Why Warmer Cities Mean More Rats

A study tracking rat populations across 16 cities found that numbers rose significantly in 11 of them. Washington, D.C. experienced the steepest increase, followed by San Francisco, Toronto, New York City and Amsterdam. Only Tokyo, Louisville and New Orleans recorded declines. Dallas and St. Louis showed no significant change. The strongest predictor was not how poor a city was, how cold its winters were or how much money officials could throw at pest control.

It was climate warming.

Cities experiencing greater long-term temperature increases also experienced larger rises in rat sightings. Warming accounted for 40.7% of the variation between cities. Less vegetation, used as a measure of urbanisation, accounted for another 34.3%. Human population density accounted for 19.4%.

This is not a story about rats suddenly deciding to invade human civilisation. It is a story about human civilisation manufacturing ideal conditions for rats and then punishing them for taking advantage.

A Climate Made for Rats

Brown rats and black rats now live across almost every continent. They have become extraordinarily successful because they are able to live alongside humans.

We provide the food.

We provide the shelter.

We provide the buildings, underground systems, discarded furniture, rubbish containers and restaurant waste.

Now we are extending the time they can remain active.

Cold weather restricts rats’ movement, foraging and reproduction. As winters become milder, rats may experience lower mortality, longer periods of activity and longer breeding seasons. The researchers could not determine exactly which mechanism was responsible, but the overall relationship was clear: cities that warmed more tended to experience faster increases in rat numbers.

Urban areas are already hotter than the countryside surrounding them because roads, buildings and other artificial surfaces trap heat. Continued climate change adds another layer of warming.

Humans have effectively built heated feeding stations across the planet. Then we call the animals who arrive pests.

Concrete, Waste and Population Growth

Temperature was not the only factor. Cities with less vegetation experienced faster growth in rat sightings. Cities that lost more vegetation between 1992 and 2020 also tended to see larger increases. Replacing green space with buildings and pavement does not simply remove habitat for other animals. It creates infrastructure that some species, including rats, can exploit. More homes, businesses and restaurants mean more shelter and more discarded food. Less vegetation can also increase heat retention, making already warming cities even hotter.

Greater human population density was also connected with rising rat numbers. More humans produce more waste. More buildings create more hiding places. More food businesses create more opportunities to eat.

This should not be difficult to understand. A rat does not look at a city and see private property, sanitation regulations or a political boundary. They see food, shelter and somewhere to raise their young. Humans see the consequences of our own behaviour and blame the nearest animal.

The War That Does Not Work

Cities have spent decades responding with poison and traps. Globally, this war on rats costs an estimated US$500 million every year. Yet researchers have struggled to determine whether these control programmes produce meaningful long-term reductions. Many cities do not even conduct consistent population monitoring.

New York City increased rodenticide use substantially between 2014 and 2019. Rat sightings continued to rise during the same period. An intensive poisoning campaign in Salvador, Brazil, also produced only minimal reductions. Apparently, repeatedly poisoning animals without removing their food or shelter does not solve the conditions allowing their populations to grow.

Who could have predicted that?

Poisons also spread beyond the rats they are intended to kill. Birds of prey, coyotes and other predators can be poisoned when they eat rats who have consumed rodenticides. The result is a system that kills rats painfully, harms other animals and often fails to produce lasting population reductions. When new rats can move into the same territory and exploit the same food, buildings and waste, the killing begins again. This is not management. It is an endless cycle of suffering disguised as control.

Rats Are Not the Only Urban Animals

Rats are part of a much wider question about who is permitted to live in cities. As human settlements expand, encounters with wild animals become unavoidable. Some animals are pushed into urban areas as their habitats disappear. Others are attracted by the food, water, shelter and warmth humans provide. Research involving more than 1,000 residents of metropolitan Atlanta found that people’s tolerance of wild animals was strongly connected to whether they liked those animals and the emotions they associated with them.

Hummingbirds were strongly liked and were the only animals participants wanted to see increase. Bobcats, coyotes, opossums and snakes were less tolerated, with respondents preferring their populations to decline. This was not necessarily because these animals presented a serious danger. Fewer than 1% of participants reported being threatened or injured by a wild animal. Fear, disgust and annoyance can shape public attitudes even when severe conflicts are rare.

Animals humans consider attractive, gentle or entertaining are welcomed. Animals associated with dirt, danger or disease are trapped, poisoned or driven away. The boundary between friend and foe is often not ecological. It is emotional.

Rats have the additional disadvantage of being associated with rubbish and disease, even though human behaviour provides the rubbish and human urbanisation creates the conditions bringing rats into closer contact with people.

The Risks Are Real

None of this means urban rat populations should simply be ignored. Rats can damage buildings, consume crops, contaminate food and carry pathogens and parasites transmissible to humans. Their presence has also been linked with poorer mental health among people living with severe infestations. These are genuine public health and social concerns. But recognising a problem does not justify clinging to methods that are cruel, environmentally damaging and ineffective.

The study relied largely on public complaints and municipal inspection records rather than direct city-wide population surveys. Reporting can be influenced by public awareness, trust in authorities and willingness to contact government agencies. The 16 cities also included no tropical locations and only one subtropical city. The research therefore has limitations. It does not tell us the precise number of rats living in each city or prove exactly why warming increases sightings. It does, however, show a strong pattern across years of data: rat numbers tended to rise fastest in cities experiencing more warming, heavier urbanisation and denser human populations. Those are human-created pressures.

Stop Creating the Problem

The most promising response is not finding a more powerful poison. It is making cities less attractive to rats. That means secure, rat-resistant bins. More frequent collections. Food waste diversion. Building standards that prevent animals from entering. The removal of discarded materials that provide shelter. Proper surveillance so cities know where populations are changing. Public education about preventing conflicts.

New York City has already introduced rules requiring some buildings to place waste in containers rather than leaving bags on pavements. Early data suggested complaints may have fallen in those areas.

Tokyo and New Orleans, two of the three cities where rat numbers declined, also offer useful lessons. Tokyo maintains strong cultural expectations around cleanliness. New Orleans uses proactive surveillance and works with residents and city departments on prevention.

The principle is straightforward.

Remove the food. Block access to buildings. Reduce waste. Preserve green spaces. Track whether the strategy works. Stop killing animals for responding predictably to the world humans constructed.

Climate Action Includes Food

Cities cannot solve global warming alone, but humans are not powerless. Two randomised clinical trials published in 2026 found that low-fat plant-based diets reduced diet-related greenhouse gas emissions by 55% and 57%. In one trial, cumulative energy demand fell by 44%. In the other, energy demand fell by 55%. A Mediterranean diet reduced emissions by 20% but produced no significant reduction in total energy demand. The largest environmental savings came from removing meat and dairy, the most resource-intensive parts of the diets. The participants also experienced improvements in measures including weight, insulin sensitivity and cholesterol. Among people with type 1 diabetes, the plant-based group reduced insulin requirements.

Food systems produce (by conservative numbers) roughly one-third of global greenhouse gas emissions. Changing what we eat is one of the most immediate actions available. It does not require inventing a new technology or waiting for governments to rebuild every city. It requires humans to stop eating animals.

Animal agriculture contributes to the warming that is changing ecosystems, extending the activity of urban rats and increasing conflict between humans and other species.

We then respond to one group of animals by breeding and killing them for food, and another by poisoning them for adapting to the resulting climate. Different industries. Same entitlement.

Coexistence Requires Change

Humans and rats are unlikely to stop sharing cities. Even the study’s authors acknowledge that most cities will probably never be free of rats entirely. The real choice is between endless killing and meaningful prevention.

We can continue scattering poisons through urban ecosystems while rat populations recover, predators are contaminated and temperatures rise. Or we can address waste, buildings, urban design and climate change.

Rats did not create disposable food systems. They did not pour concrete over green space. They did not design overflowing bin collections or build cities that trap heat. They did not create animal agriculture or burn fossil fuels. They adapted.

Humans created the problem.

The least we can do is stop blaming rats for surviving it.