Carbon dioxide will have to be extracted from the atmosphere and stored underground to prevent “severe, pervasive and irreversible” impacts of climate change, according to the UN’s scientific advisory body.

The intergovernmental panel on climate change (IPCC) said that within the lifetime of today’s children, net emissions would have to fall below zero to have the best chance of preventing a dangerous temperature rise.

The IPCC’s synthesis report, summing up 5,000 pages of work by 800 scientists published in three previous reports, will underpin efforts by governments to agree on a global deal on emissions by December next year. It said emissions would have to fall by 40 to 70 per cent by 2050 compared with 2010, and be “near zero or below in 2100”.

To achieve “negative emissions”, it would be necessary to extract carbon dioxide from the atmosphere, such as by planting billions of trees that soaked up carbon as they grew, before harvesting the wood and burning it in power plants fitted with carbon capture and storage (CCS) systems.

The report said that many computer models used to project warming found that building CCS plants was the only way to prevent the global average temperature rising by 2C (3.6F) above pre-industrial levels, the increase deemed to have dangerous consequences.

However, CCS is very expensive and only one commercial-scale plant has been built: the £750 million Boundary Dam project in Canada.

Rajendra Pachauri, the IPCC chairman, said that fossil fuels could continue to be burnt on a large scale if CCS were widely deployed. “We have little time before the window of opportunity to stay within 2C of warming closes. The cost of inaction will be horrendously higher than the cost of action,” he said.

Unless there were a much greater effort to cut emissions, the temperature could rise by 4.8C by 2100, resulting in “substantial species extinction [and] global and regional food insecurity”, the report said. Delaying action would shift the burden on to future generations, who would have to make much deeper cuts while coping with the impacts of more extreme weather.

Sir Mark Walport, the government’s chief scientific adviser, said: “We can still avoid the most serious impacts. We need to transform the way we power our lives. This will be very challenging, but the challenges for humanity if we do not are likely to be far greater.”

Lord Stern of Brentford, who wrote an influential report on the economics of climate change, criticised Tony Abbott, the Australian prime minister, for refusing to make climate change a pressing issue at the G20 meeting in Brisbane this month.

“It is simply outrageous that a discussion about managing the risks of climate change, which is of fundamental importance to the future prosperity and wellbeing of the world’s population of seven billion people, is being shunted to the sidelines because of the local politics of a country of less than 25 million,” he said.

Myles Allen, a climate scientist at the University of Oxford and one of the report’s lead authors, said the writing team had avoided making “alarmist” claims about climate change made by Greenpeace and others.

Jim Skea, professor of sustainable energy at Imperial College, London, and a contributor to the report, said it made the case that, the faster emissions were cut, the lower long-term costs would be.

The emissions targets

• Emissions to fall at least 40 per cent by 2050
• Emissions to fall to zero or below by 2100
• Eighty per cent of electricity from low-carbon sources by 2050
• Phase out fossil fuel emissions by 2100