Photochemical or ozone problems, late to arrive on the scene, first came to public attention in Los Angeles, when people noticed that despite the fact that the air looked clean, residents were getting sick. Detective work carried out by researchers at the California Institute for Technology proved that the problem was ozone, but the question of the origin of the ozone remained. Ozone, it was revealed, was a secondary product of the interaction of oxides of nitrogen produced by automobiles, hydrocarbons, and sunlight. The complicated chemistry of ozone, states McElroy, means that the wrong policies could bring about ineffective or unexpected results.

Our climate issue is the end product of extracting energy by burning such fossil fuels as coal, oil, or natural gas, and producing carbon dioxide ( CO2). The concentration of CO2 in the atmosphere has been increasing at an accelerating rate in the past 250 years. The CO2 derived from fossil fuel, is the single largest waste product that we produce as an industrial society. On a global basis, we produce more than six billion tons of carbon as CO2 by burning fossil fuel, the equivalent of a ton of carbon per person per year. The United States alone produces 22 percent of this total; in other words, the U.S., with 5 percent of the world's population, produces roughly a quarter of the world's emissions.