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. Once destroyed peatlands will not return note the researchers: \"Constraints imposed by the postmining landscape and the sensitivity of peatland vegetation prevent the restoration of peatlands that dominated the premining landscape.\" Instead drained peatlands will be turned into upland forests, which will store considerably less carbon. \"Claims by industry that they will \'return the land we use—including reclaiming tailings ponds—to a sustainable landsca that is equal to or better than how we found it\' and that it \'will be replanted with the same trees and plants and formed into habitat for the same species\' are clearly greenwashing,\" the researchers write. Already carbon emissions from the tar sands produce significantly more carbon than conventional sources with various research showing around 20 percent higher than conventional oil to three times higher. However, such estimates have not included the loss of carbon due to peatland destruction, which the researchers estimate will be equal in total to \"seven years worth of carbon emissions by mining and upgrading (at 2010 levels).\" A recent study has found that if the entirety of the tar sands were exploited it would raise global temperatures 0.64 degrees Fahrenheit (0.36 degrees Celsius). This represents around 45 percent of how much the world has warmed since the Industrial Revolution. \"Oil sands mining is frequently criticized as a carbon-intensive means of acquiring oil. Its contribution to the global carbon imbalance has provoked numerous calls to slow oil sands development, including, most recently, a letter to Canada’s prime minister signed by eight Nobel Peace Laureates,\" the authors write. Criticism of the tar sands does not rest on carbon emissions alone. The tar sands has resulted in the destruction of pristine environments, consumes massive amounts of freshwater, and is allegedly linked to high cancer rates in nearby communities. The mines themselves have been dubbed the world\'s largest industrial project. Still the Canadian government, under Prime Minister Stephen Harper, has relentlessly pursued the expansion of the mines and is now pushing controversial pipelines to bring tar sands oil to a global market either south through the U.S. (the Keystone XL Pipeline) or west to the coast of British Colombia. The government argues exploiting the full-scale of the tar sands is essential to the Canadian economy.