The announcement by China that it will implement a national emissions trading scheme confirms the status of this instrument as the pre-eminent policy choice for mitigating climate change. China will join the dozens of existing and emerging schemes around the world - from the EU to California, South Korea to New Zealand - that use carbon units (otherwise known as emissions permits or carbon credits) to trade in greenhouse gas emissions in a multi-billion dollar global carbon market. However, to date, there has been no consensus about this pre-eminent policy instrument being regulated by international economic law through the World Trade Organization, international investment agreements, and free trade agreements.