Air pollution is on its way to being eliminated entirely in the U.S. in about another 20 years. Levels of air pollution have fallen between 25 and 99 percent (depending on which pollutant you measure), with the nation’s worst areas showing the most progress. For example, Los Angeles has gone from having nearly 200 high ozone days in the 1970s to less than 25 days a year today. Many areas of the Los Angeles basin are now smog-free year round. Water pollution is more stubborn and harder to measure (and is being made worse in the Mississippi River basin by the government’s crazy ethanol mandate), but here too there have been major improvements since the first Earth Day in 1970. The Great Lakes have been cleaned up, with many previously endangered species of birds now thriving. The Cuyahoga River in Cleveland doesn’t catch fire any more. The amount of toxic chemicals used in American industry has fallen by 61 percent over the last 20 years, even as industrial output has grown. Forestland in the U.S. has been expanding at a rate of nearly 1 million acres a year over the last generation.