There’s No Evidence That Climate Change Has Increased the Rat Population

As the earth gets warmer, there’s one species that supposedly will really benefit.”Climate Change is amazing,” reported National Geographic. “If you’re a rat.”

The horrific prospect of these pizza-dragging, toilet-bathing, plague-spreading, baby-eating, cannibalistic beasts swarming the sweltering streets of our major cities helps to explain why a recent study allegedly demonstrating a global warming-induced increase in the urban rat population received such widespread media coverage. As is often the case, journalists were not sufficiently skeptical, nor did they take the time to read the study closely.

Published in Science Advances with 19 co-authors, this paper contains nothing meaningful about either climate change or rats. It relies on weak data and inaccurate statistics, and uses misleading references to support its claims. There is no evidence to suggest that global warming is contributing to an increase in urban rat populations.

So, how did the study authors measure the growth in rat populations? By counting rat complaints reported by residents.

It uses these complaints to compare rat populations in different cities, which is the study’s first major problem. The data don’t allow for an apples-to-apples comparison. In San Francisco, for example, the authors examined the trend in all pest complaints, including those involving rodents and insects, from 2010 to 2022. In Boston, only actual dead rats or rat bites were included. In Dallas, the trend was estimated from 2013 to 2019. Some cities changed categorizations and added or eliminated categories over time.

The city of Cincinnati keeps a record of the entire complaint, and many of the incidents included in the study had nothing to do with rats. There were calls about roaches, bedbugs, cats, dogs, raccoons, and mice. One complaint was about a pregnant tenant. Yet these were all counted as rat complaints. 

If your data mixes apples and oranges, you’ll get meaningless results. 

The problems with the underlying data alone would render the study’s findings invalid. But we’re just getting started.

The next problem is that rat complaints aren’t a good measure of rat populations. While the authors acknowledged the limitations of their approach, they also cited three studies (1, 2, 3) to support the claim that rat complaints accurately measure the growth of the rat population. 

However, these three papers actually say—as one did explicitly—that “citizen complaints for rats…were bad predictors of measured rat activity.” 

They point out that there were more rat complaints in areas with fewer rats because one rat can cause alarm but when rats are common, people don’t bother notifying the city.

They also found

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