The finding by the National Aeronautics and Space Administration (NASA) follows three years in a row in which global temperature hit a new record.
The National Oceanic and Atmospheric Administration and the United Kingdom's meteorological office on Thursday announced that 2017 was the third hottest year on record.
But one thing that has been common in both the reports is that 2017 has made the last four years the hottest period in their recorded history of 138 years.
"Despite colder than average temperatures in any one part of the world, temperatures over the planet as a whole continue the rapid warming trend we've seen over the last 40 years", NASA's Goddard Institute for Space Studies (GISS) director Gavin Schmidt said in a statement.
2017 was unequivocally the warmest year on record that was not influenced by the periodic El Nino phenomenon, which releases added warmth from the Pacific Ocean and was present in the record warm years of 2015 and 2016.
The difference between the two agencies in ranking 2017 is somewhat driven by the different methodology the two agencies use to measure temperatures in the Arctic, the fastest-warming part of the planet, said Zeke Hausfather, a climate scientist who also closely tracks annual temperatures with Berkeley Earth.
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The globe hasn't had a cooler-than-average year since 1976 - a stretch of 41 consecutive warm years - NOAA said. In order to avoid the worst consequences of climate change, scientists say global temperatures must not increase more than 2 degrees Celsius.
Either way, scientists say it showed a clear signal of man-made global warming because it was the hottest year they've seen without an El Nino boosting temperatures naturally.
"We are getting dangerously close to the limit of the 2°C temperature rise set out in the Paris Agreement and the desired goal of 1.5° will be even more hard to maintain under present levels of greenhouse gas emissions", he underscored.
The five warmest years on record have all occurred since 2010.
The global average temperature in 2017 was 58.51 degrees (14.7 degrees Celsius), which is 1.51 degrees (0.84 Celsius) above the 20th century average and just behind 2016 and 2015, NOAA said.
NOAA and NASA analyses use temperature measurements from weather stations on land and at sea.
But US President Donald Trump's decision to withdraw from the Paris accord has rattled the global community and complicated efforts at forging joint action - even though many US state governments insist they remain committed to cut emissions.