People around the world are now living longer, healthier lives than they were just half a century ago, but climate change threatens to undo that.
All over the planet, animals—and the diseases they carry—are changing to adapt to an altered planet. And they are not alone: ticks, mosquitoes, bacteria, algae, and even fungi are changing or expanding their historical ranges to adapt to climate conditions that are evolving at an unprecedented rate.
These changes do not occur in a vacuum. Deforestation, mining, agriculture and urban sprawl are wiping out the world’s remaining wilderness, contributing to a loss of biodiversity that is occurring at a rate not seen in human history.
Populations of species on which humans depend for their livelihoods are dwindling and pushed into ever smaller tracts of habitat, creating new pockets of zoonoses: a disease or infection that occurs in animals and is transmissible to people under natural conditions.
At the same time, the number of people experiencing the extreme repercussions of a warming planet is increasing. Climate change displaces an estimated 20 million people each year, people in need of housing, health care, food and other essentials putting pressure on already fragile systems that are under increasing strain.
All of these factors create conditions conducive to human disease. The old evils and the new ones are becoming more prevalent and even appearing in places where they have never been found before. Researchers have begun to piece together a mosaic of evidence that shows the enormous threat that climate change-induced diseases pose to human health today and the scope of the dangers to come.
“This is not just something in the future,” says Neil Vora, a doctor at Conservation International (Conservation International, a nonprofit organization). “Climate change is here. People are suffering and dying right now.”
Research shows that climate change influences the spread of disease in several important ways.
To escape rising temperatures in their native ranges, animals are already beginning to move to higher and cooler areas, bringing diseases with them. This poses a threat to the people living in those areas and also leads to a dangerous mix between newly arrived animals and existing species. Bird flu, for example, is spreading more easily among wildlife as rising sea levels and other factors push shore-nesting bird species inland, where they are more likely to encounter others. species. Sooner or later, diseases that jump between species tend to have an easier time making the jump to humans.
Warmer winters and milder fall and spring allow carriers of pathogens—ticks, mosquitoes, and fleas, for example—to remain active longer throughout the year. Extended active periods mean extended mating seasons and less active during the cold winter months. Over the past decade, the northeastern United States has seen a massive proliferation of black-legged ticks, carriers of Lyme disease, and warmer winters have been instrumental in that trend.
Erratic weather patterns, such as periods of extreme drought and flooding, create conditions for certain diseases to spread. Cholera, a waterborne bacterium, thrives during the monsoon season in South Asian countries when flooding contaminates drinking water, especially in places lacking quality sanitation infrastructure.
Valley fever, a fungal-borne pathogen that grows in the soil of the western United States, flourishes during periods of rain. The severe drought that tends to follow rain in that part of the world withers the spores of the fungus, allowing them to disperse more easily into the air at the slightest disturbance—such as a hiker’s boot or a rake in a garden—and find their home. way into the human respiratory system.
These climate-induced impacts are taking a heavy toll on human health. Cases of illnesses related to mosquitoes, ticks and fleas tripled in the United States between 2004 and 2016, according to the Centers for Disease Control and Prevention (CDC). The threat extends beyond commonly recognized vector-borne diseases. Research shows that more than half of all pathogens known to cause disease in humans may worsen with climate change.
The problem worsens as time goes by. The World Health Organization estimates that between 2030 and 2050, just a handful of climate-related threats, such as malaria and water insecurity, will claim an additional quarter of a million lives each year.
“I think we have drastically underestimated not only how much climate change is already changing disease risks, but also how many types of risks are changing,” says Colin Carlson, a global change biologist at Georgetown University.
He points out that while connecting the dots between tick-borne diseases and climate change, for example, is a relatively straightforward scientific job, the scientific community and the public should be aware that global warming impacts on disease as well. they can manifest in many other ways that are less obvious. The COVID-19 pandemic is an example of how quickly a disease can spread across the globe and how profoundly complicated the public health response to such threats can be.
“I think there is a lot more to worry about in terms of threats from pandemics and pandemics,” he adds.
The world has the tools it needs—wildlife surveillance networks, vaccinations, early warning systems—to mitigate the impacts of climate-induced diseases. Some of these tools have already been implemented locally with great effectiveness. What remains to be seen is how quickly governments, non-governmental organizations, healthcare providers, doctors and citizens can work across borders to develop and implement a global action plan.
EDITOR’S NOTE: This report is part of a collaboration between The Associated Press and Grist to explore the intersection of climate change and infectious disease.
The Associated Press’s climate and environmental coverage is supported by several private foundations. The AP is solely responsible for all content.