Climate Change and Human Health: An Urgent and Evolving Threat

By Aparna Mele, MD

Climate change is no longer a distant concern—it’s a present and escalating crisis with profound implications for human health. Climate change makes many existing diseases and conditions worse, and it helps pests and pathogens spread into new regions. The most vulnerable people—children, the elderly, the poor, and those with health conditions—are at increased risk for climate-related health effects.  From intensifying heatwaves to shifting disease patterns, the interplay between a warming planet and our well-being is complex and alarming and there is an urgent and desperate need for adaptation and mitigation strategies.

Heatwaves and Rising Temperatures

One of the most immediate health risks posed by climate change is heat-related illness and death. As global temperatures rise, heatwaves have become more frequent, intense, and prolonged, and consequently, there have been and will continue to be more heat-related illness and deaths in both urban and rural areas.  These conditions strain hospital resources and lead to a spike in emergency visits. Urban environments are especially susceptible to the “urban heat island” effect, where concrete and asphalt absorb and re-radiate heat, making cities significantly hotter than surrounding areas.

 Health Consequences of Extreme Heat:

• Heat exhaustion and heatstroke can be fatal, especially among elderly populations, children, and those with chronic conditions.
• Dehydration and kidney stress increase as people lose fluids rapidly in extreme temperatures.
• Cardiovascular and respiratory stress worsens in hot conditions, especially in people with pre-existing conditions.

Infectious Diseases

Climate change alters the habitats of disease-carrying organisms like mosquitoes, ticks, and rodents—bringing infectious threats to new regions and populations.

Vector-Borne Diseases are on the rise! For example,

• Malaria and dengue fever are spreading to higher altitudes and latitudes as temperatures warm.
• Lyme disease, transmitted by ticks, is expanding in North America and Europe due to milder winters and earlier springs.
• Waterborne illnesses such as cholera may surge due to flooding and contamination of drinking water sources.

The frequency and intensity of heavy downpours has increased and is likely to increase further, raising the risk of flash flooding. More frequent heavy rain events foster conditions that allow bacteria and viruses to thrive and will likely increase human exposure to water-borne illnesses, including those linked to sewage contamination of drinking water. Recreational waters are likely to experience more outbreaks of aquatic pathogens, including Vibrio bacteria and harmful algal blooms.  As ecosystems shift, previously localized diseases may become global concerns, stressing healthcare systems that are unprepared for their arrival.

Natural Disasters

Climate change contributes to the severity of natural disasters such as hurricanes, floods, and wildfires. The health effects of these disasters go beyond physical injuries—they include long-term mental health consequences and displacement-related risks. Communities in coastal and low-lying areas are particularly vulnerable.

Aftermath of Extreme Events can include:

• Physical injuries from collapsing structures, drowning, or burns.
• Mental health disorders like PTSD, anxiety, and depression are common among survivors.
• Displacement leads to overcrowded shelters, reduced access to medical care, poor sanitation, and increased transmission of disease.

Food and Water Security

Climate change disrupts agriculture through unpredictable rainfall, droughts, and extreme temperatures, jeopardizing global food systems and water supply.

Consequences for Nutrition include:

• Crop failures and reduced yields lead to food shortages and increased prices.
• Malnutrition and hunger rise as food insecurity grows, especially in developing nations.
• Reduced nutritional value in crops—research shows elevated CO₂ can lower zinc, iron, and protein in staple foods.
• Food safety in multiple ways including lowering the nutritional quality of staples like wheat and rice, causing greater accumulation of mercury and other toxins in seafood, and increasing the chance for food-borne pathogens to enter to food supply.

Threats to Water Quality and Availability involve:

• Droughts which strain water supplies and affect sanitation.
• Flooding which contaminates water with bacteria, chemicals, and waste.
• Melting glaciers and reduced snowpack which threaten freshwater sources for billions of people.

Safe and sufficient food and water are the foundations of good health. As climate change compromises these essentials, entire populations face elevated health risks.

Air Quality

Air pollution is both a driver and consequence of climate change. Fossil fuel combustion releases greenhouse gases as well as pollutants that harm respiratory health.

Respiratory and Cardiovascular Risks:

• Particulate matter  contributes to asthma, lung cancer, and heart disease.
• Ground-level ozone, formed in hot, sunny weather, triggers asthma attacks and reduces lung function.
• Wildfires, intensified by droughts and heat, release smoke and toxic particles that travel hundreds of miles.

Children, older adults, and those with preexisting respiratory issues are especially vulnerable. In 2023, wildfires in Canada sent smoke drifting across the eastern U.S., leading to air quality alerts from New York to North Carolina.

Mental Health

While much attention is given to physical effects, climate change also has serious psychological impacts. Fear about an uncertain future, experiences of disaster, and long-term environmental degradation all contribute to mental distress.

Mental Health Challenges Include:

• Eco-anxiety, particularly among young people, driven by feelings of helplessness and grief over environmental loss.
• Depression and hopelessness following loss of home, livelihood, or loved ones in climate-related disasters.
• Isolation and disruption in communities dealing with long-term climate shifts like drought and sea-level rise.

Mental health services must evolve to address these emerging needs, especially in frontline communities and among climate refugees.

Vulnerable Populations

Climate change exacerbates existing social and economic inequalities. The effects fall disproportionately on those least able to adapt: young children, the elderly, low-income families, Indigenous groups, and people with disabilities. These populations have limited access to healthcare, cooling, clean water, or safe housing; their pre-existing health conditions are worsened by climate stressors; and they have  a reduced ability to relocate, recover, or rebuild after disasters.  Global health equity demands climate policies that include and protect the most vulnerable—those who contribute least to climate change but bear its heaviest burdens.

Preparing for Tomorrow: What Do We Do/What Can Be Done?

Public health systems must adapt and anticipate the growing challenges posed by climate change.

Example strategies:

• Climate-informed healthcare planning, including heat response protocols and vector surveillance.
• Strengthening infrastructure to withstand extreme weather and ensure continuity of care.
• Community education and preparedness, helping people respond to heatwaves, poor air quality, and evacuation orders.
• Mental health support, particularly for disaster survivors and youth experiencing eco-anxiety.

Doctors, nurses, and public health leaders are increasingly calling for action that links climate and health policy. Medical organizations like the American Public Health Association have declared climate change a “public health emergency,” urging governments to treat it as a top priority.

Climate Action Is Health Action

Human health is inseparable from the health of our planet. Every degree of warming, every disrupted ecosystem, and every extreme weather event is a reminder that climate change is not just an environmental issue—it’s a human one. The good news? Many solutions that reduce emissions also improve health: cleaner air, safer transportation, plant-based diets, and green urban spaces.

As we look toward a climate-resilient future, protecting human health must be at the center of our efforts. Whether you’re a policymaker, healthcare worker, educator, or concerned citizen—your actions matter. Climate action is not only an investment in our environment, but in our collective well-being.