Imagine a world in which animals were not farmed for protein and all people consumed only plants. The authors of a new study from Stanford recognize that this would involve a huge change in attitudes, but say their research indicates that a dietary shift away from meat would effectively halt the increase of atmospheric greenhouse gases for 30 years while countries phased out the use of fossil fuels.
“We wanted to answer a very simple question: What would be the impact of a global phase-out of animal agriculture on atmospheric greenhouse gases and their global-heating impact?” said study co-author Professor Patrick Brown.
For their model, the researchers used publicly available data on livestock production and livestock-linked emissions. They examined four dietary scenarios: an immediate replacement of all animal agriculture with plant-only diets; a more gradual and more realistic 15-year transition to a global plant-only diet; and versions of each where only ruminants were replaced with plant-only products.
The authors assumed that all non-agricultural gas emissions would remain constant and that the land formerly used for livestock production would be converted back to grasslands, prairies, forests and scrublands that would absorb atmospheric carbon dioxide (CO2).
The experts then used a simple climate model to project how these changes would impact the evolution of atmospheric greenhouse gas levels and warming for the rest of the century.
“The combined effect is both astoundingly large, and – equally important – fast, with much of the benefit realized by 2050,” said Professor Brown. “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 and offset almost 70 percent of the heating effect of those emissions through the end of the century.”
The results of the modeling exercise showed that phasing out animal agriculture over the next 15 years would have the same effect as a 68 percent reduction of CO2 emissions through the year 2100. This would provide 52 percent of the net emission reductions necessary to limit global warming to two degrees Celsius above preindustrial levels, which scientists say is the minimum threshold required to avert disastrous climate change.
The changes would stem, the authors say, from the spontaneous decay of the potent greenhouse gases methane and nitrous oxide, and the recovery of biomass in natural ecosystems on the more than 80 percent of humanity’s land footprint currently devoted to livestock.
“Reducing or eliminating animal agriculture should be at the top of the list of potential climate solutions,” said Professor Brown. “I’m hoping that others, including entrepreneurs, scientists and global policymakers, will recognize that this is our best and most immediate chance to reverse the trajectory of climate change, and seize the opportunity.”
While many other scientists have recognized that emissions from animal agriculture contribute significantly to global warming, what has not been emphasized before is the much more impactful “climate opportunity cost” – the potential to reduce the presence of current greenhouse gases by eliminating livestock.
“As the methane and nitrous oxide emissions from livestock diminish, atmospheric levels of those potent greenhouse gases will actually drop dramatically within decades,” said Professor Brown. “And the CO2 that was released into the atmosphere when forests and wild prairies were replaced by feed crops and grazing lands can be converted back into biomass as livestock are phased out and the forests and prairies recover.”
It would certainly be challenging to get billions of people to change their attitudes towards eating meat, but the model also shows that even phasing out the use of ruminants alone (cattle, sheep) would achieve a 90 percent reduction in the gas emissions from livestock agriculture.
The scientists acknowledge that 15 years is a short time for people to adopt dietary changes, but they point out that many other revolutionary changes have been accepted in shorter time spans. “We went from having no cell phones to cell phones being ubiquitous in less time than that. Electricity, cars, solar panels – all became common in a relatively short period of time,” said study co-author Professor Michael Eisen.
Professor Brown noted that societal attitudes toward food are far from fixed. “Five hundred years ago, nobody in Italy had ever seen a tomato. Sixty years ago, nobody in China had ever drunk a Coke. Mutton was once the most popular meat in America. People around the world readily adopt new foods, especially if they are delicious, nutritious, convenient and affordable.”
The authors acknowledge that the economic and social impacts of a global transition to a plant-based diet would be acute in many regions and locales. They added that substantial global investment will likely be required to ensure that people who make a living from animal agriculture do not suffer when it is reduced or replaced.
However, they write, “in both cases, these investments must be compared to the economic and humanitarian disruptions of significant global warming.”
Professor Brown is the founder and CEO of Impossible Foods, a company that has developed alternatives to using animals in food production, and Professor Eisen is an advisor to the company.
The scientists have made all of the raw data they used, as well as their calculations and the computer code used to carry out the calculations, publicly available so that others can make up their own minds.
“The great thing about science is that, in the end, it all comes down to whether the conclusions are supported by the evidence,” said Professor Brown. “And in this case, they are.”
The study is published today in the open-access journal PLoS Climate,