What made the acid rain myth finally evaporate?


DR WILLIAM REVILLE UNDER THE MICROSCOPEWhatever happened to acid rain? Back in the 1970s and 1980s it was killing our forests, acidifying lakes so they could no longer support life, and leaching metals out of soil into waterways where they could attack human health. Feelings ran high.

In 1993, John Gummer, UK secretary for the environment was called a drittsekk ("sack of shit") by Thorbjorn Bernsten, Gummer's Norwegian counterpart, for failing to take air pollution seriously.

Nowadays we don't hear of acid rain. Have we solved the problem, and how big was it anyway? The answer to the first question seems to be a qualified yes, and to the second - not very big.

Acid rain was mainly caused by emissions of sulphur dioxide to the atmosphere from coal-fired power stations, and by emissions of oxides of nitrogen from various sources. These gases, combined with water in the atmosphere to form sulphuric and nitric acids. The acids fell to earth as acid rain and studies purported to show acid rain damaged trees, polluted streams, lakes and rivers and damaged wildlife and buildings. It was estimated that 4,000 lakes in Sweden were acidified to the extent that no fish could survive and thousands of lakes in America were likewise "killed". In the UK, acid rain was blamed for destroying toads and for eroding the structure of important buildings.

Acid rain was dealt with in the 1980s and 1990s. By switching from coal to gas and installing "scrubbers" to clean up power station and factory emissions, huge reductions were made in acid rain pollution in Europe. Catalytic convertors on car exhausts reduced nitrogen oxide emissions. The US Clean Air Act Amendments, designed in part to control sulphur dioxide emissions, were passed in 1990.

Emissions of sulphur dioxide and nitrogen oxides are now under control in Europe and America generally, but emissions from shipping still cause acid rain in coastal areas. Some experts warn that increasing acidity of the oceans could destroy all coral by 2065. Also, acid rain persists in China, which now burns half of all coal burned in the world annually.

How dangerous was acid rain? The most comprehensive study was commissioned in 1980 by US president Jimmy Carter. The National Acid Precipitation Assessment Programme (NAPAP) examined the damage caused by acid rain and recommended solutions. In 1982 president Ronald Regan raised the annual budget for NAPAP to $100 million. The final cost of NAPAP, the most costly environmental study in US history, was $537 million.

The situation turned out to be much more complex than had been predicted. The acidity of a lake is determined as much by the acidity of the local soil and vegetation as it is by acid rain. Many lakes in north-eastern America, dead in the 1980s, had plenty of fish in 1900. It was surmised by environmentalists that 20th-century sulphur dioxide emissions had choked these lakes to death with acid rain. But the NAPAP showed many of these lakes were acidic and fishless even before European settlement in America. Fish survived better in these lakes around 1900 because of extensive slash and burn logging in the area. The soil became more alkaline as the acid vegetation was removed, reducing the acid flowing into the lakes and making the water hospitable to fish. Logging stopped in 1915, acid soils and vegetation returned and the lakes became acidic again. The study also found that in many cases forests were suffering debilitation due to insects or drought and not acid rain.

The NAPAP reported in 1990. The findings were explosive: first, acid rain had not injured forests or crops in US or Canada; second, acid rain had no observable effect on human health; third, only a small number of lakes had been acidified by acid rain and these could be rehabilitated by adding lime to the water. In summary, acid rain was a nuisance, not a catastrophe.

The findings of NAPAP were not welcomed by the powers-that-be, many of whom had staked their reputations on the impending Clean Air Act which would call for drastic reduction of sulphur dioxide emissions. The NAPAP was ignored.

Acid rain was succeeded by the "hole in the ozone layer" as the next environmental worry, which in turn was pushed off the stage by global warming. Oops, I forgot! Just before global warming we briefly worried about global cooling, causing drought, famine, frozen oceans etc, fears triggered by a small dip in average northern hemisphere temperatures from 1940 to mid-1970s. As the fella said - "You'd have to wonder".

William Reville is associate professor of Biochemistry and Public Awareness of Science Officer at UCC - http://understandingscience.ucc.ie