Is Global Warming Going To Create An Urban Rat Population Explosion?

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Of all of the possible impacts of a warming climate, one that’s probably not considered too often is the potential for an enormous explosion in the number of urban rats throughout many parts of the world.

That’s unfortunate, though, as the potential is certainly there for urban rats to become an enormous problem as temperatures continue to climb, particularly with regard to the spread of many dangerous diseases.

Signs are that things are already veering dangerously close to the point of urban rat populations becoming completely unmanageable. As it is, most attempts to control growing rat populations in heavily urbanized areas of the US have proven expensive and effective only over the short term. This being the case … how much worse can things get?

One of the top experts out there on urban rats, Bobby Corrigan, was recently quoted as saying: “I travel all over the world with this animal, and the amount of complaints and feedback and questions I hear right now are all, ‘We’ve never seen rats in the city like this before,’ he said. ‘They’re all expressing the same concern: Our rat problem is worse than ever.’ ”

Rat populations seem to be growing rapidly, in other words, but individual rats are also “ballooning to the size of human infants” — primarily due to rising temperatures, but also due to growing urbanization and the accompanying profligate human waste of resources.

Something that should explained up front here, by the way, is that resistance to common poisons amongst urban rat populations has been growing rapidly in recent years. That’s another one of the advantages of high and growing population numbers: an ability to rapidly develop resistance to “control methods.”

The New Republic provides more: “What they don’t know is how this all will end. Houston, Texas, is seeing a rat spike this year, and so is New York City. In Chicago, rodent complaints for the early part of the summer have increased about 9 percent from last year, forcing city officials to start sprinkling the streets with rat birth control. Philadelphia and Boston were recently ranked the two cities with the most rat sightings in the country. And it’s not just this year; as USA Today reported last year, major cities saw spikes in rodent-related business from 2013 to 2015. Calls to Orkin, the pest control service, were reportedly ‘up 61 percent in Chicago; 67 percent in Boston; 174 percent in San Francisco; 129 percent in New York City; and 57 percent in Washington, D.C.'”

Those figures are something, aren’t they? Well, we can apparently expect more of the same for the foreseeable future.

Corrigan continues: “Breeding usually slows down during the winter months.” With warming winters, however, the rate of breeding and population expansion surges. “They have an edge of squeezing out one more litter, one more half litter,” Corrigan explained.

The New Republic coverage continues: “One more litter or half litter makes a serious difference when a population boom is not only a nuisance, but a public health and economic crisis. Rats breed like rabbits; as this alarming Rentokil graphic shows, two rats in an ideal environment can turn into 482 million rats over a period of three years. Urban rats caused $19 billion worth of economic damage in the year 2000, partially due to the fact that they eat away at buildings and other infrastructure. Imagine how much they’re costing now.”

So, even not considering the fact that rats are carriers for all sorts of diseases that are dangerous to humans, there’s also the direct impact on infrastructure, which, as revealed above, is shockingly substantial.

So, why isn’t more being done to deal with urban rats? Because it isn’t particularly cost effective to do so. Even New York City’s $32 million program hasn’t and isn’t expected to curtail population growth for more than a few years.

Corrigan noted: “Rats are very incredible, wildly intelligent mammals, and human beings keep going around trying to exterminate (them) as if it’s the opposite. These cities are up against one of the most incredible mammals on the planet, which only stand to increase in number.”


That reminds me of what I read about a relatively recent attempt to reduce urban coyote populations in the Chicago area: even after dropping millions of dollars on the project, and being fairly aggressive in the use of dangerous poisons, the impact on coyote numbers wasn’t substantial. The population was expected to recover completely within only a few years. So, several million dollars down the drain in other words.

The reality seems to be that some animals (those in a position to do so) have become adapted enough to urban environments that doing away with them would be either cost prohibitive or completely impossible. There are some urban regions in the US where this certainly seems to be the case as regards rats, coyotes, and perhaps crows as well. Many insect pests are, of course, in a similar situation.

With antibiotic resistance a looming issue, it seems likely that diseases that have become much less common in the developed world over the last century will be making a comeback, partly on the backs of surging populations of organisms that have become well adapted to human-created urban environments.

Something to keep in mind as you continue watching temperature records being broken — every year for the rest of your life.

Top photo by Edal Anton Lefterov (some rights reserved)

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James Ayre

James Ayre's background is predominantly in geopolitics and history, but he has an obsessive interest in pretty much everything. After an early life spent in the Imperial Free City of Dortmund, James followed the river Ruhr to Cofbuokheim, where he attended the University of Astnide. And where he also briefly considered entering the coal mining business. He currently writes for a living, on a broad variety of subjects, ranging from science, to politics, to military history, to renewable energy.

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