The Lancet study also found that indoor air pollution, largely from smoky coal- or wood-burning cook stoves in countries in Africa, and in India, caused some 3.5 million premature deaths in 2010. That number has tumbled over the past two decades, but it's still high. Efforts to promote cleaner-burning cook stoves in the developing world have been fairly sluggish, although the problem has attracted plenty of global attention in recent years.
So will the pollution problem get worse or better in the years to come? A big reason that soot and other pollutants killed 2.1 million people in 2010 is that China and India are growing so quickly. On the whole, that's terrific news. But it means more people can afford to drive cars and trucks in cities like Beijing and Delhi. That means more fine particle pollution that can bury deep into the lungs and enter the bloodstream. High levels of soot have been linked to everything from asthma to heart attacks to, yes, death.
That trend won't stop anytime soon. China currently has one car for every 17.2 people. In the United States, there's one car for every 1.3 people. If China were to catch up with the U.S. car ownership rate, the country would field a billion vehicles all by itself.
Still, that doesn't have to mean mass death from pollution. The usual argument is that environmental indicators typically get worse as countries grow. But when countries reach a certain point of development, its citizens will start demanding cleaner air and water and push for stricter pollution controls. This is known as the "environmental Kuznets curve" — though it's still not clear at exactly what point the curve breaks. Yet as Bryan Walsh points out, there are plenty of European cities with much higher rates of car ownership than Delhi and much less pollution. Cleaning up soot is perfectly doable; it just takes a bit of money.
(Incidentally, there's a good debate about whether the environmental Kuznets curve applies to trickier environmental problems like global warming. Recently, Bill Blackwater wrote a long essay arguing that it doesn't.)
In any case, while the new Lancet report talks a lot about death and all the things that are killing us, there's some good news too. As this map from New Scientist shows, life expectancy has soared since 1970 in most parts of the world — apart from the Caribbean, Lesotho (AIDS) and Belarus (heavy drinking):
So, it's true, cleaning up air pollution is an urgent public health problem. But in the grand scheme of things, it's a good problem to have.