Calgary Herald: Two of President Barack Obama’s top advisers on energy and climate change said Monday the Alberta oilsands are a key part of the U.S. energy mix, but warned its development must be cleaned up because there’s “a lot of concern” south of the border about the environmental footprint. U.S. Energy Secretary Steven Chu and Nancy Sutley, chairwoman of the White House Council on Environmental Quality, said the Obama administration is committed to ramping up clean-energy production in the U. …