David King: There is a way ahead after Copenhagen

As the dust begins to settle and the delegates return home, the mood from the Copenhagen climate meeting appears to be one of disappointment, even dismay. I don't think this is fair. Certainly there were disappointing aspects, though they weren't entirely unexpected. But the underlying message was positive in one crucial regard: at last, the developing world has found its voice in the climate change debate.

The agreement thrashed out late on Friday night by President Obama and his small, hastily convened cabal of key states was not in itself very meaningful. By the time the text emerged it had lost its most important statement – a timeline to achieve a legally binding protocol by the end of 2010. This was a clear demonstration of Obama's weakness. He is a hostage to his own Congress and Senate, and if he goes beyond what they can stomach, they will certainly give him a bloody nose.

But it did have two positive aspects. First, it was not in itself a fully fledged protocol. This was a relief since at this stage a weak protocol would have been very much worse than nothing at all. Second, none of the nations that Obama felt he needed to turn to were in the so-called Annex I group of rich countries. Instead, he brought in China, India, Brazil and South Africa, all rapidly emerging countries that are now seen as essential participants at the negotiating table.

This shows how much has changed since the early days. The first meeting of the Kyoto protocol was entirely driven by Annex I countries, while the rest of the world declared that climate change was not their problem. This began to change at Gleneagles in 2005. I had for some time argued that we needed the rapidly emerging nations to be invited to a G8 meeting to bring them into the discussions. Tony Blair responded to this argument by inviting five nations to join discussions with the G8. Four of those five were at Obama's negotiating table on Friday night.

Moreover, the meeting in Copenhagen marked the first time that the poorest nations of the world made their presence felt. The African nations showed their muscle by walking out en masse when they feared the Kyoto treaty was about to be abandoned. The small island states, notably the Maldives and Tuvalu, also found their voice. At last it seems the whole world has begun to engage in the climate problem. If, as has been suggested, the Chinese were obstructive, we should not be too critical. I fear Obama's speech was less than diplomatic and to Chinese eyes will have appeared high-handed. Their premier is making considerable efforts to decarbonise his economy and is well aware of what needs to be achieved.

But the fact that the whole world is engaged in the issue is the most positive result from Copenhagen. We need a solution that involves everybody – industrialised, rapidly emerging and developing countries alike, or emissions will simply "leak" from the countries where CO2 rules apply to those that are not part of the agreement.

But to achieve this, poorer countries need money to deal with the impacts of climate change and the cost of switching to a low-carbon path. Kyoto offered a patched solution with its bureaucratic Clean Development Mechanism. Following Gordon Brown's plea the Copenhagen conference went further, committing $25bn per year by 2012. (It's another sign of Obama's current weakness, though, that $11bn of this will come from the EU, $11bn from Japan, but only $3.7bn from US.)

This is a necessary short-term measure. But in the longer term we need to go beyond such handouts with their associated culture of dependency. Instead, we need a fully integrated system in which all parties can participate, regardless of their current state of development. Such a system would incentivise developed nations to defossilise their economies and poor countries to develop low carbon economies while adapting against the impacts of climate change. In my view we need a fully global cap and trade scheme that puts a single, high price on carbon's head.

Let's talk numbers. By 2050, global average emissions of CO2 must fall to two tons of CO2 per person per year. What if we set this value as a trading limit? Each nation in the industrialised world would be assigned a straightforward downward trajectory to two tons per person per year. Rapidly developing countries such as China and India, which have relatively low levels of emissions per capita, could temporarily increase their emissions before these too would start to fall towards the magic figure of two tons.

The world's poorest countries, which are also the ones that will be hardest hit by climate change, would benefit significantly. For example, Rwanda with current per capita emissions of 0.35 tons, could receive carbon credits for remaining below two tons, and trade these with any country that has exceeded its cap. This naturally produces cash for poorer countries to adapt to climate change; it also provides an incentive for them to develop low carbon technology, solving the problem of leakage.

Such a scheme could set conditions that any country would have to meet to join the trade. For example, there could be standards of governance to ensure the money was not simply siphoned off into corrupt coffers. Each country would also need to demonstrate how they would use the money to achieve low-carbon growth. And to avoid encouraging population growth, the allowance could depend on the population size at a country's point of entry in the trading scheme.

Rwanda's President Kagame gave support to this general idea at the UN heads of state meeting on climate change in September when spoke on behalf of the African Union. Strikingly, he declared that Africans want to be part of the solution, not part of the problem. But to work this idea up to a fully functioning protocol will take time.

For these reasons, I think that all eyes should now turn to the meeting in Mexico in December 2010, the last-chance saloon. There can be no more excuses. By then we must, and I hope we will have developed a legally binding international protocol that provides the developing world with the tools to help themselves, and enables us to tackle the problem of climate change once and for all.

Sir David King is Director of the Smith School of Enterprise and the Environment, Oxford University, and former chief scientific adviser to the PM