How to curb discharge of the most potent greenhouse gas: 50-percent reduction in meat consumption and emissions

The findings are results of a study by Dr. Eric Davidson and are published April 13 in IOP Publishing's Environmental Research Letters. Dr. Davidson, who is President and a Senior Scientist at the Woods Hold Research Center in Massachusetts, demonstrates the magnitude of changes needed to stabilize N₂O concentrations in the atmosphere.

N₂O is the third highest contributor to climate change behind carbon dioxide (CO₂) and methane (CH₄); however, it poses a greater challenge for mitigation since nitrogen is an essential element for food production. It is also the most potent of these three greenhouse gases, as it is a much better absorber of infrared radiation. But total anthropogenic emissions are about 6 million metric tons of nitrogen as N₂O, compared to 10 billion metric tons of carbon as CO₂.

The main sources of N₂O in the atmosphere are due to the spreading of synthetic nitrogen fertilizers onto agricultural soils and the use and storage of livestock manure. The nitrogen contained in fertilizers and manure is broken down by microbes that live in the soil and released into the atmosphere as N₂O. In order to reduce emissions, it will be necessary to apply certain changes to the food production process.

Dr. Davidson believes that this can be achieved through improved management of fertilizer and manure sources, as well as through reduction of the developed world's per capita meat consumption that will relieve pressure on fertilizer demand and reduce growth in the amount of manure being produced. "We have the technical know-how and the tools to greatly improve efficiencies of fertilizer use in agriculture," states Davidson, "although several economic and political impediments often stand in the way of their adoption."

In a draft of the IPCC's Fifth Assessment Report, four scenarios, known as representative concentration pathways (RCPs), have been adopted, and these represent possible means of reductions for a number of greenhouse gases. Dr. Davidson evaluated the scale of changes needed to meet the predicted N₂O pathways.

Three of the IPCC's less aggressive scenarios could be met by reducing meat consumption, improving agricultural practices, or reducing emissions from industry. The most aggressive scenario, where atmospheric N₂O concentrations stabilize by 2050, can only be met if a 50 percent reduction, or improvement, is achieved for each of the above.

To make these calculations, Dr. Davidson relied on data provided by the Food and Agricultural Organization, which assume that the global population will increase to 8.9 billion by 2050 and the daily calorific intake per capita will increase to 3130 kcal. They also assume that the average meat consumption of each person in the developed world will rise from 78 kg per year in 2002 to 89 kg per year in 2030 and from 28 kg per year in 2002 to 37 kg per year for each person in the developing world.

Assessing the likelihood of reducing meat consumption in the developed world by 50 percent, Davidson said, "If you had asked me 30 years ago if smoking would be banned in bars, I would have laughed and said that would be impossible in my lifetime, and yet it has come true. Similarly, there would be beneficial health benefits for most Americans and western Europeans to stop 'supersizing' and rather to reduce portion sizes of red meat."

Are such changes possible for diet? "That will depend," says Davidson, "not only on education about diet, but also on prices of meat. Some agricultural economists think that the price of meat is going to go way up, so that per capita consumption will go down, but those are highly uncertain projections."