Growing the Body of Evidence for Climate Change’s Impact on Health
By Christiane Truelove
Type the words “climate change” into Google and hundreds of news headlines pop up. On July 27th, the United Nations warned that the “era of global boiling” has started, with UN Secretary-General António Guterres saying that “short of a mini-Ice Age,” July 2023 would likely “shatter records across the board.”
“Climate change is here. It is terrifying. And it is just the beginning,” the UN chief said in a statement, warning of consequences such as “children swept away by monsoon rains, families running from the flames, (and) workers collapsing in scorching heat.” Scientists from the World Meteorological Organization (WMO) and the European Commission’s Copernicus Climate Change Service stated that new data showed that so far, July has seen the hottest 3-week period ever recorded and the 3 hottest days on record.
The possibility that the world will only get warmer is real, as ocean temperatures are at their highest-ever recorded levels for this time of year. According to WMO’s Director of Climate Services Chris Hewitt, 2015 to 2022 saw the 8 warmest years on record, based on a 173-year dataset. The La Niña sea-cooling phenomenon towards the end of that period in the Pacific region reined in global average temperatures slightly, Hewitt says, but now has been replaced by the sea-warming El Niño effect, which is beginning to heat up in the tropical Pacific and brings the “almost certain likelihood that 1 of the next 5 years will be the warmest on record.”
“The climate crisis threatens to undo the last 50 years of progress in development, global health, and poverty reduction, and to further widen existing health inequalities between and within populations.” — World Health Organization
What does this mean for human health? According to the World Health Organization’s (WHO) fact sheet on climate change and health from October 2021, between 2030 and 2050, climate change is expected to cause approximately 250,000 additional deaths per year from malnutrition, malaria, diarrhea, and heat stress. The direct damage costs to health, excluding costs in health-determining sectors such as agriculture and water and sanitation, is estimated to be between $2 billion to $4 billion a year by 2030. And areas with weak health infrastructure —mostly in developing countries—will be the least able to cope without assistance to prepare and respond.
“The climate crisis threatens to undo the last 50 years of progress in development, global health, and poverty reduction, and to further widen existing health inequalities between and within populations,” WHO says. “It severely jeopardizes the realization of universal health coverage (UHC) in various ways—by compounding the existing burden of disease and by exacerbating existing barriers to accessing health services, often at the times when they are most needed. Over 930 million people (approximately 12% of the world’s population) spend at least 10% of their household budget to pay for healthcare. With the poorest people largely uninsured, health shocks and stresses already push nearly 100 million people into poverty every year, with the impacts of climate change worsening this trend.”
Linking Health Conditions to Environment
There are a growing number of studies generating data to tie environmental conditions such as excessive heat to an adverse impact on human health, especially in regions that have not been subject to such heat before. A study by Sahani et al in the May 2022 issue of Sustainable Cities and Society attempted to correlate daily maximum temperature and mortality using the distributed lag non-linear model (DLNM) in 2 areas of the United Kingdom, Southeast England and Aberdeenshire. The goal of the study was to examine the effect of heat on those living in bucolic areas, since earlier studies had focused on more urban, developed areas. In their modeling, researchers found heat waves are making more people in rural areas of England severely ill today than they were in the 1980s.
“Heat waves’ impact is well known to be more pronounced in urban and built areas but how the risk varies in semi-urban, suburban, and rural areas is not vastly explored,” these researchers say. “Across the globe, hot days are getting hotter and more frequent, while experiencing fewer cold days. As a result, heat waves are becoming a more common challenge in small cities, towns, and in the landscape areas too.”
On July 27, the University of Waterloo announced that researchers from there and Toronto Metropolitan University in Canada have refined and expanded a method of data collection to assess the health impacts of extreme heat. The study, “Heat and Air Quality Related Cause-Based Elderly Mortalities and Emergency Visits,” appears in the journal Environmental Research. These researchers discovered that even moderate temperature increases, for example, nighttime temperatures starting at 18.4 degrees Celsius, can lead to increased hospital visits and death for older adults and those with cardiorespiratory conditions.
Researchers say the new method will help municipalities make a strong case for choosing which mitigation and adaptation measures to pursue to effectively respond to climate changes. The options could include planting more trees for shade, investing in emergency warning programs, or planning to have more staff available to run ambulances and support hospitals and long-term care homes.
“Communication is very important, especially in less well-educated or disadvantaged populations, climate change isn’t something that’s on their radar.” — Jun Wu, PhD
“Heat waves cause more deaths in Canada than any other climate hazard,” stated Mohamed Dardir, PhD, MSc, postdoctoral researcher in the School of Environment, Enterprise and Development at the University of Waterloo. “We are getting better at being proactive and planning for climate emergencies, but we still aren’t responding to temperatures in the same way we respond to big weather events, such as floods and fires.”
The study analyzed the spring and summer in Mississauga and Brampton, Ontario. By integrating data on air quality and heat, the researchers achieved the most detailed picture of the short-term health risks impacting the vulnerable population on a municipal level. The findings confirm there was an increase in the total deaths and hospital visits in these areas with the highest impact happening on the day of the heat and poor air quality and extending 2 days after these events.
In the future, the team plans to expand its analysis to include more environmental hazards, such as storms and floods, and factors including ambulatory calls across municipalities in Ontario and other provinces. The researchers say that this work will help civil society and policy makers grasp the magnitude of these climate events and equip decision makers to justify investments in climate resiliency.
Jun Wu, PhD is codirector of the UCI Center for Environmental Health Disparities Research at the University of California at Irvine that focuses on environmental health, including exposure assessment of various environmental agents, health impacts of environmental exposures, and environmental justice/environmental health disparity. In 2022, a team of researchers including Wu received a $3.2 million R01 grant from the National Institute of Aging to study the impact of climate change on life expectancy in a multi-ethnic population. The goal of the study is understanding the contribution of long-term extreme heat and wildfire smoke on life expectancy.
“Our estimates are that roughly 1400 people a year, adults 20 years of age and older, are dying related to extreme heat.”
— Sameed Khatana, PhD
Wu has also examined the impact of exposure to green space on maternal postpartum depression. The study, published online in the journal The Lancet Regional Health – Americas, determined that exposure to green space and tree coverage was associated with a decreased risk of postpartum depression among mothers, and suggests that researchers, city planners, and public health professionals should work together to develop policies and interventions that increase the amount of tree coverage to create a beneficial environment for community members—especially new mothers who are at risk of postpartum depression.
In her research, Wu says she is increasingly interested in environmental health and how research can help improve public health, particularly through actual practical interventions with communities.
“Throughout the years of research, we have been focusing on the impacts of air pollution,” she says. “We found a number of health risks and maternal health pregnancy complications from air pollution, such as gestational diabetes, preterm birth, low birth weight, etc.” Wu and her colleagues also have found that extreme heat can increase the risk of preterm birth.
The impetus for the wildfires and health impacts research is while there is existing research linking wildfires to adverse effects on health, it is difficult to distinguish whether the impact is from the smoke or just the stress of the wildfire event, especially for people living nearby. Wu and her colleagues are building models to estimate wildfire-specific air pollution and then further examine the health impact using data in California.
Wu says clinicians and others engaged in healthcare outcomes research, who are mostly focused on the health side or disease side of the problem, may not be well educated on climate change’s impact on health. Although there have been increasingly more severe, higher frequency extreme climate events happening in recent years, “there’s always a lag between what you start to be aware of and how much you really know,” she says.
Education about climate change and its impact on health should be established for medical students, doctors, and nurses, and healthcare workers should be taught about how to share this information with patients, Wu says. For example, when hospital patients are discharged, their notes should include explanations of the risks of wildfires and heat waves, and patients should be more aware of their actual risk and understand how they can reduce risk to their health.
“A lot of our patients aren’t really aware that extreme heat is a health issue. I would say many healthcare providers probably aren’t aware of this issue either.” — Sameed Khatana, PhD
Wu says the healthcare sector should work closely with community organizations to deliver these messages as well as to set up mobile clinics. Additionally, because there is more community trust for physicians than government, physicians can be very helpful in delivering information about the health risks of environmental factors.
“Communication is very important, especially in less well-educated or disadvantaged populations,” Wu says. “Those subpopulations are usually at a higher risk for climate change” especially since they have greater worries such as job security and high costs of housing and food—”climate change isn’t something that’s on their radar.”
A Clinician’s View of Environmental Impacts
Sameed Khatana, PhD, of the University of Pennsylvania is a practicing cardiologist at the Philadelphia Veterans Affairs Medical Center who has done research on the impact of extreme heat on patient health. “It’s been known for some time that the effect of extreme heat on individual’s health is related to their preexisting medical conditions, and for people who already have things like heart disease and risk factors for heart disease like diabetes, they might be at some of the highest risk for adverse health effects related to extreme heat,” Khatana says.
The work of Khatana and his colleagues—”Association of Extreme Heat With All-Cause Mortality in the Contiguous US, 2008-2017,” published in JAMA Network Openin May 2022, and “Association of Extreme Heat and Cardiovascular Mortality in the United States: A County-Level Longitudinal Analysis From 2008 to 2017,” published in Circulation in June 2022—explores the burden of extreme heat-related deaths. In looking at both all-cause mortality and then cardiovascular mortality, Khatan and his colleagues found that extreme heat was associated with higher levels of mortality, both for all-cause and cardiovascular disease.
“There are a lot of data out there, and scientists need to be cautious about using it without understanding the proper context of what is the source of these data and how best to apply it.” — Sameed Khatana, PhD
“Our estimates are that roughly 1400 people a year, adults 20 years of age and older, are dying related to extreme heat, with about half of these deaths associated with cardiovascular disease specifically,” Khatana says.
Khatana observes that in comparing all studies looking at the health impact of heat, it is difficult to see what the exact burden is because the definition of extreme heat varies from study to study and different regulatory bodies have different definitions of extreme heat. “But the bottom line is that that people are dying due to this issue,” he says.
He and his colleagues also wanted to determine which populations are particularly impacted by extreme heat. “We found that older individuals are the ones that were more likely to be affected by extreme heat exposure. Then looking at race and ethnicity subgroups, we found that non-Hispanic Black adults had a disproportionately greater increase in mortality when exposed to extreme heat compared to non-Hispanic White adults,” Khatana says, probably due to differences both in the burden of preexisting medical conditions and differences in the lived environment.
The researchers also found some regional differences in the burden of extreme heat-related deaths. In particular, they determined that in areas that traditionally have fewer extreme heat days, when extreme heat does occur, people had a disproportionately greater increase in cardiovascular mortality. This suggests, Khatana says, areas such as the Northeast or the Mid-Atlantic might be less well prepared for extreme heat when it does occur. “This may be due to lower access to air conditioning or people culturally not used to thinking of heat as being a health issue.”
Like Wu, Khatana believes that in terms of next steps, providers and researchers need to be thinking about work around awareness. “A lot of our patients aren’t really aware that extreme heat is a health issue,” Khatana says. “I would say many healthcare providers probably aren’t aware of this issue either. I think it’s becoming more and more notable, something that people are talking about a lot more in the past couple of years, so I’m assuming awareness will increase.”
The problem is many people, policy makers included, still think of extreme heat as more of a nuisance than a health issue. This means researchers should be advocating for patients, Khatana says, adding that the people who suffer health impacts from extreme heat are usually some of the most marginalized people in society—the homeless and people who are socially isolated. “Many of these people might not be able to be able to advocate for themselves, and I think they rely on researchers and healthcare workers to speak up for them.”
Khatana says extreme heat is not the only health impact of climate change that researchers need to look at. “It causes floods, it causes crop failures, it causes mass migration,” he says. Because of this, researchers need to start thinking about how these different impacts of climate change subsequently impact human health. “I think any true understanding will need to account for all of these different factors.”
While the federal government is trying to put additional policies into place to lower the greenhouse effect, “the health impacts are already here,” Khatana says. “So, now our society and our government need to start thinking about mitigation and how we can lessen the impact of extreme heat as well as other extreme weather conditions that occur due to climate change.”
Because climate change impacts virtually every aspect of society, any research on climate-related health impacts requires a multidisciplinary approach, Khatana states. “If an economist is using satellite data that is mapping either temperature or humidity, it perhaps makes sense to be working with researchers in those fields to really understand where the data are coming from, what the limitations of the data are, and how would it best be applicable for the question that the researcher is trying to answer,” he says. “There are a lot of data out there, and scientists need to be cautious about using it without understanding the proper context of what is the source of these data and how best to apply it. Obviously, people in the climate science community have been working on this for decades. And now researchers such as health services researchers like myself, perhaps health economists in the near future, are going to start working on these issues. But I think it’s good to come from a position of humility and to think really deeply about having a multidisciplinary approach to research.”
