Earth had one of its warmest years on record last year, continuing an alarmingly steady trend where each of the past four decades has ranked hotter than the one before it, government science agencies announced Thursday.
The global average surface temperature in 2021 was the sixth-highest in recorded history, coming in 1.51 degrees Fahrenheit warmer than the 20th century average, according to officials at NASA and the National Oceanic and Atmospheric Administration.
The newly announced figures are based on independent analyses done yearly by both agencies. The report's findings are an important indicator of the planet's long-term health and provide a gauge of how Earth's climate has changed from year to year since record-keeping began in 1880.
NASA said global average surface temperatures last year tied with 2018 as the sixth-warmest on record, but noted that the past eight years have collectively been the warmest years in recorded history.
"Science leaves no room for doubt: Climate change is the existential threat of our time," NASA Administrator Bill Nelson said in a statement.
Ocean heat content, which is a measure of the amount of heat stored in the upper levels of the ocean, hit a record high in 2021, according to the NOAA report. Russell Vose, chief of climate monitoring at NOAA’s National Centers for Environmental Information, said the warmth of the world’s oceans last year was “the highest since records began six decades ago.”
“The point is, the oceans are storing a heck of a lot of heat,” he added.
Though oceans naturally absorb and store heat, the pace of ocean warming is a concern because increasing temperatures in these bodies of water can contribute to ocean acidification, sea-level rise and extreme weather.
NOAA said 2021 marked the 45th consecutive year since 1977 in which global temperatures ranked higher than the 20th century average, providing yet another indication of the effect of climate change on the planet.
"There's a lot of collected information that paints this coherent picture of a warming world," Vose said Thursday in a news briefing. "It's pretty clear that it's getting warmer."
Polar sea ice also continued to decline in 2021, with the ninth-smallest average yearly sea ice coverage recorded in the Arctic since 1979, according to NOAA.
While 2021 was one of the warmest on record, it was actually slightly cooler than in recent years. Average global temperatures in 2019 and 2020 ranked among the top three warmest years in recorded history. The hottest year in NOAA's 141-year climate record remains 2016. That year's record warmth was supercharged by a strong El Niño event, a naturally occurring climate pattern that has far-ranging effects on global temperatures, rainfall, hurricanes and severe storms.
Both the NOAA and the NASA reports match recent findings from other agencies, including the European Union's Copernicus Climate Change Service.
While some small statistical differences exist between the analyses, the overarching conclusion that the Earth is warming remains consistent, said Gavin Schmidt, director of the NASA Goddard Institute for Space Studies in New York City.
"The differences are smaller than they were, and because the signals is larger, they're even less important," he said. "The big story is the long-term trend and not the individual ranking."