Rats could breed too quickly for NYC's successful new extermination method to keep up

• New York City is known for its rat problem. 
• Despite gains in extermination technology, climate change might make the future a more ratty place.
• Warmer temperatures mean more rat sexy time and could lead to the spread of disease. 

New York City has a new, highly lethal method for treating rats. But this, like the many methods it's tried to manage rat populations before, might not stop what some predict is a rat-filled future. 

In fact, some experts have warned that New Yorkers are in for a rude awakening as the planet continues to warm, fostering an even more rat-friendly environment. 

In a normal year, rat populations naturally fluctuate. Rats tend to avoid reproducing in cold weather, Jason Munshi-South, a biologist and associate professor at Fordham University, told Insider. 

But if the world continues warming, it might not get cold enough to slow rat reproduction, which means the rodents could theoretically continue reproducing more months out of the year, increasing the population overall. "It's going to be an issue," Munshi-South said, "especially in northern cities like New York City. Our winters just aren't very cold, anymore." 

Rats on the rise

The number of rats has increased in New York City in the past decade, but it's difficult to say by how much, Robert Corrigan, a rodentologist told The Atlantic.

By running his own surveys with exterminators around the city, Corrigan concluded, "there are more rats. The question we don't know is: Is it 20% more rats? Is it 36.6%? Empirically, we'll probably never get that answer," he said. 

Munshi-South also witnessed this trend. "Last year, year before, I was seeing flowers in bloom in December. And you'd see rat babies, young rats, running around. In previous years, it would've been cold by then and rats would've stopped reproducing," in NYC, he told Insider. 

What more rats could mean for humans

In addition to whatever personal reactions you might have to an increase in the rat population, there's another serious matter at hand – the spread of disease. 

In a 2020 study, published in the journal Proceedings of the Royal Society B, veterinarians found that rodents, including rats and mice, were responsible for 61% of diseases spread by animals.

There were a record 15 cases of a rodent-borne disease called leptospirosis in New York in 2021. One man died from it.

Over a 15-year period, there had only been 57 cases of leptospirosis reported in New York, making 2021 an especially high year.  A health department spokesperson told Insider that climate change was likely a factor in the outbreak. 

As long as we continue to have problems managing waste in the city, and as long as the world continues warming, Corrigan told The Guardian, we're fighting a losing battle. 

"We are at war but we don't have weapons to fight the war," Corrigan said. "We need to rethink our whole system of doing things."