Study: Global warming creates a perfect storm of rats

Published On: February 1, 2025
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A recent study published in Science Advances indicates that urban rat populations have surged by as much as 390% over the past decade, and the study authors attribute this dramatic increase primarily to climate change. Warmer temperatures and altered weather patterns create more favorable environments for rats, enabling them to thrive and proliferate in urban settings. This “perfect rat storm” highlights the intricate connections between climate conditions and urban wildlife dynamics, raising concerns about public health and pest control challenges in cities worldwide.

A global trend

According to the researchers, the rapid growth in population in 11 out of 16 major cities across the globe is likely to persist due to rising temperatures. The warmer climate is facilitating breeding among certain animal species, leading to an increase in population numbers.

The trend of growing rodents numbers is being observed in cities like Delhi, Bangkok, and Ho Chi Minh City, while the cities Washington DC, San Francisco, Toronto, New York City and Amsterdam had the greatest increases, with the researchers concluding that this trend will likely continue.

According to researchers, during the past ten years, rats populations increased by 390% in Washington DC, 300% in San Francisco, 186% in Toronto and 162% in New York, based on public sightings and infestation reports.

The study authors indicated that their findings, despite the absence of data from major cities like London and Paris, are likely applicable to similar urban environments globally. Lead researcher Jonathan Richardson of the University of Richmond expressed confidence that these results would hold relevance in other locations as well.

Among the worst infestations

Toronto is grappling with a significant rat infestation, described as a “perfect rat storm,” as the local rodent population steadily rises. Residents are increasingly concerned about the implications for public health and urban living conditions, urging city officials to implement more effective pest control measures to address the growing problem in Canada’s largest city.

The Guardian: “When you walk the streets of Toronto, under your feet, deep in the sewage system, is a place teeming with rats,” said Alice Sinia, lead entomologist for Orkin, the country’s largest pest control company. “Increasingly we’re flushing them out into open spaces – either through construction or floods – and they have to go somewhere.

Toronto city’s helpline fielded 1,600 rat-related calls in 2023, up from 940 in 2019 and Orkin has also experienced a surge in calls.

“But the reality is, we don’t know how big the population is because no one has ever really studied it formally,” said Sinia.

Two Toronto city councillors, Alejandra Bravo and Amber Morley, last year called for a formal management plan as a way to blunt the crisis.

“It’s a really critical quality-of-life problem when people have all of a sudden been confronted with rats coming into their home or into their business or their place of work,” Bravo told the Canadian press, adding that it had morphed into a “kind of perfect rat storm”.

The study highlighted rising rat populations in several U.S. cities, including Oakland, Buffalo, Chicago, Boston, Kansas City, and Cincinnati, as well as in international cities like Amsterdam, Toronto, and Tokyo. While the research emphasized the relative increases in rat sightings over time, it did not provide a comprehensive assessment of the total rat population in these locations.

Climate warming correlates

Rising temperatures are linked to an increase in rat numbers, as warmer conditions allow them to breed and forage for longer periods. In cities like Toronto, mild winters are disrupting the natural balance, as cold temperatures previously acted as a form of “mother nature’s pest control”, killing off a significant portion of the rat population, but now enabling rodents to breed continuously, leading to a surge in their numbers.

Richardson’s observations highlight a concerning trend, as rising urban temperatures correlate with a rapid increase in rat populations, suggesting that climate change may disrupt ecosystems and contribute to urban pest proliferation. With 2024 marking the hottest year on record at an average of 1.6°C above preindustrial levels, the data paints a troubling picture of how warming environments can exacerbate challenges in city management and public health.

Rats pose a significant threat to human health, economy, and ecology, causing billions of dollars in damage and transmitting over 60 diseases to humans, while also harming urban biodiversity, particularly in regions where they are an invasive species. The impact of rats on human wellbeing is also evident in their link to poorer mental health in individuals who frequently encounter them, with the global effort to combat rat infestations costing an estimated $500m annually, highlighting the need for effective measures to mitigate the effects of these rodents.

A positive note

The declining rat populations in Tokyo, Louisville, and New Orleans suggest that cultural practices and proactive community efforts play a significant role in pest control. Tokyo’s emphasis on cleanliness encourages residents to report rodent sightings promptly, while New Orleans has implemented educational outreach to help prevent infestations. These approaches highlight the importance of public awareness and community engagement in effectively managing urban rodent populations.

Implementing measures such as securely storing garbage in containers, sealing entry points to buildings, and maintaining clean public spaces can significantly deter rodent populations and prevent them from proliferating, ultimately reducing the reliance on removal methods that may only provide temporary relief.

Richardson emphasizes the need for research on wild urban rats, noting that despite extensive studies on lab rats, there’s a surprising lack of understanding about the resilient nature of wild colonies, which can number up to 100 within a small area. He acknowledges the public’s disdain for rats while also recognizing their remarkable ability to thrive alongside humans globally, indicating the complexity of managing urban rat populations amid ongoing “wars” against them in cities.

 

Teaser image by Erich Röthlisberger from Pixabay. Header image by Squirrel_photos from Pixabay.

 

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About the Author: Chris Machens

Chris Machens
Chris covers the climate since 2011, and when not posting articles to the site he usually works on our next video production.
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