Toronto: One third of the world’s arable land has been lost to soil erosion or pollution in the last 40 years, and preserving topsoil is crucial for feeding a growing population, scientists said in research published during climate change talks in Paris.

It takes about 500 years to generate 2.5 cm (one inch) of topsoil under normal agricultural conditions, and soil loss has accelerated as demand for food rises, biologists from Britain’s Sheffield University said in a report published on Wednesday.

Preserving valuable topsoil is crucial if the world is to produce enough food for more than 9 billion people by 2050, the scientists said.

‘Soil is lost rapidly but replaced over millennia, and this represents one of the greatest global threats to agriculture,’ Sheffield University biology Professor Duncan Cameron said in a statement with the report.

He recommends that farmers engage in ‘conservation agriculture’ where crops are rotated more frequently, organic matter is restored to the soil and less energy is spent on nitrogen fertilisers.

At present, intensive farming maintains crop yields through the heavy use of fertilisers, made by an industrial process that consumes five percent of the world’s natural gas production and two percent of the world’s annual energy supply, the report said.

On Tuesday French officials launched a plan to raise soil carbon levels in order to take carbon dioxide out of the atmosphere, presenting the scheme at international climate change negotiations in the French capital.

The French-led plan, backed by the United Nation’s Food and Agriculture Organisation (FAO), aims to increase soil carbon stocks by 0.4 percent annually to boost soil fertility while combating global warming.