"A lot of the progress we have made in reducing carbon dioxide emissions so far has been down to circumstances -- the end of the de-industrialisation of Britain in 1990 and the dash for gas replacing coal in power generation," he said.

"Now the difficult stuff starts and we no longer have those factors in our favour," the polymath businessman and academic added in an interview. "But it can be done. I would describe my position as one of optimistic rationality."

The Climate Change Bill sets a target of cutting Britain's carbon dioxide emissions by 26-32 percent by 2020 and at least 60 percent by 2050. It is the first time any government will have set itself such legally-binding targets.

But Turner's committee has been asked by the government to decide in December whether that end target should be raised to the 80 percent many environmentalists have been pushing for.

"Whatever we decide it should be -- 70, 80 or even 90 percent -- is not the problem. I am confident that by 2050 we can have decarbonised electricity generation, and that is crucial," the non-executive director of Standard Chartered Bank said in the bank's plush London headquarters.

"What is much more difficult is what you do in the medium term. What should you aim for in 2020 or 2030. There is a very strong argument for really stretching medium-term targets. We have to see what policy levers are available."

When setting the carbon budgets Turner said his committee of scientists, technologists and economists would look at economic growth forecasts then add technological factors and investment lead times, taking account of the need to front load action.

Scientists predict that world temperatures will rise by 1.8 to 4.0 degrees Celsius this century due to carbon emissions from burning fossil fuels for power and transport, bringing floods and famines and putting millions of lives at risk.

Turner said promoting energy efficiency and getting the carbon out of electricity through renewables, nuclear power and carbon capture and storage -- grabbing and storing the emissions from fossil-fuelled power stations -- should be relatively easy.

Transport, on the other hand was much trickier.

Road transport, he said, might cut carbon emissions by improved engine performance driven at least in part regulations and in part by different fuels and even electrification.

What was needed there were long term policy frameworks that would survive both economic and political change and give manufacturers clear indicators to push their research and development.

Air transport, on the other hand, was a much harder nut to crack not just because of the personal choice it involved but the fact that it was growing so fast globally that it would become one of the chief causes of carbon-induced climate change.