And as a re-elected president talks about global warming again, climate activists are cautiously optimistic that the U.S. will be more than a disinterested bystander when the U.N. climate talks resume Monday with a two-week conference in Qatar.

"I think there will be expectations from countries to hear a new voice from the United States," said Jennifer Morgan, director of the climate and energy program at the World Resources Institute in Washington.

The climate officials and environment ministers meeting in the Qatari capital of Doha will not come up with an answer to the global temperature rise that is already melting Arctic sea ice and permafrost, raising and acidifying the seas, and shifting rainfall patterns, which has an impact on floods and droughts.

They will focus on side issues, like extending the Kyoto protocol — an expiring emissions pact with a dwindling number of members — and ramping up climate financing for poor nations.

They will also try to structure the talks for a new global climate deal that is supposed to be adopted in 2015, a process in which American leadership is considered crucial.

Many were disappointed that Obama didn't put more emphasis on climate change during his first term. He took some steps to rein in emissions of heat-trapping gases, such as sharply increasing fuel efficiency standards for cars and trucks. But a climate bill that would have capped U.S. emissions stalled in the Senate.

"We need the U.S. to engage even more," European Union Climate Commissioner Connie Hedegaard told The Associated Press. "Because that can change the dynamic of the talks."

The world tried to move forward without the U.S. after the Bush Administration abandoned the Kyoto Protocol, a 1997 pact limiting greenhouse emissions from industrialized nations. As that agreement expires this year, the climate curves are still pointing in the wrong direction.

The concentration of heat-trapping gases like carbon dioxide has jumped 20 percent since 2000, primarily from the burning of fossil fuels like coal and oil, according to a U.N. report released this week. And each year, the gap between what researchers say must be done to reverse this trend, and what's actually being done, gets wider.

Bridging that gap, through clean technology and renewable energy, is not just up to the U.S., but to countries like India and China, whose carbon emissions are growing the fastest as their economies expand.

But Obama raised hopes of a more robust U.S. role in the talks when he called for a national "conversation" on climate change after winning re-election. The issue had been virtually absent in the presidential campaigning until Hurricane Sandy slammed into the East Coast.

The president still faces domestic political constraints, and there's little hope of the U.S. increasing its voluntary pledge in the U.N. talks of cutting emissions by 17 percent by 2020, compared to 2005 levels.

Still, just a signal that Washington has faith in the international process would go a long way, analysts said.

"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.