In a paper published by a respected US thinktank, the Worldwatch Institute, two World Bank environmental advisers claim that instead of 18 per cent of global emissions being caused by meat, the true figure is 51 per cent.
They claim that United Nation's figures have severely underestimated the greenhouse gases caused by tens of billions of cattle, sheep, pigs, poultry and other animals in three main areas: methane, land use and respiration.
Their findings – which are likely to prompt fierce debate among academics – come amid increasing from climate change experts calls for people to eat less meat.
In the 19-page report, Robert Goodland, a former lead environmental adviser to the World Bank, and Jeff Anhang, a current adviser, suggest that domesticated animals cause 32 billion tons of carbon dioxide equivalent (CO2e), more than the combined impact of industry and energy. The accepted figure is 18 per cent, taken from a landmark UN report in 2006, Livestock's Long Shadow.
"If this argument is right," write Goodland and Anhang, "it implies that replacing livestock products with better alternatives would be the best strategy for reversing climate change.
"In fact, this approach would have far more rapid effects on greenhouse gas emissions and their atmospheric concentrations than actions to replace fossil fuels with renewable energy."
Their call to move to meat substitutes accords with the views of the chairman of the UN's Intergovernmental Panel on Climate Change, Dr Rajendra Pachauri, who has described eating less meat as "the most attractive opportunity" for making immediate changes to climate change.
Lord Stern of Brentford, author of the 2006 review into the economic consequences of global warming, added his name to the call last week, telling a newspaper interviewer: "Meat is a wasteful use of water and creates a lot of greenhouse gases. It puts enormous pressure on the world's resources."
Scientists are concerned about livestock's exhalation of methane, a potent greenhouse gas. Cows and other ruminants emit 37 per cent of the world's methane. A study by Nasa scientists published in Science on Friday found that methane has significantly more effect on climate change than previously thought: 33 times more than carbon dioxide, compared with a previous factor of 25.
According to Goodland and Anhang's paper, which has not been peer-reviewed, scientists have significantly underestimated emissions of methane expelled by livestock. They argue that the gas's impact should be calculated over 20 years, in line with its rapid effect – and the latest recommendation from the UN – rather than the 100 years favoured by Livestock's Long Shadow. This, they say, would add a further 5bn tons of CO2e to livestock emissions – 7.9 per cent of global emissions from all sources.
Similarly, they claim that official figures are wrong to ignore CO2 emitted by breathing animals on the basis that it is offset by carbon photosynthesised by their food, arguing the existence of this unnecessary animal-based CO2 amounts to 8.7bn tons of CO2e, 3.7 per cent of total emissions.
On land use, they calculate that returning the land currently used for livestock to natural vegetation and forests would remove 2.6bn tons of CO2e from the atmosphere, 4.2 per cent of greenhouse gas. They also complain that the UN underestimated the amount of livestock, putting it at 21.7bn against NGO estimates of 50bn, adding that numbers have since risen by 12 per cent.
Eating meat rather than plants also requires extra refrigeration and cooking and "expensive" treatment of human diseases arising from livestock such as swine flu, they say.
One leading expert on climate change and food, Tara Garnett, welcomed Goodland and Anhang's calculations on methane, which she said had credibility, but she questioned other aspects of their work, saying she had no reason to dispute the UN's position on CO2 caused by breathing. She also pointed out that they had changed scientific assumptions for livestock but not for other sources of methane, skewing the figures.
She said: "We are increasingly becoming aware that livestock farming at current scales is a major problem, and that they contribute significantly to greenhouse gases. But livestock farming also yields benefits – there are some areas of land that can’t be used for food crop production. Livestock manure can also contribute to soil fertility, and farm animals provide us with non food goods, such as leather and wool, which would need to be produced by another means, if it wasn’t a byproduct from animal farming.”
While looking into the paper's findings, Friends of the Earth said the report strengthened calls for the Government to act on emissions from meat production. "We already know that the meat and dairy industry causes more climate-changing emissions than all the world's transport," said Clare Oxborrow, senior food campaigner.
"These new figures need further scrutiny but, if they stack up, they provide yet more evidence of the urgent need to fix the food chain. The more damaging elements of the meat and dairy industry are effectively government-sponsored: millions of pounds of taxpayers' money is spent propping up factory farms and subsidising the import of animal feed that's been grown at the expense of forests."
Justin Kerswell, campaign manager for the vegetarian group Viva!, said: "The case for reducing consumption of meat and dairy products was already imperative based on previous UN findings. Now it appears to have been proven that the environmental devastation from livestock production is in fact staggeringly more significant – and dwarfs the contribution from the transport sector by an even greater margin.
"It is essential that attention is fully focused on the impact of livestock production by all global organisations with the power to affect policy."
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