Summer may officially be over, but mosquito season is showing no signs of subsiding. If you curse the influx of winged naggers, you’re saving some vitriol for climate change, which definitely played a role in exacerbating mosquito ddon this year.

It was an unusually warm summer – the hottest summer ever for the adjacent United States – and that helped the mosquitoes thrive. However, experts say the main reasons for the mosquito population explosion this year are the season’s record storms and above-average rainfall in many states.

Parts of the northeast saw half a meter of rain in just three weeks in July due to a series of consecutive thunderstorms and the remnants of Hurricane Elsa. In August, Tropical Storm Fred and his remains flooded the east coast from Florida to Massachusetts, and Tropical Storm Henri hit New England head-on. Less than two weeks later, Ida soaked the Gulf Coast as Category 4 and blasted the northeast with record-breaking rainfall as a disorganized storm system. In the southwest, a “super” monsoon season has eased drought conditions in parts of Arizona, making July the wettest month on record in Tuscon.

Climate change plays a role in exacerbating these storms. The air becomes 4 percent saturated with water for every 1 degree Fahrenheit the planet warms up. According to the latest National Climate Assessment, the torrential rains in the northeast now trigger 55 percent more rain compared to the 1950s and could increase by a further 40 percent by the end of the century.

Unfortunately for humans, the amount of mosquitoes varies massively with rainfall. The more rain there is, the more pools of water there are in the landscape in which the insects can lay their eggs. This summer’s rains basically made half of the United States the perfect breeding ground for mosquito larvae.

“The mosquito is the state bird of New Jersey,” Andrew Dobson, professor of ecology and evolutionary biology at Princeton University, told Grist. “But this year seems a lot worse than normal.”

It’s too early to say how exactly this year compares to previous years in terms of mosquito populations. But the mosquito surge has so far been measured by experts and officials in several states.

“This is actually one of the worst mosquito seasons in recent history with a record number of insects plaguing communities across New York,” said Senator Chuck Schumer, a Democrat from New York, at a news conference over the weekend. He called on federal authorities to provide New York with funds to fend off the invasion. In Lucerne County, Pennsylvania, officials told a local news channel that more mosquitoes brought to their county in 2021 than they have seen in the past decade. In New Orleans, city officials reported more mosquitoes than usual, and the nearby St. Tammany community reported a 300 percent increase in two types of mosquitoes. Steven Oscherwitz, an infectious disease specialist in Arizona, told Grist that he had seen an increase in mosquitoes in the southwest due to the extremely heavy monsoon season. Even southern California sees more mosquitoes than usual, not because of rain, but because of heat and humidity.

Some of these mosquitoes are more than just a nuisance. The mosquito genus Culex carries West Nile virus, a disease in the yellow fever family that causes no symptoms in most people but causes serious illness – including high fever, headache, tremors, paralysis, and even death – in the elderly and immunocompromised. Several state health officials have warned of the West Nile virus in the past few weeks. Arizona, Arkansas, California, Idaho, New Jersey, and Texas have each reported one or two deaths related to the disease to date, and many more states have recorded human cases from the West Nile.

The West Nile virus is relatively new in the United States as far as vector-borne diseases are concerned. The first cases were reported about 20 years ago. The disease has no cure and there is no vaccine to prevent infection. But Princeton-based Dobson said that many Americans are unknowingly immune to the West Nile from exposure to bites from mosquitoes that carried the virus for several summers in a row. However, the COVID-19 pandemic may have contributed to decreased immunity this year, Dobson suggested, as people were stuck indoors last summer and weren’t bitten as often, leading to a decrease in the number of people fighting the virus got immune last year. “You could expect more West Nile cases to occur because people have isolated themselves because of COVID,” Dobson said.

Climate change has helped mosquitoes, which carry West Nile and other diseases such as malaria and dengue, penetrate new and higher areas, where warmer temperatures help insects survive and bite people. And higher temperatures can also affect the amount of virus the mosquitoes carry, Oscherwitz said. “When it’s really hot, the West Nile virus can multiply more in them, so they each carry a higher load of this virus than if we had cooler weather,” he said.

Experts in general are concerned about the effects of climate change on vector-borne diseases. “We need to think a lot more about planet change and what we’re going to do to stop it,” said Dobson. “Otherwise we will have more floods, more diseases.”


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