From New York to Taipei: How Climate Change and Urban Density Are Fueling a Global Rat Surge

Taipei's rat problem has moved far beyond a simple hygiene issue. A Hantavirus death in Da'an District earlier this year, together with widely circulated videos of dozens of rats swarming near Shuanglian Market, has turned the situation into a major public-health worry and a growing political headache for Mayor Chiang Wan-an.

What feels like a sudden local explosion is in fact part of a much larger global trend. Researchers say rising temperatures, rapid urbanization, and increasing population density are creating perfect conditions for rats to thrive in cities everywhere.

A major 2025  study published in Science Advances examined 16 large cities worldwide and found rat populations rising in 11 of them, including New York, Washington D.C., Amsterdam, and Toronto. The research directly tied the increases to warmer temperatures, which allow rodents to breed more often and survive winters that once kept their numbers in check.

The same pattern is playing out across Europe and North America. London, for example, continues to receive a high volume of rat complaints, while many cities struggle with aging infrastructure and tight budgets.

In Taipei, these worldwide findings match what residents are seeing on the ground. In a May 5, 2026 Facebook  post, National Taiwan University public-health professor Chan Chang-chuan(詹長權) wrote that the city's rat surge stems from the same three drivers identified in international research: climate warming, urban density, and abundant food waste. The post was widely cited in local media, including  Storm Media.

Experts stress that the problem cannot be solved by cleaning streets alone. Three deeper forces are at work.

Warmer Temperatures Are Changing Rat Biology

Milder winters are removing one of nature's main checks on rat numbers. “The warmer cities are getting, the faster their rat populations are increasing,” lead researcher Jonathan Richardson  explained in coverage of the Science Advances study. Even small rises in temperature can lengthen breeding seasons and boost survival rates year-round.

Taiwan's subtropical climate, with its lengthening warm periods, is amplifying this effect.

Urban Density Creates Hidden Habitats

Modern cities offer rats countless hiding places — underground sewers, construction gaps, and building cavities. As green space disappears, rodents are pushed closer to people and their food sources. Taipei's high population density makes these structural advantages especially significant.

Food Waste Sustains Population Growth

More people produce more waste. In food-rich cities like Taipei, with its famous night markets and street vendors, even small amounts of improperly managed garbage can support large rat colonies. Researchers call rats “commensal animals” — their success is tightly linked to human activity.

The Hantavirus fatality and viral market footage have intensified criticism of the city government. Opposition voices are framing the outbreak as a failure of urban management in the run-up to elections. In his Facebook post, Prof. Chan argued for a fundamental shift: instead of chasing rats with short-term clean-ups, Taipei should redesign waste management, infrastructure, and public-health systems to make the city structurally less attractive to rodents.

• New York: The city now requires sealed garbage containers for businesses and residents. Rat sightings dropped 23% citywide in December 2024, with a 55% reduction in the Hamilton Heights pilot zone (NYC Department of Sanitation, 2024).

• Tokyo: A strong culture of public cleanliness, combined with rapid community reporting, keeps rodent numbers low despite extreme urban density.

• New Orleans: Long-term monitoring, cross-department coordination, and public education have delivered one of the largest sustained declines in rat populations among cities studied.

The risks go well beyond annoyance. According to the World Health Organization, Hantavirus fatality rates vary significantly by strain and region: the type prevalent in Asia and Europe carries a fatality rate of less than 1% to 15%, while the most severe form found in the Americas reaches 20–40%. The virus spreads through airborne particles from rodent droppings and urine — no direct contact with rats is needed. According to the Science Advances  paper, rats harbor and transmit more than 50 zoonotic pathogens and parasites to people worldwide, with associated diseases including leptospirosis, murine typhus, and bubonic plague.

WHO Hantavirus Fact Sheet​

Traditional methods are losing effectiveness — and in some cases, actively making the problem worse. The Science Advances paper estimates the global “war on rats” costs cities and governments an estimated US$500 million every year, yet populations in most cities continue to rise.

The Science Advances study documented that even as New York dramatically increased rodenticide use between 2014 and 2019, rat sightings continued to climb. The reason is straightforward: poisons and traps address symptoms, not causes. Remove a rat population without changing the environment that supports it, and the remaining rats — with less competition for food and nesting space — quickly replenish the numbers.

There is also a growing biological threat. Researchers at the University of California have identified a genetic mutation in roof rats associated with resistance to second-generation anticoagulant rodenticides — the most potent class of rat poisons currently in use. As resistance spreads, the effectiveness of chemical control is expected to decline further.

Beyond their limited effectiveness, rodenticides carry significant collateral risks. Anticoagulant poisons accumulate in the livers of rodents that consume them, and when those rodents are eaten by predators — hawks, owls, coyotes — the toxins transfer up the food chain in a process known as secondary poisoning. California has responded by enacting some of the world’s most restrictive rodenticide legislation, including the Poison-Free Wildlife Act (AB 2552), which sharply limits the use of anticoagulants in urban areas.

Experts now advocate for what researchers call Integrated Pest Management (IPM) — a structural approach that treats chemical control as a last resort rather than a first response. The core strategies include improving waste containment, sealing building entry points, eliminating food sources, and establishing long-term monitoring systems. Emerging technologies are also entering the toolkit: Bluetooth-enabled smart traps that transmit real-time rodent activity data, and contraceptive baits designed to reduce populations gradually without lethal methods. According to a 2024 peer-reviewed study in the Journal of Pest Science, the most durable results come from coordinated, community-wide campaigns that combine habitat modification with sustained public engagement — not one-off extermination drives.

Taipei's experience is not unique — it is an early warning of a trend that will intensify as the planet warms and cities grow denser. The challenge is no longer whether cities can wipe out rats entirely, but whether they can adapt fast enough to keep populations under control.

For Taipei, the coming years will test not only public-health systems but also political accountability and the city's ability to modernize urban policy. The rats visible in markets and the recent Hantavirus death may be the first clear signals of a much larger shift already underway.

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