Sept. 22 (Bloomberg) -- President Barack Obama told the United Nations that efforts to reach a global accord on climate change will face “doubts and difficulties” in an economy struggling to emerge from a recession.

“There should be no illusions that the hardest part of our journey is in front of us,” Obama said today at a UN conference on efforts to curb greenhouse gas emissions. “We seek sweeping but necessary change in the midst of a global recession, where every nation’s most immediate priority is reviving their economy and putting their people back to work.”

Obama and China’s President Hu Jintao, leaders of the world’s two largest greenhouse gas emitters, spoke at the UN meeting as about 190 nations face a deadline to craft a new climate-change accord in time for a meeting in December in Copenhagen. Obama said the richest nations must lead the push and fast-growing countries such as China must step up their efforts.

“We cannot meet this challenge unless all the largest emitters of greenhouse gas pollution act together,” Obama said. “There is no other way.”

Industrialized nations such as the U.S. and developing countries led by China are deadlocked on matters such as how much rich nations should help poor ones deal with climate change and how much industrialized nations should cut emissions.

“Yes, the developed nations that caused much of the damage to our climate over the last century still have a responsibility to lead, and that includes the United States,” Obama said. “But those rapidly growing nations that will produce nearly all the growth in global carbon emissions in the decade ahead must do their part as well.”

Fossil-Fuel Subsidies

The president said he would work at the G-20 conference in Pittsburgh later this week on proposals to “phase out fossil- fuel subsidies” as part of the battle against climate change.

The U.S. said this week that it will for the first time begin tracking how much greenhouse gas pollution is being emitted throughout the country. The Environmental Protection Agency will sign the new rule today, Carol Browner, the White House’s top energy and environmental adviser, said in New York.

Obama recounted his administration’s efforts to reduce greenhouse gases, including development of clean-coal technology, steps to increase the fuel efficiency of cars and trucks and legislation to create a proposed cap-and-trade system for pollution allowances. While that measure passed the House, the Senate has yet to act.

Hu, whose government has rejected calls to accept overall limits on greenhouse gas emissions, said today for the first time that China will reduce the so-called carbon intensity of its economy. That requires cutting the amount of CO2 produced for every increment of gross domestic product.

Hu’s Pledge

“We will endeavor to cut carbon-dioxide emissions per unit of GDP by a notable margin by 2020 from the 2005 level,” Hu said, without naming a specific goal. “Out of a sense of responsibility to its own people and people across the world, China has taken and will continue to take determined and practical steps to tackle this challenge.”

The U.S. and China are under pressure to reach agreement before the Copenhagen meeting on key issues holding up the talks to replace the 1997 Kyoto Protocol, which set emissions limits on industrialized countries and expires in 2012. Neither the U.S. nor China is part of that agreement.

Failing to act on pollution contributing to global warming risks “consigning future generations to an irreversible catastrophe,” Obama said.

“We seek an agreement that will allow all nations to grow and raise living standards without endangering the planet,” he said.

The European Union says binding targets are needed to keep the increase in global temperatures to within 2 degrees Celsius (3.6 degrees Fahrenheit) of pre-industrial times, a target that averts the worst effects of climate change.

‘Seal a Deal’

UN Secretary-General Ban Ki-Moon, who is overseeing today’s climate meeting of about 100 world leaders, said talks for a new emissions-limiting treaty are moving too slowly.

“I urge you to seal a deal in Copenhagen in December of this year,” Ban said. “The science demands it, the world economy needs it.”

Obama’s top negotiator, Todd Stern, told reporters in New York today that agreement on some provisions, including “significant” ones, may not be reached and may have to be resolved after the Copenhagen conference.

To contact the reporters on this story: Kim Chipman in New York at kchipman@bloomberg.net; Jim Efstathiou Jr. in New York at jefstathiou@bloomberg.net.

Last Updated: September 22, 2009 13:04 EDT