At the end of the last century, a great environmental crisis came from above in the form of acid rain. As the precipitation “killed” lakes and streams, alarming studies reported massive die-offs of trees and fish. A 1984 Congressional report estimated that acid rain caused the premature death of about 50,000 people in the United States and Canada. But in the last decade, acid rain has all but fallen off the radar. So is the threat really over, or just in hiding?
As long as we’ve been burning fossil fuels, acidic liquid has been falling from the sky. A British chemist coined the term “acid rain” in 1856, in the early throes of the industrial revolution, but it wasn’t until the 20th century that the world took notice. In the 1974 Science paper “Acid Rain: A Serious Regional Environmental Problem,” which made “acid rain” a household term, scientist Gene Likens and his team reported on New Hampshire rain showers as acidic as lemon juice.
“You sing in the rain, you wash your hair in the rain, you walk in the rain,” Likens says. “And then you see the rain, there’s something wrong with it.”
Throughout the 1980s, the complex and widespread effects of acid rain became visible to the naked eye, all over the world. Tall smokestacks burned coal and released airborne sulfur and nitrogen, which returned to Earth as sulfuric acid and nitric acid. In highly acidic streams and lakes, the fish eggs stopped hatching, and in acidic soil, trees withered and died.
Streams of dying fish running through forests of dead trees are just the beginning: Acid rain also causes the corrosion of building materials like limestone and marble. In particulate form, as sulfates and nitrates, it gets lodged in the tiniest recesses of human lungs and causes major health problems.
In 1990, Congress strengthened the Clean Air Act to limit the amount of sky-borne sulfur. As a result, rainwater has become less acidic and most of the toxic lakes and streams are improving—and supporting life. People are breathing easier, too: according to a 2003 government study, the action to curb acid rain resulted in the “largest quantified human health benefits of any major federal regulatory program implemented in the last 10 years, with benefits exceeding costs by more than 40:1.”
Even with the program’s success, Likens cautions, the soil still hasn’t recovered, and the threat of nitric acid remains. And that’s just in the United States: as other countries increase energy production by incinerating fossil fuels, acid rain is on the rise.
These problems plague much of the industrialized world: In parts of Russia, where the trees are long dead, acid precipitation is so dense that enterprising engineers have begun collecting the residue and mining it for metals.
“It is a widespread problem around the world and is an absolutely burgeoning problem in China, where they’re ramping up the burning of coal,” Likens says. “The only way to resolve this problem is to cut back the emissions.”