The world's wealthiest nations failed to specify a target for cutting greenhouse-gas emissions in the coming decade, a vital stepping stone for meeting the mid-century goal, said Rajendra Pachauri.

"There's a serious omission in terms of not addressing the Bali action plan, which has called for deep cuts in emissions by 2020," Pachauri told AFP in an interview from New Delhi.

UN negotiations last December in Bali, Indonesia yielded an agreement to forge a new climate-change treaty by the end of 2009 that would succeed Kyoto Protocol provisions expiring at the end of 2012.

"I think there should have been at least an endorsement, that the leaders of the G8 countries fully support actions to bring about those deep cuts," he said.

Pachauri said climate change was moving faster and more destructively than once thought and only seven years remained for decisive action.

To limit global temperature increases at century's end to no more than 2.0 to 2.4 degrees Celsius (3.6 to 4.3 degrees Fahrenheit), emissions have to peak no later than 2015, he said.

"It is absolutely essential not to postpone the kinds of actions that we have identified with stabilisation of the Earth's climate and limiting the temperature increase to about 2 C [3.6 F]," Pachauri said.

"The sooner we start reducing emissions, the greater the likelihood of avoiding some of the more serious impacts and temperature increases that are going to take place a decade or two down the road," he said.

Since 2002, Pachauri has chaired the Intergovernmental Panel on Climate Change (IPCC), which synthesises the research of thousands of scientists into a benchmark report.

The IPCC was awarded the 2007 Nobel Peace Prize along with former US vice president Al Gore.

Last year, the IPCC's Fourth Assessment Report warned that, without action, the planet's rising temperatures could unleash potentially catastrophic change to Earth's climate system, leading to hunger, drought, storms and massive species loss.