The music legend took his campaign for 'Meat Free Mondays' to the European Parliament in Brussels, hoarse from the start of his first major live tour in five years in the historic Beatles haunt of Hamburg, Germany.
McCartney, 67, was joined by Rajendra K. Pachauri, chair of the 2007 Nobel Peace Prize-winning Intergovernmental Panel on Climate Change, and the pair signed a joint declaration with the parliament calling for a political step change.
Their statement called on governments worldwide "to adjust their agriculture, development, environment and public health policies to reflect the role of livestock production in climate change."
Citing United Nations reports he said drew him to the issue, passionately vegetarian McCartney told a hearing of lawmakers that 18 percent of harmful emissions come from agriculture - more than the 13 percent attributed to transport.
"I would be glad if this weren't true, and we could just carry on as we are forever quite happily and not bother with this whole subject," he said.
"But I've got a nasty feeling that this is true."
McCartney's solution is simple; "Our campaign says 'try one meat-free day in the week'," McCartney said, adding that as a young Catholic boy growing up in Liverpool he had routinely done much the same thing.
"It's very do-able. If you say to people, 'go vegetarian,' that's very hard to do.
"But if you suggest to people 'one day,' I think most people will have a bit of a blow-out over the weekend and Monday they go to the gym.
"So I'm suggesting they also cut out meat on that day. Once, for instance, we didn't recycle - we weren't interested, but now it's an accepted part of our lifestyles," he argued.
Pachauri, who bemoaned the fact that the livestock issue is not high on the Copenhagen agenda, told a press conference with McCartney afterwards that a surcharge on beef would help focus minds.
"I think a tax would make a lot of sense - in Japan, beef costs a lot more than white meat or fish," Pachauri said.
"If there is enough awareness among the public, governments won't have to impose taxes. But it's something we should think about seriously."
Eric