Climate Change and Human Health Toolkit

“Climate change is the single biggest health threat facing humanity.”

The World Health Organization (WHO) makes that statement in an October 2021 report that comes as increasingly frequent extreme weather events and other climate impacts threaten our lives and our health. And while no one is safe from climate-related health hazards, these risks disproportionately affect the most vulnerable and disadvantaged. 

This toolkit, along with two recorded webinars Webinar on Climate And Health (February 2020) and Climate Solutions are Health Solutions (March 2021), explain how weather and climate change affect human health today, how that could change in the future, and what we can do to reduce climate-related health risks.  

Climate Central has resources on multiple health impacts of climate change, including locality-specific data and background information. We also help identify specific vulnerable populations and groups that are at increased danger from various weather- and climate-related physical and mental health risks.



Extreme heat and longer heat waves can cause illness or death. As the climate warms, there are increasingly more dangerous hot days, and even more hot nights. Climate change has resulted in less cooling at night which puts additional heat stress on vulnerable individuals. 

Groups that are most at risk from heat-related risks include the elderly, very young children, outdoor workers, people with chronic diseases, the socially isolated, low income populations, and some communities of color.  Large cities that generate strong urban heat islands can be particularly dangerous.

Air Quality 

Climate change often makes air pollution worse.  Several groups are particularly susceptible to harms from poor air quality including infants and young children, the elderly, people with respiratory diseases or other serious health conditions, outdoor workers and athletes.

A variety of climate-related air pollutants affect our health.


Ozone accumulates in hot stagnant air, and concentrations increase as temperature rises. The longer, hotter summers we are experiencing as the climate warms increase exposure of millions of people to this dangerous pollutant.  Risks include asthma attacks, pneumonia, coughing and shortness of breath, cardiovascular damage, increased susceptibility to infections, and decreased lung functions. Children, people with asthma, and those with certain lung and heart illnesses are at particular risk. 


Wildfire and smoke

Large wildfires are becoming more frequent and widespread, particularly in the western United States, fueled in part by climate change. The smoke from these fires creates serious health risks regionally and beyond.

Wildfires are a source of particulate matter pollution. Particulates less than 2.5 micrometers in diameter (PM2.5) are especially dangerous as they can reach deeply into the lungs and can trigger or worsen health problems such as asthma and heart disease, with emerging evidence linking it to premature births.  High-risk groups include pregnant women, infants, children, the elderly, asthmatics, people with serious heart, lung or other medical conditions and anyone who is required to spend long hours outside. 


Allergies: Pollen and Poison Ivy

More days above freezing creates a longer growing season, which in turn means a longer allergy season. More carbon dioxide in the atmosphere also means more pollen and stronger pollen for common airborne allergens like ragweed. 

Poison Ivy thrives in a climate changed world.  Plants grow faster, bigger and have more toxic oils with increasing concentration of CO2 in the atmosphere and higher temperatures.

Extreme Events: Storms, Floods and Rising Seas

As the climate warms, we are seeing more frequent and more severe extreme weather events, many involving water. Direct effects from storms and floods can cause injury or death. Indirect effects can include mental and physical health effects from displacement and disruption of important infrastructure such as schools, work, food supply, sanitation and medical care.  

As with many extreme weather events, the elderly are among the most vulnerable. In some hurricanes, the difficulties and stresses of moving vulnerable older adults has caused more deaths than the actual storms. 

Pests and Contamination

Our warming climate is promoting more illness that thrives in hot weather and survives in milder winters.  Some of these infections are carried by pests (called vectors) such as mosquitoes and ticks. Others occur when people are exposed to contaminated water or food.   

Vector-borne Diseases

Mosquitoes and ticks carry infections dangerous to humans like the West Nile and Zika viruses and Lyme disease. Earlier springs and warmer falls mean longer pest seasons. Warmer, more humid air makes for more favorable conditions for mosquitoes and even changes in behavior of ticks and where they live. Shorter, warmer winters mean less winter die-off as well.  


Contaminated Food and Water 

Warm weather also makes many microorganisms grow more efficiently. Both food and water can become contaminated. Vulnerable individuals can get sick.


Climate-related health risks are not equally shared. Children, the elderly, low-income communities, and some communities of color face a greater share of risks.  

Extreme urban heat is a public health risk, especially for individuals and communities that are more vulnerable due to health, social, economic, or other reasons. Sea level rise can disproportionately affect vulnerable groups.




Mental Health

The impacts of climate change challenge not only our physical health, but our mental health as well. Large-scale studies link exposure to extreme weather events and increased temperatures to worse mental health outcomes.  

Weather-related disasters can result in significant life upheavals that are challenging to quantify such as job loss, relocation, and rupturing of social networks. These impacts can in turn give rise to mental illnesses such as anxiety, depression, post-traumatic stress disorder (PTSD), and substance abuse.

Extreme weather catastrophes are becoming more frequent as the climate warms. That means the time to recover — physically and mentally — from the damage done by these billion-dollar disasters is shrinking.  



Climate Solutions with Health Benefits

Many of the solutions to climate change also have direct positive effects on human health and the systems we depend upon. Planting trees lowers carbon dioxide and purifies air. Driving an electric car reduces emissions and improves air quality. Composting also lowers carbon dioxide and improves soil and crop health.  As these stories are told, we collect them here.

Additional Resources 

Other Toolkits

Guides and Reports



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