A duration of six days, two documents, three major knots, some sparkles in negotiations, and the place is China -- these might be all, if no more, about the upcoming UN climate talks in Tianjin.

On Oct. 4-9, two special working groups under the United Nations Framework Convention on Climate Change (UNFCCC) and its Kyoto Protocol respectively, each involving negotiators from more than 190 parties, will meet side by side to seek consensus and narrow their gaps, mainly on two draft documents.

There is not a duel between the two working groups. They will work on two tracks, or in a duel-track way, to push forward the UN climate talks to combat global warming.

Negotiators in Tianjin talks, like in other working group meetings, have two primary tasks. One is to narrow their differences and make a 70-page negotiating text under the UNFCCC "slimmer" to submit to the Cancun Conference scheduled for Nov. 29-Dec. 10 this year in Mexico.

Another task is that negotiators need to focus on a draft proposal and prepare a better document under the Kyoto Protocol for the Cancun Conference to facilitate the Conference to reach agreement on more points under the Kyoto Protocol and push ahead the process.

However, analysts believe that neither track is easy to move on due to three major obstacles, or knots which are difficult to be unbuckled.

First, the United States refused to return to the Kyoto Protocol. The world's top developed country refused to sign the revised Kyoto Protocol in Bonn in 2001 and pulled out, asking for a lower emissions target among others.

"Friends of the Earth", an international environmental organization, said in a recent statement that criticism on the United States may rise in the Tianjin climate talks.

"Lack of climate legislation in the U.S. may lead to less tolerance for U.S. efforts to torpedo Kyoto Protocol," it said.

"The U.S. remains the only wealthy country that has not ratified the Kyoto Protocol, the only international instrument related to climate change that contains legally binding emission reduction targets," it noted.

In the past, some countries might tolerate the United States' stance to leave or try to act against the Kyoto Protocol, because they believed that tolerance is the only way to let the United States return, analysts said. But now their tolerance is decreasing.

Secondly, unreasonable requirements that press big developing countries, such as China, India, Brazil and South Africa, to reduce emissions also will undermine the smooth proceeding of the talks, as it was an alternative way in which the developed countries shift their responsibility.

Some developed countries even sought to monitor the voluntary emissions reduction process in these developing countries, triggering intensive controversy in the talks.