Tara Garnett, co-ordinator of the UK-based Food Climate Research Network (FCRN), explored some of the issues in a recent briefing paper and found no clear answers.

Intensive production tends to use less land — even when grain production is taken into account — and produces less emissions than extensive systems, but other issues are in play.

From a greenhouse gas perspective, intensive pig and poultry production — which are more efficient producers of protein than cattle lotfeeding — could be seen as the “least bad” option, Ms Garnett observed.

“This analysis holds true in the case of greenhouse gas emissions, but, we emphasise, not for other forms of air and water pollution, and not in the case of water use, where intensive systems are particularly demanding. There are other issues to consider, including animal welfare.”

She added: "I think the point about methane is that it needs to be seen in the context of trends in demand for animal products, and in terms of land and land use."

The need for efficient land use also broadens the issue.

“In a land constrained world, one could argue that the priority is to make the best use of the different qualities of land available,” Ms Garnett wrote.

“Not all land ... can support crop production and the question then arises — what should be done with this poorer quality, more marginal land?”

“Traditionally the answer has been to graze ruminants which then provide us with meat, milk and other outputs.

“This represents a form of resource efficiency—the land is being used to produce food that would otherwise need to be produced elsewhere — and that ‘elsewhere’ could either be existing prime agricultural land, where competition with grain production for human food consumption could arise, or on land deforested for the purpose.

“Livestock also have a role to play in maintaining ecosystem services and the biological diversity of the landscapes that they have helped shape over millennia.”

Under well-managed grazing, livestock may also be a tool for sequestering carbon in the soil, Ms Garnett noted.

The full report can be downloaded here.