Developed nations have drastically improved air and water quality while sustaining economic growth. Between 1990 and 2008, the US cut emissions of six common pollutants by 41 percent, while gross domestic product (GDP) grew 64 percent, according the US Environmental Protection Agency (EPA). Much of that success is attributed to the the Clean Air Act, first signed in 1970 and revised in 1990. The nation's water, too, is cleaner. Since the passage of the Clean Water Act in 1972, billions of pounds of sewage, chemicals and trash have been averted from US waterways, and the number of American waters that meet standards for swimming and fishing has doubled, according to the EPA.
Still, conventional pollutants still pose a challenge to developed nations and are a rising challenge for the developing world – The skies of Los Angeles may be clearer, but Beijing is coming to grips with a smog problem of its own. Meanwhile, the risks of greenhouse gas emissions have reached new levels of urgency.