When Sandbag begun in 2008, the European Union led the way with its carbon market. Now, countries across the world have followed, and even surpassed the EU. Carbon markets exist in China, the east and west coasts of the USA, New Zealand, Kazakhstan, Taiwan, Australia, Canada, South Korea, and new schemes appear each year.

The theory goes that the cap (the total number of emissions permits) delivers lower carbon emissions, whilst the trading allows the market to find the cheapest place to make these cuts.

The debate about how to tackle climate change has always been fierce, with many alternatives suggested, but so far it is cap and trade that has proved the most attractive option and the only large-scale policy yet implemented to cut carbon emissions.