Monday, January 12, 2009

Cows, cars and climate

Letter writer Gil Osman is right to indicate that there is nowhere near enough emphasis on the greenhouse gas methane as one major cause of climate change (here). It is generated in very large and rapidly growing amounts by human activity, beef and dairy farming in particular, because cows produce many litres every day (Gil says 40 litres but some estimates go into hundreds of litres)! Pigs, chickens and other farm animals make a significant contribution also (and methane is also generated in landfill sites and by growing rice and is released to global warming by various means eg as permafrost melts).

The figures Gil gives are certainly credible estimates, with the greenhouse gas contribution from animals raised for food (18%) being higher than the greenhouse gas contribution from all transport (13%). Its not just the methane emitted by the animals that is the problem - meat production makes intensive use of fossil fuels, chemicals, drugs, land, plus money, and the international trade in meat only makes this worse!

Meat production is inherently inefficient. A food chain involving meat is longer, with more links. The ecological rule of thumb is that there is a 90% energy transfer ‘loss’ (used for the organism's life processes or lost as heat to the environment) at each link in the chain! On average a meat eater’s diet uses twice as much land per person as a vegetarian’s and five times as much as a vegan’s. Over two thirds of UK land is used for farming, most of this being used for meat. Around two thirds of the vegetable crops grown in the UK are fed to farm animals.

According to the book ‘Sharing Nature’s Interest’ the ecological footprint of meat is 6.9 to 14.6 hectare years per tonne, depending on the type of animal rearing (pasture-fed animals have a lower footprint than grain-fed ones). Comparable figures for other foods are: non-aquaculture fish 4.5 to 6.6; fruit and vegetables 0.3 to 0.6; milk 1.1 to 1.9; grain such as wheat and rice 1.7 to 2.8; and pulses such as beans and peas 3.6 to 2.8. Even allowing for the fact that these are broad estimates the comparison is stark and is rooted in basic science.

The UN Food and Agriculture Organisation’s figures show that meat consumption has tripled since 1961. World meat consumption is now well over 230 million tonnes per year. By 2020 demand for meat will surge nearly 60%. Meat consumption has been and still is a feature of a ‘developed’ country given that someone living in a developed nation consumes three times as much as someone in a ‘developing’ one.

Put the facts on methane emissions and land/energy/chemical use from meat production together with fast rising meat consumption and you can see that we have trouble – not just in terms of climate change but also in economic terms, with food and fuel prices reaching very high levels during 2008 helped by high and rising demand. You’ll note that I’ve not even touched on the ethical/animal welfare issues or the health and disease issues involved in eating animals in large quantities!

So when Gil writes ‘Perhaps governments should be encouraging people to cut down on their meat consumption…’ I’d agree (although this should be in addition to tackling the environmental impacts from transport, energy generation and use, and so on which are many, varied and significant). It is especially important to tackle a meat industry parts of which, as Gil says, are clearing forests to create farmland for cattle rearing, boosting climate damage from cow methane, releasing carbon dioxide from the soil, rapidly releasing carbon dioxide when forests are burned and cutting the extraction of carbon from the air by forests simultaneously (more here).

I’ve spent some time describing the evidence and the problems. Solutions wont be easy. Action is needed across a wide range of policy areas, from environmental and health education informing personal food choices, to UK and EU action on personal and household carbon budgeting, to international agreements on deforestation and global trade…Would I advocate that we all go vegetarian or vegan? No, and I’m not a vegetarian myself, though I would strongly advocate that people consider a low meat diet, making dietary choices to stay within a carbon budget, and taking into account health, disease and animal welfare issues. Its certainly environmentally friendly to eat less meat whilst at the same time being cheaper, healthier and more ethical.


  1. Comparisons of the ecological footprint of different foods should be made on the basis of the calorific value of the food rather than its weight.

    Milk, fruit and vegetables are largely water so the calorific and nutritional value of a kilo is going to be tiny compared to say a kilo of meat, which typically contains a lot of fat which is a concentrated source of energy.

  2. I suppose one could argue for various ways of making comparisons Chris, including as you suggest on the basis of calorific value, or perhaps by mass of protein, or both, or some other way. Its tricky to know the best way to do it given the range of food types/compositions and given the fact that we all eat a range of foods.

    The figures from Sharing Natures Interest are not from a single study - they've been put together from a range of sources by the authors and should be considered with some caution. Nevertheless they are of interest in terms of accounting for the average global yield plus transport, processing and agricultural energy.

    Perhaps the thing to compare is diet types rather than individual food types. In the UK to provide a diet of 68.7g of protein and 2370 kcal, meat eaters use 0.32 hectares of land per person, a vegetarian 0.14 and a vegan 0.07.

  3. That last comparison makes more sense, but it doesn't take account in the variations in the amount and type of meat eaten. There's a big difference between a typical north American diet and one where meat and fish is a minor supplement to a largely vegetarian diet.

  4. Yes I agree, the comparison is an average and there are many variations in diets. Its one of the reasons why I wouldn't advocate vegetarianism or veganism. We can all eat sustainably with meat and fish in our diets if we adjust the amount and type to suit. Meat amount and type are crucial to sustainability given the inefficient use of land - happily this is also likely to be a healthier and cheaper diet!


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