A new study published in the journal Science Advances revealed an increase in urban rat populations, primarily driven by climate change. Researchers from the University of Richmond, led by urban ecologist Jonathan Richardson, found that rising temperatures and urbanization are contributing to the surge in rat numbers across major cities.
"We think we're explaining the majority of the variation in rat trend numbers across the cities," said Richardson, a biologist at the University of Richmond, according to The Globe and Mail.
The study analyzed records of rat sightings in 16 cities over an average period of twelve years, examining public rat sighting and inspection data. In 11 of these cities, rat numbers surged during that period. Washington, D.C. experienced a reported 390% rise in rat populations, as reported by The Raw Story. San Francisco and Toronto also saw increases in rat sightings over the past several years. Toronto reported a 186% rise in rat populations, placing it third among the cities studied.
An analysis revealed that rat populations are growing fastest in areas where average temperatures are rising quickest. About 40 percent of the overall increase in rat sightings is linked to rising temperatures, according to The Washington Post. While rising temperatures are the dominant factor in this growth, urbanization and increasing human populations also contribute.
"Long term increase in temperature was by far the strongest predictor," said Richardson, according to The Globe and Mail. The study found that warmer temperatures, especially in winter, enabled rats to forage longer and reproduce more frequently throughout the year, potentially allowing for an extra reproductive cycle. Richardson explained that even a week or two of abnormally warm temperatures during the winter could help rats replenish their food stores and search for food.
Cities like New Orleans, Tokyo, and Louisville saw their rat populations decrease, partly due to more diligent pest control, with New Orleans showing the biggest drop in rat reporting, according to Digi24. "There are important lessons probably to be gleaned from those cities," said Richardson. However, the majority of cities studied showed increases in rat populations. "We need to know the battle that we're fighting. Pretty much every city announces that they have a war on rats," he added.
Cities across the globe are already spending $500 million each year to try and keep the rats at bay, as reported by The Washington Post. In New York City, rat sightings increased by 162 percent over the past decade. Mayor Eric Adams has declared a "war on rats," stepping up efforts such as replacing garbage bags with rat-resistant containers and hiring a "rat czar," as reported by Vox.
Under Mayor Adams's administration, containerization is "the hallmark" of New York City's battle with rats. Kathleen Corradi, NYC's director of rodent mitigation, noted that the rollout is expected to impact rat populations due to reduced food sources, according to Vox. "We're so optimistic and excited to see that rollout and its impact on rats, because food source is what has allowed rats to thrive for so long in New York City and other urban centers," Corradi said.
Experts say that controlling rat populations is challenging. "What makes fixing rat infestations so hard is that rat issues are human issues. It's human behavior that allows rats to thrive in the first place," said Corradi. Richardson emphasized the need for proactive measures, stating, "Securing food waste and making it inaccessible to rats is the approach that will have the biggest impact on controlling rats," according to New Scientist.
Scientists warned that unless effective steps are taken to keep rat numbers in check, the rat problem in cities is expected to worsen in the decades ahead, with current rat control methods failing. "Understanding that climate warming may lead to a general increase in rats isn't good news, but it's really important to know the challenges you're facing ahead of time so that you can dedicate more resources to try to slow that trend," said Richardson, according to The Washington Post.
The article was written with the assistance of a news analysis system.