Last year was the hottest on record – and it wasn't close, new data shows. Global warming, driven primarily by burning fossil fuels, pushed temperatures so high in 2023 that scientists were astounded.

"We're frankly astonished," by how warm 2023 was, says Gavin Schmidt, the director of NASA's Goddard Institute for Space Studies.

The global average temperature in 2023 was significantly warmer – by nearly three tenths of a degree Fahrenheit – than the previous warmest year, according to measurements released Friday by the National Oceanic and Atmospheric Administration (NOAA) and NASA. European Union measurements released earlier this week came to a similar conclusion.

The global average includes temperatures measured throughout the year over both land and oceans, and changes are usually an order of magnitude smaller.

"Most records are set on the order of a few hundredths of a degree," says Russell Vose of NOAA, so a few tenths of a degree is a "big jump."

Other federal scientists echoed that sentiment. "The findings are astounding," says NOAA chief scientist Sarah Kapnick.

Reliable U.S. measurements of the Earth's temperature only go back about 175 years, but 2023 was also likely the hottest year going back much further. Scientists can use tree rings, soil, polar ice and other methods to estimate what the climate was like thousands of years ago, and have found that 2023 is likely the hottest year going back 125,000 years.

The effects of 2023's heat were catastrophic. Rising temperatures drove more extreme weather events including heat waves, floods, wildfires and droughts, which destroyed lives and livelihoods around the world last year. In the United States, millions of people suffered through dangerously hot weather as well as widespread flooding and deadly wildfires.

While the U.S. was spared major hurricane damage last year, climate-driven storms still caused tens of billions of dollars in damage and killed dozens of people in China, Mexico and both northern and southern Africa.

Such devastating climate impacts will only get worse in the coming years, scientists warn. The overall warming trend, which is more relevant than any one or two record-breaking years, is sobering. The last 10 years were the hottest on record, according to NOAA.

And the next decade will be hotter still, scientists warn.

That's because humans are releasing huge amounts of carbon dioxide and other greenhouse gasses into the atmosphere, primarily by burning fossil fuels like coal, oil and natural gas. Global emissions are still rising, despite some efforts to rein in planet-warming pollution. U.S. greenhouse gas emissions dropped by about 2% last year, a decline which remains far short of the nation's climate targets.

Scientists warn that 2024 has a good chance of being another record-breaking year. There's a one-in-three chance that this year will be warmer than last year, according to NOAA.

That's in part because of El Niño – a natural, cyclic climate pattern that can push global temperatures even higher. Many of the hottest years on record occur when El Niño is strong.

The current El Niño took hold in June 2023, and led to higher water temperatures in the Pacific Ocean, which helped drive global temperatures up in the second half of the year. But scientists say last year's temperatures were even higher than they expected under current El Niño conditions, making it difficult to predict what 2024 might hold.

Still, forecasters are confident that El Niño conditions will persist well into 2024, potentially setting up another record-breaking year for the planet.