2025 started off with a flurry of intense weather. Southern California experienced bursts of that spread record-breaking destructive wildfires. Major winter storms have dumped snow and cold weather on the Mid-Atlantic and the South. And in the midst of the weather news, scientists from major meteorological associations around the world reported that human-caused climate change drove .
In the past, climate scientists often said that individual weather events couldn't be connected to human-caused climate change. But in the last decade, has allowed researchers to pinpoint the impact of climate change on weather disasters like , , and even .
Not every weather fluctuation is demonstrably affected by climate change. But the impact of the steady increase in global temperature is now detectable in many extreme weather events鈥攁nd likely many of the more normal ones, too, says Justin Mankin, a climate scientist at Dartmouth College.
"The trends in climate are shaping new weather possibilities that were maybe unprecedented," Mankin says.
What's the difference between climate and weather, anyway?
Scientists have a saying: climate is what you plan for and weather is what you get.
Climate scientist Danielle Touma of the University of Texas, Austin, explains it this way. "The climate is basically the clothes you have in your closet," but what you pick out to wear every day tells you about the weather. So in Colorado, where Touma used to live, her winter wardrobe was full of jackets and sweaters鈥攔eady for the winter climate. But sometimes there was a warm day when she would dig a T-shirt from the back of a drawer.
Scientists usually define the climate of a place as the 30-year average of its weather. So weird weather does factor in, but isn't as important to the average as more common conditions, says Deepti Singh, a climate scientist at Washington State University. And scientists expect the variation in day-to-day weather to persist, even as climate change evolves.
Does human-caused climate change affect weather?
Earth's temperature has risen about, when people started burning vast amounts of fossil fuels. The pollution from that burning traps heat inside Earth's atmosphere, slowly heating up the air, oceans, and land.
The temperatures' slow creep upward doesn't always noticeably affect daily weather, at least not in obvious ways, Singh says. But planet-scale warming is , even if the impacts are subtle.
"Everything we're experiencing, it is occurring in a different environment," Singh says. So the weather itself, "to some extent, is being influenced by these changes."
There are in many parts of the U.S. and beyond: states like experience more than a week fewer freezing days now than they would in a world without climate change. And heat extremes have also increased. The number of heat waves in the U.S. has .
A changing climate also reshapes complicated atmosphere and ocean patterns鈥攕ometimes introducing new or extraordinary weather outside of what people have experienced in the past. The deadly 2021 heat wave in the Pacific Northwest, for example, was demonstrably hotter because of climate change鈥攂ut in the first place were also essentially unprecedented in the region.
"We've kind of put the climate on steroids," says Alex Hall, a climate scientist at the University of California, Los Angeles. "But once in a while there'll be something really extreme that will occur that will be way outside the range of what the atmosphere was capable of before."
How do we know?
In the past decade, called "detection" and "attribution." They use climate models that represent Earth's physics to simulate how the planet's climate and weather events would behave if humans had not burned vast quantities of fossil fuels. By comparing that hypothetical situation to the one that exists, they can see if human-caused climate change affected the likelihood of weather events happening鈥攁nd in many cases, how big the influence was.
For example, they could see that Hurricane Helene's deadly rainfall was absent human-caused climate change, and at least 40% more likely.
Mankin compares the technique to clinical trials in medicine. "You want to compare a distribution of medical outcomes in a population that received the drug, the treatment group, to a control group that didn't receive the drug," Mankin says. Only in this case, the drug is fossil fuel burning.
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