Tiempo Climate Cyberlibrary

Globally, food production accounts for at least a quarter of greenhouse gas emissions. A recent Food and Agriculture Organization report estimates that the biggest share of this - 18 per cent of total global emissions - comes from livestock.

The tendency for populations to consume more animal products as they become richer has been strong. Predictions based on "business as usual" assumptions are for a doubling of global livestock production by mid century, mainly in response to rising incomes in low- and middle-income countries.

But it will not be possible for this business to continue "as usual". The only geopolitically feasible path to dietary sustainability is "contraction" of ecologically disruptive production for high-income countries to make room for some upward "convergence" in low- and middle-income countries.

Global average meat consumption is now about 100 grams per person per day. This is consumption in the economic sense of "using up" and includes waste. The corresponding level of intake is probably about 70 to 80 grams per day. If, by 2050, the population increases by 40 per cent and mitigation (reduction in GHG emissions per unit product) improves by 20 per cent, then mean global meat consumption would need to fall slightly to around 90 grams per day. This means more than halving average consumption levels in high-income countries.

Achieving these modest but necessary objectives will require radical changes. Reducing consumption of red meat, which makes the heaviest environmental demands, will help. Within high-income countries, an appreciable minority already have a pattern of low red meat consumption. This could be generalized to the whole population.

Reducing consumption of red meat is also likely to bring health benefits, yielding a double dividend for those who make the change. A large United States National Institutes of Health-sponsored study has compared high and low red meat consumers (who turned out to have similar white meat intakes). The low consumers enjoyed a mortality advantage of about one quarter.

If our planet can only sustain a limited number of livestock, making room for higher consumption of milk, eggs and meat in low- income countries should be an important goal of global climate change policy.

Undernutrition remains the leading cause of lost healthy life globally. Increasing the supply of animal foods in the diets of growing children in poor countries will be central to the achievement of further health gains. Increasing animal protein intake in adults (in countries where it has been very low) should also lower the risk of stroke - a major cause of premature death and disability.

Diet, of both rich and poor, should be central to climate change policy.