f an infectious disease was killing 7 million people a year, it would be ludicrous to work to allay its impact decades from now rather than taking immediate action against it. Yet that is exactly how we are approaching the causes of climate change, which are both immediate and long-term killers.

This week’s “airpocalypse” in New Delhi shows just how urgently action is needed to prevent the air pollution that is not only damaging our planet and human health in the long term but killing millions of people around the world in the present.

As the United Nations Conference on Climate Change reconvenes in Marrakech, Morocco, many experts are concerned that little concrete progress has been made in the year since the Paris agreement was crafted on preventing an irreversible increase in global average temperature that will have catastrophic consequences in the future. This concern is given new impetus because of President-elect Donald Trump’s skepticism about climate change, his vow to cancel the Paris agreement, and his commitment to exploiting fossil fuels as energy sources.


Yet there is a daily catastrophe that adds urgency to the need to contain fossil fuel emissions and the burning of biomass: the enormous numbers of deaths due to air pollution.

Scientists who measure the burden of disease around the world have only recently appreciated the global scale of death and disability due to air pollution. The World Health Organization has estimated that in 2012 almost 1 in 8 of all global deaths — that translates into 7 million deaths — were due to indoor and outdoor air pollution. UNICEF has estimated that 300 million children around the world breathe toxic air and 600,000 die each year from air pollution.

These numbers are far greater than the number of deaths due to HIV/AIDS, tuberculosis, and malaria combined. In addition to these deaths, air pollution causes immense disability through its contributions to asthma, chronic obstructive pulmonary disease, and heart disease and stroke. The grim death statistics also don’t include the hospitalizations, compromised lung function in children, premature births, and associated health care costs due to air pollution.

When it comes to climate change, carbon dioxide and other greenhouse gases get most of the attention. And though they certainly contribute to the immediate avalanche of death and disability, the biggest culprit is the very tiny particles in the air that also come from burning fossil fuels in power plants and automobile engines and in burning biomass to cook food, to heat homes, and to prepare fields for planting and clear land for cultivation.

Taking action to mitigate climate change would not only reduce the levels of carbon dioxide emitted into the atmosphere, but also would reduce emissions of the associated air pollutants — particulate matter, sulfur dioxide, nitrogen oxides, mercury, and more — that are directly harming human health today.

Why have we have underestimated the short-term health benefits of the climate change mitigation policies?

First, most of the cost-benefit analyses of climate change mitigation strategies project its harmful health impact decades from now. Surprisingly, they have not factored in the millions of lives that would be saved almost immediately as a result of reducing air pollution as well as limiting the occurrence of catastrophic weather-related events, such as heat waves, floods, blizzards, and forest fires.

Second, we initially thought that the steps to remove the larger, soot-like particles from fossil fuel emissions — the ones that caused smog events like the one that crippled London in 1952 — would be enough to eliminate the adverse health effects of fossil-fuel-related air pollution. Although removing larger particles from smokestack and tail pipe emissions has helped clear the skies in London and many other Western cities, we are coming to understand the health threat posed by even very low levels of smaller particles and their numerous chemical constituents.

These are called particulate matter 2.5, which refers to their size — under 2.5 microns in width, or about 20 times smaller than the width of a human hair. The smallest of these are so tiny that several thousand could fit on the period at the end of this sentence.

Third, the larger particles emitted by burning fossil fuels cause obvious damage to the lungs. Scientists initially thought that respiratory diseases like asthma and chronic obstructive pulmonary disease were the chief consequences of air pollution. More recent data show that particulate matter 2.5 also increases the risk of heart disease and stroke. Since these are major killers around the world, anything that increases their frequency has an outsize effect on premature death.

Finally, even as skies have become bluer in many developed countries, the “brown cloud” of air pollution has intensified rapidly along the east coast of China and in parts of India — some of the most densely populated regions of the world. Add in a new appreciation of the harmful health effects of indoor air pollution due to smoke from cooking fires, and air pollution has become one of the world’s major killers.

The steps needed to mitigate climate change in the future are substantially the same as those needed to reduce the burden of death and disability due to air pollution in the present — cut back on burning fossil fuels and biomass. In the dry terms of environmental economists, the enormous near-term health benefit of reducing these emissions is a “co-benefit” of climate change policies. Even climate change skeptics who deny the scale of future environmental impact should not tolerate of the millions of deaths currently caused by air pollution today.

This death and disability is not limited to other countries. Analyses of another program Trump has targeted for dismantling, the Clean Power Plan, project substantial short-term health benefits from controlling climate change in the US.

As the delegates in Marrakech continue their work, we ask them to also consider the urgency of the present. We also implore the incoming US administration to take stock of the health burdens of air pollution as they consider energy and environmental policies. Reducing air pollution is not only a matter of the future health of the planet, it is a matter of life and death in the here and now.

David J. Hunter is professor of cancer prevention and Francesca Dominici is senior associate dean and professor of biostatistics, both at the Harvard T.H. Chan School of Public Health.

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