Posted 1 November 2009

The Scientific Alliance comments on the odd proposal in the Times of London by Lord Nicholas Stern that humans should give up eating meat to save the planet from global warming.

Can vegetarians save the world?

The Times this week devoted three pages to an interview with Lord Stern (of the eponymous report): a double page spread with his pre-Copenhagen thoughts and a front page headlined 'Climate chief: give up meat to save the planet'. Not surprisingly, this sparked considerable debate over the following few days. The noble lord himself said that his remarks had been taken out of context, that he was pointing out the carbon intensity of livestock farming rather than suggesting a wholesale change of diet. No matter, the story had been written, and the debate ensued.

This quite neatly encapsulates a whole range of important questions. What kind of diet should we be eating? Should we be raising animals for food? Could changing farming practices reduce greenhouse gas emissions significantly? If so, does it matter?

On the diet question, this just stirs up the usual pro- and anti-vegetarianism arguments once more. Ignoring for the moment any ethical or moral considerations, we have to accept that humans are natural omnivores. We have teeth which can cope with pretty much any kind of food. Carnivores such as dogs and cats have no teeth suitable for chewing, herbivores such as cows and horses cannot physically cope with meat. We can do both.

Hunter/gatherer societies which existed before farming was established would have had a diet high in animal protein. Archaeological evidence suggests that they may have been better nourished than many later peasant farmers who subsisted primarily on their crops. This does not mean that a vegetarian diet is bad, just that it is easier to get enough high-quality protein and many micronutrients from animal sources. Strict vegetarians may have to supplement their diet with micronutrients (such as B Vitamins) to avoid deficiency diseases, and vegans must be even more careful to balance their diet.

Experience suggests that vegetarian societies are the exception. As people can afford it, meat eating tends to increase, a trend which is now very evident in China . Most people like meat, although they often consume more than they need: a large proportion of calories can easily come from carbohydrates rather than protein.

But Lord Stern 's point was that a reduction in meat consumption would have a beneficial environmental effect. Each kilo of meat requires several kilos of animal feed to produce it, and animals are themselves a significant source of methane emissions. Follow-up letters to the editor gave two responses to this from very different sources.

First, Clare Oxborrow of Friends of the Earth wrote in support not of vegetarianism, but of 'planet-friendly farms and home-grown animal feeds' to provide 'less but better meat and dairy'. This was essentially an attack on the present system of intensive agriculture, dependent on large imports of soy protein. Consumption of animal products would certainly go down in this scenario, since they would become much more expensive.

This plea for more extensive farming, although it did not use the word 'organic', is the approach called for by the Soil Association and others in the organic farming movement. The true believers argue for conversion of global agriculture to their principles, despite clear evidence that the sector remains a niche even in prosperous Europe . When presented with the evidence that farming without synthetic fertilizers could only feed perhaps 4 billion people, the response tends to be that we should all become vegetarians, when the available food would in fact be sufficient.

What this argument ignores is that organic farming is essentially a closed-loop system, relying heavily on animal manure as a source of nitrogen. Livestock numbers would have to increase significantly, and the corollary of this is that meat and dairy produce would be an integral part of a global organic diet unless farm animals were to be simply a source of fixed nitrogen.

The alternative, if the diet was to be vegetarian, would be the use of green manures, crops of clover and other legumes to be ploughed in to provide soil fertility. But this would mean that one-third or more of farmland would be unproductive in any season, to allow for the growth of legumes. Whichever way you look at it, organic farming does not add up, with or without meat in the diet.

The second letter to the Times was from Ian Crute , of the Agriculture and Horticulture Development Board. His point is that producing meat is part of the overall balance of agriculture, and eliminating it from the mix would make only a marginal difference to emissions of greenhouse gases. Livestock grazes on the large proportion of land which is best suited to growing grass and would not be productive arable land, and also consumes large quantities of the by-products of human food production: soy and rape meal and citrus and sugar-beet pulp, for example.

Estimating the greenhouse gas emissions from farming is very complex, and not altogether helpful. Farm animals are undoubtedly a significant source of methane, but this is outweighed by wild animals (and termites, which produce huge amounts). And much of the methane comes from marshland and paddy fields, not animals.

We hear that methane has a much higher warming effect than carbon dioxide. But this is partly because there is much less of it in the atmosphere, so each addition has a much greater relative effect. Overall, methane makes a much smaller contribution to the greenhouse effect than CO₂, and this in turn is outweighed by the effect of water vapour.

We should also not forget that, although concerns are often expressed about methane emissions, the concentration in the atmosphere has been stable or declining in recent years. This is just one more facet of the enormously complex web of factors which have an influence on our climate. It is important that politicians recognise how much we simply do not know, rather than assume we know enough to make far-reaching decisions which will affect the lives of all of us.

But that is the trajectory we are on at present, with all eyes focussed on the summit meeting in Copenhagen in December. One of Lord Stern 's key messages (although this was not clear from the front page story) was that President Obama should be present in Copenhagen and use his prestige and influence to help achieve a post-Kyoto climate deal. Given his lack of success in securing the 2016 Olympic games for Chicago when he last visited the Danish capital, he may think otherwise.

Vegetarianism is not going to save the world, and neither will anything agreed in Copenhagen , whatever fine words are used. If there truly are dangers we face from changes to the climate, it is best that we understand them properly before taking expensive, perhaps unnecessary, and almost certainly ineffective, action.