It’s been a strange few weeks for weather across the US.
A dust storm in Illinois earlier this month led to a 72-vehicle pileup that killed seven people. In April, more than 25 inches of rain — 88 billion gallons — drenched Fort Lauderdale, Florida. Wisconsin declared an emergency as more than 80 wildfires ignited amid hot temperatures, low humidity, and high winds. A three-day storm caused floods and set new rainfall records in Denver, Colorado. Just this past weekend, a historic heat wave baked the Pacific Northwest, more than a month before summer officially starts.
There is a lot of natural variability in weather, and oddly timed or extreme events have occurred in the past. However, average temperatures are rising around the world, altering the odds of mixing the right raw ingredients behind early heat waves, sudden downpours, and expanding fire seasons. In some cases, they will become more frequent or more extreme.
“Often these are happening on a background of a changing normal, a changing baseline,” said Barbara Mayes Boustead, a meteorologist at the National Weather Service. “As that shifts, we may see events like these more often in the future, and things that might have once been very, very rare become less rare.”
The planet has already warmed by 2 degrees Fahrenheit (1.1 degrees Celsius) on average since the industrial revolution. That change is worsening events like coastal flooding, stemming from rising seas and more extreme rainfall — the kind of catastrophes that grab headlines. “When the average changes, the biggest impact we often see is actually in the extremes,” Boustead said.
But the fact that the average itself has moved also has important implications. Climate change is often told as a story of record-breaking disasters that destroy homes, flood the land, and take lives. But outside of the extremes, the weather is undergoing more subtle transformations, extending the length of seasons, drying out some areas, and adding water to others.
That moving baseline is now starting to change how we grow food, where certain animals live, and is having effects on our health.
The climate is changing faster at local levels
Extreme weather — severe heat, torrential rainfall, drought, and the like — is usually defined based on historical conditions in a given area, usually the top 10 percent of such events. That means the threshold for what counts as extreme is different based on where you are. A 100°F summer day in Phoenix, Arizona is mundane, but 90°F in Anchorage, Alaska is one for the record books.
Timing is important too. A sudden burst of rain in the dry season can trigger damaging flash floods.
As global average temperatures rise, events that happened once a century may end up happening every generation or more. And disasters never seen before could recur as the dials get turned up around the world.
“What feels extreme to us are often those things that don’t happen very often in our lifetime,” Boustead said.
But that’s not the whole story. If you zoom into just about any part of the planet you can see that larger movements in average temperature, rainfall, humidity, and so on are already afoot. The Arctic, for instance, has been warming upward of four times as fast as the Earth as a whole.
It’s these local averages that play the dominant role in the kind of weather that emerges. Florida is one of the fastest-warming states and just saw its hottest year to date. “In the last eight or 10 years, the state of Florida has seen a dramatic rise, in average, temperature of over 2 degrees Fahrenheit,” said David Zierden, Florida’s state climatologist and a researcher at the Center for Ocean-Atmospheric Prediction Studies at Florida State University.
And for every 1.8°F increase in temperature, air can hold onto 7 percent more moisture. As a result, hotter air allows storms to dish out more water. The Fort Lauderdale rainstorm fits this pattern.
“It’s very consistent with the theory and what modeling studies are showing us,” Zierden said.
But part of what made the April downpour in Fort Lauderdale so stunning was that it didn’t spawn from a hurricane. “It was not associated with the tropical storm or tropical system so that made it an interesting event in and of itself,” he added. Nonetheless, it’s likely such events will become more common.
Researchers are also working to quantify just how much burning fossil fuels have made such events worse. It’s part of a new subfield of climate science called extreme weather attribution. Using models and measurements, they can tease out humanity’s fingerprints on a weather disaster. For example, Hurricane Harvey in 2017 drenched Houston, Texas in a record deluge. Researchers calculated that warming since 1980 added another 20 percent to rain gauges during the storm.
It will take scientists more time to see how much climate change played a role in some of the recent extreme weather in the US, like the Fort Lauderdale flooding (the attribution study on Hurricane Harvey took eight months).
The trickier problem is figuring out how much humans are altering the middle of the bell curve of weather events rather than the tails — the sort of weather we experience day in and day out. Here, the natural capriciousness and chaos of weather collide most with the underlying rise in temperatures, and it’s hard to tease out their respective roles in the less severe but still out of the ordinary weather we see.
“We will always have the interplay of the variability of weather on the background of climate as it is changing,” Boustead said. “We may have a harder time separating it from the other signals that contribute to any given weather event.”
Pay attention to rising minimums
With average temperatures rising, the floor is also lifting at the bottom end of the temperature scale. Cold extreme temperatures are becoming less common, but again, outside of the extremes, there are other significant changes underway. Across the US, winters in general are warming up faster than summers.
These changes don’t have to trigger catastrophes to have consequences. With fewer days below freezing temperatures, for example, more insects can survive into the spring. Bark beetles, combined with an epic drought, have killed millions of trees across the Western US, leaving ample fuel for wildfires. Their range and survival in the winter increased with climate change. The yellow fever mosquito Aedes aegypti, which also carries diseases like dengue and Zika, migrates farther north in the United States as the country warms up. Lyme disease-carrying ticks are moving up to 34 miles north per year into Canada due to warming, particularly in cooler times of the year.
Warmer winters also give pollen-spewing plants a head-start. That’s why allergy seasons get longer and more irritating every year. Higher winter temperatures also mean more precipitation falls as rain instead of snow, which can lead to flooding in the spring followed by drought in the summer rather than a slow release of water from a snowpack. Until this past winter, this trend helped fuel an early burst of vegetation in the Western US that dried out in the summer, contributing to wildfire risk. Even with the epic snowfall this winter in the Sierra Nevada, there is worry that intense summer heat could create more fuel for fires.
Rising minimum temperatures can also significantly affect agriculture. Nicholas Bond, the Washington state climatologist and a research scientist at the University of Washington, explained that nighttime temperatures are generally rising faster than in daylight hours, both in the winter and the summer. That can put stress on crops like corn, cotton, and peanuts, reducing their overall output. Rice, for example, can see a 4.6 percent drop in yield for every 1.8°F increase in nighttime minimum temperature.
The last US National Climate Assessment, a government report that examines the effects of climate change across the country, warned that “yields from major US commodity crops are expected to decline as a consequence of higher temperatures, especially when these higher temperatures occur during critical periods of reproductive development.” (The next version of the report is due out later this year.)
A study last year from the Environmental Defense Fund found that almost all of Iowa would see corn yields decline by at least 5 percent by 2030. In Minnesota, half the counties in the state would experience soybean declines of at least 5 percent.
Higher nighttime temperatures can even reduce the quality of Washington’s prized grapes. “Quality wines need cool nights for the development of acids to give the grapes their flavor and so forth. And so if the nights get too hot — and they’re not there yet — but if they get too hot, then conceivably the quality of those wines go down,” Bond said. “There are no great cabernets that are coming out of Mississippi.”
The most important consequences of these shifts play out for human health. Longer warm seasons increase the chances of severe heat waves occurring earlier. Heat waves that unfold in the early summer or spring tend to be deadlier because people aren’t as acclimated to the higher temperatures at that point. Similarly, people living in cooler climates tend to suffer more under unusual heat. A 2021 heat wave across Oregon, Washington, and British Columbia killed at least 800 people.
And higher minimum temperatures, especially at night, worsen these effects. Without evenings to cool off, people face higher aggregate stress from heat, which can disrupt sleep and worsen underlying heart and lung problems. One study found that a hot night following a hot day could push mortality risk up to 50 percent higher compared to a hot day followed by a cooler night. Rising minimum temperatures also worsen the effects of conditions like kidney stones and multiple sclerosis.
It’s clear then that these slower, less-visible changes in the climate still add up to major disruptions. The consequences are already manifesting now, but the future will grow even warmer and weirder.
The good news is that we can see where these trends are going and take steps to dampen their blows. Better ecological management and restoring natural predators can slow the spread of some invasive species. Improving infrastructure and sound water regulations can help ensure that rags-and-riches rainfall patterns get smoothed out so that enough water is available to everyone throughout the year. White roofs and greenspaces can offset some of the warming underway in urban areas. New crop varieties that can withstand drought and resist heat can help bolster the food supply. Greater awareness of the health impacts of heat and more access to cooling can save lives.
We also haven't seen the full extent of warming from the greenhouse gases humanity has already emitted, and temperatures will continue to coast upward for a period even if carbon dioxide pollution suddenly stopped. But unless humanity zeroes out these emissions, the ratchet will continue to tighten in the direction of more warming indefinitely.
So while we may be able to endure and adapt to many of the shifts we can’t avoid, there are limits, so it’s critical to halt humanity’s contributions to warming overall.