Also known as laughing gas, nitrous oxide (N2O) is a powerful greenhouse gas, and bringing its release under control will need the world to make very serious changes. That’s what Eric Davidson, executive director at the Woods Hole Research Center in Falmouth, Massachusetts, has found by looking at likely future N2O emissions.
Improvements in farming, industry and transportation could help reduce levels of the gas from what they might become. So too could the hard-to-swallow suggestion for many that people in the world’s richest countries halve the amount of meat they eat. But to meet the hardest target scenario to be used in an important climate report scientists are working on, we need to do all of these, Eric says. “Mitigating N2O emissions will be a huge challenge, and I’ve outlined the scope of the magnitude of change necessary,” he told Simple Climate. “They are not outside the realm of possibility, although they will be very challenging.”
In 2008, the UN Intergovernmental Panel on Climate Change (IPCC) agreed it would produce its fifth assessment report looking at global warming in detail by October 2014. To try and predict what will happen in the future, the scientists involved have drawn up four “representative concentration pathway” (RCP) scenarios that humanity could follow. These are based on a range of values for how much the atmosphere would be heating up in 2100. But there has been little work so far to see what will need to happen to reach the greenhouse gas levels these scenarios imply.
Slimming down emissions
Eric works with the International Nitrogen Initiative, which presents the science behind the need to use nitrogen better to improve human nutrition, while minimising unintended environmental impacts. For example, synthetic nitrogen fertilisers spread on agricultural soils and livestock manure storage and use are the main sources of N2O. The nitrogen is broken down by microbes living in the soil and released into the atmosphere as N2O. Eric therefore decided that he would try and look how N2O levels for the RCP targets could be reached.
To create his predictions, Eric took figures from the UN Food and Agriculture Organisation for future population growth, plus average calorie and meat intake per person in developed and developing worlds. Meat intake is important because more livestock farming produces more manure, and creates more demand for fertiliser to growing feed crops. From those figures he could work out what would happen if the world continued on its current path or adopted specific measures – or mitigations – to reduce N2O emissions. In one mitigation scenario, farmers improve how efficiently they use nitrogen-containing fertilisers by half. In another, how much N2O is produced by industry, transport, and burning living and dead vegetation falls by half. In the final mitigation, the developed world cuts the amount of meat it eats by half.
Writing in the research journal Environmental Research Letters last week, Eric found that each individual mitigation could make an important contribution to reducing emissions. “With no additional mitigation, N2O in the atmosphere just keeps going up and up, which is consistent with the graph of the business-as-usual RCP,” he said. “Increasing only agricultural efficiencies or only changing dietary habits helps slow the rate of N2O growth. But to have N2O level off, we have to adopt all of the above strategies.”
While the world needs to be prepared to pay out to improve farming, we do already know what changes we need to make in that area, Eric explained. “There are social, economic, and political impediments, but it is not lack of know-how that is stopping us,” he said. “Improving nitrogen use efficiency on the farm will cost some money that will have to be passed on to consumers or to taxpayers, although some practices can save farmers money.”
When it comes to changing people’s diet Eric pointed out that his mitigations are trying to show what could happen, but not recommendations for what should happen. “I am certainly not advocating that everyone must become vegetarians,” he said. “I am simply objectively pointing out that it will be very difficult to stabilize this important greenhouse gas in the atmosphere under business as usual trends, including current trends in dietary preferences.”
But making those food changes, could be good for both the economy and the environment – if we can bring ourselves to make them, the scientist added. “Reducing the portion size and frequency of eating meat will save consumers money and will probably lower some health costs in the developed world,” Eric said. “Few of us would have guessed 30 years ago that smoking would be banned in bars. Can we now imagine reversing the ‘supersize it’ trend of meat portions at restaurants? Most of us are sceptical, but human behaviour does change over decade time scales.”