United States officials have enforced a law called The Clean Air Act for more than half a century. The measure gives the federal government power to control air pollution across the country. Since 1963, the Clean Air Act has helped clean the air Americans breathe, control acid rain, and slow reductions in Earth’s ozone layer. The ozone layer helps protect people and other living things from the sun’s harmful radiation. In recent years, Presidents George W. Bush and Barack Obama used the act to control carbon dioxide and other greenhouse gases. Studies have linked those gases to rising temperatures and changes in Earth’s atmosphere. Obama, in particular, sought to limit the amount of carbon dioxide American power stations could produce. But President Donald Trump is not likely to continue on that path. Trump has questioned the reality of climate change. And, he suggests that federal environmental rules are hurting American businesses.