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By Roger Highfield on

How a global plant-based diet could curb greenhouse emissions

Science Director Roger Highfield reports on an American study that suggests a radical change in diet could buy valuable time to slow damaging climate change.

The global food system is becoming ever more energy intensive and more than one-third of global greenhouse gas emissions caused by human activity can be linked to how we produce, process and package what we eat.

The quest for new thinking has intensified in the wake of the historic ‘Glasgow Climate Pact’ agreed last year at the 26th global climate summit — COP (‘Conference of the Parties’) – where the outcome was better than some expected but fell short of what many hoped.

Now a new study suggests that a global switch to a plant-based diet would curb the increase of atmospheric greenhouse gases for three decades, altering the trajectory of global climate change to give humanity more time to end its reliance on fossil fuels.

‘Research shows that livestock farming is a major source of methane, a greenhouse gas that is many more times more powerful than carbon dioxide, and a very inefficient way of producing food because of the amount of land required,’ commented Science Museum advisor, Bob Ward, policy and communications director at the Grantham Research institute on Climate Change and the Environment at the London School of Economics and Political Science.

‘The over-consumption of processed meat is also linked to poor health,’ he added. ‘If we reduce meat consumption, we could improve our diets and cut the amount of land required for livestock, creating space for more vegetation that will soak up carbon dioxide from the atmosphere. Indeed, it is difficult to see how the world can reach net zero emissions of greenhouse gases without a drastic cut in livestock farming.’

The new research to quantify the impact of a global change in diet was carried out by Patrick Brown, professor emeritus at Stanford University, and Michael Eisen, professor of genetics and development at the University of California, Berkeley.

Both are vegans and are united by their interests in Impossible Foods, a company that sells plant-based meat substitutes, from burgers to nuggets. Brown is CEO of the company while Eisen is a consultant, and both are candid that they would benefit from a switch away from animal agriculture.

The Food and Agriculture Organisation estimates 14.5 per cent of annual anthropogenic greenhouse gas emissions are linked to animal agriculture, so the authors posed a simple question:

What would be the impact of a global phase-out of animal agriculture on global-heating?

In the journal PLoS Climate they report that, using forecasts with a simple climate model, phasing out animal agriculture over the next 15 years would have the same effect as a 68 percent reduction of carbon dioxide emissions through to the year 2100. That is around half of the net emission reductions necessary to limit global warming to two degrees Celsius above pre-industrial levels, which many regard as the minimum required to avert disastrous climate change.

Eisen said animal agriculture contributes to global warming in via emissions and because that land would otherwise be holding carbon but ‘most analyses only look at one of those things.’

While many have highlighted the contribution of emissions from animal agriculture to global warming there is also a more impactful ‘climate opportunity cost‘.

In other words, there is the potential to unlock negative emissions by both eliminating livestock along with their emissions of the more potent (than carbon dioxide) greenhouse gases methane and nitrous oxide, from fertiliser, digestion and manure, and by restoring native vegetation on the 30% of Earth’s land surface currently used for livestock so as to sequester carbon from the atmosphere.

They found that the resulting drop in methane and nitrous oxide levels, and the conversion of 800 billion tons of carbon dioxide to forest, grassland and soil biomass, would have the same impact as cutting annual global carbon dioxide emissions by 68%. ‘Ending animal agriculture has the unique potential to significantly reduce atmospheric levels of all three major greenhouse gases,’ said Eisen.

While the phase out of animal-based agriculture was projected to have the largest impact, as much as 90 percent of the emission reductions could be achieved by only replacing cattle and sheep, the study says.

‘Reducing or eliminating animal agriculture should be at the top of the list of potential climate solutions,’ Brown said. ‘If animal agriculture were phased out over 15 years and all other greenhouse-gas emissions were to continue unabated, the phase-out would create a 30-year pause in net greenhouse gas emissions.’

While there would be investment required to soften the economic and social impact of a global transition to a plant-based diet on the people and communities who currently make a living from animal agriculture, they write, ‘these investments must be compared to the economic and humanitarian disruptions of significant global warming.’

In response to scepticism that billions of people can be convinced to switch to a plant-only diet within 15 years, Eisen points out that other revolutions have happened in less time, such as the rapid rise of mobile phones and solar power.  Brown added: ‘Eliminating animal agriculture would have a quicker and greater impact over the next 20 to 50 years, the critical window for avoiding climate catastrophe.’

One caveat, however: their model rests on a number of simplifying assumptions, from neglecting technological advances to the viability of switching to plant-based agriculture worldwide. It also focuses on terrestrial agriculture, excluding aquaculture and fishing.

Recent research in the UK, India and Brazil commissioned by the Science Museum Group has revealed while people often mention a desire to reduce meat and dairy consumption, there is relatively low scientific awareness of the benefits, as outlined today.

However, the Group’s study did show an eagerness among many people to learn more about the solutions to the challenge of sustainable food as the race is on for the science, technology and consumer choices that will enable food to be produced more efficiently and in a way that is kinder to the environment as the global population of 7.6 billion is expected to soar to almost 10 billion by 2050.