In the mountain forests of Hawaii, native honeycreepers—small songbirds found nowhere else in the world—are dying. Of the roughly 50 species that once existed, the majority are extinct and most of the remaining are endangered.
The dwindling honeycreeper population is a ripple effect of climate change: Warmer temperatures allow mosquitos to invade places that were once too frigid for them to face. In Hawaii, mosquitos carrying avian malaria are flying upslope into land where honeycreepers hunt for nectar. In some species, the bite from an infected mosquito is fatal up to 90 percent of the time.
On the other side of the globe, a similar story is taking place—not in another bird population, but in communities in the east African highlands, where malaria-carrying mosquitos are infecting people who have never been exposed to it before.
"This is a really bad situation, actually, because malaria is most problematic, most likely to kill people and especially little kids, when there's no immunity in a population," says Richard Ostfeld, a disease ecologist and senior scientist at the Cary Institute of Ecosystem Studies.
As heterotherms, mosquitos—and ticks, for that matter—gravitate toward warm-weather areas since their bodies adopt the temperature of the outside air. As temps rise worldwide, the biting bugs are surviving and thriving in more places than ever before: Scientists have found climate-induced increases in infections from blacklegged ticks carrying Lyme disease and mosquitos carrying malaria, dengue fever, and Zika.
It's one of the many ways global warming is transforming our health. (Not to mention that by 2100, scientists expect we'll experience up to 74 percent more deadly heat waves and 14 nights per month of restless sleep.) Last year was the hottest on record since modern tracking began, according to the National Air and Space Association, and climatologists anticipate that trend will continue if we keep burning fossil fuels at the rate we are today.
"There is considerable risk of increases in a number of vector-borne diseases as the climate continues to warm, but it will not be uniform across the globe or across all diseases," Ostfeld says. For people in developing countries with less protection, the risk is much greater.
The longer growing seasons and milder winters that come with climate change are moving these vectors into higher elevations as well as into colder regions, like the northeastern United States, where long, freezing winters used to keep them out.
But it goes beyond geographic expansion. As temperatures continue creeping up, mosquitos won't just invade more places—they'll also eat (read: bite) more often. That's because they don't regulate their own body temperatures, so their metabolic rates speed up as temps heat up. With faster metabolisms, the mosquitos get hungry more often, they eat more, and they fly faster to find their next host and bite again.
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It's bad enough that in warmer weather, hungrier mosquitos zip around and nip at us. But the world will also become wetter, with extreme and variable rainfall like droughts and floods. That's certainly true for most of the eastern United States, Ostfeld says.
And since mosquitos lay their eggs in standing water, floods create the perfect baby-making conditions. A flood followed by a drought is even better, because then the bags of larvae have time to develop before getting flushed out by the next rainfall. That means more mosquitos will hatch. More mosquitos in more places that bite more often? That doesn't bode well for us.
"It's really insidious, this climate change-induced expansion of things like malaria into places they didn't occur before," Ostfeld says. "It takes an enormous toll on human health and wellbeing, it causes massive suffering, and it's something to be taken very seriously."
The bites from these little buggers will become dangerous more often as we continue burning fossil fuels and pumping more carbon dioxide into the atmosphere than we can handle. But there's another place where pathogens will fester: our drinking water.
Jonathan Patz, director of the Global Health Institute at the University of Wisconsin-Madison, stresses that waterborne diseases like gastroenteritis, pediatric diarrheal disease, and cholera are highly susceptible to changes in climate. Patz analyzed 46 years of data and found that 68 percent of waterborne disease outbreaks were preceded by heavy rainfall.
This is especially concerning in developing countries that lack the necessary infrastructure to protect water from contamination. But even in the United States, more than 700 communities combine storm-water runoff and sewage, Patz says. That ups the risk of combined sewage overflow events, when sewage seeps into reservoirs of clean water.
In fact, his own research shows that extreme rainfall brought on by climate change could double the number of combined sewage overflow events in Lake Michigan, Chicago's primary source of drinking water, by 2050. "Our infrastructure is failing," Patz says. "[Climate change] puts more stress on the system…so it will worsen the issue and at the same time, it makes it that much more urgent to make these changes to protect the water systems."
We have layers of protection against disease: window screens to keep bugs out, repellents to turn them away, filters to clean our water, and the funds to pay for emergency response to outbreaks. But our protections shouldn't downplay the risks to others. "It would be unfortunate if we were so focused on the developed world that we didn't focus on how much climate warming makes disease worse in the developing world," Ostfeld says. Plus, higher temperatures make localized outbreaks at home more likely and more difficult to contain.
It's important to not only think about the problem on a global scale, but to also consider what's causing the growing disease risk in the first place. "Health and disease preparedness goes far beyond the health sector," Patz says. "We want to get to the root of the problem, tackle the issue of climate change, and reduce our consumption of fossil fuels so we're not continuing to mop up the mess when we don't even attempt to turn off the faucet."
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