He noted that the Obama administration has taken a series of steps, including sharply increasing fuel efficiency standards for cars and trucks, and made good on promises of climate financing for poor countries. A climate bill that would have capped emissions stalled in the Senate.
"It doesn't mean enough is being done," Pershing said. "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."
The two-decade-old U.N. talks have not fulfilled their main purpose: reducing the greenhouse gas emissions that scientists say are warming the planet.
The goal is to keep the global temperature rise under 2 degrees C (3.6 F), compared to pre-industrial times.
Efforts taken so far 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.
Scientists warn that dangerous warming effects could include flooding of coastal cities and island nations, disruptions to agriculture and drinking water, the spread of diseases and the extinction of species.
Attempts to forge a new climate treaty failed in Copenhagen three years ago, but countries agreed last year to try again, giving themselves a deadline of 2015 to adopt a new pact.
Several issues need to be resolved by then, including how to spread the burden of emissions cuts between rich and poor countries. That's unlikely to be decided in the current talks in the Qatari capital of Doha, where negotiators from nearly 200 countries are focusing on extending the Kyoto Protocol, and trying 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, South Africa.
The U.N. process is often criticized, even ridiculed, both by climate activists who say the talks are too slow and by those who challenge the scientific near-consensus that the global temperature rise is at least partly caused by human activity, primarily the burning of fossil fuels like coal and oil.
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.
"Climate change is no longer some distant threat for the future, but is with us today," said Greenpeace climate campaigner Martin Kaiser, who was also at the Doha talks. "At the end of a year that has seen the impacts of climate change devastate homes and families around the world, the need for action is obvious and urgent."
Many scientists say that 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 individual weather events to climate change.
The Kyoto Protocol is seen as the most important climate agreement reached in the U.N. process so far. It expires this year, so negotiators in Doha will try to extend it as a stopgap measure until a wider deal can be reached.
The problem is that only the European Union and a handful of other countries that together are responsible for than 15 percent of global emissions are willing to set emissions targets for a second commitment period of Kyoto.
The U.S. rejected the Kyoto accord because it didn't impose binding commitments on major developing countries such as India and China, which is now the world's top carbon emitter.
China and other developing countries want to maintain a clear division, saying climate change is mainly a legacy of Western industrialization and that their own emissions must be allowed to grow as their economies expand, lifting millions of people out of poverty.
That discord scuttled attempts to forge a climate deal in Copenhagen in 2009 and risks a recurrence in Doha, as talks begin on a new global deal that is supposed to be adopted in 2015 and implemented in 2020.
Environmentalists found the choice of Qatar as host of the two-week conference ironic. The tiny Persian Gulf emirate owes its wealth to large deposits of gas and oil, and it emits more greenhouse gases per capita than any other nation.
Qatar has not even announced any climate action in the U.N. process, and former Qatari oil minister Abdullah Bin Hamad al-Attiyah didn't do so when he opened the conference Monday.
"We should not concentrate on the per capita (emissions). We should concentrate on the amount from each country," al-Attiyah told reporters. "I think Qatar is the right place to host" the conference, he said.
AP Environment Writer Michael Casey contributed to this report.
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