"Rat Storm" Sweeps 11 Cities Around the World At a cost of $500 million a year.

A recent study revealed that there is a sharp increase in the number of rats in 11 out of 16 cities, and this is expected to continue with the increase in temperatures that encourage reproduction.

The study included data from 16 cities around the world, and Washington DC, San Francisco, Toronto, New York, and Amsterdam recorded the largest increase in the number of these rodents, according to the British newspaper "The Guardian".

The research paper, published in the journal "Science Advances", confirmed that 11 cities showed significantly increasing trends in the number of rats, and reproduction is likely to continue at a terrifying rate.

The number of rats increased by 390% in Washington DC, 300% in San Francisco, 186% in Toronto, and 162% in New York, according to researchers who analyzed public reports on the spread of rats.

The study did not include major cities such as London and Paris because they did not provide the necessary data, but the researchers said the findings would be applicable to many similar cities around the world.

"There is no reason to expect that it would be different elsewhere," said lead researcher Jonathan Richardson of the University of Richmond in Virginia.

Toronto is one of the places most affected, facing a perfect storm of rats, with rats outnumbering people.

Climate change

Other cities that have seen rat population increases include Oakland, Buffalo, Chicago, Boston, Kansas City and Cincinnati, as well as Amsterdam, Toronto and Tokyo, where similar data showed a jump in rat populations.

The researchers wrote in their study that rising temperatures correspond to an increase in rat populations.

Rats, small mammals, struggle in winter, but at higher temperatures they can reproduce for longer periods of the year and feed for longer periods.

Last year was the hottest on record, with temperatures averaging 1.6 degrees Celsius above pre-industrial levels. Rats cause billions of dollars in damage each year by burrowing into buildings, and can transmit 60 diseases to humans. Rat control costs an estimated $500 million a year, according to the study.