Many of the effects of climate change play out at a very large scale: Heatwaves that grip entire continents. Flooding that submerges vast swaths of island nations and continental coastal areas. Other effects are far less visible because they’re taking place inside people’s bodies.
That doesn’t make them any less dangerous.
Diseases linked to problems in immune health have been steadily rising over the past few decades. Nasal allergies in children more than doubled from 2012 to 2022. Food allergies, which can be deadly, have also spiked. The global prevalence of rheumatoid arthritis has jumped 14% since 1990. Young people are increasingly vulnerable to colorectal cancer.
To be sure, climate change isn’t the only culprit here: diets heavy in ultra-processed foods, lack of exercise, high levels of stress, and improved testing all likely contribute to rising disease rates. Yet there is also strong evidence, at both the biological and the epidemiological levels, that the environment plays a crucial role in the rise of immune-mediated diseases. As I and a group of colleagues from the U.S. and Europe just reported in Frontiers in Science, climate-driven stressors are driving immune dysregulation at a scope that has contributed to an increase in immune-mediated diseases.
As a physician and a scientist, I believe this epidemic of immune disease must be treated at its source. And that includes tackling climate change.
Climate change derails the human immune system in two keys ways: it breaks down the body’s defenses and also prevents the body from rebuilding them.
Consider the wide array of irritants that climate change routinely brings into communities all around the world. Wildfires release dangerous quantities of tiny soot particles into the air. Flooding dumps industrial chemicals into waterways, and often leaves mold spores sprouting in homes. Unusually warm springs boost the production of ragweed and other pollens. All these exposures damage the structures that have evolved to protect humans from infection, including the skin and the mucous membranes of the gut and lungs.
How does climate change make it harder to build strong immune systems in the first place? Humans need nutritious diets and exposure to a vast array of microbial, fungal, plant, and animal species to train and sustain a robust immune system. All of that is under threat with climate change. Warmer climates irrevocably alter ecosystems, forcing species to move or become extinct. For the humans left behind, fewer interactions with diverse species means a less resilient immune system.
Extreme weather has also destroyed crops and livestock in many parts of the world, leading to an alarming rise in hunger and famine. Even when crops do grow, they may not be as nutritious: food staples such as wheat, corn, rice, and soy lose significant nutrient content when exposed to high levels of carbon dioxide in the atmosphere. Malnourishment also prevents healthy immune system development.
The impact of all these stressors is visible at the cellular level. Scientists have traced the impact of many exposures through cascades of chemical interactions that damage the body’s protective barriers and disrupt the delicate balance of the immune system. In many cases, this actually activates the body’s inflammatory response, and leaves it on, even when it should be turned off. Such persistent inflammation fuels an array of diseases, including cancer.
Scientists understand why more and more of the world’s people are experiencing higher rates of immune-mediated diseases. The question now is whether anything can be done about it.
Fortunately, the answer is an unequivocal yes.
In our paper in Frontiers in Science, my colleagues and I reviewed the global rise in immune-mediated diseases. We concluded that every $1 spent on mitigating climate change would save at least $3 in health care costs. That’s an impressive return on investment — and it doesn’t even account for the reduction in human suffering.
These improvements aren’t hypothetical; where policies have changed, health benefits have followed. In the 1980s and 1990s, for instance, efforts to tackle air pollution in the U.S. led to a dramatic decrease in fine particulate soot in Southern California and cut the incidence of asthma among local children by 20%. In Seoul, South Korea, clean air policies prevented half a million hospital visits for asthma over the course of four years.
There is now an urgent need to implement such policies at a global scale.
My colleagues and I call for a renewed focus on balancing human needs with ecosystem needs to protect the health of both our planet and its people. We urge rapid global action to cut greenhouse gas emissions from activities including agriculture, waste management, and transportation.
Addressing immune health problems on a global scale will also require major investment in food security and sustainable agriculture, in a bid to improve every community’s access to nourishing foods. Policymakers can promote their citizens’ exposure to a broad array of plant and animal life — which also fosters strong immune systems — by creating and protecting more green spaces and encouraging access to wilder ecosystems such as national parks.
Even housing policy can be brought to bear on this crisis: funds to help people strengthen their homes against the ravages of extreme weather, remove mold, and improve indoor air quality can all help reduce exposures to immune irritants.
In addition to bold policy changes, the U.S. and other governments must fund more research focused on understanding immune health problems in the context of climate change. This will require global investments in data collection and analysis, as well as concerted efforts to evaluate the impact of mitigation and adaptation strategies on population health. New economic models to better account for the health benefits of policies designed to reduce greenhouse gas emissions are needed. These should help make the case for those policies even stronger.
Above all, it is essential for scientists, clinicians, journalists, politicians — anyone with a platform, really — to keep explaining to the public that climate change has very real effects on the human body. These aren’t spread evenly across the globe; some communities and regions are more vulnerable than others. We must work together to combat this shared threat.
The destructive force of climate change is already showing up in an epidemic of immune health problems. Only by acting now can the worst damage be prevented.
Kari Nadeau, M.D., Ph.D., is the John Rock Professor of Climate and Population Studies at the Harvard T.H. Chan School of Public Health.