The number of rats in cities is increasing due to rising global temperatures and drastic climate changes.
This is stated in a study published in the journal Science Advances.
The study looked at 16 major cities around the world. Washington, San Francisco, New York (USA), Toronto (Canada) and Amsterdam (Netherlands) saw the largest increases in rodent numbers. Another 11 cities saw a “significant trend” towards an increase in rat numbers.
Over the past decade, rat populations in Washington, D.C., have increased by 390%, San Francisco by 300%, Toronto by 186%, and New York by 162%. The researchers analyzed public observations and reports of infestations.
Some major cities, such as London and Paris, were not included in the study because they did not provide the necessary data. But the researchers believe the results there would be similar — as in many similar cities around the world.
“When you walk the streets of Toronto, there’s a place beneath your feet, deep in the sewer system, that’s infested with rats,” said Alice Sinia, lead entomologist at the pest control organization Orkin.
In 2023, Torontoʼs rat hotline received 1 600 calls complaining about rats. In 2019, there were only 940 such calls. The exact number of rats in the city is unknown because no one has studied it. So it is compared to "rat rain".
Rat populations have also increased in Auckland (New Zealand), Buffalo, Chicago, Boston, Kansas City and Cincinnati (USA). However, the scientists did not determine the total number of rats living in the cities.
Rising temperatures correlated with an increase in rat populations, the researchers wrote. At higher temperatures, rats can breed for more of the year and have access to food for longer.
Meanwhile, in Tokyo (Japan), Louisville, and New Orleans (USA), rat populations have declined. In Tokyo, this was attributed to cultural norms that prompt people to report a rat quickly. In New Orleans, education efforts were conducted with local residents.
Researchers say the best strategy to combat rats is to make cities less hospitable for them, for example by throwing trash in bins rather than just throwing it out on the street.
- In 2024, climate change caused annual global temperatures to exceed the internationally agreed target of 1.5°C for the first time. The average temperature last year was 1.6°C above pre-industrial levels .The pre-industrial temperature level is the average global temperature observed on Earth before the beginning of the industrial era (approximately until the middle of the 19th century, usually the period 1850–1900).
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