Earth & Sky

Gene E. Likens is Director and President of the Institute of Ecosystem Studies in Millbrook, New York. His research focuses on the ecology and biogeochemistry of forest and aquatic ecosystems in the White Mountains of New Hampshire. He and his colleagues were the first scientists to document the link between the combustion of fossil fuels and an increase in the acidity of precipitation in North America.

Frank: Acid rain is an environmental problem that received a lot of attention several years ago. Why haven’t we heard about it recently? Has anything changed since the days when acid rain was all over the news?

Likens: Let’s start with talking about acid rain. Acid rain is a relatively simple phenomenon. It results from the combustion of fossil fuels, coal and oil, which releases sulfur and nitrogen oxides to the atmosphere. And then those oxides get converted into strong acids and come back to the land and water surface, or they may come back to the land surface in gaseous form or particulate form. Those acidifying substances then change environments, freshwater, land, vegetation, buildings, and so forth and deteriorate them.

The problem was a very large and visible one during the 1980s, a period that I call the acid rain wars, in which there was a lot of research done. There was a lot of federal funding in something called the National Acid Precipitation Assessment Program, NAPAP. Then in 1990, President Bush the senior signed into law the 1990 Clean Air Act amendments. That was the first time that we had passed legislation specifically to address the problem of acid rain. Concurrent with that action the topic of acid rain kind of disappeared, from the public media, from the funders of view point and so forth. So your question about why we haven’t heard much about it recently I think is explained in that way.

I would hasten to add, however, that the problem has not gone away. In the eastern United States, rain, snow, sleet, and hail still are about 10 times more acid than they should be if the atmosphere were not polluted by sulfur and nitrogen oxides.

And there are some very interesting changes, and I think important changes that are going on such that sulfur dioxide emissions have been declining since about 1970 or so and nitrogen oxides have been increasing. The 1990 amendments to the Clean Air Act didn’t really call for a very large reduction in nitrogen oxide emissions. And so we predict, from our long term studies, that in about five years or so, nitric acid will be the dominant acid in acid rain instead of sulfuric acid. Sulfuric acid has been the dominant acid, has been the one that all of the legislation has been focused on in terms of its reduction.

Frank: In what ways does acid rain impact ecosystems?

Likens: Well I think there are several. Both sulfur and nitrogen are important plant nutrients but they’re different. I think that nitrogen is an important plant nutrient often in low supply in forest ecosystems, for example. So the fact that it is increasing and has different ecological impacts in both freshwaters, like lakes and streams, and in soils than does sulfur leads to a whole series of interesting questions about what will be the result if this trend continues.

Now the trend is likely to change because we continue to burn more fossil fuels. But the mix of those fossil fuels, whether it’s coal or oil or natural gas, is important in terms of the emissions. Recently we have instituted a new regulation, the EPA regulation called Clean Air Interstate Rules (CAIR.) That has pushed the reductions more into the immediate time frame, rather than far into the future, as the president’s Clear Skies Initiative had done.

So how these things are going to play out, I don’t know. That’s dependent upon a lot of things: our economy and regulations and efforts to reduce emissions from smokestacks and so forth. But it’s nevertheless impacting systems and continuing to do so.

One of the things that we found recently was that the acid rain has been leeching significantly large amounts of calcium and magnesium out of forest soils. The area that I work, the Hubbard Brook Experimental Forest in the White Mountains in New Hampshire, we’ve found that very significant amounts of particularly calcium have been leeched out of the soils by acid rain. Calcium and magnesium are also plant nutrients but they also contribute to the buffering capacity of the soils so that by leeching these materials from the soils it’s sort of like depleting the Rolaids and Tums component, if you will, from the soil system. Therefore, the soils are much more sensitive to continuing inputs of acid rain than we knew before and that means that continuing inputs of acid rain have a continuing impact that is potentially larger than we thought. So these are all changes that are occurring and I guess, again, the bottom line is that the problem has not gone away.

Frank: With the focus on climate change over the past few years, we’ve learned a lot about how global systems are interconnected. How does acid rain interact with other environmental systems?

Likens: Let me say first that we now know that acid rain is a widespread problem throughout the world, particularly in southeast Asia and in China, places like that. It’s either already a problem or an emerging problem that will need to be dealt with in the future, but there are other aspects. The sulfur particles in the atmosphere are also, as aerosols, and important part of the climate change scenarios in terms of those aerosols and their affect in radiation balance. So there are many aspects. We have largely, in the developed parts of the world, cleared up the black smoke emissions which are interacting obviously with global warming in terms of the balance of radiation. But the emissions of nitrogen and sulfur oxides, the increased amounts of particularly nitrogen oxides from vehicles, all kinds of vehicles, is increasing. We’ve instituted reductions in the amount per vehicle, but we have more vehicles and we are driving them more miles. All of these things are connected.

The root cause, by and large, of CO2 emissions related to global warming and climate change, and/or acid rain, is the combustion of fossil fuels, coal and oil. Dealing with that problem head on is where we are in terms of the interconnectedness.

Frank: Is there anything else you’d like to add?

Likens: Maybe one thing. That is that there’s always a discussion about cost or the economics, isn’t there? We’re all concerned about that, and it’s a legitimate question. The EPA reported to Congress in 2003, for example, that the cost of the 1990 Clean Air Act in dealing with acid rain was somewhat more than eight billion dollars. But the estimated benefits, and these are broad scale benefits, were more than 100 billion dollars. So the benefits were more than 10 times greater than the costs.

Always when we think about these problems at the beginning, we think “Oh the costs are going to be so large and we can’t afford it and it’s going to mean jobs and whatever.” But when the real costs and benefits are analyzed, in the case of acid rain, it was a very effective and economical thing to do, plus it went a long way in helping us protect these life support systems of clean air, clean water, clean soil, and clean and nourishing food.

Frank: Thank you, Dr. Likens. We appreciate the update.