While there are many voluntary emissions trading schemes—that is, mechanisms through which a price is put on each ton of greenhouse gas emissions produced, as part of a trading market—it's generally understood that only regulated emissions markets pack a punch. Which is why Australia’s decision to make its 500 largest greenhouse gas-emitting companies pay a carbon tax, thereby laying the groundwork for the largest emissions trading scheme outside of the European Union, caused a stir this year. And California broke ground in the U.S. by approving its own regulated carbon market this year. But some say the only market that will work—since energy exports, such as coal, are generally not covered by national programs—is a global one. Something like that will require international accords that make reducing emissions legally binding, especially for the biggest polluters. The United Nations' yearly convention on climate change tends to fall into arguments over whether and how much developing countries should bear the brunt of responsibilities. In early December, talks in Durban, South Africa, ended with an agreement…to keep negotiating. Nothing ground-breaking there, but delegates did decide to prevent the Kyoto Protocol from expiring next year. And they committed to decide on a new legally binding accord by 2015.
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