Deforestation accounts for almost 20 percent of global emissions — more than the world’s entire transportation sector. But saving the trees — as beneficial as it would be to the changing climate — comes at a significant cost as a growing, wealthier population competes for food, says a new MIT study.
“With a larger and wealthier population, both energy and food demand will grow,” says John Reilly, the lead author of the study and the co-director of the MIT Joint Program on the Science and Policy of Global Change. “Absent controls on greenhouse gases, we will see more emissions from fossil-fuel use and from land-use change. The resulting environmental change can reduce crop yields, and require even more land for crops. So this could become a vicious circle.”
Reilly’s study, recently published in Environmental Science & Technology, compares the effects of slashing emissions from energy sources alone to a strategy that also incorporates emissions associated with land use.
The report finds that, with a growing global population, fast-developing nations, and increasing agricultural productivity and energy use, the world is on the path to seeing average temperatures rise by as much as 6 degrees Celsius by the end of the century. Even with an aggressive global tax on energy emissions, the planet will not be able to limit this warming to 2 C — the target world leaders have agreed is needed to avoid dangerous climate change. But when the tax is applied to land-use emissions, the world community could come much closer, with temperatures by the year 2100 rising 2.4 C above pre-industrial levels.
To go one step further in reducing emissions the study incorporates biofuels production, which could increase carbon storage on land and be a cleaner source of energy, lessening the use of fossil fuels. The researchers find that increased biofuels production could cut fossil-fuel use in half by the end of the century — from 80 percent of energy without a tax to 40 percent with a tax — and further limit warming to bring the world just shy of the target.
The world could get even closer to the target, the study shows, by creating economic incentives for storing carbon on land — such as through reforestation. In combination with the global carbon tax, this could “bring the world closer to keeping warming below the 2 degree Celsius temperature,” Reilly says.
But there are always drawbacks.
“The environmental change avoided by reducing greenhouse-gas emissions is substantial and actually means less land used for crops,” Reilly says. “The big tradeoff is that diverting this amount of land to carbon storage, and using land to produce biofuels, leads to substantial rises in food and forestry prices.”
Food prices could rise more than 80 percent, the study shows. Along with this, nations could become wealthier, with global GDP increasing fivefold. On average, the share of a household’s budget for food, even with higher prices, might fall from 15 percent to 7 percent. But for poorer regions of the world, the food budget share could increase, meaning these food price impacts could have disproportionate effects on poorer regions.
Food shortages and higher food prices are becoming a major challenge, according to Jonathan Foley, director of the University of Minnesota’s Institute on the Environment, who spoke at a recent MIT event.
“In the last 20 years we’ve produced 28 percent more crops. But in the next 38 years, we need to double that growth,” Foley said. “We’re not going to grow our way out of the problem … we must look at other possibilities.”
An advocate of ending deforestation, Foley said we need to grow food more efficiently.
Reilly agrees, and says his study puts an emphasis on more effective use of land to produce food. Part of this means more efficient (intensive) use of pasture and grazing land. But, he says, the carbon tax scenarios he tests make the problem that much more difficult — with biofuels and carbon sequestration using up more land.
“And with all three of these demands for land — food, biofuels and carbon storage — the competition is intense, and as a result, food prices rise. So this is an important tradeoff the world needs to consider.”