The year was the second-hottest in recorded history, NASA said, while scientists from the National Oceanic and Atmospheric Administration reported 2017 was the third-warmest they have ever recorded.
The two government agencies use different methodologies to calculate global temperatures, but by either standard, the 2017 results make the past four years the hottest period in their 138-year archive.
The renewed evidence of climate change, driven by human emissions of greenhouse gases, comes as the Trump administration moves to open new areas for oil drilling and rolls back regulations that sought to reduce global warming, most prominently by moving to repeal the Obama administration's Clean Power Plan.