The ongoing UN climate conference began its high-level talks here on Tuesday, after the first week of meetings made little progress.
Heads of states or governments or ministerial delegates from over 190 countries are participating in the second phase of talks which runs until Friday.
UN Secretary General Ban Ki-moon, speaking at the opening ceremony, urged participants to "sustain the momentum for change so painstakingly built in Bali, Poznan, Copenhagen, Cancun and Durban."
Pointing to water stress, land degradation, melting icecaps, Ban said "we are in a race against time to stay below the agreed threshold of 2 degrees Celsius above pre-industrial levels that will avoid the worst impacts of climate change."
Qatari Emir Sheikh Hamad bin Khalifa Al-Thani attended the opening ceremony and highlighted the importance his country attaches to averting climate change and protecting the environment.
The emir also pledged Qatar's contribution to green technologies which can help strike an optimum equilibrium between the need for energy and emission reduction.
Christiana Figueres, executive secretary of the UN Framework Convention on Climate Change, reminded the delegates that "the eyes of the world" and "the urgency of the science" are upon them, encouraging them to improve long-term global adaptation and mitigation responses and chart the course of future efforts.
In the high-level segment, the delegates will continue to discuss the two thorny issues left unsolved at the lower level of talks -- the extension of the Kyoto Protocol (KP) and the implementation of developed countries' pledged finance support.
Talks on the KP track last week divided on the details of the accord's second commitment period, including its length and strength as well as the carry-over unused carbon permits to the extension.
The negotiators also disagreed on whether to allow countries that plan to retreat from KP to continue using its market mechanism to meet their national emission cut targets.
On the finance support front, the developing countries demand transparency on the rich nations' contribution to the Fast Start program, whose target, 30 billion U.S. dollars, the donors claimed to have exceeded.
Also, more specific plans need to be set out for the long-term Green Climate Fund, whose aim is to ramp up annual provisions by 2020 to 100 billion U.S. dollars but now remains an empty shell.
"Daunting tasks faces the high-level segment," Chinese top negotiator Su Wei said earlier at a press briefing. "Overnight meetings and intensive talks are expected."
He expressed hope that senior officials' participation will prompt the conference to make a breakthrough on both the KP extension and the finance support.