BANGKOK - Representatives of more than 160 countries began formal negotiations here on Monday on a treaty to address climate change, with the secretary general of the United Nations, Ban Ki-moon, urging governments to help in "saving the planet."
The weeklong meeting will lay out the agenda for the talks, which are scheduled to conclude at the end of 2009. A rancorous meeting three months ago in Indonesia exposed deep fissures over how countries plan to approach global warming.
"Saving our planet requires you to be ambitious in what you aim, and, equally, in how hard you work to reach your goal," Mr. Ban told delegates in a recorded video message.
One of the main challenges for negotiators over the next 21 months will be reintroducing the United States to a global system of emissions reductions. The United States signed but never ratified the Kyoto Protocol, the 1997 agreement that binds wealthy countries to make specific cuts in greenhouse gases. The new treaty would follow the Kyoto Protocol after its binding terms expire in 2012.
Angela Anderson, director of the global warming program at the Pew Charitable Trusts, the American philanthropy, said negotiators were watching the United States election campaign closely for signs of increased willingness to grapple with climate change.
"We have three presidential candidates, all of whom have said they will re-engage in climate negotiations," Ms. Anderson said. "There will definitely be a new voice in the U.S."
The November presidential election will come roughly halfway through the negotiations, and many here believe negotiators will defer tough decisions until a new president is inaugurated.
The American public also appears more aware of the issue of global warming than at the start of the Bush administration.
Former Vice President Al Gore, who won a Nobel Peace Prize for his environmental advocacy, is starting a $300 million campaign this week to encourage Americans to push for aggressive reductions in greenhouse emissions.
Some countries disagree over what role wealthy and poor countries should play in reducing emissions. And even among wealthy countries there is significant discordance.
Last week, the Japanese vice trade minister, Takao Kitabata, said the method used to measure reductions in greenhouse gases in the Kyoto Protocol was "extremely unfair."
The Kyoto agreement uses 1990 as a reference point for greenhouse gas levels, mandating that industrialized countries as a group cut their emissions by at least 5 percent below 1990 levels by 2012. Japan proposed using 2005 as a new reference point, a change that would put other countries at a severe disadvantage, among them Germany. For Germany 1990 is an ideal starting point because western Germany absorbed and cleaned up the heavily polluting eastern Germany in the 1990s, allowing for a marked reduction in emissions over all.
Countries also disagree on how much to compensate developing countries for their efforts in reducing global warming. The agreement reached on the resort island Bali in December called for wealthier countries to help finance cleaner-burning energy technologies and non-fossil-fuel alternatives in developing countries.
The United Nations calculates that at least $200 billion will be needed by 2030 for these changes. As a measure of the enormous potential shortfall, the world's wealthiest country, the United States, has so far proposed to contribute $2 billion over two years.