How climate change threatens public health

Originally published on August 19, 2019 by Samantha Harrington on Yale Climate Connections.

Major medical groups call climate change ‘a true public health emergency.’

From prolonged droughts to dangerous sun exposures, the weather affects human health in numerous ways, and climate change has already ratcheted environmental health threats up a notch. Disease-carrying bugs have expanded their range, hotter heat waves last longer, and storms have gotten more extreme.

“Climate change is impacting our communities, in our backyards, right now,” says Amir Sapkota, a professor at the Maryland Institute for Applied Environmental Health.

Citing health threats posed by climate change, more than 70 major medical groups in the U.S. released a call to action in June 2019 declaring climate change “a true public health emergency.”

Jonathan Patz, M.D., MPH, director of the Global Health Institute at the University of Wisconsin, is an expert on climate change and public health. His view: “It’s so important that people recognize that climate change is about our health. There are so many pathways through which climate impacts our health.”

Those pathways include heat, air pollution, extreme weather, vector-borne diseases, and access to safe water and food. The health risks posed by climate change already disproportionately harm marginalized groups including people with disabilities or infirmities, low-income families and individuals – and climate change is likely to deepen those disparities.

1. Heat-aggravated illnesses

As global temperatures warm, hot days are expected to become more common and severe. Heat stroke and exhaustion are some of the most directly heat-related illnesses, but heat stress can also cause or exacerbate cardiovascular and kidney problems.

In a 2016 assessment on climate change and health, the U.S. Global Change Research Program reported that a predicted increase of thousands to tens of thousands of premature deaths can be expected in summer months across the United States as a result of rising temperatures.

Certain risk factors make people more vulnerable to the heat. Children and older adults are more at risk, as are people with some chronic medical conditions and those taking certain medications like water pills and anti-psychotic medications. The heat is also particularly hard on people who work outside or spend most of their time outdoors.

Living in urban areas can also increase one’s chances of heat exposure because of the urban heat island effect. Paved surfaces and the built environment retain heat and, according to EPA, can make air temperatures in cities as much as 22 degrees Fahrenheit warmer than nearby rural areas.

2. Respiratory illnesses

Without reductions in greenhouse gas emissions and atmospheric concentrations, climate change is expected to make air quality worse. Warmer days lead to an increased amount of ground-level ozone, the main ingredient in smog; wildfires are burning bigger and more frequently, unleashing dangerous particles and gases into the air; and allergy seasons are lengthening and intensifying.

“From your respiratory health such as asthma, to cardiovascular diseases, to mortality, you name it, air pollution affects so many different things,” Sapkota said.

The World Health Organization has estimated that air pollution is responsible for about seven million deaths a year worldwide and found that reducing the burning of fossil fuels could avoid 2.5 million premature deaths each year by 2050.

3. Diseases transmitted by insects and arachnids

As places warm up and frost-free seasons lengthen, disease-carrying creatures like mosquitoes and ticks are expected to expand their range and activity. Already, the Aedes aegypti mosquito, which thrives in warm climates and can be a vector for the Zika, chikungunya, and dengue viruses, has been expanding its range in the U.S. Cases of West Nile, a virus carried by a different mosquito, are also expected to increase in a warmer world.

Michael A. Robert, an assistant professor of mathematics at the private University of the Sciences in Philadelphia, Pennsylvania, has studied risks of increased dengue transmission in the U.S. in a warmer climate. He says that warming expands the mosquitoes’ range and also can shorten the time diseases need to incubate before being transmitted.

“If it’s warmer, to a certain point anyway, the mosquitoes live longer, and the incubation period is much shorter,” Robert said. “That creates a scenario when there can be a lot more transmission.”

Tick-borne diseases are also affected by climate change. In particular, according to a 2016 study by researchers at the Public Health Agency of Canada’s National Microbiology Laboratory, warmer winters are likely to increase the number of ticks that survive and lengthen their active season. Authors of that study also noted that because ticks have long life cycles and are less mobile than flying insects, tick-borne diseases are likely to expand to other areas more slowly than mosquito-borne diseases.

Water is also important for both mosquito and tick populations – mosquitoes depend on standing water for breeding, and ticks need humid environments to rehydrate – so areas of the U.S. that may see more drought as a result of climate change are likely to be less at risk from this particular health concern.

4. Access to safe food and water

Climate change is expected to affect, in many cases negatively, crop yields and food security, as floods, droughts, and storms can wipe out fields. Warmer summer temperatures may make growing some crops, like corn, more difficult. Pest infestations and pathogen exposure are likely to increase. And elevated levels of carbon dioxide reduce the nutritional value of some crops like wheat and rice.

Heat has also been shown to reduce milk production on dairy farms. Research by the U.S. Department of Agriculture shows not only that cows produce less milk during hot spells, but the milk produced is lower in fat, solids, lactose, and protein content.

Decreased production may lead to increased grocery prices, hitting low-income individuals and communities hardest.

Rising temperatures and extreme weather may also result in reduced water quality. Warm water temperatures and increased stormwater runoff can cause growth of harmful algae blooms, while storms and sea-level rise threaten aging drinking water, wastewater and stormwater infrastructure. That sea-level rise itself has adverse public health implications, both in terms of flooding and in terms of exposing more people to direct exposures to contaminated flood waters.

In cities with combined stormwater and wastewater overflow infrastructure, heavy storms are more frequently overwhelming systems and leading to sewage flowing into bodies of water where stormwater drains. According to Patz’s research on sewer overflow into Chicago’s stormwater drainage, the city can expect 50 to 120% more overflow events by 2100.

5. Safety and well-being during extreme weather

From hurricanes to wildfires, extreme weather also poses health hazards. According to the Health and Climate Report, primary impacts include death, injury, or illness; worsening underlying medical conditions; and adverse effects on mental health.

In a study published in 2019, Todd Pugatch, an economics professor at Oregon State University, found that tropical-storm-related deaths increase under most climate change scenarios and by as much as 52%.

Extreme weather can also harm health care infrastructure, making it more difficult for people to receive care they need. In a report of lessons learned from Hurricane Sandy in 2012, the American College of Emergency Physicians wrote that six hospitals and 26 residential care facilities in New York City alone were closed during the storm. They estimated that 75,000 people with significant health issues lived in areas inundated by storm surge.

After extreme weather has passed, mental health challenges can linger. The most common mental health impacts after disasters are post-traumatic stress disorder, depression, and general anxiety.

Extreme weather isn’t the only climate challenge expected to shape mental health. Conventional air pollutants also have been linked to anxiety and depression, and heat can cause mood changes and can fuel aggressive behavior. Additionally, the very threat of climate change and uncertainty about the future can cause or contribute to anxiety and depression.

Preparing for the future

Some adverse health effects of climate change are now apparent, but with every degree of warming that’s avoided, lives can be saved, Patz said. Acting on climate, both to reduce warming and to prepare communities to manage and treat associated health risks, is something that public health departments can focus on.

“One thing that I tell health departments is that climate change is not necessarily a brand-new problem,” Patz said. “It’s something that will cut across challenges they’re already working on, be it air quality, and of course heat waves happen, monitoring for infectious diseases, water purification and water quality – all of those issues health departments deal with right now.”