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The rising health threats of a hot planet

Beth Howard , special to AAMCNews
October 8, 2019

On the one-year anniversary of the UN’s seminal report on climate change, AAMCNews explores the impact of a warming Earth on health and health care. This is the first in a series.

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Cheryl Holder, MD, first began to connect the dots a few years ago, when her patients with chronic obstructive pulmonary disease (COPD) and asthma began needing to use their prescription inhalers more often. An internist and associate professor in the Florida International University Herbert Wertheim College of Medicine, Holder cares for a population of mostly poor and uninsured patients in Miami-Dade County in Florida.

When she further investigated why her patients’ conditions seemed to be worsening, she learned that many lacked air conditioning, increasing their exposure to the heat, humidity, and unhealthy air that can exacerbate respiratory conditions. Since the 1970s, average annual temperatures in Miami have increased, leading to more 90-degree days and longer periods of unrelenting heat.

“Climate change is not 50 years in the future. It's happening now,” says Holder, who helped to found Florida Clinicians for Climate Action in 2018. “Physicians really have to change how we approach our patients, the questions we ask.” 

The average global temperature has increased by 1.4 degrees Fahrenheit since 1880, according to NASA’s Goddard Institute for Space Studies, with nine of the 10 warmest years on record occurring since 2005. Rising greenhouse gas concentrations lead to local and seasonal temperature extremes, changes in precipitation patterns, more intense weather events, and rising sea levels that threaten the planet’s food and water sources.

The health implications of this change are profound.

“Climate change is not 50 years in the future. It's happening now. Physicians really have to change how we approach our patients, the questions we ask.” 

Cheryl Holder, MD
Florida International University Herbert Wertheim College of Medicine

Increasing rates of allergies and asthma, the growing menace of tick- and mosquito-borne infections, and illnesses and deaths from heat waves and devastating hurricanes are a few of them, according to the National Institutes of Health’s National Institute of Environmental Health Sciences.

“You can’t have healthy people on a sick planet,” says Jonathan Patz, MD, MPH, professor of health and the environment at the University of Wisconsin-Madison and director of its Global Health Institute. “This is the greatest environmental public health crisis of our times.”

Physicians are on the front lines of the crisis. “Climate change is changing how we practice medicine,” says Aaron Bernstein, MD, MPH, co-director of the Harvard T.H. Chan School of Public Health’s Center for Climate, Health, and the Global Environment and pediatric hospitalist at Boston Children's Hospital.

It’s not simple. Today’s providers need to understand that medicines that impair the body’s ability to cope with heat may not be as safe as they used to be because of more frequent and severe heat waves.

At the same time, climate change is making it harder for doctors to do their jobs. “After [Hurricane] Maria, we had nationwide shortages of IV fluids, which form the foundation of medical care,” Bernstein says. “And climate models indicate that hurricanes are likely to be more destructive as climate change unfolds.”

These challenges are expected to grow and increasingly will inform patient care and policymaking. Here are the health consequences that most concern scientists.

Air quality

Climate change affects air quality in two main ways. First, warmer temperatures promote ground-level ozone, or smog, which inflames lungs and makes it harder to breathe for everyone, but especially for people with asthma or COPD.

“Particulate air pollution, originally found to cause problems for lung and heart diseases, is now thought to contribute to Type 2 diabetes, worse pregnancy outcomes, brain damage in developing fetuses, lung cancer, and perhaps dementia, among other health outcomes,” Bernstein says.

Warmer and drier weather also promotes wildfires. “Smoke from fires carries a host of toxic substances that if inhaled make many health problems — such as diabetes, heart disease, and lung disease — worse,” Bernstein says. “Some of the pollutants are known to lead to premature death.”

Outdoor air pollution kills millions of people each year, and air quality in cities around the world has been getting worse, on average, in recent years. According to the American Lung Association, more than four in 10 Americans now live in counties that have unhealthy ozone and/or particle pollution. In 2018, the number of people in the United States exposed to unhealthy air increased to nearly 141.1 million. That’s 7 million more than in 2017.

At the same time, Patz says, studies show that the combined effect of warmer temperatures and carbon dioxide (a major greenhouse gas) leads to more ragweed pollen, which increases allergy misery and is dangerous for asthmatics. “There’s clear evidence that the pollen season is increasing in the United States in parallel with warming temperatures,” he says.    

A warming planet may help explain why the rate of asthma in the United States grew 28% from 2001 to 2011. The CDC reports that approximately 39.5 million children and adults suffer from the ailment.  

Food production and nutrition

A warming planet might seem to be a plus for growing foods but the stress on plants from heat actually decreases crop yields. “Changes in temperature and precipitation — on average but also in the frequency and intensity of extreme events like droughts and floods — are expected to cause agricultural yields to decline for most major crops,” says Matthew R. Smith, PhD, a research associate at the Harvard T.H. Chan School of Public Health.  

Fresh water for irrigation is likely to become more scarce, he says. Higher-ground ozone levels caused by hotter temperatures could poison crops and people. Heat stress is expected to endanger the health of livestock and the quality of animal source foods like eggs and milk. Agricultural pests will become more prolific and destructive. 

“Conditions may become more favorable for the spread of disease in some places and less favorable in others. Lyme disease is now present in Canada, where it wasn’t a few decades ago.”

Aaron Bernstein, MD, MPH
Harvard T.H. Chan School of Public Health

Marine-based foods are also threatened. “Warming oceans are predicted to shift fish populations poleward and reduce plankton abundance, thereby imperiling the marine food web and shrinking fish populations,” Smith says.

High carbon dioxide levels will also likely affect the nutritional value of food. “Many major crops grown under higher CO2 levels, such as those that could occur as soon as 2050, have a lower concentration of nutrients such as iron, zinc, and protein by as much as 17%. This decline may lead to significantly increased risks of micronutrient deficiency,” Smith says. Based on his research, published in 2018 in Nature Climate Change, an additional 175 million people are at risk of becoming zinc deficient due to this effect alone, and 122 million people could become protein deficient.

Infectious diseases

The threat of diseases carried by insects like the Aedes aegypti mosquito — Zika virus, as well as yellow fever and dengue — is climbing as global temperatures rise and the habitat of insects spreads. (Aedes aegypti was recently identified in a Nebraska county.) As a result of the Zika virus outbreak in 2016 that hit parts of Florida, Texas, and Puerto Rico, a Centers for Disease Control and Prevention (CDC) report shows that from July to December 2016, areas where Zika was identified had a 21% increase in the number of babies born with Zika-linked birth defects, compared to the first part of the year.

“Diseases transmitted by mosquitos and ticks — such as malaria, dengue, Zika, and Lyme disease — all are in play as insects change where they live based upon temperature and precipitation,” says Bernstein. “Conditions may become more favorable for the spread of disease in some places and less favorable in others. Lyme disease is now present in Canada, where it wasn’t a few decades ago.”

The CDC also reported a record number of cases of tickborne diseases, including Lyme disease and Rocky Mountain spotted fever, in 2017. Reported cases of Lyme disease in the United States have tripled since the late 1990s, according to a recent study in the Canadian Journal of Infectious Diseases and Medical Microbiology.

Not only do warmer temperatures expand the territory of the insects into once uninhabitable areas where they can affect more people, but they also accelerate the reproductive cycle so that more mosquitos are born each year. And they lengthen the incubation period of the virus inside the insects, giving them a longer time to bite and infect people.

Heat waves and extreme weather events

When heat spikes to the high 90 degrees and into the triple digits, those who can retreat to air-conditioned homes and offices to wait it out. But more people, including those who work outside and vulnerable populations — children, the elderly, those with chronic illnesses, and the poor — face illness, from heat stroke to heart attacks and death.

“More warmth promotes hotter, longer, and more frequent heat waves,” says Bernstein. “In July [2019], more than half of the people in the United States were exposed to unsafe heat.”  

High temperatures killed 172 people in Phoenix, Arizona, in 2017, compared to 150 in 2016 and 85 in 2015. One factor was a week of scorching temperatures that topped out at 122 degrees in June 2017. And it’s expected to get worse. The city will have 132 days above 100 degrees by 2060, predicts Climate Central, a national consortium of researchers and reporters.

Warming patterns also cause more fierce tornadoes, hurricanes, storm surges, and floods, which can lead to injuries and drownings. In addition to the immediate threats, the lack of access to toilets, clean water, and medications in the aftermath can put people at risk for disease.

“With climate change, patients are already having geographically specific health threats. In the Northeast, we are seeing impacts from hurricanes, whereas in the West, we have wildfires. … We need to help patients adapt to these impacts.”

Laalitha Surapaneni, MD, MPH
University of Minnesota

Hurricane Dorian, which ravaged the Bahamas in September 2019, was the fifth Category 5 hurricane in the past four Atlantic hurricane seasons, joining Hurricanes Matthew, Irma, Maria, and Michael. Research published in Nature in June 2019 also shows that more such storms are slowing as Dorian did, leading to more destruction and rainfall.

“You can’t call these severe climate events acts of God anymore,” says Patz. “They can be attributed to greenhouse gases being emitted into the atmosphere.”

The disruption and displacement caused by these events can also result in long-lasting psychological trauma. A 2015 study of 100,000 New Jersey residents who had experienced significant damage to their homes in the wake of “Superstorm” Sandy found that 27% were experiencing moderate to severe mental health distress and 14% reported symptoms suggestive of PTSD some two and a half years after the storm. 

Already vulnerable populations may be at an even higher risk. In a study of 532 low-income mothers affected by Hurricane Katrina, Princeton University researchers found that about 33% still had PTSD and 30% had psychological distress four years after the storm.

The role of physicians

Physicians have a pivotal role to play by arming patients with information, whether the goal is to minimize the health consequences of climate-related disasters or generalized threats like air pollution and extreme heat.

“With climate change, patients are already having geographically specific health threats,” says Laalitha Surapaneni, MD, MPH, assistant professor in the department of general internal medicine at the University of Minnesota and the school’s climate champion. “For example, in the Northeast, we are seeing impacts from hurricanes, whereas in the West, we have wildfires. In Minnesota, we worry about the rise of tickborne illnesses like Lyme [disease]. We need to help patients adapt to these impacts.”

Doctors can educate patients about how to keep tabs on weather conditions and make plans for emergencies and unhealthy exposures, says Perry Sheffield, MD, assistant professor of pediatrics and environmental medicine and public health at the Icahn School of Medicine at Mount Sinai in New York City, New York. “This counseling is even more critical for patients with chronic (or temporary) conditions that increase their risk of getting sick from these exposures,” she says.

That could mean talking to patients about how to find the air quality index for their location and stay indoors or wear an N-95 mask and avoid strenuous activities, depending on the air quality. “It could also involve making sure patients, especially the elderly and those with mental illness, know where they can go to keep from overheating during heat waves and maybe even adjusting medications to avoid those medications that interfere with heat loss,” says Thomas B. Newman, MD, MPH, professor emeritus of epidemiology and biostatistics and pediatrics at the University of California at San Francisco. “It’s also reasonable to bring up climate change when talking about disease prevention, for example, in patients considering moving toward a plant-based diet or walking or cycling rather than driving to work.”

Beyond patient care, physicians can also advocate for policies that reduce stress on the planet and generally sound the alarm.  “Research has shown that health messages are the most powerful in transforming climate change from a politicized issue to one that we can all get behind doing something about,” says Bernstein. “Studies also make clear that physicians may be the best messengers for health messages. If we need to change how we think about climate change in order to tackle it, we may have no better people to do this than physicians.”

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