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That year, a series of atmospheric rivers pummeled the state with rain, triggering landslides and rockslides that the iconic thoroughfare wasn’t built to withstand.
“When they engineered these roads, they made big assumptions that we weren’t going to have big changes in precipitation,” says Paul Chinowsky, professor emeritus of civil engineering at the University of Colorado at Boulder. Planners also didn’t anticipate severe erosion that’s become more common on a warmer planet. “We literally built the roads on the edge of land,” he says.
Global warming is upending those climate assumptions. In California’s climate, research suggests that climate change is increasing the severity of rain brought by atmospheric rivers, making washouts like those that hit Highway One more likely. Increased rainfall also washed away a large chunk of Wyoming Highway 22 last summer, cutting off a vital corridor between Jackson, Wyoming, and Victor, Idaho. And road closures remain a persistent problem in Western North Carolina months after Hurricane Helene, which was supercharged by climate change.
Worldwide warming temperatures are hammering roads that, like Highway One, were built for a different climate, ballooning repair budgets and sometimes cutting off entire communities from essential goods and services. The 2022 Pakistan floods destroyed 8,000 miles of roads, causing average travel time to market in some places to increase from 2.6 hours during a typical monsoon season to 13 hours.
There are places across the world “where you’ve got one road that services a resort town or a coastal city, and there’s going to be a lot of rethinking because economically the lifeblood of these towns is that one road,” says Chinowsky.
Chinowsky co-authored a study that looked at the impact of climate change on US road budgets if global carbon emissions keep rising until 2040. It found that the cost of maintaining roads in just the US will increase by $100 billion a year by 2050 (in 2018 dollars), or roughly half of what state and local governments spent on roads in 2021.
Most roads are either made of concrete, which is costly and mainly relegated to highways, or asphalt which is lower cost and more common — and most at risk from climate change.
While on the surface all asphalt roads appear similar, their composition can vary significantly depending on the region. This is why asphalt roads in Dubai don’t melt despite desert heat, but Tour de France organizers are finding that they have to water the asphalt roads to stop them from melting during France’s increasingly hot summers.
Long periods of high heat can cause roads that aren’t built for those temperatures, like those in France, to melt and buckle, causing deep ruts that can be risky for drivers. Similarly, if a road receives more rain than it was designed for then that water can infiltrate below the surface into the base layer, eroding the road. When a ca