Reuters: A U.S. cap-and-trade market on greenhouse gases should be designed carefully to avoid unfair economic pain in fossil fuel industries and other parts of the economy, experts told lawmakers on Wednesday. The aim of a cap-and-trade market on greenhouse gases at the center of the climate bill introduced by Senate leaders this month would transform the economy from being based on fossil fuels to more nuclear and renewable power. “The shifts will be significant,” Douglas Elmendorf, …