A few facts. a)The overall goal of an emissions trading plan is to reduce emissions. The cap is usually lowered over time - aiming towards a national emissions reduction target b)Because emissions trading uses markets to determine how to deal with the problem of pollution, it is often touted as an example of effective free market environmentalism. While the cap is usually set by a political process, individual companies are free to choose how or if they will reduce their emissions. c) It's worked in the U.S. before and in each case it was found that the least cost solution was dramatically less costly than the same amount of pollution reduction produced by any conventional abatement strategy