Rats added to list of bad things that climate change is making worse 

More rats: that’s the latest indignity that climate change is dumping on major cities around the world, including in Canada’s largest city, according to a new study from a group of global rodent and public health scientists.Growing rat populations are correlated with rising temperatures driven by global warming in at least 11 major cities across the world, according to the study. The cities seeing rat increases include Toronto, famously rat-prone New York City, and many other major centres like Washington, San Francisco and Amsterdam.The study’s authors say it’s a wake-up call for cities to move away from a whack-a-mole approach to dealing with rodent complaints.”I think every large city should have a dedicated team that focuses on nothing but rodents and the issues with rodents,” said Jonathan Richardson, lead author of the study and an urban ecologist at the University of Richmond in Virginia. A rat in downtown Toronto. The city is working on a rat strategy. (Bruce Reeve/CBC)The study used data on public complaints and inspections about rats from 16 cities around the world. The 11 cities that saw significant increases in rats also experienced greater temperature increases over time, though that correlation doesn’t prove the temperature caused the increase. Cities with more dense human populations and more urbanization also saw larger increases in rats.The research comes at a time when rats have become a big issue in Toronto, which is seeing a large increase in rodent-related complaints after a brief decline during the COVID-19 pandemic. City officials are currently working on a new strategy to proactively deal with the rats.”Even when you leave city hall or walk around city hall, you can see the burrows in the tree wells. I’ve walked along one of the streets and a giant rat ran past me in the middle of the day,” said Alejandra Bravo, a Toronto city councillor who proposed the successful motion to build a rat strategy. “I think people need to see action.”Why are rats thriving?Rats are resilient and remarkably adaptable to different environments, says Alice Sinia, entomologist with pest control company Orkin Canada. It makes biological sense that warmer temperatures would be helping them out, for three big reasons.The harsh winter acts as a sort of “nature’s pest control,” with the cold killing rats every year. Climate change has led to milder winters in Toronto, allowing greater numbers of rats to make it through the season.Urban ecologist Jonathan Richardson, right, has co-authored a study linking climate change to a growth in rat populations in several major cities, including Toronto. (Jamie Betts)Meanwhile, the warmer seasons have become longer, and that’s when the rats breed and reproduce. Sinia says that could further boost their numbers.And finally, climate disasters themselves could be bringing rats closer to people and buildings. Sinia used the example of the floods in Toronto in July last year, caused by a line of storms that dumped r