Climate change puts heat on public health

September 5, 2018

Climate change certainly has caused a cascade of calamities, from extreme heat and droughts to torrential storm and destruction of crops and forests.

And while scientists investigate the fingerprints of climate change, health researchers are learning how – and whom – bear the physical and social brunt.

The World Health Organization (WHO) projects some 250,000 additional deaths per year between 2030 and 2050 from the consequences of climate change, including from extreme heat, poor air quality, exposure to pathogens and insecure food and water supplies.

When it comes to heat and poor air, millions of people around the world felt, saw and smelled it this summer.

Environmental conditions will only worsen, and, like most global health issues, the poor and isolated are the most susceptible and defenseless, says Tarik Benmarhnia, a climate change epidemiologist with a joint appointment at UC San Diego’s Scripps Institution of Oceanography and School of Medicine.

Benmarhnia focuses on the relationship between climate change and population health, especially on vulnerable populations. And his work hopes to shed light on how to correct a new layer of “environmental injustice” rooted in climate change.

David Lopez-Carr, co-director of the UCGHI’s Planetary Health Center of Expertise, explained the climate change injustice. “The most culpable parties for climate change are not random,” he said. “They are concentrated among very wealthy corporations. The fossil fuel industry, and high consumers of their products, are particularly responsible for a disproportionate amount of climate relevant emissions.

“The most vulnerable are not geographically random,” said Lopez-Carr, professor of geography and director of the Human-Environment Dynamics Lab at UC Santa Barbara. “They are people in delayed stages of economic, health and demographic transitions, who have limited access to natural and capital resources. They are more likely to be located in geographically sensitive areas. They are the least likely to have the social, economic and political wherewithal to be resilient under climate duress.”

Scorching world

When we think of the extreme heat, deserts and other dry areas understandably come to mind. But urban areas are a growing concern. WHO estimates that 60 percent of people will live in cities by 2030, and the more densely populated cities become, the hotter they’ll get.

In urban areas -- where asphalt, concrete and dark roofs soak in the heat – the elderly, homeless, low-paid workers whose jobs don’t allow them to escape scorching temperatures and people who can’t afford or access air conditioning are the most vulnerable.  

UC San Diego’s Benmarhnia has studied heat waves around the globe. And he not only points to the risks of blistering heat, but also emphasizes possible solutions.

“We can likely expect heat waves to increase in intensity, frequency and duration,” he said. “And because there is a limit to what humans can handle, eventually it will simply be impossible to live in some places without concerted mitigation strategies, and efforts to control the contributing factors.”

One of his studies found a strong link between an area’s green spaces and its wealth. And people living in less vegetated areas, such as cities, had a six percent higher risk of illness and death from heat-related causes. It suggests that adding a little shade in cities in the form of urban tree canopies can help ease the effects of extreme heat.

A recent study co-authored by Benmarhnia looked at heat-related mortality in Montreal during hot summers, and concluded that “heat action plans” that targeted vulnerable people, including the elderly and people in low-education neighborhoods went a long way in preventing heat-related deaths and illnesses.

Another study, which he co-authored, found that even areas not usually considered extremely hot, are feeling harsh impacts of heat waves. Research in San Diego County found that residents were more sensitive to heat than those who lived inland. Heat-related problems were observed at lower temperatures, suggesting adaptation strategies are needed in coastal regions, too. 

The study also found heightened heat sensitivity in zip codes on the coast where fewer residents have air conditioning (AC). Additionally, when looking at access to AC, researchers found notable disparities related to income level, race/ethnicity and homeownership. Of course, homeowners and those in higher-income brackets were more likely to have AC and able to adapt to rising temperatures.

But solutions aren’t as simple as providing everyone with AC, said Benmarhnia. That may not be economically feasible, and large scale use of AC could add to environmental harm. Policymakers could focus and narrow efforts in key areas.

Breaking social isolation, identifying the “invisible” people most at risk, and bringing them into the community where they can be educated about heat risks and cared for should be part of mitigation efforts, said Benmarhnia.

While some of his current UC studies look at populations locally, they can have relevance globally, particularly in parts of the world were temperatures are even more searing and urbanization is rapid. He urges more focus on high-risk areas of the world.

“Most of the research into heatwaves and public health has focused on western countries,” said Benmarhnia. “More studies have been done on the city of Phoenix, Arizona, than the entire continent of Africa.”

Wildfires stoke disparities

Higher temperatures, drier conditions, larger areas of brush and fuel, and longer warm seasons – all linked to climate change – are posing wildfire dangers. The number of large wildfires – those covering more than 1,000 acres -- has increased from 140 to 250 a year in the western US states over the past 12 years, according to Union of Concerned Scientists.

Benmarhnia and UC co-researchers are studying wildfires in California. Studies of fires and wind patterns show that smoke and pollution are blowing, even hundreds of miles, to coastal and urban areas.  Like climate change-induced heat waves, pollution from wildfires picks more on the vulnerable populations – homeless, poor and workers who can’t escape bad outdoors air – who become more at risk for respiratory and other health problems.

While much effort and resources go to wildfire prevention and safety at and near fire sites, Benmarhnia hopes this research will guide policymakers to coastal and urban regions where alert and mitigation efforts can be implemented statewide and beyond.

Some of Benmarhnia’s heat and wildfire research is part of a project funded by the UC Office of the President. It is a multi-campus and multi-disciplinary effort that includes researchers from UCLA, Berkeley, Merced and San Diego that allows Behnmahrnia, a health scientist, to team with climatologists, hydrologist, ecologists, geologists, geographers and others to study health impacts of climate change.

“If we are to understand the causes of climate change, its effects and solutions, it will take collaborations with scientists from so many fields,” said Benmarhnia.

West Nile virus lingers

The project, titled “Drought and Public Health in a Warming California,” also examines the threat of West Nile virus (WNV)and Valley fever, two infectious diseases whose transmission cycles are sensitive to temperature and surface water dynamics influenced by climate change.

WNV – like malaria and dengue, which are more common in underdeveloped countries – is carried by mosquitoes, and it can be transmitted to humans.

In the US, it is the leading cause of mosquito-borne disease. From 1999 to 2013, a total of 39,577 cases of WNV disease were reported in the US. The locations of outbreaks vary, but several states, including California, have reported consistently high rates of disease in recent years.

Research has shown vegetation, humidity and soil moisture have made it easier for mosquitoes to thrive during the summer months. Now, the UC team will use hydrological model-based reconstructions of soil moisture combined with mosquito vector data to study the relationship between county and level incidence of WNV and hydroclimate variability.

While smoke-related illnesses are mostly an issue for coastal urban populations, WNV mostly affects inland populations of lower socioeconomic status.

The multi-campus UC study, with various specialists, is the kind of research required to learn about the many impacts of climate change on health.

We need teamwork,” said UCGHI’s Lopez-Carr. “No one of us can master all the burgeoning literature on the topic. To avoid being too narrow in our approach while bringing sufficiently deep expertise to the table, we need to collaborate.”