COPENHAGEN - Exhausted negotiators, working late into the night, painstakingly threaded together blocks of text in a last-ditch effort to seal a climate deal that can be signed Friday by President Obama and more than 100 other world leaders. Prospects for an agreement to reduce greenhouse gas emissions improved after Secretary of State Hillary Rodham Clinton said yesterday the United States would help create a $100-billion-a-year fund by 2020 to help developing countries adapt to climate change and shift to greener technologies. Clinton did not say what the US portion would be, and the total amount was less than the $200 billion a year many developing countries were seeking from industrialized nations, which have caused most of the warming from power plant and other emissions. Still, the US support for the fund, which has also been endorsed by the European Union, was seen as a signal the real nitty-gritty negotiations had begun. While the last day of talks produced more movement than the two years leading up to the Copenhagen climate conference, it was unclear last night whether it would be enough to bridge the enormous divides here between rich and poor countries - and complete a pact to limit global warming to the widely accepted goal of 2 degrees Celsius above pre-industrial levels. Unresolved issues were everywhere. It is likely, though not certain, observers say, that developing countries will accept Clinton's financing offer. A bigger obstacle may be China's refusal to allow international monitoring of whether it achieves its pledge to slow the growth of emissions. 'There has to be a willingness to move toward transparency in whatever form we finally determine is appropriate,' Clinton said at a press conference. 'So, if there is not even a commitment to pursue transparency, that's kind of a deal-breaker for us.' Speaking later in the day, the Chinese vice minister of foreign affairs, He Yafei, said his country would not be monitored as 'a matter of principle.' He said the foundation language of the Copenhagen talks does not require developing countries to submit to binding emission targets regulated by the international community. But he stressed that his country had every intention of abiding by its target - a 44 percent reduction in carbon intensity, the amount of carbon dioxide emitted per unit of economic production, below 2005 levels by 2020. And he signaled some flexibility, saying China was 'willing to have explanations and clarifications' about its progress toward emissions goals, though nothing that is viewed as 'intrusive' or an 'infringement on China sovereignty.' The deadline negotiators are under is intense: Expectations of reaching a binding climate treaty in Copenhagen were dashed months ago, but if Obama and the other national leaders do not agree to at least some language today, it would be a major embarrassment. 'All international negotiations are condemned to success' because so many heads of state would never risk the political capital to say it was a failure after so much effort, said Adil Najam, a Boston University professor and an adviser to the Pakistan delegation here. He is also a former lead author of the Intergovernmental Panel on Climate Change, the leading scientific authority on global warming. He said the true test of the Copenhagen talks' success will be if timetables to deal with outstanding issues are adhered to - and a binding agreement on meaningful emissions reductions is signed by a meeting in Mexico City this time next year. US Representative Edward Markey, a Massachusetts Democrat who arrived in Copenhagen with 20 other House members including Speaker Nancy Pelosi, lent his voice to calls to put aside differences and strike a deal. 'The US is ready to do its fair share,' Markey, who co-wrote climate legislation that passed the House in June, said at a press conference. 'Our goal is to work with the world.' In an interview afterward, he said an agreement 'won't be the text anyone wants,' but one that everyone could probably live with. Even if a deal is struck, it's unclear how much it will mean. The IPCC says developed nations would need to cut emissions by 25 to 40 percent from 1990 levels by 2020, and far more after that, to avoid the worst consequences of global warming. The collective amount countries are offering, at least as of a few days ago, did not meet that target. An internal negotiating document, obtained by an environmental group, was circulating at the conference yesterday. Dated Dec. 15, it concluded that countries' emissions-reduction offers as of earlier this week were far too timid to keep average temperatures from rising more than 2 degrees Celsius above pre-industrial levels. Without more stringent targets, the document said, 'global emissions will remain on an unsustainable pathway that could lead to' a temperature rise of about 3 degrees Celsius. Still, there was optimism. 'Hold tight and mind the doors, the cable car is moving again,' UN climate chief Yvo de Boer said at a press conference early in the afternoon. Jake Schmidt, international climate policy director for the Natural Resources Defense Council, said the tone of the talks had shifted. It will be impossible to 'dot all the i's and cross the t's,' Schmidt said. But he said the most important thing would be to get 'a clear path and timeline to finalize the treaty in a matter of months, not years.' Beth Daley can be reached at bdaley@globe.com. 