Environmentalists have targeted the oil-producing tar sands in Canada in part because its crude comes with heftier carbon emissions than conventional sources. Now, a new study in the Proceedings of the National Academy of Sciences (PNAS) has found an additional source of carbon that has been unaccounted for: peatlands. Mining the oil in the tar sands, dubbed “oil sands” by the industry, will require the wholesale destruction of nearly 30,000 hectares of peatlands, emitting between 11.4 and 47.3 million metric tons of additional carbon.