As the climate warms in the decades ahead, billions of acres, most of them in the northern hemisphere, will become suitable for agriculture and could, if plowed, emit a massive, planet-altering amount of greenhouse gases.
New research, published Wednesday in Plos One, a science journal, finds that these new "climate-driven agricultural frontiers"—if pressured into cultivation to feed a surging global population—could unleash more carbon dioxide than the U.S. will emit in nearly 120 years at current rates.
"The big fear is that it could lead to runaway climate change. Any time you get large releases of carbon that could then feed back into the system," said Lee Hannah, a senior scientist at Conservation International and co-author of the new research, "it could lead to an uncontrollable situation."
Large amounts of land, especially in the northern hemisphere, including Russia and Canada, are inhospitable to farming now. But already, some of these areas are thawing and could become farmland. Hannah and his fellow researchers wanted to understand what would happen if that land gets plowed up for farming over the next century.
They found that, as warming temperatures push farmers farther north, the churning up of lands, especially those with rich, peaty soils, could release 177 gigatons of carbon dioxide into the atmosphere. (Most of the shifts will occur in the northern hemisphere because it contains larger landmasses.) That's more than two-thirds of the 263-gigaton-limit for keeping global temperatures within 2 degrees Celsius over pre-industrial levels.
Scientists estimate that, with a projected global population of nearly 10 billion by 2050, the world will need to produce 70 percent more food. How—and where—to produce that food remain open questions. Pressure to produce more could push farming into these new agricultural frontiers if policies aren't put in place now, the researchers say.
"We hope this is a wake-up call," Hannah said. "Canadian and Russian governments are trying to promote agriculture in these areas. They're already working in micro-pockets that are beginning to get more suitable. Climate change is a slow process, so these areas aren't going to open up overnight, but it could lead to a creeping cancer if we're not careful."
Using projections from 17 global climate models, the researchers determined that as much as 9.3 million square miles could lie within this new agricultural frontier by 2080, under a high-emissions scenario, in which global emissions continue at their current rate. (If emissions continue on this business-as-usual path, global temperatures could rise by 4.8 degrees Celsius by century's end.) They found that some of the world's most important crops, including wheat, corn and soy, will grow in these new frontiers.
They note that their estimates lie at the upper range of total possible acreage because soil quality, terrain and infrastructure will determine how much land actually gets farmed. Policy will also play a huge role.
The land with greatest potential to produce crops happens to be especially carbon-rich. If that land is churned up, the additional carbon released will stoke temperatures, creating yet more land that's suitable for farming.
"We're already worried about carbon-rich arctic soils. Russia is already subsidizing homesteading in Siberia," Hannah said. "This is the time to get good policy in place that excludes the most carbon-rich soils or we really risk runaway climate change."
Hannah added, "This land isn't suitable now, but when people can make money off of it, it's going to be much harder to get good policies in place."
Among those, Hannah said, are policies that require soil conservation methods or limiting some areas from being plowed up in the first place.
"It's a big future problem," said Tim Searchinger, a research scholar at Princeton's Woodrow Wilson School and a senior fellow at the World Resources Institute, who has written extensively on land-use, but was not involved in the study. "One of the partial solutions, however, is to work hard to reforest the areas that will be abandoned as agriculture shifts north."