The pre-emptive U.S. approach underscores one of the major showdowns expected at the two-week conference as China pushes developed countries to take an even greater role in tackling global warming.

Speaking for a coalition of developed nations known as the G77, China’s delegate, Su Wei, said rich nations should become party to an extended Kyoto Protocol — an emissions deal for some industrialized countries that the Americans long ago rejected — or at least make “comparable mitigation commitments.”

The United States rejected Kyoto because it didn’t impose any binding commitments on major developing countries such as India and China, which is now the world’s No. 1 carbon emitter.

American delegate Jonathan Pershing offered no new sweeteners to the poor countries, only reiterating what the United States has done to tackle global warming: investing heavily in clean energy, doubling fuel efficiency standards and reducing emissions from coal-fired power plants. Pershing also said the United States would not increase its earlier commitment of cutting emissions by 17 percent below 2005 levels by 2020. It is half way to that target.

“I would suggest those who don’t follow what the U.S. is doing may not be informed of the scale and extent of the effort, but it’s enormous,” Pershing said.

“It doesn’t mean enough is being done. It’s clear the global community, and that includes us, has to do more if we are going to succeed at avoiding the damages projected in a warming world,” Pershing added. “It is not to say we haven’t acted. We have and we have acted with enormous urgency and singular purpose.”

The battles between rich and poor nations have often undermined talks in the past decade and stymied efforts to reach a deal to keep global temperatures from rising more than 2 degrees C (3.6 F), compared to preindustrial times. Efforts taken in the absence of a deal to rein in emissions, reduce deforestation and promote clean technology are not getting the job done. A recent projection by the World Bank showed temperatures are expected to increase by up to 4 degrees C (7.2 F) by 2100.

Countries are hoping to build on the momentum of last year’s talks in Durban, South Africa, where nearly 200 nations agreed to restart stalled negotiations with a deadline of 2015 to adopt a new treaty and extend Kyoto between five and eight years. The problem is that only the European Union and a handful of other nations — which together account for less than 15 percent of global emissions — are willing to commit to that.

Delegates in the Qatari capital of Doha are also hoping to raise billions of dollars to help developing countries adapt to a shifting climate.

“We owe it to our people, the global citizenry. We owe it to our children to give them a safer future than what they are currently facing,” said South African Foreign Minister Maite Nkoana-Mashabane, who led last year’s talks in Durban.

Environmentalists fear holding the talks in Qatar — the world’s biggest per capita emitter — could slow progress. They argue that the Persian Gulf emirate has shown little interest in climate talks and has failed to reign in its lavish lifestyle and big-spending ways.

There was hope among activists that Qatar might use Monday’s opening speech to set the tone of the conference. But Abdullah Bin Hamad Al-Attiyah, the president of the conference and a former Qatari oil minister, didn’t offer any voluntary emission targets or climate funding for poor nations.

“Some countries, especially the one where we are sitting, have the potential to decrease their carbon emissions. They have the highest per capita emissions, so they can do a lot,” said Wael Hmaidan, a Lebanese activist and director of the Climate Action Network.

“If nations that are poorer than Qatar, like India and Mexico, can make pledges to reduce their carbon emissions, then countries in the region, especially Qatar, should easily be able to do it. … They still haven’t proven they are serious about climate change.”

Al-Attiyah defended Qatar’s environmental record at a later news conference, insisting it was working to reduce emissions from gas flaring and its oil fields. Qatar is already doing plenty to help poor countries with financing, he said, adding that it was unfair to focus on per capita emissions.

“We should not concentrate on per capita. We should concentrate on the amount and quantity that each country produces individually,” al-Attiyah said. “The quantity is the biggest challenge, not per capita.”

The concentration of greenhouse gases such as carbon dioxide has jumped 20 percent since 2000, according to a U.N. report released last week. The report also showed that there is a growing gap between what governments are doing to curb emissions and what needs to be done to protect the world from potentially dangerous levels of warming.

At the same time, many scientists say extreme weather events, such as Hurricane Sandy’s onslaught on the U.S. East Coast, will become more frequent as the Earth warms, although it is impossible to attribute any individual event to climate change. The rash of violent weather in the U.S., including widespread droughts and a record number of wildfires this summer, has again put climate change on the radar.

“While none of these individual events are necessarily because of climate change, they are certainly consistent with what we anticipate will happen in a warming world,” Pershing said. “The combination of these events is certainly changing minds of Americans and making clear to people at home the consequences of increased growth in emissions.”

In Washington, Rep. Ed Markey, D-Mass., urged the U.S. delegation at the talks to “heed the warnings from Sandy and other extreme weather supercharged by climate change.”

“If the United States does not aggressively pursue sharp reductions in carbon pollution following the droughts, storms and other extreme weather events we have endured, the rest of the world will doubt our sincerity to address climate change,” Markey said. “It’s time to attack the carbon problem head on, and adapt to a climate already changed for the worse.”

Many countries referenced Hurricane Sandy as a rallying cry for tough action to cap emissions, including a group of small island nations that said the monster storm may have jolted the world to recognize “that we are all in this together.”

“When the tragedies occur far away from the media spotlight, they are too often ignored or forgotten,” the island nations said in a statement.