To ease impact of climate change on health, take a local focus: experts

From the spread of mosquito-borne diseases to a rise in childhood asthma to surging numbers of heat-related deaths to increases in undernutrition – as the world continues to warm, the link between climate change and adverse health effects is growing more evident and more urgent. Rising temperatures expose people to longer and more intense periods of heat stress, while extreme and unpredictable weather makes it harder for farmers to grow nutritious foods and expands the areas where food-borne, water-borne, and vector-borne diseases can take hold. The World Health Organization (WHO) estimates that between 2030 and 2050, climate change is expected to cause approximately 250,000 additional deaths per year, from undernutrition, malaria, diarrhea, and heat stress alone.

About 45% of the world's population live in contexts that are "highly vulnerable" to climate change, according to the Intergovernmental Panel on Climate Change (IPCC), and many are already experiencing climate-related health issues. Researchers in India point to higher temperatures as a main cause behind the rise in cases of dengue fever in the country, where antibodies against the virus have been found in 50% of the population. A study in England showed that the risk of hospitalization for patients with chronic obstructive pulmonary disease increases by 1.5% for every one degree Celsius rise in temperature above 23.2 degrees Celsius. And in Nigeria, which has the world's second-highest rate of under-five stunting prevalence at 32%, researchers have found that the likelihood of a child being stunted increased by up to 0.71% per year with every one degree Celsius rise in temperature.

As a growing chorus of scientists and health experts call on policy makers working on climate change adaptation and mitigation to recognize the climate crisis as a health crisis, this year's COP28 climate conference featured its first-ever Health Day. The aims of the day, which was held on December 3, included promoting "health arguments for climate action," highlighting the challenges and best practices for strengthening the climate resilience of health systems and developing adaptation measures to address the impacts of climate change on human health.

As COP28 wraps up in the United Arab Emirates, Exemplars News spoke with experts about the many ways climate change can be harmful to our health and what can be done to protect communities from the harmful effects of rising temperatures.

Open-minded solutions to protecting pregnant women and newborns

For health workers who focus on women and newborn health, the challenge isn't just identifying the detrimental impacts of climate change on pregnant women and newborns, which, in part, are already known. Prolonged extreme heat, frequent heat waves, and exposure to air pollution due to the burning of fossil fuels have all been linked to increased rates of stillbirth, preterm birth, birth defects, hypertensive disorders of pregnancy, and more, although there is the need for continued research in some areas to better understand how they're connected. The issue is also how to capture robust data on both the climate hazard and the health impacts to help guide possible solutions, especially in lower- and middle-income countries (LMICs).

"It's not just temperature, there are so many other variables that have to be taken into account when assessing the effects of heat on health," said Dr. Francesca Conway, an obstetrician gynecologist based in Rome and consultant with the WHO. "From solar radiation to the type of clothing being worn, to wind speed, humidity levels, and acclimatization – these factors all contribute to heat stress which occurs when the body is unable to get rid of the excess heat and that can be quite dangerous and lead to heat strain. The thresholds at which heat stress is experienced may be very different among pregnant women and newborns, but we just don’t know what these thresholds are in vulnerable populations. In addition, the epidemiological evidence we have right now comes from high-income settings, so it's very skewed. In terms of how average summer temperatures are experienced, that could be very different in lower- and middle-income contexts."

Health experts are still not sure how the body's physiological response to extreme heat leads to adverse pregnancy outcomes. One leading theory is that when a pregnant woman sweats as her body tries to cool itself down, blood flow is diverted from the placenta to her skin, which can lead to dehydration, generating heat strain on the fetus. Another theory says exposure to extreme heat might generate the release of inflammatory markers or other types of stress hormones that can trigger physiological responses with negative health outcomes for both the mother and the fetus. "What studies have shown is that when the exposure to extreme heat happens in the earlier phases of pregnancy – within the first trimester, which is a critical vulnerability window, because it’s when the placenta is still being developed – there are associations with the development of conditions such as pre-eclampsia," said Conway. "When the exposure happens later in the pregnancy, for example in the second or third trimesters, that’s when we have observed associations with stillbirths or pre-term births."

Conway and her colleague Anayda Portela, a scientist at the WHO's Department of Maternal, Newborn, Child, and Adolescent Health and Ageing, are both part of a team looking at the solutions different countries have tried to combat heat-linked health impacts on maternal and child health. They said some of the most effective are long-term interventions that keep people cool while also improving other aspects of their lives. "The term 'co-benefit' comes up a lot," said Portela. "Mitigation of climate change in various sectors, such as housing, transportation, and energy, has many co-benefits that lead to substantial health gains and reduced health risks."

The team highlighted a project in Freetown, Sierra Leone, designed to protect street vendors from extreme heat. Street vendors make up a large number of the two billion workers in the global informal economy, and in LMICs the majority of street vendors are women. The Freetown Market Shade Cover Project, which was launched last year by the city's Chief Heat Officer Eugenia Kargbo in partnership with the Adrienne Arsht-Rockefeller Foundation Resilience Center (Arsht-Rock), installed shading covers over three outdoor markets to shelter vendors who work all day under the hot sun. Designed to be inexpensive and easily copied and maintained, the covers also contain solar panels that store energy during the day and power lights at night. This allows the women to make more money, some of which can go toward keeping themselves and their families healthier.

Keeping populations healthy as governments work on climate mitigation and adaptation will require an open-minded, multi- sectoral approach, said Conway. "There's no part of the world that's safer than other parts, in terms of rising temperatures. And, at the same time, the experience of heat stress is very diverse and unique in its relation to many different factors." she said.

"We don't have a one-size-fits-all solution, and that's part of our struggle," she added. "We do what works for each area or community, then in a few years we can bring those solutions together and say with more confidence what works and what doesn't. But that's only going to happen if we have a coordinated way forward."

Breaking the link between heat and mental health

The detrimental effects of climate change on mental health are well documented. People who live through climate-driven infectious disease outbreaks and spikes in air pollution, as well as extreme weather events such as floods, storms, and droughts, experience higher levels of psychological distress, which in some cases can develop into more serious mental health conditions, including post-traumatic stress disorder, depression, or substance abuse. The relatively new phenomenon of climate anxiety is also on the rise, with a growing number of people reporting some level of distress about the dangers of climate change. In one survey of 10,000 children and young people in 10 countries, 45% said their worries about climate change negatively affect their daily life.

There is also mounting research that heat itself is linked to a variety of mental health issues. "At least as far back as the 1800s, you can see sociologists who noted seasonal patterns in mental health outcomes, but it's only been in the past five to 10 years that we've had enough comprehensive data to relate mental health outcomes to changes in climate," said Marshall Burke, associate professor in the Global Environmental Policy unit at Stanford University's Doerr School of Sustainability, who has studied the connection between rising temperatures and suicide rates. "Our research shows that hot days and hot months are associated with increases in suicide risk. Other studies have shown that hot days are similarly associated with increases in visits to emergency departments for mental health-related challenges," he said.

In a study published in Nature Climate Change, Burke and his colleagues looked at the relationship between hotter weather and mortality data in the United States and Mexico over several decades. Controlling for seasonal factors, they found that suicide rates rose 0.7% in the U.S. and 2.1% in Mexico for every one degree Celsius increase in monthly average temperature. Using projections from global climate models, the researchers calculated that unmitigated climate change could lead to between 9,000 and 40,000 additional suicides across the United States and Mexico by 2050.

"All the studies that have looked at this [problem] show a very linear relationship: the hotter it gets, the more negative mental health outcomes you get," said Burke. "There's no threshold below which you're fine and above which you're in trouble."

The reasons that heat can contribute to higher suicide rates and other mental health conditions is still a mystery. "Science can't yet give us a crisp answer as to why – it's probably some combination of physiological changes and changes in social interactions. But we have enough data to know that it is indeed changes in temperature and not changes in something else that are causing these psychological reactions," Burke said.

Researchers have only recently begun to systematically evaluate the effects of interventions designed to shield people from the health impacts of climate change. While there are no proven solutions yet, there are plenty of projects and policies that show potential. But they are sorely under-adopted, Burke said. "Heat action plans are one way to reduce the negative impact on health and mortality. They help cities and communities know what they're going to do during a heat wave before it hits."

Cities with heat action plans often have dedicated cooling centers – buildings such as schools and churches equipped with fans or air conditioning where people can escape the heat. The plans also assign community groups and community health workers to do targeted outreach to vulnerable community members, such as the elderly and unhoused people, to warn them about incoming heat waves and check on anyone who may not be able to get somewhere cooler on their own.

Burke pointed to India as a role model. The country's first heat action plan launched in Ahmedabad, Gujarat state, in 2013, and includes sending text message warnings to everyone in the city when temperatures are forecast to rise above 40 degrees Celsius, painting the roofs of the homes of poor and vulnerable communities white to reflect heat, and keeping the gates to public parks unlocked during heat waves to allow outdoors workers to sit in the shade of the trees.

"Studies have shown that where these heat action plans have been put in place, they can be pretty successful in reducing mortality during heat waves, which is to me a great example of an intervention that can help break the link between heat and mental health," Burke said.

Hope in heat action plans

Jeni Miller, Executive Director of the Global Climate and Health Alliance, also credits heat action plans with effectively keeping communities safe from the health consequences of rising temperatures. And the most successful plans give communities a say in the design of interventions meant to protect them, she said. "It's not a simple thing to do, particularly in under-resourced communities because they have more pressing day-to-day issues, like can they feed their families," Miller said. "But there's enough evidence that shows if community members are involved and supported in decision-making around climate resilience, you end up with better and more effective plans for them to take action and protect themselves in extreme heat."

While many governments have had heat warning systems in place since the 1990s, the shift from simply alerting people to incoming heat waves to developing a set of steps and interventions to help them cope with extreme heat happened around 2003, when Europe was scorched by deadly summer heat waves. Parts of Europe experienced their hottest weather in 500 years and by the time the region started to cool back down, more than 20,000 people had died. The tragedy led scientists to ramp up research on the links between heat and health and awoke governments to the benefits of preparing communities before extreme heat events. Since then, a growing number of countries and communities have been implementing heat action plans, also called heat-health action plans, to lessen and manage the public health impacts of heat waves.

Just as important as dealing with the immediate health effects of extreme heat is fortifying communities and public health systems for future heat waves, Miller said. And that requires longer-term thinking. "What does it mean to be facing assault after assault in the climate space on people's health, on our health systems, and our collective capacity?" she asked. "We're already starting to see the overwhelming of our health systems and our humanitarian response systems. That problem is under-recognized at the moment, but we are seeing some concrete thinking about it in some places. The U.S. Centers for Disease Control's BRACE program (Building Resilience Against Climate Effects), for example, has provided grants and support to public health departments to develop their climate change capacity. And elsewhere in the world, there's work being done to address the long tail of impacts of climate events on health."

But these projects and initiatives cost money, and many countries are still unwilling or unable to devote significant amounts of funding to bolster resilience against the health effects of climate change. Of the average US$630 billion in global climate financing every year, less than 10% goes toward adaptation, with the bulk spent on cutting carbon emissions.

Finding more funding is the obvious solution. But for countries with limited resources, more important is figuring out how and where to spend whatever funding is available, Miller said. "Some communities don't even have basic access to the health care they need in the first place, access to clean water, healthy foods, clean energy," she said. "And we can't pull money away from doing the mitigation we need to do. There just needs to be a bigger pot of money. The conversation needs to shift towards, 'What are the costs if we don't make those investments [into adaptation]?' And those costs are overwhelming. So, it doesn't just make good sense for public health, but also good economic sense to increase investment in adaptation measures."