KNOXVILLE, Tenn. — A new global climate report finds that 2025 ranked among the warmest years on record for the planet and was the third-warmest on record for North America, according to scientists who say the trend is showing up in extreme weather across East Tennessee as well.
The State of the Climate report is published each year by the American Meteorological Society and compiled by hundreds of scientists worldwide.
AMS President Alan Sealls said 2025 was among the top three warmest years on record, and that the two years that were warmer both occurred during El Niño conditions, when the Earth's average temperature tends to run higher.
"We're talking fractions of degrees, but still the overall trend is what's critical," Sealls said.
Sealls said the world's oceans continue to absorb most of the excess carbon dioxide humans are producing, which he compared to a storage unit that keeps filling up largely unnoticed. That absorption is contributing to sea level rise at a faster rate, he said.
"That's where we stand with climate change," Sealls said. "It's something that is slow motion but has big impact down the line."
Nationally, the report highlights several of 2025's costliest disasters, including catastrophic flash flooding in central Texas that killed more than 135 people, one of Canada's worst wildfire seasons on record, and the devastating Los Angeles fires in January.
Extreme swings show up in Tennessee data
The same pattern is showing up closer to home, said William Tollefson, assistant state climatologist for Tennessee.
"2025 was definitely a warmer year," Tollefson said, adding that a few counties in northwest Tennessee saw one of their five warmest years on record. He said rainfall was similarly extreme in both directions.
"Precipitation-wise, we saw a lot of extremes, which is something that the report highlighted, both drought and flooding concerns," Tollefson said.
Tollefson said the state also saw an active start to severe weather season, with tornadoes and damaging thunderstorm winds in the first half of the year. He pointed to an April flooding event in West Tennessee so extreme that forecasters estimated it had less than a one-in-10,000 chance of occurring in a given year.
"We saw similar events with Helene in East Tennessee in 2024," Tollefson said. "And in between, we had these drought periods ... but it doesn't seem to be coming nice and spread out. It's in these bigger rainfall events, with more dry days in between."
Sealls said that swing between extremes — rather than uniformly less snow or less cold — is the pattern scientists expect as the planet warms.
"Places that didn't normally get a lot of snow could actually get more snow, simply because there's more moisture in the air," Sealls said.
Tollefson said Tennessee's winter storm activity has itself shifted geographically in recent decades, with the western half of the state affected more than East Tennessee.
"That's a pattern that we have seen play out across Tennessee, where these winter storms have really impacted the western half of the state more so than East Tennessee," Tollefson said. He said East Tennessee saw a declining trend in winter storm activity from the 1990s through the early 2020s, after a more active stretch in the 1990s and early 2000s.
Sealls cautioned against attributing any single storm or event — even one as damaging as Helene — directly to climate change.
"Weather is day-to-day changes in the atmosphere. Climate is long-term averages of weather," Sealls said. "They sound the same, but they're not exactly the same."
Impacts on farms, gardens and infrastructure
Both scientists said a couple of degrees of average temperature change can be enough to shift an entire planting zone, and Sealls said a warming planet also raises concerns for human health, including shifts in where certain diseases occur.
Tollefson said the swings between drought, flooding and temperature shocks are already affecting agriculture and home gardening in Tennessee. He pointed to corn crops damaged by summer droughts, including stretches of two weeks or more without rain in June, when corn is in its tasseling stage.
"Where you go two weeks without rain in June, when it's in the tasseling stage, and now you've lost your crop," Tollefson said.
He also described warm spells in February that prompt plants to leaf out or grow, only to be followed by cold blasts that kill them off.
"It gets really warm in February and things start to leaf out or grow, and then you get these cold blasts that end up killing our gardens," Tollefson said. "That's something we've seen over the last few years especially."
Tollefson suggested gardeners and farmers weigh the cost of irrigation as conditions grow less predictable, though he said more research is needed in Tennessee to fully understand how the varying conditions are affecting specific agricultural sectors.
"Thinking about how these actual weather patterns are affecting day-to-day lives and what we can do to get ahead of that," Tollefson said.
Both scientists advised local planners to design infrastructure with a changing climate in mind. Tollefson said flooding thresholds once considered rare may need to be reconsidered.
"Maybe what used to be a one-in-100-year storm is more like a one-in-75 or a one-in-50 year," Tollefson said, "and planning for those higher-end extremes, especially when it comes to flooding."
The takeaway: prepare, don't panic
Both scientists said the point of the report isn't to cause alarm, but to encourage preparation — starting with knowing how to receive weather warnings.
"Everyone needs to make sure that they have ways to get weather warnings from trusted sources, a local meteorologist, the National Weather Service," Tollefson said. "As we're seeing these sort of extreme events increasing, it's becoming more and more important that you just know what's happening."
Sealls said the long-term goal is straightforward.
"You want the earth to be better than it was when you were a kid, for the future kids," he said.
