Ensia: As forest fires devastated Fort McMurray, Alberta, last month, a different sort of fire may have started beneath the ground. Peat, a carbon-rich soil created from partially decomposed, waterlogged vegetation accumulated over several millennia and the stuff that fueled Indonesias megafires last fall, also appears in the boreal forests that span Canada, Alaska and Siberia. With the intense heat from the Fort McMurray fires, theres a good chance the soil in the area could have been ignited, says...