Christian Science Monitor: The nation’s first-ever law requiring a reduction in greenhouse gas emissions goes into effect today, mandating that automakers progressively chop the amount of tail-pipe gases emitted from US cars. The first cars to be affected by the law will be automakers’ 2012 lines. By 2016, model year greenhouse gas emissions must not exceed an average of 8.8 ounces per mile – a 21 percent reduction from today’s levels. To get there, vehicles’ gas mileage will need to achieve on average 35.5 …