A Warming World

In the preceding chapters, we’ve focused largely on what is often called “traditional pollution”: soot and smog and their precursors, sulfur dioxide and nitrogen oxides. But power plants are also the nation’s largest source of a very different sort of pollutant: carbon dioxide. Unlike traditional pollution, atmospheric CO2 does not pose a threat to public health through inhalation. As every schoolchild learns, humans exhale CO2 during normal respiration, and plants absorb it as part of the photosynthesis that fuels their growth. Carbon dioxide does, however, act as a “greenhouse gas.” Like the glass of a greenhouse, molecules of CO2 let sunlight pass through to warm the earth but then trap some of the heat that radiates back from the planet’s surface. Up to a point, this heat-trapping effect is beneficial; without it, the earth would be too cold to support life. But when humans burn fossil fuels, carbon that has been sequestered underground for millions of years is rapidly released in the form of CO2, and the natural carbon cycle is altered. As the concentration of CO2 in the atmosphere increases, the greenhouse effect becomes stronger, and the earth’s surface temperature rises. Over time, warming driven by ever-increasing industrial emissions of CO2 is expected to have serious, possibly devastating consequences for all corners of human society. (There are other greenhouse gases, like methane, but CO2 is by far the most common, accounting for more than 75 percent of global greenhouse gas emissions and almost 85 percent of U.S. emissions.) And yet, when President Obama took office in 2009, almost forty years after the U.S. Congress passed a piece of legislation designed to eliminate all air pollution that posed a threat to public health and welfare, emissions of carbon dioxide were still entirely unregulated at the federal level. As the President observed in his first Earth Day address on April 22, 2009: “[W] e place limits on pollutants like sulfur dioxide and nitrogen dioxide and other harmful emissions. But we haven’t placed any limits on carbon dioxide and other greenhouse gases. It’s what’s called the carbon loophole.”