Research findings indicate that as climate change warms winters, rat populations are skyrocketing in major cities worldwide. Increased urban density and reduced green spaces are also significant contributing factors, prompting urgent calls for damage prevention.
A research team led by Jonathan Richardson, a professor at the University of Richmond, published this study in the international journal "Science Advances" on the 31st (local time). The study included a total of 16 cities, comprising 13 cities in the United States, Toronto in Canada, Amsterdam in the Netherlands, and Tokyo in Japan, where rat sightings and pest control records are officially provided.
The study found that over the past 12 years, Washington, D.C., had the highest rat population growth rate with an astonishing increase of 390%. Following closely were San Francisco (300%), Toronto (186%), and New York (162%), where rapid increases were also confirmed. Statistically significant increases were observed in 11 out of the 16 cities examined.
The research team identified temperature rises, urban density, and lack of green spaces as the primary factors contributing to the increase in rat populations. Notably, temperature rise accounted for approximately 40% of the issue, having the most significant impact. It was also found that the higher the human residential density and the fewer green spaces, the faster the rat population increased.
In contrast, rat populations decreased in Tokyo, New Orleans, and Louisville. The researchers noted that rat control education was conducted in New Orleans, and in Tokyo, the cultural factor and high expectations for cleanliness may have led to quickly reported rat sightings, which could be a key reason for the decrease.
Many cities are intensifying pest control efforts due to the surge in rat populations, but there are limits to effective control. Washington, D.C., is conducting rat eradication training for property managers and pest control companies, and has also introduced rat hunting methods using dogs. New York City has issued a notice to recruit a rodent damage reduction coordinator, pushing forward with a comprehensive rat eradication strategy.
Kayli Byers, a co-investigator on the urban rat problem, told The Washington Post, "This research is the first direct analysis of the impact of climate change on urban ecosystems," and warned, "If temperature rises continue, the urban rat problem will become more severe."
The researchers stated, "Rat populations are rapidly increasing due to climate change," and advised, "Systematic pest control strategies should be established for each city, and sufficient personnel and budget need to be secured."
Reference materials
Science Advances (2025), DOI: https://doi.org/10.1126/sciadv.ads6782