Kyoto, which was adopted in 1997 and entered into force in 2005, commits most developed states to binding emissions targets. The talks are the last chance to set another round of targets before the first commitment period ends in 2012.
Major parties have been at loggerheads for years, warnings of climate disaster are becoming more dire and diplomats worry whether host South Africa is up to the challenge of brokering the tough discussions among nearly 200 countries that run from Monday to December 9 in the coastal city of Durban.
There is hope for a deal to help developing countries most hurt by global warming and a stop-gap measure to save the protocol. There is also a chance advanced economies responsible for most emissions will pledge deeper cuts at the talks known as the Conference of the Parties, or COP 17.
But the debt crisis hitting the euro zone and the United States makes it unlikely those areas will provide more aid or impose new measures that could hurt their growth prospects.
"The South Africans are desperate to ensure that the COP does not fail, but they will not be able to deliver much," said Ian Fry, lead negotiator for the tiny Pacific island nation of Tuvalu, which could be erased by rising sea levels.
Fry blamed the United States, which has not ratified Kyoto, for blocking progress and said: "The EU seems to be going weak at the knees and will opt for a soft continuation of the Kyoto Protocol with a possible review process in 2015 to think about new legal options."
Envoys said there may be a political deal struck with a new set of binding targets, but only the European Union, New Zealand, Australia, Norway and Switzerland are likely to sign up at best. Any accord depends on China and the United States, the world's top emitters, agreeing binding action under a wider deal by 2015, something both have resisted for years.
China is unwilling to make any commitments until Washington does while Russia, Japan and Canada say they will not sign up to a second commitment period unless the biggest emitters do too.
Emerging countries insist Kyoto must be extended and that rich nations, which have historically emitted most greenhouse gas pollution, should take on tougher targets to ensure they do their fair share in the fight against climate change.
Developing nations say carbon caps could hurt their growth and programmes to lift millions out of poverty.
The stakes are high, with many experts urging immediate action. This month, two separate U.N. reports said greenhouse gases had reached record levels in the atmosphere while a warming climate is expected to lead to heavier rainfall, more floods, stronger cyclones and more intense droughts.
Despite individual emissions-cut pledges from countries and the terms of the Kyoto pact, the United Nations, International Energy Agency and others say this is not enough to prevent the planet heating up beyond 2 degrees Celsius.
Global average temperatures could rise by 3-6 degrees by the end of the century if governments fail to contain greenhouse gas emissions, bringing unprecedented destruction as glaciers melt and sea levels rise, the OECD said last week.
The warning from the OECD, whose main paymasters are the United States and other developed economies, underscored fears that the commitment to curb climate-heating gases could falter at a time when much of the world is deep in debt.
"The COP is being held on the African continent which bears the greatest social injustices due to the impacts of climate change," environmental group Greenpeace said.
Rich nations have committed to a goal of providing $100 billion a year in climate cash by 2020, which the Green Climate Fund will help manage. But the United States and Saudi Arabia have objected to some aspects of the fund's design.
South Africa has said it wants to advance an African agenda at the conference but is seen by many diplomats as not having the diplomatic muscle or prestige to broker complex talks.
As the world's poorest continent, Africa is also the most vulnerable to the extreme weather conditions and rising sea levels brought by climate change. In the Horn of Africa, some 13 million people are going hungry due to prolonged drought. In Somalia, the crisis is compounded by conflict.