Urban rat populations have surged dramatically in recent years, with some cities experiencing increases of nearly 400%, according to a new study published in Science Advances.
Researchers found that rising global temperatures are fueling the boom, allowing rats to breed longer and survive in milder winters.
The study analyzed rat sighting and infestation reports across 16 major cities worldwide, with Washington, D.C., San Francisco, Toronto, and New York City showing some of the highest increases. Over the past decade, rat numbers rose by 390% in Washington, D.C., 300% in San Francisco, 186% in Toronto, and 162% in New York.
"Increasingly, we're flushing them out into open spaces—either through construction or floods—and they have to go somewhere," Alice Sinia, an entomologist with Orkin, Canada's largest pest control company, told The Guardian. Toronto, in particular, has been hit by what city councilor Alejandra Bravo called a "perfect rat storm," as milder winters allow rodents to reproduce year-round.
Beyond being a nuisance, rats cause billions in property damage, spread at least 60 diseases, and negatively impact mental health. The study suggests that cities must adopt more effective pest management strategies—such as improving waste disposal—rather than relying solely on extermination efforts.
While most cities saw increasing rat populations, Tokyo, Louisville, and New Orleans bucked the trend. Experts believe public education campaigns and cultural cleanliness standards may offer valuable lessons in rodent control.
"Pretty much every city announces that they have a war on rats," lead researcher Jonathan Richardson, from the University of Richmond in Virginia said. "We need to know the battle that we're fighting."
With global temperatures continuing to rise, researchers warn that urban rat infestations are likely to worsen unless cities take proactive measures to curb their spread.
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