Mexico, host of the Cancún climate talks that began Monday, enforced tougher environmental standards in its notoriously dirty capital and vastly improved air quality.

America has adopted a tough all-or-nothing position at the Cancún climate change summit, fuelling speculation of a walk-out if developing countries do not meet its demands. At the opening of the talks at Cancún, the US climate negotiator, Jonathan Pershing, made clear America wanted a "balanced package" from the summit.