Factbox: What next for the Kyoto Protocol?

LONDON (Reuters) - Uncertainty is growing over the future of the Kyoto Protocol, the first legally binding treaty to cut emissions of greenhouse gases blamed for heating up the planet.

Nearly 40 industrialized nations -- all except the United States -- are supposed to meet agreed emissions targets during the pact's 2008-2012 first phase. Many countries are on track to meet their targets.

But agreement appears months or years off on a new round of targets for developed countries from 2013.

The complex talks have seen a stand-off where developed countries want emerging economies, and especially top carbon emitter China, to shoulder more responsibility in the fight against climate change.

The U.N.'s climate agency has for the first time detailed contingency options if the world cannot agree a new round to the pact in time before 2013.

Here are some questions and concerns about Kyoto:

* WHAT IS THE KYOTO PROTOCOL?

It is a pact agreed by governments at a 1997 U.N. conference in Kyoto, Japan, to reduce greenhouse gases emitted by developed countries by an average of 5.2 percent below 1990 levels during 2008-2012.

A total of about 190 nations have ratified the pact. Developing nations do not have binding emissions targets under Kyoto but are encouraged to take voluntary steps to curb the growth of carbon dioxide pollution from power stations, cars and industry.

* IS IT LEGALLY BINDING?

Kyoto has legal force from February 16, 2005. It represents more than 60 percent of developed nations' total emissions.

The United States, the world's second largest carbon emitter after China, decided against implementing Kyoto in 2001, reckoning it would be too expensive and wrongly omitted developing nations from a first round of targets to 2012.

* HOW IS IT ENFORCED?

Countries overshooting their targets in 2012 will have to make both the promised cuts and 30 percent more in a second period from 2013.

* WILL ALL COUNTRIES MEET THEIR TARGETS?

Unlikely. Canada has said it will miss its targets by a wide margin, despite the threat of penalties. This has led to criticism that Kyoto is a failure, raising doubts nations will meet much tougher targets for the second compliance period from 2013.

* SO WILL KYOTO FADE AWAY?

There's a real chance of that happening. Negotiators remain far apart on deciding the shape of a future, broader, climate pact that extends the fight against climate change.

One idea is to extend Kyoto into a second period and create another climate treaty, perhaps based on an Accord agreed in Copenhagen in December which is not legally binding.

Big developing nations India and China, while broadly supporting the Accord, firmly back Kyoto and the current U.N. talks to try to extend it and do not want to turn the Accord into a legal text. The United States refusal to join Kyoto and the failure of the U.S. Congress to pass emissions targets is another big uncertainty.

(Compiled by Alister Doyle, David Fogarty and Gerard Wynn; Editing by Janet Lawrence)