Consider markets for emissions allowances, in which firms that can cheaply cut air pollution trade with those that cannot. A decade ago, the idea that such markets could achieve desired environmental goals at relatively low cost was widely recognized and implemented.
以排放配额市场为例，在市场里那些可以低成本减少排放的企业可以和其他企业做交易。十年前，一直有主张认为这类市场可以用相对低廉的成本来实现既定的环保目标，并且得到了广泛的认同和实施。但如今政治却在扼杀“设限+交易”（cap and trade）方案。