What's on your plate? Agriculture, meat and carbon
Jamal Gore and Suzy Hodgson examine the environmental impacts of livestock and intensive farming.
Most greenhouse gas reduction initiatives - including those promoted on these pages - have focused on energy, industry and transport as these sectors comprise the bulk of measurable human-induced emissions.
In addition, international climate negotiations (UN-REDD) have focused increasing efforts on reducing emissions from deforestation and degradation.
In general, agriculture has received less attention in carbon management policy and legislation, despite the fact that more of the Earth's surface is dedicated to farmland than to cities.
Agriculture is estimated to account for anywhere from 10 per cent to 40 per cent of global anthropogenic GHGs.
One agricultural topic that has received more attention is the environmental consequence of the globalisation of food as a commodity product. Should the carbon impact of our globalised food system and meat-intensive diet be part of the debate? Are there farming practices closer that could reverse this pattern?
Loving our livestock
Modern society seems to have a love-hate relationship with livestock. An ice cream manufacturer might use images of grazing cows to symbolise fresh, natural products, and yet food scares from BSE to E. coli infections highlight some of the apparent risks of industrial agriculture.
A similar contradictory relationship exists when it comes to greenhouse gas emissions from agriculture. Intensive livestock rearing generates both direct and indirect greenhouse gas emissions, while improved practices can result in quantifiable emission reductions and support the transition to a lower-carbon economy.
The extent to which agriculture is a source or sink for GHGs depends on existing regional land-use and management practices. An important related question is what the alternative uses for the land would be, and whether those uses would generate even greater emissions than agriculture.
The beef carbon footprint
Greenhouse gas emissions arise at every step in getting a hamburger or steak to our tables, from preparing the soils, to growing the animal feed, to housing and feeding animals, managing their waste, transporting the animal to market, to meat processing, packing, refrigeration, transport, and finally cooking.
At each stage, GHG emissions are released - and can be mitigated. How cows are raised - eg whether grain fed or pasture raised - makes a difference. Most cattle are fed a diet rich in corn and alfalfa. These grains are often grown using artificial fertilisers produced through energy intensive means and harvested with mechanised farm equipment. However, the lower GHG intensity of grass-fed cattle is not always better if pastures are overgrazed and cause soil degradation and soil carbon loss. And the demand for grazing lands can put pressure on nearby forests resulting in significant emissions from deforestation.
The multi-stomached cow, while well equipped to digest otherwise inedible grasses, burps large volumes of the greenhouse gas methane - anywhere between 100 and 700 litres per animal per day.
The animal waste is also a source of methane emissions if it is stored in large lagoons where it decomposes anaerobically. And depending on the application of manure and/or nitrogen fertilisers for feed crops, nitrogen can be released into the atmosphere as nitrous oxide. Both methane (CH4) and nitrous oxide (N2O) are particularly significant greenhouse gases as the former has a global warming potential 21 times that of carbon dioxide (CO2) and the latter, 310 times that of CO2.
By adding up all of these emissions sources and dividing by the amount of meat produced, it is possible to estimate the carbon footprint of each piece of beef. According to a 2009 analysis, a 150g burger is responsible for approximately 2kg CO2 equivalent - the same as driving 15km in an average car.
The cumulative effect of our burger eating is huge. According to the US Environmental Protection Agency report, ‘Inventory of US Greenhouse Gas Emissions and Sinks: 1990-2004', beef cattle accounted for 71 per cent of methane emissions in that country in 2004.
The FAO estimates that cows and other livestock worldwide are responsible for a total of 18 per cent of greenhouse gas emissions, a bigger share than for transport. As incomes rise in poorer countries, so does global meat consumption, potentially undermining efforts to reduce emissions.
Carbon management on and off the farm
While attention is turning increasingly to the problem of carbon-intensive global livestock production, campaigners, policy-makers and journalists have said less about the opportunities for better management practices on domestic farms. It is possible to adapt the well-tested ‘reduce, reuse, recycle' hierarchy to our production and consumption of food to find ways to reduce the greenhouse gas impact of the food we eat.
Accordingly, the first approach is to reduce demand of high emissions foods like beef by reducing food waste. Careful meal planning and better storage can significantly reduce the amount of food purchased and sent to landfill without being eaten.
A second approach is to encourage a shift in favour of lower-carbon protein sources like pork (single-stomach pig), poultry and legumes which will reduce GHGs. In the short term, however, it will prove difficult to separate people from their beef burgers and Sunday roasts. What is more, these efforts may be swamped by changing diets in the developing world.
Farm and carbon management synergies
Is it possible, then, to raise cattle that emit less methane, and to reduce emissions associated with feeding them? Here the results to date have been promising. Studies have shown that changing pasture can reduce gaseous emissions by 20 per cent, and including garlic in cattle feed can reduce emissions by 50 per cent and lead to healthier cattle1. Optimising the diet of animals not only improves the efficiency of weight gain for animals (ie meat) but also reduces the methane emissions. About six per cent of the energy input to the cow is released as methane gas from the cow.
Best practices on farms have great potential to mitigate GHGs and improve carbon sequestration. Biomass and carbon comprises much more than the plants and animals immediately obvious on the farm. Land-use practices such as ploughing or tillage intensity can determine the extent to which soil is a sink or source for GHGs. Ploughing up grassland releases up to 84 tonnes per hectare CO2e in England and up to 330 tonnes CO2e per hectare in Scotland.2
On the other hand, grazing animals can help maintain grasslands if grazing is controlled and pastures are rotated. By reducing land clearing and minimising soil disturbance, soil's role in storing carbon and available nitrogen for plants can be maximised and soil structure and microbial activity can be enhanced to increase agricultural productivity.
In short, best practice pasture management can help soils sequester carbon while, on the other hand, poor practices (eg overgrazing, excessive nitrogen use and forest destruction) will lead to increases in GHGs. "Using existing technologies and best management practices, US agriculture could sequester 350-550 million tonnes of CO2e per year and current N2O and CH4 emissions could be decreased by 20-40 per cent."3
Reducing or eliminating nitrogen-based artificial fertilisers as part of a programme of integrated farm management can reduce greenhouse gas emissions from soil. Spreading manure on croplands has the dual benefits of replacing artificial fertilisers and reducing the volume of methane-generating waste lagoons.
Where waste lagoons are unavoidable, they can be aerated to break down the waste aerobically, producing carbon dioxide instead of the more powerful greenhouse gas methane. An alternative is to capture the methane and flare it or use it to generate renewable heat and electricity. Feed-in tariffs and standard contracts in the UK and US provide generous incentives for farmers to generate power in this way, in order to displace fossil fuel-fired generation (as described in our article in issue 104 of ‘the environmentalist').
A final approach is to look at local land use practices. The decision about the best use of a given parcel of land is made jointly by landowners, local communities, government and other stakeholders. Allowing livestock grazing may be considered the best way to preserve open space, which also allows recreation and provides habitat for native species. The challenge then is to ensure that the practice helps to reduce net emissions rather than contributing to them.
Reducing over-grazing and using perennial grasses helps to maintain soil structure and reduce soil carbon emissions. Managing sites for some woodland growth can aid carbon sequestration and conservation. Indeed, livestock can be part of a programme to control invasive species and encourage native ones.
As farmers in the US have learnt, wind farms are often a perfect complement to livestock grazing. Around the town of Klickitat, Wisconsin, landowners have given wind developers permission to install over 600 turbines, generating enough power to supply 300,000 to 400,000 homes.
In this way, local farmers are making a significant contribution to the low-carbon economy. What is more, the landowners earn approximately $18,000 (about £11,000) per year for each turbine on their land - a significant boost to modest local incomes.4
Conclusion
Domesticated livestock have been with humanity since before written records began. It is important that we recognise the carbon cost of our intensive agriculture and food choices, and continue to seek ways to balance our meat consumption with our need to combat climate change.
2Ibid
3Climate Change and Greenhouse Gas Mitigation: Challenges and Opportunities for Agriculture, US Council for Agricultural Science and Technology, May 2004
References:
Soil Carbon and Organic Farming, Soil Association, November 2009
www.soilassociation.org
Climate Change and Greenhouse Gas Mitigation: Challenges and Opportunities for Agriculture, US Council for Agricultural Science and Technology, May 2004
Nathan Fiala, ‘The Greenhouse Hamburger', Scientific American, February 2009