A deal between China and the United States to combat global warming is "heartening" although it falls short of the action needed to avert the worst impacts, the head of the U.N. panel of climate scientists said on Wednesday.



China said 2030 would be peak year for its soaring greenhouse gas emissions, the first time it has set a maximum, and the United States said it would cut emissions by more than a quarter from 2005 levels by 2025.



The accord by the two, by far the biggest greenhouse gas emitters, is largely symbolic. But it erodes a divide between rich and poor nations over their respective responsibilities for tackling climate change that has prevented a global deal for years.



"This is a heartening development," Rajendra Pachauri, chair of the Intergovernmental Panel on Climate Change (IPCC), told Reuters. "This is a good beginning and I hope the global community follows this lead and maybe builds on it."



He acknowledged that the deal fell far short of a road map towards zero net emissions by 2100 that an IPCC report on Nov. 2 indicated was needed to avert the worst.



The IPCC said unchecked climate change could have "severe, widespread and irreversible impacts" on human society and nature with heatwaves, floods, storms and rising sea levels.



The United Nations welcomed the pact as a spur to almost 200 nations which have agreed to work out a U.N. climate accord at a summit in Paris in late 2015.



Developing nations say rich countries, which have burned the most carbon dioxide since the Industrial Revolution, must do far more to cut emissions. Rich nations, meanwhile, say emerging economies led by China have to accept both caps and cuts.



Cooperation between China and the United States chips away at the distinction.



"It breaks down the artificial divide that has bedevilled the negotiations. That wall is now crumbling," Abyd Karmali, global head of carbon markets at Bank of America Merrill Lynch, told Reuters.



The new U.S. goal for 2025 works out as a 16 percent cut in emissions from 1990, the U.N. benchmark year. Emerging economies have often called for cuts of 25 to 40 percent in rich nations' emissions by 2020, from 1990 levels.

(By Alister Doyle, Reporting by Alister Doyle; editing by Andrew Roche)