We've left it too late for anything other than a radical emissions reduction policy, a succession of speakers argued at a conference on climate change in London this week.

Global action has stalled. National governments have lost confidence. And after 20 years of little progress in cutting greenhouse gas emissions, supply-side solutions are no longer enough, said Professor Kevin Anderson from the Tyndall Centre in the UK.

Assuming that poorer developing nations, including China, peak their emissions by 2025, then richer historical emitters, including Europe and the US, will need to reduce their own emissions by 10% year-on-year - a 90% reduction by 2030. This is far beyond the EU's current proposal of a 35-45% cut in emissions; however, it is the only equitable way to keep emissions low enough to avoid dangerous levels of climate change, said Professor Anderson.

"Radical change needs to occur in the rich parts of the world for the poor parts of the world to get the better part of the cake," he said.

Such a significant cut in emissions is viable, said Professor Anderson, if historic polluters are willing to cut levels of consumption and move away from a model of GDP-led growth. The alternative was a focus on prosperity without growth, an idea previously outlined by former government sustainability advisor Tim Jackson.

As it stands, however, the government policies adopted by historic emitters show little sign of meeting what the speakers say is a necessary ambition.

For example, although the UK has committed to reducing emissions by 80% by 2050, it is currently expanding its aviation sector, opening new ports, re-opening coal mines, offering tax breaks to shale gas companies, promoting oil extraction in the North Sea, looking to reduce its own targets for cuts in carbon emissions and opening a consulate office in Alberta (the centre of Canada's tar sands industry).

Commenting on the lack of political action in tackling climate change, Caroline Lucas, the UK's first and only Green Party MP, said it was "a game of chicken and egg". "Politicians, by their very inaction entrench public misunderstanding while using it as an excuse not to do so much."

Climate change campaigners and scientists should not despair, suggested Professor Corinne Le Quere from the Tyndall Centre. "It won't be long before policymakers pick up on the calculations and realise that it will cost them more if they continue to ignore tackling climate change," she said, pointing out that the impact of Hurricane Sandy in the US was worsened by higher sea levels.