Climate Change Threatens Health

October 13, 2015

Climate change is one of the most serious public health threats facing the nation, but few people are aware of how it can affect them. Children, the elderly, and communities living in poverty are among the most vulnerable. Click on a state on the map for more information on climate-health threats, actions being taken to prepare communities, and what you can do.



Six Ways Climate Change Threatens Health

Air Pollution

Rising heat worsens smog. Burning coal and oil emits carbon and particle pollution; plants produce more allergenic pollen, affecting respiratory health threats like asthma.

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Rising temperatures can make smog pollution worse and increase the number of "bad air days" when it's hard to breathe. This puts many of us at risk for irritated eyes, noses, and lungs—but it is particularly dangerous for people with respiratory diseases like asthma. As the climate changes, unhealthy air pollution will get worse. Here's how:

Ozone smog forms when pollution from vehicles, factories, and other sources reacts with sunlight and heat. Increasing temperatures speed this process and result in more smog. Added to the mix are ragweed and other allergens in the air—which are expected to worsen as rising carbon dioxide levels cause plants to produce more pollen. Also, as dry areas get dryer, wildfire risks go up and smoke from burning landscapes intensifies poor air quality.

Exposure to increased smog, pollen pollution, and wildfire smoke puts a wide range of people at risk for irritated eyes, throats and lung damage (the U.S. EPA likened breathing ozone to getting a sunburn on your lungs). This includes outdoor workers, children, the elderly, and those who exercise outside.

But people with asthma, allergies, and other respiratory diseases face the most serious threats, since exposure to increased pollution heightens sensitivity to allergens, impairs lungs, triggers asthma attacks, sends people to the hospital, and even results in death. In 2010, the American Lung Association estimated that about 23 million Americans suffered from asthma.

Communities must take steps to improve air quality, but everyone should know the risks that climate change poses and learn how to best protect themselves when bad air days get worse.

Eleven states and various local governments have developed preparedness measures to address the air quality impacts associated with climate change. The most frequent recommendation is developing or strengthening statewide air monitoring programs; gathering information is often the first step towards preparing for climate change related threats.

Extreme Heat

Heat waves send thousands to emergency rooms and cost health care systems millions of dollars; climate change brings longer, more intense heat waves.

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Across the nation, climate change is making hot summer days hotter and stretching their numbers into heat waves that never seem to end. And the heat is causing more than just discomfort—as temperatures rise, so are the number of illnesses, emergency room visits, and deaths.

At least 37 states saw record highs in the summer of 2010, and in many regions, it didn't cool off at night. Nationwide, over 28.5 million people lived in counties where 2010's average temperature set records, and over 36 million people lived in counties where the hottest summer nights ever were recorded.

The record heat experienced in the United States in the summer of 2010 was no isolated event. Global temperature data compiled by NASA show that 2010 was tied with 2005 as the hottest year on record. This comes on top of the warmest decade on record (2000-2009).

Extreme heat waves cause the most harm among elderly people and young children. City dwellers are at particular risk because of elevated temperatures in cities, known as the "urban heat island effect" due to the magnifying effect of paved surfaces and the lack of tree cover.

In the United States, an average of 400 deaths per year are directly related to heat, and an estimated 1,800 die from illnesses made worse by heat—including heat exhaustion, heat stroke, cardiovascular disease, and kidney disease. Deadly heat waves swept across most of the nation in 2006, hitting California the hardest; the state saw an additional 16,000 emergency room visits during the two-week heat wave.

Scientists predict that average temperatures in the United States will rise between 5 and 9°F (3-5°C) over the next century; these hot summer days and heat waves could be the norm by 2100.

Communities across the nation must educate themselves about the risks from extreme heat and learn how to protect their most vulnerable residents.

Twelve states and several local governments have developed preparedness measures to prevent the health impacts of increasing extreme heat associated with climate change. The most frequent recommendation is developing or strengthening statewide heat early warning systems, with an emphasis on alerting the most vulnerable populations.

Infectious Diseases

Hotter summers can make disease-carrying insects more active, for longer seasons; illnesses like dengue, West Nile, and Lyme can spread into new areas.

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While many infectious diseases were once all but eliminated from the United States, there's evidence that climate change is a factor that could help them expand their range and make a comeback.

Mosquitoes capable of carrying and transmitting diseases like Dengue Fever, for example, now live in at least 28 states. As temperatures increase and rainfall patterns change—and summers become longer—these insects can remain active for longer seasons and in wider areas, greatly increasing the risk for people who live there.

The same is true on a global scale: increases in heat, precipitation, and humidity can allow tropical and subtropical insects to move from regions where infectious diseases thrive into new places. This, coupled with increased international travel to and from all 50 states, means that the U.S. is increasingly at risk for becoming home to these new diseases.

Nearly 4,000 cases of imported and locally-transmitted Dengue Fever were reported in the U.S. between 1995 and 2005, and that number rises to 10,000 when cases in the Texas-Mexico border region are included. In Florida, 28 locally-transmitted cases were reported in a 2009-2010 outbreak, the first there in more than 40 years. Dengue Fever, also known as "Breakbone Fever", is characterized by high fever, headaches, bone and joint aches, and a rash. Recurrent infection can lead to bleeding, seizures, and death.

Lyme disease—transmitted primarily through bites from certain tick species—could expand throughout the United States and northward into Canada, as temperatures warm, allowing ticks to move into new regions.

West Nile virus, which first entered the U.S. in 1999, expanded rapidly westward across the country. By 2005, over 16,000 cases had been reported. Warmer temperatures, heavy rainfall and high humidity have reportedly increased the rate of human infection.

Communities across the nation must educate themselves about the risks from climate change and spreading infectious diseases and learn how to protect their most vulnerable residents.

Eleven states and several local governments have developed preparedness measures to address the spread of infectious diseases associated with climate change. The most frequent recommendation is improving statewide surveillance for vectors such as mosquitoes, and the presence of vector-borne diseases.


Hotter days and nights, and changing rainfall patterns reduce water supply quantity and quality, and diminish food security.

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Water is life, and climate change is threatening this precious resource. Nearly every U.S. region is facing some increased risk of seasonal drought.

Climate change will significantly affect the sustainability of water supplies in the coming decades. As parts of the country get drier, the amount of water available and its quality will likely decrease—impacting people's health and food supplies.

Parts of the Western U.S. are already experiencing water crises because of severe dry-spells, but with climate change, the entire country will likely face some level of drought. NRDC's Climate Change, Water, and Risk report found that 1,100 counties—one-third of all counties in the lower 48 states—face higher risks of water shortages by mid-century as the result of climate change. More than 400 of these counties will face extremely high risks of water shortages.

As temperatures rise and precipitation decreases, water quality can be jeopardized. Shrinking amounts of water can concentrate contaminants such as heavy metals, industrial chemicals and pesticides, and sediments and salts. During drought, drinking water supplies are susceptible to harmful algal blooms and other microorganisms.

Of course, drought means more than not having access to clean drinking water. Changes in precipitation and water availability could have serious consequences for commercial agriculture – crops yield less and food security suffers. Drought conditions can also help fuel out-of-control wildfires.

Local communities across the country can prepare for drought by learning to conserve water and improving drinking water safeguards.

Nine states and several local governments have developed preparedness measures to address the drought impacts associated with climate change. The most common recommendation is improving general preparedness measures for droughts and ensuring an adequate water supply.


Climate change intensifies rainfall; heavy rains increase risk of drinking water contamination and illness; floods can force communities to relocate.

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Climate change has contributed to a rise in extreme weather events—including higher-intensity hurricanes in the North Atlantic and heavier rainfalls across the country. Scientists project that climate change will increase the frequency of heavy rainstorms, putting many communities at risk for devastation from floods.

Flooding can cause a range of health impacts and risks, including: death and injury, contaminated drinking water, hazardous material spills, increased populations of disease-carrying insects and rodents, moldy houses, and community disruption and displacement.

As rains become heavier, streams, rivers, and lakes can overflow, increasing the risk of water-borne pathogens flowing into drinking water sources. Downpours can also damage critical infrastructure like sewer and solid waste systems, triggering sewage overflows that can spread into local waters.

Cities like New York City and Chicago, where older sewer systems carry sewage and rain water in the same pipes, are at greater risk for sewage spills. During heavy rains, these pipes cannot handle the volume of stormwater and wastewater, and untreated sewage is often discharged into local waters where people swim and play.

Exposure to pathogens from sewage and unclean water can sicken vulnerable communities with illnesses like cryptosporidiosis, giardiasis, and norovirus (which cause diarrhea, abdominal pain, nausea, vomiting, headache, and fever).

Local communities across the country can prevent floods and heavy rains from devastating their homes and buildings by updating infrastructure, improving drinking water safeguards, and creating public plans for what to do in case disaster strikes.

Eight states and various local governments have developed public health preparedness measures to address increased flooding risks associated with climate change. These measures are a good start at addressing some of the risks but comprehensive response plans addressing the multiple threats and hazards highlighted above are lacking.

Extreme Weather: Record-Breaking Events in 2011

In 2011, thousands of record-breaking extreme weather events harmed communities and health in the US. Climate change is contributing to more intense and frequent extreme weather events.

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2011 was a year of unparalleled extremes: 14 disastrous weather events in the US each resulted in over a billion dollars in property damage. This was an all-time record breaking number—and their estimated $53 billion price tag did not include health costs. When health-related costs of extreme events are calculated, the total tally increases by billions more dollars, as shown recently, in a first-of-its-kind study published in the journal Health Affairs.[1] Costs will likely continue to climb as climate change continues.

Since climate is the baseline for weather, alteration of the climate affects extreme weather events, too. Some people have likened the effects of climate change to "weather on steroids": taking steroids makes hitting a home run more likely for a ball player, and climate change makes some types of extreme weather events more likely.

A troubling trend has been identified by the international reinsurance company MunichRe[2]; they concluded that from 1980 through 2011, the frequency of damaging extreme events increased substantially in the U.S. Many of the 2011 extreme events, such as record temperatures, devastating storms, wildfires, and extreme droughts and floods, are among the types expected to worsen as climate change continues. A newly-released analysis by international climate scientists (the IPCC)[3] concluded that climate change will amplify extreme heat, heavy precipitation, and the highest wind speeds of tropical storms.

We need to be prepared. Emergency planning must incorporate risks from climate change. For example, maps describing flooding zones need to account for increased risks caused by extreme rainfall and sea level rise resulting from climate change. While these plans are made at the local level, the Federal Emergency Management Agency (FEMA) must also prioritize addressing and preparing for climate change by providing guidance and resources to state and local governments.

  1. Knowlton K, Rotkin-Ellman M, Geballe L, Max W, Solomon GM. 2011. Six climate change-related events in the United States accounted for about $14 billion in lost lives and health costs. Health Affairs 30(11):2167-2176.
  2. Munich Re. 2011.Half-Year Natural Catastrophe Review, July 12, 2011. MR NatCatSERVICE. Available at: A webinar regarding the entire year of 2011 by MunichRe is available at:
  3. IPCC Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation, Summary for Policymakers (Nov. 18, 2011), available at:
Climate Change Threatens Health: Data Sources and Map Methods >>