Q&A: How Climate Change Hurts Health

Aaron (Ari) Bernstein, MPH ’09, has studied the health effects of climate change from many angles. As associate director of the Center for Health and the Global Environment at the Harvard Chan School, he has explored the public health effects of such environmental stresses as global warming and loss of biodiversity and has shared the science with students, educators, policymakers, and the public. As a hospitalist at Boston Children’s Hospital, he has treated young patients with asthma and infections connected to environmental degradation. He spoke recently with Madeline Drexler, editor of Harvard Public Health, about the public health threats that await humanity if it fails to reverse climate change.

Q: Right now, what is the most salient public health problem tied to climate change?

A: If you want to find some of the least healthy people on the planet, you can find them among those who have been forced to move from their homes. This happened in Syria, where the 2006 to 2011 drought forced pastoralists who lived in rural areas to give up their herds and move to cities, where they were not welcome. In a politically unstable country, that was the last straw on the camel’s back that turned the tide to violence.

It also happened in Somalia, where the drought that began in 2011 precipitated a famine, displacing millions of people into neighboring countries that could scarcely afford to take them in. The trauma, violence, infectious disease, mental health problems, and nutritional deficiencies of migration: This is a pattern we will continue to see. And these severe droughts are expected to be more common as climate change unfolds.

Q: From a public health point of view, will removing carbon from the atmosphere equally benefit rich and poor countries?

A: If we mitigate greenhouse-gas emissions, the health benefits in developing nations will actually be far greater than in developed countries. Think about events like Hurricane Matthew, which struck Haiti this fall. Forecasting models tell us that although hurricane frequency is likely to decrease, hurricane intensity is likely to increase over this century—we’re expecting more intense storms.

In a place like Haiti, there’s mass deforestation, huge potential for mud- slides. You throw at it this enormous storm with 145-mile-per-hour winds and 40 inches of rain—the consequences are wildly, wildly more severe for a place like Haiti than if that same storm with the same intensity hit any U.S. city.

Q: You’ve pointed out that some greenhouse gases directly influence plants. Why is that important to human health?

A: Greenhouse gases not only warm the atmosphere and alter the water cycle—they have direct effects on many species, including plants. If you elevate the concentration of atmospheric carbon dioxide, that changes the nutritional profile of certain staple food crops.

A 2014 study in Nature, which was co-authored by the School’s Samuel Myers [senior research scientist in the Department of Environmental Health], looked at the carbon dioxide levels expected in the atmosphere by 2050—not so far off. The researchers found a 9 percent decrease in the zinc content of wheat. That’s important because zinc deficiency is a major risk factor for morbidity and mortality related to many childhood illnesses, particularly infectious illnesses. Kids who are zinc-deficient are much more likely to get sicker and potentially die from diarrheal disease or pneumonias.

The researchers also found an almost 8 percent decrease in the amount of protein in rice. That’s important because for the majority of the world’s population, particularly Asians, most dietary protein comes from the consumption of plants, not from meat. For corn, there was roughly a 5 percent reduction in zinc, iron, and protein.

If you look at where existing iron deficiency, zinc deficiency, and protein deficiency occur, and you look at the foods that people around the world eat, these decreases in crop nutritional content will have huge effects on nutritional status.

Q: Today, there is a mountain of data about climate change and health. What remains your biggest scientific question?

A: How is it that people can look at what we know about climate change and conclude that the science is uncertain, or that the health effects are so unpredictable as to justify inaction? A look at the forecasts in the U.S. government’s National Climate Assessment for the year 2100 makes you realize how many lives could be saved, how many illnesses could be prevented, by doing what we already know how to do to mitigate climate change. Reducing greenhouse gases in the Earth’s atmosphere may be the greatest public health intervention ever.