Reuters: Half a kg of salmon; two kg of potatoes; a tonne of greenhouse gas reductions — shoppers at one Norwegian mall can now buy cuts in their carbon footprint as they pick up their weekly groceries. The Stroemmen Storsenter shopping centre outside Oslo began selling the certificates on Saturday, at 165 Norwegian crowns ($30.58) per tonne, to people who feel bad about contributing to climate change. By midday on Monday, its second day of offering the U.N.-approved Certified …