(AP) -- The host nation of the U.N. climate talks in Cancun on Wednesday called the U.S. pledge to cut greenhouse gas emissions "modest," while praising other nonbinding offers made by India and China.
President Barack Obama has proposed reducing U.S. emissions by 17 percent by 2020 from 2005 levels.
Mexican climate envoy Luis Alfonso de Alba said that level of ambition, "which I consider to be still modest," was not likely to improve after Republican gains in midterm elections.
"I believe that, as all of you know, President Obama has a willingness to make progress on this issue, but the domestic conditions are not necessarily there, particularly because of the legislative elections," de Alba said.
Many Republicans dismiss scientific evidence of global warming, and fought against Democrat-sponsored energy legislation the past two years.
The U.S. has insisted it will agree to binding pollution limits only if China also accepts legal limitations. China, now the world's biggest polluter but also the biggest investor in renewable energy, rejects international limits, saying it still needs to overcome widespread poverty and bears no historic responsibility for the problem.
But China has pledged to slow the growth of its emissions, cutting carbon intensity - emissions per unit of GDP - by 40 to 45 percent by 2020 from 2005. India, another major emerging economy, has offered to reduce its carbon intensity by 20 to 25 percent.
"China and India have put forward ambitious figures," de Alba said.
Analysts agree that China has moved swiftly to adopt green technology but is still the heaviest user of coal has overtaken the U.S. as the world's biggest carbon polluter.
Negotiators at the two-week conference in Mexico are hoping to formalize the voluntary emissions pledges made last year in the Copenhagen Accord, a nonbinding document that wasn't formally adopted at the climate summit in the Danish capital.
But deep-seated disputes continue to block agreement on a new binding global climate accord. At best, the delegates in Cancun are expected to concur in a handful of decisions on secondary issues.
Christiana Figueres, the top U.N. climate official, acknowledged that formalizing the emissions pledges was one of the most politically charged issues being discussed in Cancun.
In its last detailed report, in 2007, the Intergovernmental Panel on Climate Change - the U.N. climate science network - recommended that global emissions of carbon dioxide and other greenhouse gases be reduced by 25 percent to 40 percent of 1990 levels by 2020, to keep temperatures from rising more than 2 degrees Celsius (3.6 degrees Fahrenheit) above preindustrial levels.
Expert analysis of current pledges to rein in emissions finds that, even if fully applied, they'll go only 60 percent of the way toward that goal.
IPCC chief Rajendra Pachauri told The Associated Press in an interview Tuesday that world governments need to spend more on cutting-edge research to "get a handle" on how much and how quickly the world will warm in decades to come.
"There are huge gaps in the effort as far as scientific research is concerned," Pachauri said, pointing to concerns that the Arctic's thawing permafrost is releasing powerful global warming gases, and the oceans might eventually turn from absorbing carbon dioxide to spewing it into the atmosphere.
"What is being done today is certainly far from adequate," he said.
Explore further: New report highlights 'significant and increasing' risks from extreme weather