The greatest emerging threat to the global climate may rest in the side pocket of your trousers — or wherever you keep the car keys. Emissions from transportation may rise at the fastest rate of all major sources through 2050, the United Nations will say in a report due April 13. Heat-trapping gases from vehicles may surge 71 percent from 2010 levels, mainly from emerging economies, according to a leaked draft of the most comprehensive UN study to date on the causes of climate change. Rising incomes in nations like China, India and Brazil have produced explosive demand for cars and for consumer goods that must be delivered by highway, rail, ship or air. The new pollution, measured in millions of tons of greenhouse gases, may exceed all of the savings achieved through initiatives like subsidies for public transport and fuel efficiency. Cutting back on transportation gases “will be […]