Climate change has wreacked all sorts of havoc on city residents, but for a different kind of urban dweller, it’s been a boon: Milder winters are helping boost rat populations in cities worldwide, according to a new study. Metropolitan areas that saw a larger rise in temperature over time also saw larger increases in rats, as did places with more dense human population. Washington, DC, and San Francisco topped the list of places with the greatest rat growth, while just three cities saw significant declines.

It only takes a handful of warmer weeks a year — during which the pests will forage for food and breed — to boost rat numbers, Kendra Pierre-Louis writes. The findings come as cities are already spending $500 million each year on rat control. They also point to yet another way humans are helping their beady-eyed foes thrive. Today on CityLab: Climate Change Is Helping Fuel an Urban Rat Boom

— Linda Poon

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