A new study has linked climate change to the increasing spread of mice in several American cities and urban centers worldwide. 

The research, conducted by Jonathan Richardson, a biology professor at the University of Richmond, examined rodent populations in 13 U.S. cities, as well as Toronto (Canada), Tokyo (Japan), and Amsterdam (Netherlands).

Warmer Winters Extend Rodent Breeding Seasons

Published in Science Advances on Friday, the study analyzed 12 years of data and identified several key factors behind the rising mouse populations:

-High population density

-Declining vegetation cover

-Rising average temperatures (the most significant factor)

Richardson explained that mice are small mammals whose activity is limited by cold temperatures. Warmer winters extend their breeding seasons, allowing them to search for food longer and reproduce more frequently.

"A warmer climate can also lengthen growing seasons, giving mice more food and vegetation to hide in," said Michael Parsons, an urban ecologist and wild rat expert not involved in the study.

Additionally, Parsons told CNN that warmer temperatures increase the range of food odors, making it easier for rodents to locate and access food sources.

Economic and Health Risks

The expanding rodent population poses major challenges for cities, causing:

- Infrastructure damage

- Food contamination

- Fire hazards (by gnawing on power lines)

According to CNN, rats cause an estimated $27 billion in damages annually in the United States alone.

From a public health perspective, Cornell University pest expert Matt Fry—who was not involved in the study—warned that rats are linked to more than 50 pathogens that infect humans. These include leptospirosis (Weil’s disease), which can cause kidney and liver damage and may be fatal if untreated.

A Growing Urban Challenge

As climate change accelerates, cities worldwide may see a surge in rodent populations, requiring new strategies to mitigate health and infrastructure risks. Researchers stress that understanding these climate-driven shifts is essential for urban planning and public health responses in the years ahead.