Every year, more than four million people around the world die prematurely from breathing dirty air. In China alone, the number of deaths attributable to air pollution exceeds one million annually.
That figure may not come as a surprise; after all, we are routinely treated to images in the media of thick, sooty smog enveloping Beijing, Shanghai and other Chinese cities. But America's air kills, too - and it is getting a lot less attention.
A 2013 Massachusetts Institute of Technology study estimated that poor air quality accounts for 200,000 early deaths in the United States each year, more than the number killed by car crashes and diabetes (other studies have put the number lower, closer to 100,000).
Yet, while China today is aggressively tackling its air pollution problem, the US is rolling back air-quality protections in the name of economic growth - an ill-conceived strategy that will have a devastating impact on human health.
Ever since the publication of Harvard's Six Cities study in 1993, scientists and public-health officials have been aware of the links between mortality and fine particulate matter, or PM2.5 (airborne particles with a diameter of less than 2.5 microns).
When people inhale PM2.5, microscopic solids and liquid droplets of dust, dirt, organic chemicals and metals can travel deep into the lungs and even enter the bloodstream. Research over the past 20 years has tied PM2.5 to a range of adverse health outcomes, including asthma, acute bronchitis, lung cancer, heart attacks and cardiorespiratory diseases.
We know, too, where PM2.5 mostly come from: power plants, heavy industry and motor vehicles. During fossil-fuel combustion, carbon dioxide - the world's most prevalent greenhouse gas - is emitted into the air, along with particles of incompletely combusted solids and gases (mainly sulphur dioxide and nitrogen oxides) that react chemically in the atmosphere to form fine particulate matter.
Knowing the killer pollutant and its sources, the US Environmental Protection Agency (EPA), under the 1990 Clean Air Act, issued new standards to reduce PM2.5 levels. The EPA estimates that between 1990 and 2015, the national concentration of particulate matter fell by 37 per cent, and that in 2010, some 160,000 premature deaths were averted as a result of the regulations. In short, despite a considerable number of deaths still linked to dirty air, the US had, until this year, been heading in the right direction.
Now, however, US President Donald Trump has promised to create "unbelievable prosperity" by discarding regulations intended to reduce toxic emissions from coal-fired power plants, lowering or eliminating fuel-efficiency standards for automobiles, and dismantling the EPA. He has also vowed to repeal limits on fracking, open up more public lands to coal mining, and expand oil and gas production in the Arctic and Atlantic Oceans.
There are alternatives that don't require a zero-sum trade-off between economic growth and human health. And, ironically, one place to look for inspiration is China.
Holding up China as a model to emulate might seem absurd. After all, its PM2.5 levels are considerably higher than those in the US, and consumption of fossil fuels, especially coal, is far greater. But Chinese policymakers are taking vigorous steps to reverse course, free the country from its dependence on fossil fuels and create a future-oriented economy powered by clean energy and green technology.
Today, China is the world's largest investor in renewable energy, with outlays in 2015 totalling US$103 billion (S$141 billion), more than double the US spending of US$44 billion. Of the planet's 8.1 million jobs in renewable energy, 3.5 million are in China, whereas fewer than one million are in the US.
Persuaded that clean energy is good for the environment and the economy, China has committed US$367 billion through 2020 to the development of renewable power sources - a level of investment that is expected to generate 13 million jobs.
China is also looking beyond its borders, by exporting the expertise it has developed in renewable energy.
China's dependence on fossil fuels has left it in a deep environmental hole, but its leaders are determined to climb out. The US, on the other hand, is literally digging its own grave.
• The writer is Professor of History at Smith College. His latest book is Environmental Pollution In China: What Everyone Needs To Know.