"The perception of many negotiators and countries is that the U.S. is not really interested in increasing action on climate change in general," said Bill Hare, senior scientist at Climate Analytics, a non-profit organization based in Berlin.
For example, Hare said, the U.S. could stop "talking down" the stated goal of the U.N. talks to keep the temperature rise below 2 degrees C (3.6 F) compared to pre-industrial levels.
Todd Stern, the U.S. special envoy on climate change, caused alarm among climate activists in August when he said that "insisting on a structure that would guarantee such a goal will only lead to deadlock." He later clarified that the U.S. still supports the 2-degree target, but favors a more flexible way to reach it than dividing up carbon rights to the atmosphere.
Countries adopted the 2-degree target in 2009, reasoning that a warming world is a dangerous world, with flooding of coastal cities and island nations, disruptions to agriculture and drinking water, and the spread of diseases and the extinction of species.
A recent World Bank report found the world is on track toward 4 degrees C (6.2 F) of warming, which would entail "extreme heat-waves, declining global food stocks, loss of ecosystems and biodiversity, and life-threatening sea level rise."
The U.S., alone among industrialized countries, didn't ratify the Kyoto Protocol because it found it unfair that China and other emerging economies, as developing countries, were not covered by any binding emissions targets. The U.S. and other rich countries say that firewall must be removed as the talks enter a new phase aimed at adopting a new climate treaty by 2015 that applies to all countries.
China - now the world's top carbon emitter - wants to keep a clear dividing line between developed and developing countries, noting that historically, the former bear the brunt of the responsibility for man-made climate change.
The issue is unlikely to be resolved in Doha, where talks will focus on extending Kyoto as a stopgap measure while negotiators work on the wider deal, which would take effect in 2020.
The 27-nation EU, Switzerland, Norway and Australia are on board but New Zealand, Canada and Japan don't want to be part of a second commitment period of Kyoto. That means the extended treaty would cover only about 15 percent of global emissions.
Delegates in Doha will also try to finalize the rules of the Green Climate Fund, which is supposed to raise $100 billion a year by 2020. Financed by richer nations, the fund would support poorer nations in converting to cleaner energy sources and in adapting to a shifting climate that may damage people's health, agriculture and economies in general.
In addition, countries need to agree on a work plan to guide the negotiations on a new treaty. Without a timeframe with clear mileposts, there's a risk of a repeat in 2015 of the hyped-up but ultimately disappointing climate summit in Copenhagen in 2009.
Judging by previous conferences, the negotiations in Doha will ebb and flow, with progress one day being replaced by bitter discord the next. And in the end, after an all-night session, bleary-eyed delegates will emerge with some kind of face-saving "accord" or "action plan" that keeps the talks alive another year, but does little to address the core problem.
"It shows that leaders and also the public in these countries - the U.S. certainly is one of them - don't yet understand the full implications of the costs associated with the path that we're on," said Alden Meyer, of the U.S.-based Union of Concerned Scientists.