If Torride waves,, destructive storms,, prolonged droughts And Growing seas are not enough to fear some people fear the consequences of climate changePerhaps it will do the trick: the more he warms, the more the rats multiply in the cities which already find it difficult to contain them.
It is certainly unwanted news for the Americans, who endure collectively More than $ 27 billion Vals of material damage each year in the hands – and teeth – rats. This does not include the cost of diseases that animals distribute, as Hantavirus,, typhus murin And bubonic plaguenor the mental health toll to live among them.
THE New discoveriesReported Friday in the journal Science Advances, are based on recordings of rats observations in 16 cities around the world. Unfortunately for humans, 11 of these cities saw their rat populations develop during the study, while two cities were stable and only three reached measurable decreases.
The fact that rodents thrive should not surprise. They are perfectly suited to urban environments, where they make their house in the walls, basements and metro stations and feast on garbage, wastewater, pooh And Abandoned pizza slices. The only continent they have not yet conquered is Antarctic.
A rat feeding in a garbage dumpster in Richmond, Virginia.
(Jonathan Richardson)
“This species is really well suited to gain food and convert the one into new rats for babies that slip into your neighborhood,” said Jonathan RichardsonBiologist at the University of Richmond in Virginia who studies fauna in cities and their impact on human health. “They really do it effectively.”
One of the few things that slows down rats is cold. And with climate change, we have less.
Causes of global warming Average temperatures to increasewhich reduces the number of winter days. In cities, the trend is aggravated by the fact that the built environment absorbs and retains more heat than the rural area that surrounds it, a phenomenon known as urban Heat island effect.
To investigate a possible link between rats populations and the increase in temperatures, Richardson and his colleagues have looked for reliable data in the 200 most populated cities in the country. The realization of an in -depth census of rats was not practical – if not impossible – they therefore used municipal inspection newspapers and observations of rats reported to government agencies.
They found 13 cities which had kept coherent registers for at least seven years. Then they extended their research and found three other cities abroad. The final group had rats data which dates back to an average of just over 12 years.
Since cities have used different data sources collected over different periods, researchers have found a standardized way to measure change in rats observations. They found that rats reports increased the most in Washington, DCFollowed by San Francisco, Toronto, New York, Amsterdam, Oakland, Buffalo, Chicago, Boston, Kansas City and Cincinnati.
Three cities – New Orleans, Louisville and Tokyo – have managed to reduce their rats populations during the study period. There was no significant change in Dallas or Saint-Louis.
Los Angeles was not included in the analysis because the systematic rats recordings were not available. Regularly ranks among the first three in the annual lists of antiparasitic control companies America's “most rant cities”, “ But Richardson said that the eternally significant volume of rodent complaints had more to do with the sprawling size of the city than an environment only suitable for rats.
Then, the researchers used statistical methods to see which factors could explain the differences in the control results of the rats of cities. About two -thirds of the variation could be explained by five things, including the human population density and the amount of area covered with vegetation.
The largest factor was the change in the average temperature of a city – the more it increased, the more the rats population grew up.
A rat crosses a metro platform in New York Times Square.
(Richard Drew / Associated Press)
The change in the minimum temperature of a city had no impact on rats. Richardson said that the team was initially surprised by this, since the cold extends the time for female rats to become fertile and reduces the number of puppies in a litter.
In more hospitable weather, a rat can become pregnant when it has only 2 months, and this pregnancy will only last from three to five weeks. The researchers realized that if the increase in average temperatures caused the arrival of winter conditions a week or two later and end a week or two earlier, it could buy a rat enough time to sneak in an additional reproduction cycle, said Richardson.
Santtu PentikainenA researcher from the University of Helsinki who was not involved in the work, said that the study authors argued that global warming is good for rats.
“The results simply make sense,” said Pentikainen, a member of the Helsinki Urban Rat project.
Co -author Maureen Murrayecologist of fauna disease at the Lincoln Park zoo in Chicago and chief of the Chicago Rat Projectsaid that she hoped that the results “will motivate people to care that climate change could exacerbate their rat problems.”
But Richardson said he was not sure that the prospect of “more rats rushing” will be more galvanizing than the photos of “the Sad polar bear floating on ice. »»
