SCIENCE

To Meet Global Warming Targets, Leave Fuels In the Ground

Hefty percentages of fossil fuels need to remain untapped to curtail the rising global temperature

January 7, 2015

Coal Trains — To reduce carbon dioxide emissions, the world would need to leave some 80 percent of current coal reserves in the ground, according to a new study. Layne Kennedy/Corbis

At the end of this year, policymakers from around the world will meet in Paris to hammer out an agreement on climate change. The overall goal is to reduce greenhouse gas emissions so that the world warms no more than 3.6 degrees Fahrenheit over pre-industrial levels. Meeting that goal requires curtailing fossil fuel extraction and use—and a new study in Nature outlines just what that means. About 30 percent of oil, 50 percent of gas and 80 percent of coal reserves need to remain in the ground come 2050.

Because those reserves are not found evenly distributed around the globe, some countries would have to leave behind even greater fractions of their fossil fuels. The United States, for example, could extract nearly all of its oil and gas but would have to leave 92 percent of its coal in the ground.

“Burning all the reserves would exceed the carbon budget [for the 3.6-degree limit] by about three times,” says lead author Christophe McGlade, an energy systems modeler at University College London. The reserves are the fraction of fossil fuels in the ground that are recoverable under current economic conditions and with current technologies. They represent less than a third of what’s actually in the ground.

All fossil fuels are not created equal. Burning coal, for instance, produces more carbon dioxide than burning natural gas. Some fossil fuels are cheaper to extract than others, or they may be used close to where they’re produced, lowering transportation costs. All of that makes determining what would be the best to cut back on rather complicated.

McGlade and economist Paul Ekins, also of University College London, plugged all those considerations into a computer model. It calculated how much oil, gas and coal from 16 global regions could be extracted and still allow the world to meet the 3.6-degree climate target.

Cost of extraction was a big consideration. “The model uses the cheapest fuels first,” McGlade notes. As a result, the study concludes that there is no need to extract expensive fuels—such as oil and gas in the remote Arctic—when something like cheap natural gas is available. To the researchers' surprise, the model also showed that carbon capture technology, which would lock up carbon emissions from the burning of fossil fuels, wouldn’t make much of a difference even if it is implemented on a commercial scale within the coming decades.

The research foreshadows some of the likely difficulties in hammering out a global climate agreement. According to the model, for example, China and India would need to leave behind about two-thirds of their gas and coal, and Africa would have to leave a whopping 85 percent of its coal untouched.

“Only a global climate agreement that compensates losers and is perceived as equitable by all participants can impose strict limits on the use of fossil fuels in the long term,” Michael Jakob and Jérôme Hilaire of the Potsdam Institute for Climate Impact Research write in an accompanying commentary. Successful climate policy, they says, hinges on whether the losses from unexploited fossil fuel resources “can be shared in an equitable way that also ensures resource owners are compensated for their losses.”

For Ekins, the study highlights an inconsistency in the hundreds of billions of dollars that oil and gas companies spend exploring for new fossil fuel resources. “One might ask why they’re doing this when there’s more in the ground than we can afford to burn.”