The scientist who discovered it warns of an imminent repeat of an environmental hazard.

The United States risks sliding back into a period of toxic acid rain — a major environmental threat that was solved decades ago — due to pollution regulation rollbacks by the administration of Donald Trump, warns a scientist who first identified acid rain in North America.

Gene Likens, whose 1960s research revealed alarmingly acidic rainwater in New Hampshire, warns in a new study that dismantling key air and water protections could undo decades of progress. Under the Trump-era Environmental Protection Agency (EPA), efforts to loosen or eliminate 31 environmental regulations threaten to revive conditions that once left skies choked with smog and ecosystems damaged by acidic precipitation.

Gene Likens in his laboratory in 2015. Credit: public domain

Likens, now 90, is still actively involved in a rainwater monitoring project that recently lost federal funding. He expressed concerns that the Trump policies would deprive the next generations of clean air, clean water, and healthy soil.

Likens’ discovery in 1963 — that rainwater was 100 times more acidic than expected — sparked years of research linking acid rain to emissions from coal-fired power plants. By 1980, rainfall in the U.S. was on average 10 times more acidic than normal, harming lakes, forests, and infrastructure.

Public outcry and scientific advocacy led to bipartisan political action. In 1990, President George H.W. Bush signed an amendment to the Clean Air Act aimed at reducing sulfur dioxide and nitrogen oxide emissions, which helped curb acid rain. Since then, acid levels in rain have dropped by 85% in some regions.

This EPA image illustrates the pathway for acid rain in our environment: (1) Emissions of SO2 and NOx are released into the air, where (2) the pollutants are transformed into acid particles that may be transported long distances. (3) These acid particles then fall to the earth as wet and dry deposition (dust, rain, snow, etc.) and (4) may cause harmful effects on soil, forests, streams, and lakes.

Acid rain was an environmental success story — a rare example of science, policy, and public will aligning – but if emissions controls are lifted, that progress will be destroyed, the scientist stated.

Former EPA administrator William Reilly, who oversaw the 1990 policy changes, echoed Likens’ concerns. “I do think this administration will take us back to a pre-EPA world. That will mean unbreathable air, places where there is pollution that you can see, rivers that burn. That is what it was like before and that is what it could be like again if enforcement is cut back,” Reilly told journalists.

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Scientists agree a return of acid rain wouldn’t happen overnight, but warn the path back has already been paved. “It would take years, but we’re moving in the wrong direction,” said Richard Peltier of the University of Massachusetts. “We know better — why would we go backward?”

Current EPA Administrator Lee Zeldin has framed the regulatory rollbacks as a strike against overreach.

“This is the greatest day of deregulation in American history,” Zeldin declared while his agency’s own data predicts the rollbacks could lead to thousands of additional deaths and increased rates of heart and lung disease across the continent.

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Likens’ longtime acid rain monitoring program near New York’s Finger Lakes had its funcind from the National Oceanic and Atmospheric Administration cut as part of broader efforts to shrink federal environmental oversight.

“There was no explanation. Without research, we’re flying blind,” Likens noted.

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