A volley of grim warnings sounded out at the start of the marathon talks, a step to a new worldwide treaty to reduce greenhouse gases and help countries exposed to the wrath of an altered climate.

Polish Environment Minister Maciej Nowicki, elected to chair the December 1-12 meeting in the city of Poznan, opened the conference with an apocalyptic vision if mankind fails to change its ways.

There will be "huge droughts and floods, cyclones with increasingly more destructive power, pandemics of tropical disease, dramatic decline of biodiversity, increasing ocean levels," Nowicki said.

"All these can cause social and even armed conflict and migration of people at an unprecedented scale."

The forum of the 192-member UN Framework Convention on Climate Change (UNFCCC) comes halfway in a two-year process, launched in Bali, Indonesia, that aims at crafting a new pact in Copenhagen in December 2009.

More gloom came from Rajendra Pachauri, head of the Nobel-winning Intergovernmental Panel on Climate Change (IPCC), which provides neutral scientific opinion on global warming and its impacts.

The number of people living in severely stressed river basins is projected to rise to as many as 6.9 billion by 2050 from 1.4-1.6 billion in 1995, he said.

"That's almost the majority of humanity," he said.

Progress under the so-called Bali Roadmap has bogged down over the sheer complexity of the deal and positioning by rich countries and emerging giants.

Rich countries, historically to blame for most of today's warming, want countries like China and India -- the big polluters of tomorrow -- to do more to tackle their surging emissions.

Developing countries, though, want the West to help pay for them to expand their economies in a sustainable manner and to stump up cash to help vulnerable countries cope with climate change.

Brazil announced on Monday it was doing its bit, promising to slash deforestation of the Amazon by 70 percent over the next decade.

Forest loss accounts for roughly a fifth of all global carbon emissions, and if implemented Brazil would avert emissions of 4.8 billion tonnes of carbon dioxide by 2018 -- "more than the reduction efforts fixed by all the rich countries," Environment Minister Carlos Minc noted in Brasilia.

Hopes for a breakthrough at Poznan have also been darkened by the global economic crisis, but delegates said they were keen for this to become an opportunity not a threat and argued that green technology created jobs and growth.

Environmental pressure groups agreed, with Greenpeace saying that the global recession was "nothing compared to the trillions of dollars that climate change will cost us."

Delegates in Poland are poring over an 82-page document containing a vast range of proposals for action beyond 2012, when emissions-curbing pledges under the Kyoto Protocol run out.

The hope is to condense this labyrinthine document into a workable blueprint for negotiations culminating in a deal in Copenhagen.

One spur for optimism is the election of Barack Obama as US president, who has vowed to sweep away George W. Bush's climate policies which caused the United States to be isolated in the world environmental arena since 2001.

Obama, who takes office January 20, has set a goal of reducing US emissions to 1990 levels by 2020 and by 80 percent by 2050, using a cap-and-trade system and a 10-year programme worth 150 billion dollars in renewable energy.

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.