of El Niño," NASA climate scientist Gavin Schmidt told Carbon Brief.
The long-term warming trend over the past few decades can be linked to the burning of fossil fuels that are releasing gases such as carbon dioxide, he said.
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The burning of the oil, gas and coal for energy releases "greenhouse" gases such as carbon dioxide and methane. These gases have caused the Earth's temperature to rise over the past century to levels that cannot be explained by natural variability.
"No world leader can afford to ignore these results, which show that people all over the globe are being exposed to increasing impacts of climate change," said Bob Ward of the London School of Economics and Political Science. "Any politician who denies this evidence from world-class climate scientists in the United States will be willfully turning a blind eye to rising risks that threaten the lives and livelihoods of their citizens," he said.
Since the start of the 21st century, the annual global temperature record has been broken five times (2005, 2010, 2014, 2015, and 2016), NOAA said.
"The science is clear and headed in one direction," said Lou Leonard with the World Wildlife Fund. "Human-caused changes in climate are putting the lives of both people and wildlife at risk. From disappearing Arctic ice in Alaska to greater storm surges along our nation's coastlines to heatwaves in America's heartland, nature is sending a distress call."
2016 was the USA's second-warmest year on record, NOAA said last week.