Climate limits room at the global dinner table

Reducing tillage used to prepare soil in farming can help reduce carbon emissions without also reducing crop yields. Credit: USDA Natural Resources Conservation Service

Reducing tillage used to prepare soil in farming can help reduce carbon emissions without also reducing crop yields. Credit: USDA Natural Resources Conservation Service

Part two of two

Another mid-winter feast has passed since I published the first part of this round-up of research linking food and global warming, its memory still pleasantly fresh in my mind. I’d hate to have to sacrifice any of it in the future. But what if I were forced to change or shrink my menu? You might not have to make these choices today, but scientists are helping farming adapt to a changing climate. They’re facing up to a big challenge: trying to reduce emissions, while maintaining food supplies.

As well as being affected by climate change, farming also produces some of the greenhouse gases that cause it – between one-tenth and one-third of the world’s emissions. Agricultural consultant Rob Carlton and his colleagues therefore looked at four different crop farming methods in March last year to see which would emit least greenhouse gas if the whole UK adopted it. The best approach was to dig up less left over plant material than conventional farming currently does, keeping more carbon trapped in the soil. This approach importantly produced the same amount of crops as conventional methods. That’s necessary, because converting pasture to arable land to make up crop shortfalls seen with other methods releases large amounts of greenhouse gas. “The need for emissions reductions should be viewed against demands on agriculture, which are increasing as the population and consumption increases and farmers diversify into industrial and fuel crops,” Rob said.

Got beef?

Because not all the energy cows eat is converted into meat, it takes more land to produce beef than other forms of meat or crops people eat directly.  Credit: Let Ideas Compete/Flickr

Because not all the energy cows eat is converted into meat, it takes more land to produce beef than other forms of meat and crops people eat directly. Credit: Let Ideas Compete/Flickr

The meat we eat can potentially have a much bigger impact on climate than crops, as it’s thought to produce four-fifths of agricultural greenhouse gas emissions. That’s partly because only about three or four parts in 100 of the feed energy livestock eat becomes meat, noted University of Exeter’s Tom Powell in July. The rest is lost as manure, heat, methane and slaughter by-products. On a simple level that means the world needs more space to grow plants to feed animals than we would if we lived off plants alone.

With the world’s population growing, and widening demand for meat, Tom looked at what this meant for our CO2 emissions. He found that meeting the world’s food needs by 2050 is set to need almost three quarters of the Earth’s land surface to be used as farmland. Converting the forests to extra farms would release large amounts of carbon into the atmosphere, increasing farming emissions even more. That could be avoided by eating less meat, or even switching from a high-emission choice like beef to pork or chicken. “Small changes to our diets and the ways we produce food have the potential to make what is currently a very environmentally damaging system a much more positive one,” Tom said.

Part of the problem with meat farming is that it causes higher emissions of nitrous oxide, or laughing gas (N2O), which is 310 times better than CO2 at trapping heat in the atmosphere. Eric Davidson, executive director at the Woods Hole Research Center in Falmouth, Massachusetts therefore looked at measures – or mitigations – the world could adopt to reduce N2O emissions. The mitigations included more efficient farming, less N2O emissions from industry, transport, and burning living and dead vegetation and the developed world halving the amount of meat it eats. “With no additional mitigation, N2O in the atmosphere just keeps going up and up,” 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.”

Yielding pressure

Around three billion people eat rice every day, and more than 60 percent of the world's one billion poorest and undernourished people who live in Asia depend on rice as their staple food. However, weedy rice does better at higher CO2 levels than modern farmed varieties. Credit: IRRI

Around three billion people eat rice every day, and more than 60 percent of the world’s one billion poorest and undernourished people who live in Asia depend on rice as their staple food. However, weedy rice does better at higher CO2 levels than modern farmed varieties. Credit: IRRI

One option that reduces the pressure on us to change our behaviour is breeding crops to take advantage of higher CO2 levels in the air. But that breeding needs concentrated direct effort, Lewis Ziska from the US Department of Agriculture told me in August. Current strains actually do worse than older varieties of wheat or weedy forms of rice in conditions with more CO2 he underlined. “Plant breeders often assume that on-going breeding efforts, for example for pest or disease resistance, would by themselves lead to adaptation to any rise in background CO2 levels,” Lewis told Simple Climate. “We’ve shown that this is not the case.”

As well as that breeding effort, more money and work are needed for the research that would provide a secure food supply, he added. But unfortunately Lewis thinks this isn’t happening, leaving us with the prospect of some hard-to-stomach choices. “These resources can, and should be, part of an integrated effort among governments, non-governmental organisations, academic and private interests,” he said. “Unfortunately, at the moment my own sense is that we seem to be in stasis, with little recognition of the scope of the problem, and little willingness to address it beyond the rhetoric.”

Journal references:
Ziska, L., Bunce, J., Shimono, H., Gealy, D., Baker, J., Newton, P., Reynolds, M., Jagadish, K., Zhu, C., Howden, M., & Wilson, L. (2012). Food security and climate change: on the potential to adapt global crop production by active selection to rising atmospheric carbon dioxide Proceedings of the Royal Society B: Biological Sciences, 279 (1745), 4097-4105 DOI: 10.1098/rspb.2012.1005
Carlton, R., West, J., Smith, P., & Fitt, B. (2012). A comparison of GHG emissions from UK field crop production under selected arable systems with reference to disease control European Journal of Plant Pathology, 133 (1), 333-351 DOI: 10.1007/s10658-012-9961-0
Powell, T., & Lenton, T. (2012). Future carbon dioxide removal via biomass energy constrained by agricultural efficiency and dietary trends Energy & Environmental Science, 5 (8) DOI: 10.1039/C2EE21592F
Davidson, E. (2012). Representative concentration pathways and mitigation scenarios for nitrous oxide Environmental Research Letters, 7 (2) DOI: 10.1088/1748-9326/7/2/024005

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