"It was a very good start," said Yvo de Boer, the executive secretary of the 12th UN Framework Climate Change Convention (UNFCCC), noting numerous positive statements from some of the 189 nations taking part.

The two-week conference is being held in conjunction with the second gathering of signatories to the Kyoto Protocol, an annex to the UN convention that seeks to reduce harmful greenhouse gas emissions by industrialized nations.

The treaty, which has been shunned by the world's leading polluter the United States and does not cover rapidly industrializing developing nations, expires in 2012 and delegates are looking at how to replace it.

Officials said a Russian proposal to bring exempted countries, like China, India and Brazil, into Kyoto voluntarily was being discussed but could offer few details of the scheme.

Kyoto came into effect in February 2005 with the intention to commit industrialized countries to bringing their greenhouse gas emissions to an average of five percent below their 1990 level, by 2012.

De Boer praised "very constructive interventions" on a post-Kyoto treaty from the European Union, Japan, Norway and Brazil, which has come under particular pressure from environmentalists to act on its emissions.

"The industrialized countries affirmed that they already felt the effects of climate change, including Europe," he said, speaking of growing consensus for additional and urgent action led by rich nations to tackle the issue.

But some environmental groups complained the delegates are lagging far behind a proper timeframe to ensure a new global warming protocol is in place by the time Kyoto expires.

"We have a small window of opportunity here to ensure there is no gap between the expiration of the Kyoto treaty and its successor," said Hans Verolme of the World Wide Fund for Nature (WWF).

"This conference is not on the right track to achieve that result," he said.

Despite noting Europe's progress in reducing emissions by 14 percent, Lars Muller of the European Commission sounded an alarm for additional measures.

"Climate change is happening and is accelerating, causing serious economic and social impacts already," he said.

Scientists say the earth's temperature has already risen 0.7 degrees Celsius since 1900 and Muller warned that a rise to more than two degrees would lead to "dangerous and large-scale" impacts, affecting billions of people.

Rising sea levels and ocean temperatures along with other calamities that some associate with global warming, such as floods and hurricanes, have already caused massive damage in the developed world.

But they also threaten some of the world's most vulnerable people, the poorest of the poor in Africa, the continent most at-risk, along with hundreds of historic and cultural sites, according to studies issued on Tuesday.

Among Africans, residents of Burundi, Rwanda, Ethiopia, Eritrea, Niger and Chad are most threatened by climate change, according to the International Livestock Research Institute (ILRI).

"The situation is alarming and not only in relation to climate change," ILRI said. "It is also alarming because of population density and the degradation of natural resources."

Meanwhile, the the United Nations Environment Programme (UNEP), which is hosting the conference at its Nairobi headquarters, warned that many universally recogized cultural treasures were under threat.

From the coral reefs off the coast of Belize to the Baroque concert halls in the Czech Republic and Venice, it said effects of climate change are endangering cultural sites cherished by millions if people.

"Adaptation to climate change should and must include natural and culturally important sites," UNEP chief Achim Steiner said.

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