"There are those who tell us that solving climate change is impossible. There are those who tell us taking radical action is too difficult," President Mohamed Nasheed said, in the first public appearance by any of the 120 heads of state due to attend the climate summit in Copenhagen.

"Well, I am here to tell you that we refuse to give up hope. We refuse to be quiet. We refuse to believe that a better world isn't possible."

Campaigners say it is vital that the summit in the Danish capital conclude this week with a deal on slashing levels of carbon dioxide, with 350 parts per million (ppm) in the atmosphere seen as the safe upper limit.

Before industrialisation, the level of concentration of CO2 in the atmosphere was estimated at around 280 ppm but it is now 387 ppm.

The rise in CO2 levels has warmed Earth's surface and caused the seas to gradually expand. This, added to increasing meltwater runoff from glaciers, is threatening deltas and small, low-lying island states.

"I am not a scientist, but I know that one of the laws of physics is that you cannot negotiate with the laws of physics. 350 is a law of atmospheric physics. You cannot cut a deal with Mother Nature," Nasheed told a rally.

"In all political agreements, you have to be prepared to negotiate. You have to be prepared to compromise, to give and take. That is the nature of politics.

"But physics isn't politics. On climate change, there are things on which we cannot negotiate. There are scientific bottom lines that we have to respect. We know what the laws of physics say."

In 2007, the UN's Intergovernmental Panel on Climate Change warned that an increase in sea levels of just 18 to 59 centimetres (seven to 24 inches) would make the Maldives virtually uninhabitable by 2100.

More than 80 percent of the Maldives, famed as a tourist paradise for its secluded beaches and coral reefs, is less than a metre (about three feet) above sea level.

Some 120 heads of state are to attend the climate summit which is due to conclude on Friday.

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