SINGAPORE - The agricultural sector is responsible for a huge amount of greenhouse gas emissions - equivalent to the emissions from all the electricity generation in the world, said Nobel laureate Steven Chu.

Hence, there is a need to transform the sector - through a fourth agricultural revolution - where higher crop yields to feed the world's populations are obtained sustainably without the use of fertilisers or insecticides.

Professor Chu, who is a professor of molecular and cellular physiology and of energy science and engineering at Stanford University, was speaking to The Straits Times at the Nobel Prize Dialogue 2022: The Future We Want Together on Sept 13.

The event was held at Raffles City Convention Centre, where Nobel laureates, students and other experts came together to discuss how to improve people's lives and how a better future can be built. It was organised by the National University of Singapore's Yong Loo Lin School of Medicine.

Prof Chu, 74, who is American, noted how the previous agricultural revolutions helped the world's population to grow through the domestication of animals, cultivation of staple crops and the use of fertilisers to boost crop yield.

"But there were also unintended consequences - fertiliser requires a lot of energy to make, and the fertiliser run-off (into rivers and streams) is a potent greenhouse gas effect," he added.

Fertiliser run-offs release nitrous oxide - which has a warming potential of approximately 300 times that of carbon dioxide.

Some solutions are being tested, such as creating microbes which can take nitrogen from the soil to feed crops like corn, wheat and rice, so that fertilisers would not be needed.

This has already been trialled on a small scale in the United States, where 50 per cent of fertiliser needed for growing corn has been replaced with microbes in some farms. This will, however, unlikely take shape on a larger scale until it is profitable for farmers to do so, Prof Chu noted.

To prevent less methane from being released through cow burps, it is also possible to reduce the number of microbes found in cattle by 90 per cent, perhaps by modifying their feed or vaccinating them, he said.

Prof Chu was energy secretary in the US from 2009 to 2013, helping to implement then President Barack Obama's agenda of investing in clean energy, reducing the US' reliance on foreign oil, and addressing the global climate crisis.

Prof Chu helped to propel the development of a funding agency called Advanced Research Projects For Energy - which invested in projects such as accelerating the development of solar power to lower its costs.

"In 2010, we had a crazy ambition to cut (the costs of solar) by one quarter in 10 years, and we managed to get it to one quarter in seven years," he said. The feat took a detailed road map and required working closely with the industry.

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4th agricultural revolution needed to cut greenhouse gas emissions: Nobel laureate - The Straits Times