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BBC NewsUN specialists are to look again at the contribution of meat production to climate change, after claims that an earlier report exaggerated the link.
A 2006 report concluded meat production was responsible for 18% of greenhouse gas emissions - more than transport.
The report has been cited by people campaigning for a more vegetable-based diet, including Sir Paul McCartney.
But a new analysis, presented at a major US science meeting, says the transport comparison was flawed.
The 2006 report - Livestock's Long Shadow, published by the UN Food and Agriculture Organization (FAO) - reached the figure by totting up all greenhouse-gas emissions associated with meat production from farm to table, including fertiliser production, land clearance, methane emissions from the animals' digestion, and vehicle use on farms.
But Dr Mitloehner pointed out that the authors had not calculated transport emissions in the same way, instead just using the IPCC's figure, which only included fossil fuel burning.
"This lopsided 'analysis' is a classical apples-and-oranges analogy that truly confused the issue," he said.
One of the authors of Livestock's Long Shadow, FAO livestock policy officer Pierre Gerber, told BBC News he accepted Dr Mitloehner's criticism.
"I must say honestly that he has a point - we factored in everything for meat emissions, and we didn't do the same thing with transport, we just used the figure from the IPCC," he said.
"But on the rest of the report, I don't think it was really challenged."
FAO is now working on a much more comprehensive analysis of emissions from food production, he said.
It should be complete by the end of the year, and should allow comparisons between diets, including meat and those that are exclusively vegetarian.
Read more:
http://news.bbc.co.uk/2/hi/science/nature/8583308.stm