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.
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.