Rodney W. Nichols and Harrison Schmitt: In the U.S., and for much of the world, the most dangerous environmental pollutants have been cleaned up. U.S. emissions of particulates, metals and varied gases—all of these: ozone, lead, carbon monoxide, oxides of nitrogen and sulfur—fell almost 70% between 1970 and 2014. But a myth persists that is both unscientific and immoral to perpetuate: that the beneficial gas carbon dioxide ranks among hazardous pollutants. It does not.
