UN Secretary General Ban Ki-moon warned Thursday that failure to tackle climate change would lead to global economic upheaval, as he appealed to nations to reach agreement on carbon emission cuts.

"Deserts are spreading. Water scarcity is increasing. Tropical forests are shrinking. Our once prolific fisheries are in danger of collapse," said Ban at the start of a three-day conference in New Delhi on sustainable development.

"Failure to combat climate change will increase poverty and hardship. It will destabilise economies, breed insecurity in many countries and undermine our goals for sustainable development."

All countries must strive to reach a "conclusive carbon emissions reduction" deal in Copenhagen in December, he said at the meeting.

The gathering in the Danish capital is set to discuss initiatives aimed at tackling climate change when the Kyoto Protocol expires in 2012.

"Copenhagen must clarify commitments of developed countries to reduce their emissions," said Ban, adding: "We must also achieve clarity on what mitigation actions developing countries will be prepared to make.

"In Copenhagen we must now bring all this all together in an ambitious, comprehensive and ratifiable agreement."

Much of the focus at the New Delhi conference will be on the United States, which was set to lay out President Barack Obama's new climate change policy, according to organisers.

John Kerry, chairman of the US Senate Foreign Relations Committee, was due to address the meeting via a video link.

The Obama administration has already begun shredding the climate policies formulated under ex-president George W. Bush and is vowing to lead the global fight against climate change.

Ban said Obama had assured him climate change was his "domestic as well as international priority" and also of Washington's "full cooperation to make Copenhagen a success."

He added he sensed a new worldwide momentum to address climate change.

"Here in India, in China, in the economies of Europe and North America, in Brazil, and also in many regions in Africa I find a new determination and new initiatives," he said, but cautioned there was no time to waste.

"Science has shown we are depleting the planet's natural assets at an unsustainable rate," Ban said. "We all realise poverty cannot be overcome if we neglect the environment or deplete our natural capital."

Indian Foreign Minister Pranab Mukherjee said New Delhi was "extremely concerned about climate change."

At the same time, he told the meeting "some of the worst impacts of climate change take place in developing countries which have had no share in having caused this problem."

India, China and other emerging economies have long argued industrialised nations are historically responsible for greenhouse gases already in the atmosphere and so must do more to fix the problem.

They have resisted targeted curbs on their own carbon emissions, claiming their ascent from poverty could be jeopardised by a straitjacket on their carbon emissions.

Developing countries were excluded from binding targets for greenhouse gases under the 1997 Kyoto Protocol -- the key reason the US refused to ratify the treaty.

However, activists say ensuring China and India take action now has become vital because their carbon output has risen dramatically with the booms in their fossil fuel-dependent economies.

China now outstrips the US as the world's biggest greenhouse gas polluter while India is poised to overtake Russia as the third biggest emitter, according to a report last September by the Global Carbon Project.