Skip to:

Q&A: Health Effects of Climate Change


FSPH professor and chair of the Department of Environmental Health Sciences Michael Jerrett addresses what’s happening, what’s projected, and the direct connection between planetary and human wellness.

“Many people don’t fully appreciate the health implications [of climate change]. They think it’s only an issue of shrinking glaciers, melting ice caps and endangered species, like polar bears.”
— Michael Jerrett

Michael Jerrett

AS A LEADING SCHOLAR IN HIS FIELD — named to the Thomson Reuters List of Highly Cited Researchers, indicating he is in the top 1 percent of all environment/ecology authors when it comes to citations by other researchers — Michael Jerrett has assessed the health impacts of climate change from many angles. Jerrett, professor and chair of the Fielding School’s Department of Environmental Health Sciences, spoke with FSPH’s Public Health Magazine about climate change’s health implications and the role for public health in limiting the negative effects. 

Q: Climate change has often been associated with events that are removed from people’s everyday lives. Beyond the threat to our natural environment, why is climate change a health issue that everyone should be concerned about?
A: Right, many people don’t fully appreciate the health implications. They think it’s only an issue of shrinking glaciers, melting ice caps and endangered species, like polar bears. It might seem like it’s solely happening far away, or that the negative effects to the planet are many years off. In fact, climate change has very real implications for human health, both here in the United States and in other parts of the world. Those effects will become more severe with time if we don’t dramatically reduce the emissions that are driving climate change, but the effects aren’t just long term; many are being felt today, and will grow as public health concerns within our lifetimes.

Q: The Earth has warmed 1 degree Celsius — 1.8 degrees Fahrenheit — since the 1800s. Why is this a big deal? In the absence of dramatic steps to reduce greenhouse gas emissions, how much warmer is it likely to become, and why does this matter?
A: The Paris Agreement — in which nearly 200 nations pledged to take steps that would keep the global mean temperature increase well under 2°C [3.6°F] through the end of this century — was premised on the goal of avoiding severe change, which is categorized as more than 2.5°C [4.5°F] above preindustrial levels. We’re currently exceeding all of the worst-case emission scenarios that were used in those models, so it appears likely that we’re headed for increasingly severe types of events involving extreme heat, flooding, wildfires, hurricanes, droughts, famines, and infectious disease outbreaks.

Q: What are some of the likely health consequences?
A: In the near term, the most certain effects are that we’re going to experience an increase in the number of extremeheat days. That’s going to affect things like how we conduct agricultural harvesting and planting, as well as construction work and other outdoor jobs. If you look at parts of the world that are already very hot, like India, and then add 30-40 more really high-temperature days each year, the ability to conduct work outside is going to be curtailed substantially, because there is a temperature beyond which the human body simply can’t function properly and people start to experience heat stress and heat stroke.

We are also likely to experience fairly dramatic changes to the water cycle. The reason we now call it climate change instead of global warming is that, while the mean temperatures are going up, the variability is also increasing substantially, which affects the hydrological cycle and is going to mean that much of our water will come in bigger storms at unusual times of the year, where you don’t get the same infiltration and recharging of the groundwater. It means longer periods during which it will be very dry, followed by heavy rain. In California this could result in more large wildfires over a longer season. We’re also seeing more extreme weather events like large storms and hurricanes, and although it’s uncertain whether that is attributable to the changing climate, it could have to do with the higher temperatures increasing the moisture in the atmosphere from the evaporation of the sea surface, and creating additional energy as it moves toward North America. Obviously, more fires and floods are going to have health effects. Then there’s the whole issue of sea-level rise, which is predicted to be around a meter by the end of the century but won’t be felt evenly — some areas are going to experience 2- or 3-meter rises. This will especially affect the low-lying coastal areas.

There is a good chance we will see more air pollution as well. The majority of models predict a so-called climate penalty within the next 30-50 years, with conditions that will become more conducive to the formation of secondary particles — nitrates, sulfates and organic carbon — that are associated with negative health effects. It’s also possible that if we do see longer, hotter, drier seasons, the ozone could become worse because it requires more sunlight to form. 

Q: What are some examples of public health strategies to combat current and future health effects from climate change?
A: You’re referring to what we call adaptation — to the extent that the climate is changing and that’s associated with negative health consequences, how can we adapt to either prevent or reduce these impacts? Adaptation includes strategies such as avoiding development in flood-prone coastal areas because of the threat from hurricanes and sea-level rise. It also includes strategies in the category of ecosystem services — ensuring that where possible, cities are building infrastructure that takes adaptation into account. One example would be managing stormwater so that as precipitation is coming from more intense storms, cities have more areas that can absorb the water either naturally or through something like retention ponds. In addition to preventing flooding and retaining water that could be used for other purposes, these ponds could have aesthetic and mental health value in the form of stress reduction.

As we think about adaptation from a public health perspective, we will need to focus those efforts on socially disadvantaged communities and populations, because they are less likely to have the resources to adapt — to be able to afford central air conditioning in their homes, for example, as a way of adapting to the extreme heat.

Q: What actions can be taken to slow or reduce the extent to which the climate is changing?
A: We call that mitigation, and that’s where the effort is being made to limit the mean global temperature increase to 2°C. That means reducing the emissions of greenhouse gases and other short-lived climate-forcing pollutants. The biggest contributor, and the key reduction point, is fossil fuel burning. Switching to renewable energy that’s more carbon-neutral is a key mitigation strategy. And in agricultural areas, the livestock put out a significant amount of methane through flatulence. Another category has to do with large-scale landscape changes. When we deforest large areas, for example, it reduces the Earth’s ability to store the carbon, so we have to be concerned about that.

One public health strategy that helps with both mitigation and adaptation involves the greening of cities. Greening public areas, as well as encouraging homeowners to have more plant cover in their yards, can have a significant cooling effect. Large studies have found that when cities have more vegetative cover as a buffer against the heat, it can make a difference of between 1.5° and 4°C. In fact, adding green space is a triple-win — potentially improving emissions, cooling cities in the face of a warming climate, and bringing health benefits by promoting physical activity and reducing stress.

Q: A report by the U.N. Intergovernmental Panel on Climate Change released last October warned that the world  has a little more than a decade to turn things around. What do you say to those who feel helpless that more isn’t being done to treat this as a crisis?
A: There are steps we can take, both as individuals and within our communities [see page 23]. And beyond the specific public health strategies I’ve mentioned, we can make it clear to policymakers that effective action to move toward zero carbon emissions is needed. For those of us in public health, we must continue to lead the way in conducting research and disseminating the scientific knowledge we gain from that research in ways that will lead to the types of policies that will make a difference for the health of the planet and the human populations that inhabit it. 


Climate change is occurring on such a large scale that it’s easy for individuals to feel helpless to stop it. In fact, according to two Fielding School experts, although the government and private sector bear significant responsibility for taking the bold actions needed to combat climate  change and adapt to its effects, there are steps individuals can take to ensure they are participating in the solution rather than contributing to the problem.

. Individuals can reduce their carbon footprint by limiting air travel, shifting to energy-efficient vehicles, and minimizing the amount of time they spend in their cars, including through such strategies as carpooling. “If it’s feasible and safe to do so, actively  commuting — on bicycle or on foot — or taking public transit is a great way to have a positive impact,” says Michael Jerrett, professor and chair of FSPH’s Department of Environmental Health Sciences, who makes his daily commute to the Fielding School by bicycle. Active commutes have an individual benefit as well, of course. “It’s much healthier to burn fat than it is to burn fossil fuels,” says Dr. Richard Jackson, FSPH professor emeritus of environmental health sciences.


 — particularly beef, pork and lamb — adds to carbon emissions. “It’s been said that our modern agricultural system is really about taking fossil fuels and converting them into food energy, because of the role of petrochemicals in our agricultural system,” Jerrett says. Another dietary strategy: Buy local. “The average piece of food on an American’s plate has come from 1,100 miles away,” Jerrett notes. “It’s not always possible in much of the country, especially in winter, but whenever you can buy locally sourced foods, it makes a positive impact.” Jackson adds that for those who can, growing food in a home garden is ideal both as a carbon-limiting strategy and for its physical and mental health benefits.


 to fight climate change involves reducing consumption of fossil fuel-based energy. Where feasible, change standard lightbulbs to energy-efficient versions and unplug appliances that aren’t in use. A side benefit is that these changes can also save money. Beyond conservation measures that many can employ, homeowners can install energy-efficiency improvements in the form of energy-saving appliances, and even switch to solar-powered water and heating, Jerrett notes. If a homeowner also has outdoor space, keeping it green is preferable to paved for two reasons — green spaces serve as a “carbon sink,” absorbing carbon dioxide rather than releasing it into the atmosphere, where it contributes to climate harm; and for the cooling effect. “Concrete and other structures absorb heat at a higher rate than the natural environment, creating an urban heat island effect, so it’s important not to unnecessarily pave over areas that would otherwise be green,” Jerrett says.