Turns out, nitrogen may be even worse for the climate than carbon dioxide - and it's not going away: "the consequences are likely to be even worse than 'just' global warming. Human health, biodiversity, ozone levels and global climate are already being affected. And if we thought the carbon problem was tricky to sort out, we're in for an even nastier shock." New Scientist.
Complete article:
STOP five people on the street and chances are they will be able to tell you that carbon dioxide emissions cause global warming. Stop another five and ask them about nitrogen emissions, and they will probably stare at you blankly.
But a growing number of scientists say that nitrogen is a problem that we ignore at our peril. While we have been fretting about the consequences of a 10 per cent increase in CO2, levels of polluting nitrogen compounds in the environment have almost doubled. If we ignore them for much longer, the scientists insist, the consequences are likely to be even worse than "just" global warming. Human health, biodiversity, ozone levels and global climate are already being affected. And if we thought the carbon problem was tricky to sort out, we're in for an even nastier shock.
"Long term, anthropogenic nitrogen is probably a greater environmental threat than anthropogenic carbon," says Ken Cassman of the department of agronomy and horticulture at the University of Nebraska, Lincoln. "There are biodiversity issues from acid rain, aerosol issues which impact on human health, and eutrophication problems from nitrates going into water," says Mark Sutton, head of atmospheric sciences at the Centre for Ecology and Hydrology in Edinburgh, UK.
There has, of course, always been a lot of nitrogen in the environment. About 78 per cent of air by volume is nitrogen gas, N2, but until it has been oxidised or reduced into a reactive form, it is neither harmful nor useful to most living things. For hundreds of millions of years, the only route to reactive nitrogen was via bacteria and lightning, which fixed nitrogen out of the air and began a series of transformations through soil, plants and animals, back into the soil, and finally, back into the air (see Diagram).
Then along came the industrial revolution and the first large-scale burning of fossil fuels, which causes nitrogen in the air to react to form nitrogen oxides (NOx). Then a century ago, German chemist Fritz Haber worked out how to make ammonia from hydrogen and nitrogen, a process that eventually led to the industrial production of nitrogen fertiliser. Soon, levels of reactive nitrogen began spiralling out of control and the natural nitrogen cycle became a bit player. Today as much as 70 per cent of reactive nitrogen cycling through the atmosphere, earth and sea is there as a result of human activity. In fact, the nitrogen "cycle" no longer exists. It's now known as a cascade (see same Diagram), although in reality it's more like a torrent.
But while CO2 has been burnt into the public consciousness as the bad guy of global warming, the nitrogen problem has gone largely unnoticed. This is partly because the nitrogen story is far more complicated. In its various chemical forms, nitrogen can have no fewer than seven apparent charges, or "oxidation states", that are a problem to health or the environment, making its passage through the environment the most complex of the major elements (see Table).
"More nitrogen falls out of the air [as acid rain and particulates] now than farmers used to put on their fields in the 1950s," says John Lawton, former head of the UK's Natural Environment Research Council, which funded the Global Nitrogen Enrichment programme - a five-year project that ended in early 2005. "But because it's from diffuse sources it's an unbelievably difficult problem to fix."
"What is unique about nitrogen is that the same atom in a molecule of reactive nitrogen can cause multiple effects in the atmosphere, in terrestrial ecosystems, in freshwater and marine systems, and on human health, as it moves through the environment," says James Galloway, who heads the International Nitrogen Initiative (INI), based at the University of Virginia in Charlottesville. "The only way to stop the cascade is to convert reactive nitrogen back to non-reactive N2".
And herein lies the problem. All this extra nitrogen in the environment has overwhelmed the natural cycle, and de-nitrifying bacteria just can't convert the excess back into atmospheric N2 fast enough. And while agricultural sources of nitrogen are mainly a local problem, nitrogen compounds from burning fossil fuels can cross national boundaries, causing acid rain in neighbouring countries and, worse, global warming.
Unanswered questions
Yet despite the scale of the problem, surprisingly little is known about the effects of nitrogen on the environment and health. "We know that at high levels you can get an effect on ecosystems," says Mark Bradford of the Institute of Ecology at the University of Georgia, Athens. "There may be unexpected effects between low and high levels, but we just don't have the figures yet."
Other unanswered questions are the difference between adding small amounts of nitrogen over a long period and adding a lot very quickly; the effects of different forms of nitrogen on the same ecosystem; and interactions with temperature, carbon and other environmental factors.
What is known, however, is alarming. "With nitrogen there is a clear link with human health, one that we don't have with CO2," says Elizabeth Holland of the National Center for Atmospheric Research (NCAR) in Boulder, Colorado.
For example, nitrates from farm run-off can get into drinking water, and this has been linked to methaemoglobinaemia, or "blue baby syndrome", in which the nitrates are converted to nitrites in the body, disrupting the ability of haemoglobin to carry oxygen. The condition causes headache, fatigue, breathing difficulties, diarrhoea and vomiting, and in extreme cases a loss of consciousness and death. The syndrome has become a major problem in parts of the US and the Netherlands, which has the highest levels of nitrogen deposition in the world.
In California, there is growing concern about how atmospheric agricultural emissions are affecting health. The San Joaquin Valley, for example, produces 20 per cent of all the milk in the US, and Fresno, the biggest city in the valley, and notorious for its smog, has the third-highest rate of asthma in the country. Many believe these statistics are linked. Dairy farms release large amounts of ammonia, which forms particulate ammonium nitrate, and although it is not yet clear whether agricultural fumes or vehicle exhausts are to blame for the smog, on particularly bad days some schools in the valley fly a red flag warning parents to keep their children indoors.
Excess nitrogen compounds are also bad news for ecosystems. Livestock farms discharge considerable quantities of nitrates and ammonia into rivers, lakes and the sea, where they wreak havoc on biodiversity and commercial fisheries. Nowhere is this more starkly illustrated than in the Gulf of Mexico, where nitrates flowing from the Mississippi river have created a "dead zone". The zone, one of 146 worldwide, was first recorded in the 1970s, and appears each year when an excess of nutrients from the Mississippi basin is washed into the sea, causing eutrophication, a bloom of plankton and algae. When these organisms die, the bacteria that feed on them go into overdrive, using up the available oxygen, and suffocating anything that can't escape the area. Last year's dead zone covered some 15,000 square kilometres, and appeared several months earlier than usual.
Nitrate leaching also causes acidification in freshwater rivers and lakes. And when nitrogen and sulphur dioxides in the atmosphere combine with moisture, nitric, nitrous and sulphuric acids are formed, killing fish and damaging tree roots and leaves.
NOx compounds from fossil fuels are also causing concern. In sunlight, NOx compounds in the atmosphere react with hydrocarbons to form ground-level ozone, a lung irritant that can cause disease. A 2002 study by the US Environmental Protection Agency pointed to ozone as a factor in the development of asthma. Another study found that children living in communities with higher atmospheric ozone had poorer lung function.
But perhaps the biggest puzzle of all is the tangled relationship between nitrogen and climate change. Nitrous oxide (N2O) is present in the atmosphere at concentrations of 311 parts per billion, compared with 360 parts per million for CO2. But molecule for molecule N2O is a greenhouse gas with over 300 times the global warming potential of CO2. And while some see nitrogen as helping to reduce global warming by stimulating plant growth, hence locking more carbon away, this benefit is likely to be overshadowed by an increased rate of denitrification in the soil, which pumps NOx back into the atmosphere.
But as the nitrogen torrent continues, answers may at last be on the way. A number of projects have sprung up in recent years, with the intention of filling in some of the gaps in our knowledge and pushing the problem up the research agenda. The most recent, NitroEurope, is a five-year European Union initiative expected to start in March. The project, which involves a core of 17 EU states, plus India and China is designed to integrate research between countries on the link between the nitrogen and carbon cycles.
At NCAR, Holland is working on a similar project. In 2003 she brought together soil scientists, air pollution specialists and biodiversity experts to thrash out the main issues concerning nitrogen pollution. The result, in November 2004, was the US Nitrogen Cycle Plan, a tool to generate funding for nitrogen research and stimulate political interest in the problem.
The first step is to find out more about where nitrogen is coming from, and what impact it is having, to shed light on the effects of the nitrogen cascade. The question then will be what to do about it. "We absolutely need a Kyoto-style agreement," says Holland. "Industrialised countries have increased nitrogen deposition fivefold [in the last century], and developing countries are right behind us."
The closest thing yet to a Kyoto-style document is the Nanjing declaration, unveiled in 2004 at the 3rd International Nitrogen Conference by Zhoaliang Zhu of the Chinese Academy of Sciences, Katsu Minami of the National Institute of Agro-environmental Sciences in Japan, and Galloway. It has since been adopted by the European Union and presented to the United Nations Environment Programme (UNEP) governing council, where it is waiting for more signatures.
The answers to the problems, though, may be difficult to come by. Worldwide, five times as much reactive nitrogen comes from food production as from energy production. That's because it's very difficult to "spoon feed" plants the exact amount of nitrogen they need, and any excess simply drains off into the environment. Similarly, animals use only about 20 per cent of the nitrogen in their feed. The rest comes out the other end and either runs back into the ground or is given off as fumes.
Cow control
Few governments are willing to hit their farmers in the pocket with restrictions on fertiliser use and husbandry. To pre-empt this major stumbling block, the INI is working on ways to reduce inputs to the cascade, while still feeding a growing population.
One possibility would be to genetically modify crop plants so they could fix their own nitrogen from the atmosphere. But even supposing this could be done, it would only be a temporary fix: crops are fed to livestock and people who then make their own mark on the nitrogen cascade.
Perhaps a better technological solution would be precision agriculture, the farming equivalent of fuel injection in car engines, in which quantities of nitrogen fertiliser would be matched to the plants' needs. Nitrogen-proofing farms could also help - woodland is particularly good at catching ammonia emissions, so planting trees around livestock farms could help dilute the impact. Finally, keeping livestock inside could enable the air to be "scrubbed" to remove nitrogen compounds before venting it to the atmosphere.
Back in California, cows are already being hit with environmental regulations normally restricted to the dirtiest cars. Any farm in the state with more than 1000 dairy cows must apply for a licence from the state's Air Resources Board. And in the eastern US, the Clean Air Interstate Rule aims to reduce NOx emissions by 60 per cent by 2015. "Agriculture had a historical exemption from some of these rules because farms were not a major source [of pollution] 20 years ago," says Mike Kleeman, an air-quality scientist at the University of California, Davis. "In the future I expect that agriculture will be asked to manage the emissions of ammonia and other organic compounds from their livestock operations."
But ultimately, since nitrogen compounds cross national boundaries, these local initiatives will need to be controlled on a global scale. Nitrogen may not yet be recognised as a global issue on the scale of CO2, but when developing countries catch up with our fuel-guzzling and fertiliser-spraying habits, it won't be long.
Ultimately there is one solution that will definitely work, but we're not going to like it. "By and large the nitrogen problem is very much one of technology-driven societies, and the only solution is a revolution to less consumptive lifestyles," says Brian Moss, professor of botany at the University of Liverpool, UK. "This won't happen voluntarily but it may be forced by the combined effects of climate change, the end of the oil economy, rising populations, economic and environmental refugees and the loss of goods and services from the 70 per cent or so of natural ecosystems predicted to have disappeared by 2050. I'll have popped my clogs by then but if you're under 30, maybe even 40, I think you're in for a very rough ride."
From issue 2535 of New Scientist, 21 January 2006, page 40
2 Comments
Read Fatal Harvest: The tradgedy of Industrial Agriculture for more on this. In depth look at the politics of globalization after the 2nd world war and how that generation's better living through chemistry attitude lead to modern agribusiness, which does and did feed the world but at what cost? Morally, which is worse? And how can we curb it?
and they call them the greatest ganeration. I think history might call that into question...
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