how climate – Extreme heat and wildfire smoke are no longer just seasonal annoyances. From cardiovascular strain to brain effects, pregnancy risks, mold at home, and kidney damage that can last for years, rising greenhouse gas emissions are pushing public health threats int
On a hot night, your body doesn’t get to recover.
Doctors and researchers have long warned that extreme heat is dangerous in the moment—when the body’s cooling system can’t keep up and core temperature rises above 103 degrees F. heatstroke can follow. along with heart failure. But the damage doesn’t stop when the sun goes down. Studies show that hot nights are even more damaging than daytime heat because they rob people of the window needed to bounce back from the heat they experienced during the day.
A warming world is putting pressure on every system in your body. and experts say the risks are widening as heat. wildfire smoke. infectious diseases. and other climate-amplified threats compound. As temperatures rise. leading medical journals warn that rising greenhouse gas emissions will result in millions of needless deaths and undermine decades of hard-won public health progress.
Some of the harms are recognizable—especially for people already immunocompromised or in poor health. Heat-related mortality has been rising since the 1990s. and wildfire smoke is linked to tens of thousands of illnesses and deaths every year. Yet researchers are now uncovering how repeat. overlapping climate stressors can leave lasting marks even on the society’s healthiest members. No one is immune.
The U.S. is seeing just one piece of a broader global shift. Extreme heat is linked to between 600 and 700 extra deaths from cardiovascular disease in the United States every year. And these effects land hardest on people who work outside and are socioeconomically disadvantaged—generally those who spend more time on average exposed to the elements—though recurring heat waves pose risk to anyone who experiences them.
Extreme heat works its way into the body through basic physiology. It widens blood vessels. flushes fluid out of the bloodstream. and forces the heart to pump two to four times as much blood per minute to cool the body. The result is dehydration, which thickens the blood and makes it harder to pump. Over time, continued exposure to heat waves across many seasons can contribute to long-term cardiovascular disease and related deaths.
In China, researchers estimated that hot nights accounted for roughly three times as many heat-related outpatient visits for cardiovascular disease. And a modeling study of countries in East Asia found that if greenhouse gas emissions continue along their current trajectory. hot nights alone could account for nearly 6 percent of all deaths in Japan. South Korea. and China by the end of this century.
Even when the immediate trigger isn’t a thermometer reading, the trail can still lead back to heat and the atmosphere it reshapes.
Wildfire smoke is one of the clearest examples. Nearly half of the world’s population now lives in the wildland-urban interface. where fire-prone wild spaces meet or intermingle with towns and cities. In the U.S., the number of people living in these areas roughly doubled between 1990 and 2010. As the atmosphere grows “thirstier” in response to rising temperatures—sucking up moisture and contributing to deep droughts—dry landscapes ignite. More people then inhale air polluted by wildfire smoke.
The lungs and blood are not passive bystanders. Studies show that the ultrafine particulate matter produced by the trees and shrubs incinerated by wildfires penetrates deep into the lungs and infiltrates the bloodstream. It triggers inflammation and reduced lung function, worsening asthma and other chronic respiratory conditions.
When wildfires burn through cities. the mixture can be more unpredictable and potentially more toxic. including volatile organic compounds. microplastics. and other pollutants. Recent research also suggests wildfire smoke can make rashes such as eczema and psoriasis worse by triggering inflammation and drying out the skin.
Smoke isn’t the only respiratory irritant accelerating alongside climate change. Extreme heat interacts with sunlight. nitrogen. and volatile organic compounds and speeds the formation of ground-level ozone. which inflames the lungs. Earlier springs mean allergy season is getting longer and more intense in many parts of the world.
And the climate story doesn’t end outdoors. More humidity and intensifying extreme weather events can create new footholds for black mold indoors, bringing climate-driven health crises into homes.
From the air to the brain, the boundaries blur.
Researchers are finding that wildfire smoke can reach beyond the respiratory system and into the brain. Exposure to particulate matter appears to contribute to neuroinflammation and processes linked to cognitive decline, dementia, and stroke.
Some of the most unsettling findings involve early life. Recent studies indicate that babies exposed to wildfire smoke in utero may have a higher risk of developing autism in childhood, though this area of research is still in the early stages.
Extreme heat, too, changes how the brain functions. Studies show that students score lower on exams. Indoor and outdoor workers make more mistakes that lead to injury. The elderly experience more confusion in higher temperatures.
These effects are especially dangerous because they’re harder to spot until after the damage accumulates. But heat also produces signals that are more visible. An assessment of violent crimes in more than 400 U.S. counties found that for every 18-degree F deviation above normal daily temperatures, the rate of violent crime rose roughly 10 percent.
Other work links hotter days to higher rates of psychiatric emergency visits, suicide, and worsening symptoms among people with severe mental illnesses such as schizophrenia.
Pregnancy is another front where climate stress shows up in the body’s most vulnerable window.
Heat exposure during pregnancy increases the risk of preterm birth by as much as 26 percent, even as researchers continue investigating the exact biological mechanism. Heat also exacerbates underlying maternal health conditions such as hypertension and cardiovascular stress.
Extreme heat affects male fertility as well: high ambient temperatures negatively impact sperm quality, volume, and movement.
Pregnancy already opens the door to more severe illnesses, and climate change raises the risks further. For example. pregnant women are three times more likely to develop severe malaria compared to nonpregnant women. linked to an immune system that partially suppresses itself to avoid rejecting the fetus during pregnancy.
Hotter temperatures and more extensive flooding are shifting the ranges of disease-carrying mosquitoes, exposing more pregnant people to malaria. In coastal regions with patchy water infrastructure. rising seas contaminate low-lying freshwater resources with salt and contribute to hypertension in pregnant women. raising the risks of preeclampsia. premature birth. and miscarriage.
Even the gut is caught in the squeeze between climate-altered ecosystems and everyday exposure.
The gastrointestinal system is especially sensitive to how climate change is reshaping water, food, and pathogenic organisms. Warmer temperatures allow many disease-causing bacteria to multiply more quickly in food and coastal waters. increasing the risk of foodborne illness. Heavier rainfall and flooding can overwhelm sanitation systems, spreading pathogens that cause diarrheal disease and contaminating drinking water supplies.
In coastal regions, warming seas are enabling marine bacteria such as Vibrio vulnificus—commonly referred to as “flesh-eating bacteria”—to thrive in places they were once rare. That raises the odds that raw shellfish, or even contact with brackish water, can lead to severe infections.
And when extreme drought or floods destroy crops and lead to food shortages, the consequences reach the gut through malnutrition. Malnutrition weakens immune defenses and leaves children especially vulnerable to intestinal infections that can stunt growth and long-term health.
Across systems, one theme keeps surfacing: some harms arrive as sudden emergencies, while others build over years.
The kidneys may be among the clearest examples of chronic damage driven by heat. Climate-driven health threats are often associated with short-term impacts like disease outbreaks and injuries due to flooding or dangerous winds. But the effect of extreme heat on the kidneys tells a different story of impacts spanning years.
Extended dehydration and heat stress injure these organs over time, triggering acute kidney damage that can progress into chronic kidney disease.
Doctors are documenting unusual patterns among agricultural workers in some of the hottest parts of the world—kidney disease affecting people with no typical risk factors like diabetes or hypertension. Chronic kidney disease isn’t limited to agricultural workers. In Nepal. migrant construction workers returning home from months or years of hard outdoor labor in the United Arab Emirates and other extremely hot Gulf countries are bringing chronic kidney conditions back with them.
What connects these stories—heart strain. inflamed lungs. neurological disruption. pregnancy complications. gut infections. and kidney injury—is not a single event. It’s the way climate stressors overlap. Hot nights don’t just add discomfort; they undercut recovery. Wildfire seasons don’t just fill the sky; they deliver particles deep into lungs and into the brain. Flooded water doesn’t only break sanitation; it carries pathogens indoors. And heat doesn’t only threaten you today; it can set the stage for disease later.
Zoya Teirstein’s reporting for Grist’s Vital Signs series. made possible with support from the Wellcome Trust. lays out what doctors already agree on: climate change is a hazard to health. and the stakes are escalating. Heat and smoke can be lethal in the short term. but the longer-term picture—chronic injury across vital systems—explains why experts warn that rising greenhouse gas emissions threaten decades of public health gains.
This is what a warming world looks like from inside the body: pressure, inflammation, dehydration, disrupted development, and injuries that can travel forward through time.
climate change extreme heat wildfire smoke cardiovascular health respiratory health neuroinflammation pregnancy preterm birth malaria ozone black mold kidney disease public health