Earth recorded its hottest year ever in 2024, with such a big jump that the planet temporarily passed a major climate threshold, weather monitoring agencies announced Friday.
It's the first time in recorded history that the planet was above a hoped-for limit to warming for an entire year, according to measurements from four of the six teams. Scientists say if Earth stays above the threshold over the long term, it will mean increased deaths, destruction, species loss and sea level rise from the extreme weather that accompanies warming.
And that would come on top of a year of deadly climate catastrophes — 27 billion-dollar disasters in the U.S. alone in 2024 — and as 2025 begins with devastating wildfires in Southern California.
Last year's global average temperature easily passed 2023's record heat and kept going. It surpassed the long-term warming limit of 1.5 degrees Celsius since the late 1800s that was called for by the 2015 Paris climate pact, according to the European Commission's Copernicus Climate Service, the United Kingdom's Meteorology Office, Japan's weather agency and the private Berkeley Earth team.
Only two U.S. government agencies had Earth below that 1.5 mark. The National Oceanic and Atmospheric Administration and NASA had last year at 1.46 degrees Celsius and 1.47 degrees Celsius, respectively.
The Copernicus team calculated 1.6 degrees Celsius of warming; Japan, 1.57; and the British, 1.53. Berkeley Earth — originally funded by a climate change skeptic — came in the hottest at 1.62 degrees.
Greenhouse gases
"The primary reason for these record temperatures is the accumulation of greenhouse gases in the atmosphere" from the burning of coal, oil and gas, said Samantha Burgess, strategic climate lead at Copernicus. "As greenhouse gases continue to accumulate in the atmosphere, temperatures continue to increase, including in the ocean, sea levels continue to rise, and glaciers and ice sheets continue to melt."
Last year was the hottest year for the United States, NOAA said. It was not only the hottest in recordkeeping that goes back to 1850, but likely the hottest for the planet in 125,000 years, Burgess said.
"There's nothing to indicate that it won't continue," NOAA monitoring chief Russ Vose said Friday. "When there's more heat in the system, that has a cascading effect on other parts of the system. Sea level goes up. Warmer air can hold more moisture, which tends to equate to more extreme storms. There's a lot of impacts that go along with a warmer world."
By far the biggest contributor to record warming is the burning of fossil fuels, several scientists said. A temporary natural El Nino warming of the central Pacific added a small amount, and an undersea volcanic eruption in 2022 ended up cooling the atmosphere because it put more reflecting particles in the atmosphere as well as water vapor, Burgess said.
Alarm bells ringing
"Climate-change-related alarm bells have been ringing almost constantly, which may be causing the public to become numb to the urgency, like police sirens in New York City," Woodwell Climate Research Center scientist Jennifer Francis said. "In the case of the climate, though, the alarms are getting louder, and the emergencies are now way beyond just temperature."
Comparing it to a car's dashboard warning light, University of Georgia meteorology professor Marshall Shepherd said, "Hurricane Helene, floods in Spain and the weather whiplash fueling wildfires in California are symptoms of this unfortunate climate gear shift."
There were 27 weather disasters in the United States last year that caused at least $1 billion in damage, just one fewer than the record set in 2023, according to NOAA. The U.S. cost of those disasters was $182.7 billion. Hurricane Helene was the costliest and deadliest of the year with at least 219 deaths and $79.6 billion in damage.
"In the 1980s, Americans experienced one [$1] billion-plus weather and climate disaster on average every four months," Texas Tech climate scientist Katharine Hayhoe said in an email about NOAA's inflation-adjusted figures. "Now, there's one every three weeks —and we already have the first of 2025 even though we're only nine days into the year."
Major threshold breached
Scientists were quick to point out that the 1.5-degree goal is for long-term warming, now defined as a 20-year average. Warming since preindustrial times over the long term is now at 1.3 degrees Celsius.
"The 1.5-degree C threshold isn't just a number — it's a red flag. Surpassing it even for a single year shows how perilously close we are to breaching the limits set by the Paris Agreement," Northern Illinois University climate scientist Victor Gensini said in an email.
A massive United Nations study in 2018 found that keeping Earth's temperature rise below 1.5 degrees Celsius could save coral reefs from going extinct, keep massive ice sheet loss in Antarctica at bay, and prevent many people's death and suffering.
Francis called the threshold "dead in the water."
Burgess said it was extremely likely that Earth would overshoot the 1.5-degree threshold, but called the Paris Agreement "extraordinarily important international policy" that nations around the world should remain committed to.
More warming likely
European and British calculations figure that with a cooling La Nina instead of last year's warming El Nino, 2025 is likely to be not quite as hot as 2024. They predict it will turn out to be the third warmest. However, the first six days of January — despite frigid temperatures in the U.S. East — averaged slightly warmer and are the hottest start to a year yet, according to Copernicus data.
Scientists remain split on whether global warming is accelerating.
There's not enough data to see an acceleration in atmospheric warming, but the heat content of the oceans seems to be not just rising but going up at a faster rate, said Carlo Buontempo, Copernicus' director.
"We are facing a very new climate and new challenges — climate challenges that our society is not prepared for," Buontempo said.
This is all like watching the end of "a dystopian sci-fi film," said University of Pennsylvania climate scientist Michael Mann. "We are now reaping what we've sown."
