Organic farming could be worse for the climate than conventional farming methods, one of the government’s scientific advisers has said, because of the greater land use required and the methods used.

Lord Krebs, who advises ministers on how to adapt to climate change, told the Oxford Farming Conference that organic farming did not necessarily mean more environmentally friendly farming.

Instead, he suggested, agricultural methods known as “no-till” – which usually involves the use of genetically modified crops or biotechnology, with herbicides to kill the weeds that tilling normally prevents – were better for the climate as they reduce the turnover of soils, a process that releases carbon dioxide into the atmosphere.

At least 10% of global greenhouse gas emissions are thought to come from agriculture, and that proportion is likely to rise as the world’s population grows and an increasingly prosperous middle class around the world opt for more meat in their diets, requiring a greater production of feed crops.

Krebs also argued that organic farming needs more land than technological methods to produce the same yield, which could be an increasing problem as the world’s population is projected to grow from more than 7 billion people today to 9 to 12 billion by mid-century, requiring a correspondingly large rise in agricultural productivity.

Krebs, formerly the first chief executive of the UK’s Food Standards Agency from 2000 to 2005, said in 2000 organic vegetables were no more nutritious than those produced from other agricultural methods. He told the BBC in that year that people who bought organic food were “not getting value for money, in my opinion and in the opinion of the Food Standards Agency, if they think they’re buying food with extra nutritional quality or extra safety. We don’t have the evidence to support those claims.”

He told the conference on Wednesday that the UK’s soils could not be relied upon to continue to produce food at current levels in future decades, as they are likely to become much more eroded by rain and wind in future. Floods and droughts are both likely to become more common across Britain in a future of global warming, he noted.

Helen Browning, the chief executive of the Soil Association, which promotes organic farming and produce, said she was “bemused by the hostility” of Krebs towards organic methods. She cited a scientific paper published last year in the Proceedings of the Royal Society that found organic farming could play an important role and for many crops did not produce a smaller yield than conventional methods.

“A global analysis has shown that organic farming stores significant amounts of carbon in the soil over time, and is a very effective way of combatting climate change,” she said.

With regard to soils, she added: “Organic techniques have a great deal to offer in building organic matter in soils and improving efficiency of fertiliser use. When the increasing use of non-renewable inputs [in the form of fertilisers, such as phosphates] is considered, non-organic farming is significantly less productive than organic, and the productivity of non-organic [farming] is falling because conventional farming is using more and more fertiliser inputs simply to keep yields level.”

The world’s soils are a major source of atmospheric carbon. So, too, is nitrous oxide, a greenhouse gas that is the byproduct of adding artificial nitrogen fertilisers to soils.

Intensive agriculture has also been blamed for soil erosion, as small fields bounded by hedgerows in the UK have been replaced by large “prairie”-type fields that make soil more vulnerable to erosion. Farmers can be encouraged to reduce this problem, for instance by ploughing along contours rather than uphill to downhill, but this is not mandatory.