Measures to fight global warming will have to be at least four times stronger than the Kyoto Protocol if they are to avoid the melting of the polar ice caps, inundating central London and many of the world's biggest cities, concludes a new official report.

The report, by a German government body, says that even if it is fully implemented, the protocol will only have a "marginal attenuating effect" on the climate change. But last week even this was thrown into doubt amid contradictory signals from the Russian government as to whether it will allow the treaty to come into effect.

Global warming already kills 150,000 people a year worldwide and the rate of climate change is soon likely to exceed anything the planet has seen "in the last million years" says the report, produced by the German Advisory Council on Global Change for a meeting of the world's environment ministers to consider the future of the treaty in Milan this week.

It concludes that the protocol must urgently be brought into force, but only as a first step, insisting that "catastrophic" climate change "can now only be prevented if climate protection targets are set at substantially higher levels than those agreed internationally until now".

The report, written by eight leading German professors, says that "dangerous climatic changes" will become "highly probable" if the world's average temperature is allowed to increase to more than 2 degrees centigrade above what it was before the start of the Industrial Revolution.

Beyond that level the West Antarctic ice sheet and the Greenland ice cap would begin gradually to melt away, eventually raising sea levels world wide by up to 30 feet, submerging vast areas of land and key cities worldwide. London, New York, Miami, Bombay, Calcutta, Sydney, Shanghai, Lagos and Tokyo would be among those largely submerged by such a rise.

Above this mark too, other "devastating" and "irreversible" changes would be likely to take place. These include a cessation of the Indian monsoon and the ending of the Gulf Stream, which would dramatically worsen the climate in Britain and western Europe, even as the world warms. Another risk is the so-called "runaway greenhouse" where rising temperatures lead to the release of huge reservoirs methane stored in permafrost and the oceans, adding to global warming and starting a self-reinforcing cycle that would eventually make the earth uninhabitable.

To avoid such catastrophe, the report says that industrialised countries will have to cut emissions of greenhouse gases like carbon dioxide by at least 20 per cent by 2020, and by up to 60 per cent by 2050. The Kyoto Protocol would at best cut them by 5 per cent by 2012, and probably less, even if it were brought into force and fully implemented.

In the meantime the world looks as if it will greatly exceed the targets. Writing in The Independent on Sunday today, Michael Meacher, the former environment minister, calculates that global emissions of greenhouse gases could increase by 75 per cent by 2020, "putting the world well on the way to doomsday".