Last nine years all among 10 hottest-ever

For 2021, the average temperature across global surfaces was 1.51 degrees Fahrenheit (0.84 degrees Celsius) above the 20th-century average, making the year the sixth-hottest in the overall record, which goes back to 1880.

"Of course, all this is driven by increasing concentrations of heat trapping gases like carbon dioxide," Russell Vose, chief of climate monitoring for NOAA National Centers for Environmental Information, told reporters.

"There's probably a 99 percent chance that 2022 will rank in the top 10, a 50-50 chance, maybe a little less, it'll rank in the top five, and a 10 percent chance it'll rank first" barring an unforeseen event like a major volcanic eruption or a large comet hitting Earth, he said.

NOAA also uses the 21-year span from 1880 to 1900 as a surrogate to assess pre-industrial conditions, and found the 2021 global land and ocean temperature was 1.87F (1.04C) above the average.

A separate analysis of global temperature released by NASA had 2021 tying with 2018 as the sixth-warmest on record.

Both data sets vary very slightly from the European Union's Copernicus Climate Change Service in their assessment, which had 2021 as the fifth warmest in records tracking back to the mid-19th century.

But the overall convergence of trends increases scientists' confidence in their conclusions.

Increases in abundance of atmospheric greenhouse gases since the industrial revolution  are mainly the result of human activity and are largely responsible for the observed increases.

Climate scientists say it is crucial to hold end-of-century warming to within a 1.5C (2.7F) rise to avert the worst impacts -- from mega-storms to mass die-offs in coral reefs and the decimation of coastal communities.

At the present rate of heating, the planet might hit 1.5C in the 2030s.

"But it's not the case that at 1.4 everything is hunky dory and at 1.6 all hell has broken loose," said NASA climate expert Gavin Schmidt.

The impacts have been increasingly felt in recent years -- including record-shattering wildfires across Australia and Siberia, a once-in-1,000-years heatwave in North America and extreme rainfall that caused massive flooding in Asia, Africa, the US and Europe.

Last year also saw nearly 700 people die in the contiguous United States due to extreme weather events, such as Hurricane Ida, and a maximum temperature in Sicily of nearly 120F, a European record if verified.