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The authors acknowledge that a transition from fossil fuels to renewable energy is easier to recommend than to achieve. Many countries are locked into using fuels like coal.

Here in Germany coal provides nearly half the electricity. But because greenhouse gases are building up in the atmosphere so rapidly, the conclusion is that it's better to make the change sooner rather than later. Professor Jim Skea at Imperial College is a leading figure on the panel.

"The message is that we need to start from 2020 onwards. If you wait as long as 2030 to put in place measures, it is going to start to get difficult. Emissions have risen more quickly in the last ten years than they have at any point in the past, and if we carry on in that kind of way till 2030, then you will be faced with these difficult choices. We need to move much more quickly than that."

One surprise is a low estimate for the cost of phasing out fossil fuels and boosting wind and solar power. The panel says that less than one tenth of 1% will be shaved off annual global growth. However, this figure rests on a host of assumptions, and for the moment, renewable energy still needs subsidies, which raises questions about public acceptance.

The panel does believe its options are feasible and it hopes they'll be implemented in the coming years.