UN success stories no one talks about: stopping acid rain

by Charles Arthur, 11 June 2025

Back in the 1970s and 80s, acid rain was a major environmental problem. Forests were dying in Europe, and lakes in parts of Canada and the United States were becoming too acidic for fish.

Acid rain is caused by sulphur dioxide and nitrogen produced by burning fossil fuel. When these emissions combine with water and oxygen in the atmosphere, they transform into sulphuric and nitric acid.

These pollutants blow over borders. Acidic droplets in clouds then fall as rain and snow. Back in the day, emissions from the UK lead to acid rain in Sweden and Norway; those from the US blew over to Canada. No country could solve the problem of acid rain on its own.

To tackle it, the United Nations stepped in. Specifically, the UN Economic Commission for Europe (UNECE) led the charge. In 1979, it brought European and North American countries together to sign the Convention on Long-range Transboundary Air Pollution (CLRTAP). It was one of the first international agreements to tackle air pollution that crosses borders.

UNECE then helped develop and implement a series of protocols (legal agreements) under the Convention. For example, the 1985 Helsinki Protocol required countries to reduce sulphur emissions by at least 30%, while the 1994 Oslo Protocol set stricter, country-specific sulphur reduction targets.

UNECE also coordinated monitoring networks, research and data-sharing systems that helped countries understand acid rain’s sources and effects. This built trust and made negotiations evidence-based.

Over the years, thanks to stricter laws, cleaner technologies and better fuel standards, sulphur emissions dropped dramatically (see the US Acid Rain Programme Results). By the 2000s, acid rain was no longer the major threat it once was.

But the problem has not disappeared altogether. Nitrates from sources like ammonia released from fertilizers and livestock feed remain a contributor to nitric acid precipitation.

There is concern that acid rain from both sulphur and nitrogen is an increasing problem in Asia. In response, the UN Environment Programme (UNEP) has promoted cooperation in Asia using lessons learnt in North America and Europe.

Meanwhile, threatening to overturn the good work in North America is the administration of US President Trump which is actively rolling back several key environmental protections that helped reduce acid rain.