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Fatal fumes: For the first time, science has proven that carbon emissions kill.

We’ve all heard the climate-change doomsday scenarios: devastating natural disasters, droughts, floods, and widespread crop failures. It’s easy to assume from those troubling predictions that higher levels of carbon dioxide emissions in the air, blamed for causing our climate woes, are probably not the best thing for human health, either. But there has been no real proof that higher CO₂ levels were actually killing people—until now. For the first time, new research directly links increased emissions to an increase in human deaths.

Using one of the most sophisticated computer climate models ever created, Mark Jacobson, a professor of civil and environmental engineering at Stanford University, has shown that, for every single-degree Celsius rise in global temperatures, increased CO₂ emissions lead to about 21,600 more deaths each year. That’s because, as the world warms, levels of corrosive ozone gas and toxic particles in the air also increase, particularly in places that already have a great deal of pollution. Inhaling the ozone gas and particles leads to more respiratory and cardiovascular illnesses, which for many people will turn deadly. As Jacobson explained in a video presentation posted on Stanford’s Web site, “Some people have said that you don’t inhale climate change. This study finds that you do.”

Drew Shindell, a climatologist at NASA’s Goddard Institute for Space Studies, calls...