The world's leading climate change experts will this week outline highly controversial plans to save the world from global warming. Their proposals - which include a major expansion in nuclear power, the use of GM crops to boost biofuel production, and reliance on unproven technologies, including the underground storage of carbon dioxide - will put the UN's climate group on a collision course with a host of environmental groups.

The proposals for saving the planet are outlined in a draft version of 'Mitigation of Climate Change' by the UN's Intergovernmental Panel on Climate Change (IPCC). This is the third part of the panel's 2007 analysis of global warming. Previous reports have focused on the science of climate change and its likely impacts. The third and final report concentrates on measures that can be taken to save the Earth from the worst, most catastrophic effects of rising temperatures triggered by the pumping of carbon dioxide into the atmosphere.

A draft version, which has been obtained by The Observer, will be debated by UN climate experts this week, and a final version will be published on Friday. It is clear that experts now believe the situation is desperately urgent.

'Global emissions must peak,' states the draft report. 'Mitigation efforts over the next two or three decades will determine the long-term global temperature increase.'

Crucially the IPCC panel insists that it is 'technically and economically' feasible to stabilise greenhouse emissions - but only if countries are prepared to pay the extra costs of transforming everything from energy supply networks to agriculture to waste. By 2030, the report estimates that the cost of stabilising greenhouse gases at levels that are considered the maximum for avoiding catastrophic climate change would cost between 0.2 and 0.6 per cent of global wealth.

As well as plans for more nuclear power, genetically modified biofuels and carbon capture and storage, the report sets out a vision of the future that is a mixture of existing policies, such as energy efficiency and renewable energy from wind and wave farms, and more futuristic ideas for hydrogen car fleets and 'intelligent' buildings which can control energy use. In addition, the report makes it clear that both developed countries, including the United States, and developing nations, in particular India and China, will have to play major roles.

Last night Tony Juniper, executive director of the environmental pressure group Friends of the Earth, said far more fundamental lifestyle changes were needed than had been considered by the UN group. 'Simply replacing one set of technologies with another set of technologies won't work, especially when there are such big downsides with some of them,' he said. Nuclear reactors are dangerous and land clearance and chemical pesticides and fertilisers used to grow fuel crops can cause huge environmental damage, he added. 'Structural change to the economy, behaviour change and culture change - those have to be elements in a world of decarbonisation,' said Juniper.

However, other groups criticised the IPCC for not being sufficiently robust in its support for technological fixes to the world's climate problems. Bruno Comby, president of Environmentalists for Nuclear Energy, said nuclear power should provide an even bigger proportion of energy than that envisaged by the UN scientists and politicians. 'Nuclear is not the only solution, but it's the biggest solution,' he said.

The news of the IPCC's controversial plans comes as Britain continues to bask in exceptionally hot weather. Yesterday the Met Office released figures which showed this month will be the warmest April for more than 140 years. The average temperature for the past month has been 11.1C (51.9F), beating the previous record of 10.6C (51F) set in 1865.

Met Office figures also indicate that the past 12 months have been the warmest in 10 years, with average figures of 11.6C. Experts at the Met Office's Hadley Centre in Exeter, Devon - which undertakes research on climate change - said this was consistent with global warming predictions. 'The effects of temperature rise are being experienced on a global scale,' said Dr Debbie Hemming. 'Many of the regions that are projected to experience the largest climate changes are already vulnerable to environmental stress from resource shortages, rapid urbanisation, population rise and industrial development.'