Cities are overrun by swarms of rats: scientists discuss the effects of global warming.

A recent study has revealed that rat populations are skyrocketing in major cities around the globe, with rising temperatures playing a significant role. Researchers analyzed public complaints and inspection data from 16 locations and found that urban areas experiencing long-term warming trends are witnessing a faster increase in pest populations. This is the first instance where a direct link between climate change and the growth of rat populations has been established.

Cities such as Washington, San Francisco, Toronto, New York, and Amsterdam have been particularly affected. Jonathan L. Richardson, an associate professor at the University of Richmond and the lead author of the study published in Science Advances, stated, "We found that in those cities where warming trends have been observed over the last 50 years or so, rat populations have also significantly increased."

Richardson's team is tracking rat populations worldwide and discovered that in 11 out of the 16 cities studied, there was a notable increase in rat numbers. Only Tokyo, Louisville, and New Orleans experienced a decline. Contributing factors to this growth include rising population density in cities, increased urbanization, and longer heat periods that expand foraging opportunities for rats. Richardson explained that warmer temperatures allow rats to stay above ground longer, leading to earlier sexual maturity in females and more frequent and larger litters.

Researchers noted that living alongside a growing number of rats has a psychological impact on people, in addition to their mere presence. Moreover, rats are known to spread over 50 zoonotic pathogens and parasites, posing a serious health risk. Controlling these populations is becoming an increasingly challenging task for cities, with annual costs for rat control estimated at $500 million. In New York alone, a 2023 investigation by journalists revealed that the rat population has increased by more than 7% since Mayor Eric Adams launched his "war on rats" in 2022.

Despite the efforts being made, rats remain difficult to control due to their intelligence and adaptability. Richardson acknowledged that dedicated individuals work in pest control, but emphasized the complex task at hand: "It’s astonishing how well rats can evade the measures we use to combat them."

The study's authors concluded that effective rodent control will require increased municipal funding, additional staff, and comprehensive strategies for eradication. Traditional extermination methods alone are insufficient, and cities must focus on eliminating the environmental conditions that allow rats to thrive. In addition to the cities mentioned in the study, global urban centers are also grappling with rat infestations exacerbated by climate change.

In a report from the Centers for Disease Control and Prevention, scientists stated that warmer winters contribute to a sustained breeding cycle for rats, complicating efforts to manage infestations. Additionally, climate change-induced flooding forces rats out of underground burrows into human-occupied spaces, further increasing instances of their interaction with us.