http://blogs.ft.com/energy-source/2010/12/07/cancun-why-kyoto-still-matters/

Developing countries and some major emerging economies – chiefly China, but also including India and others – insist that the Kyoto treaty must continue beyond 2012, when most of its current provisions expire.

This issue of a “second commitment period” in the jargon – so-called because when the treaty was originally signed, it was envisaged that the signatories would meet their 2012 targets then set a new set of tougher targets, and keep doing so at intervals – is one of the trickiest in the talks.
Developing countries like the Kyoto protocol because it binds rich countries to take action on greenhouse gas emissions but under it they have no similar obligations – not even countries such as China, now the world’s biggest emitter and second biggest economy.
Developed countries dislike the protocol for the same reasons. Japan caused a stir earlier in the week when it restated its long-standing reluctance to agree to a continuation of Kyoto. It would prefer a new treaty, one that included the US – which is willing to consider a new framework but will not countenance Kyoto – and that placed obligations on major emerging economies.
The European Union’s original position was similar, but last year member states – or enough of them, at any rate – decided that in order to keep developing countries on board, they would discuss a second commitment period. That leaves the EU as the only major party at the table willing to enter into a second period.