Health at a planetary scale

The human footprint on the earth has grown explosively over the past century or two. Two hundred years ago, there were about 1 billion of us; today, we number more than 7 billion. We have harnessed vast amounts of energy, cleared countless forests, dammed thousands of rivers, reconfigured entire coastlines and built vast cities. We appropriate about half the planet’s accessible fresh water and nearly half the desert-free land surface to feed ourselves.

The results are evident at a planetary scale. The globe is warming. Oceans are becoming more acidic. Natural cycles of nitrogen and phosphorus have been greatly altered; runoff fertilizer contributes to hundreds of “dead zones” along coasts. (This year’s Gulf of Mexico dead zone is twice the size of the Chesapeake Bay.) Almost a third of tropical forests and a fifth of coral reefs have been lost, species are disappearing at unprecedented rates, major fisheries are depleted, and persistent organic chemicals have infiltrated even remote ecosystems. Human effects on the planet are so profound that earth scientists have named a new geological epoch: the Anthropocene.

Both of us are physicians, and over the course of our careers we’ve come to realize that these trends are more than just environmental problems: They’re also urgent threats to human health and well-being. While human health is now, by most metrics, better than it’s ever been, ongoing planetary changes threaten to reverse that progress. These threats require a new approach to health research and health policy–a new paradigm that has come to be called “planetary health.”

As a young doctor, Sam spent years working on environmental conservation and human development projects, and realized that ecosystem degradation caused much of the suffering he saw. Howie worked at the U.S. Centers for Disease Control and Prevention, where he led that agency’s environmental health work; while focusing on traditional issues such as chemical contaminants, he realized that large-scale threats, such as climate change, accounted for more and more of the global burden of disease. We both saw the need to link human health directly to the health of the earth’s natural systems on which we depend.

Planetary health asserts that human beings cannot thrive over time while degrading the ecological life support systems that sustain us. Like traditional public health, it defines health broadly, including physical, mental and social well-being; it considers health not just as an individual attribute, but across entire populations; and it pays special attention to those who are most vulnerable. However, it works at large scales, both spatially (from regional to global) and temporally (anticipating the effects of current trends across generations). It regards ecology and the earth sciences as pillars of health science. It rejects the false dichotomy of people vs. nature and holds that to protect people, we must protect natural systems.

This field is growing rapidly. In the past few years, almost 20 universities have introduced programs or courses in planetary health, from the large University of California system to tiny Doane University in Crete, Nebraska. The University of Sydney recently appointed the world’s first professor of Planetary Health. The British medical journal The Lancet and the American Geophysical Union have both launched new academic journals dedicated to this field. Two leading health funders, the Rockefeller Foundation and the Wellcome Trust, are investing in planetary health. (Our work in planetary health has been supported by both funders.) A coordinating body, the Planetary Health Alliance, hosted an inaugural annual meeting in April 2017 at Harvard Medical School that drew over 350 people from 25 countries.

The planetary health framework is now shaping research in domains from river ecology to urban planning, from nutrition to land use. This research takes a systems approach to solving real world challenges, knitting together issues that have traditionally been isolated from each other.

Rivers provide one example. Rivers and lakes in many parts of the world provide habitat for the parasite that causes schistosomiasis. Along one river in Senegal, after a dam was built and altered the ecosystem, this devastating disease spiked. Researchers studied the impact of reintroducing freshwater prawns; the prawns feed on the snails that transmit this devastating disease. The research showed that shrimp farming simultaneously controls schistosomiasis, provides nutrient-rich food to the local population, and helps alleviate poverty.

Cities, where more than half the world’s population now lives, offer another example. Though they offer economic opportunity, cultural vibrancy and potential environmental benefits (due to lower per capita carbon footprints), cities can also pose such hazards as polluted air, noise, substandard housing and nature deprivation. A planetary health approach blends health science with architecture, urban planning, transportation policy, food policy, energy policy, climate science, disaster planning, ecology and more. For example, greenspace and tree canopy reduce the urban heat island and help prevent heat-related deaths. Transportation systems that emphasize walking, cycling and transit promote physical activity and reduce air pollution and CO2 emissions. Green building design reduces energy use, maximizes daylight and optimizes indoor air quality. Such evidence-based solutions help create healthy, sustainable, resilient cities.

Food is yet another example. Agronomists have known for some time that climate change reduces the yield of most major food crops. But climate change has other effects as well: rising carbon dioxide levels erode the nutritional quality of many foods, lowering the levels of critical nutrients including protein, zinc and iron. This research helps anticipate hot spots of potential malnutrition and helps drive the search for more nutritious cultivars.