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California starts new carbon emissions cutting programme

1 January 2013 Last updated at 17:21 GMT

A new system for cutting carbon emissions starts in California on new year's day 2013.

Hundreds of the biggest polluters will be forced to reduce their emissions every year or buy expensive carbon credits, as California aims to reduce its emissions to 1990 levels by 2020.

Alastair Leithead reports from California.