We have reached a defining moment in the global battle against climate change, and the role of the public is now more crucial than ever.

There are now less than 100 days until the United Nations climate change conference in Copenhagen in December, which my colleague Nicholas Stern, the former head of the UK Government Economic Service and author of the Stern review has described as "the most important international meeting since the second world war".

A strong international agreement on climate change can still be achieved at Copenhagen, which would set the world on a path that avoids the huge risks from "business as usual" emissions of greenhouse gases. But many significant hurdles remain which could prevent a treaty for action on mitigation and adaptation.

Agreement will only be possible if political leaders begin to focus now on the task of agreeing measures that will reduce emissions, while ensuring sustainable, low-carbon economic growth. The conference will be a failure if politicians are too distracted by other issues, such as the global downturn. Recession may be significant now, but it does not pose long-term risks to people's prosperity and well-being in the same way as climate change. Hence public pressure on political leaders to concentrate on reaching an agreement that can make a real impact.

But that is not all people can do to increase the chances of success in Copenhagen. They can also demonstrate firm support for constructive, far-sighted domestic measures to tackle climate change as well.

UK policies on climate change are now guided by the recommendations by the Committee on Climate Change, which has charted a route for reducing the nation's emissions by at least 80% by the middle of this century.

At present, the UK emits the equivalent of 11.6 tonnes of carbon dioxide per head of population each year. By 2050, that figure needs to be cut to about two tonnes per head. This is the UK's most important long-term challenge.

The Committee on Climate Change calculates that the UK can reach its target cost-effectively if it reduces emissions at an average rate of two or three per cent each year, over the next four decades. The 10:10 campaign could provide a big first step towards the target if it persuades many people to cut their annual emissions by 10% next year.

In a survey of European countries carried out earlier this year, 77% of UK respondents claimed to have personally taken actions aimed at helping to fight climate change, a higher proportion than for any country except Sweden. This is despite the fact that 40% thought that climate change is "an unstoppable process".

These results suggest that the overwhelming majority of the public will take at least some action to tackle climate change, even if many do not believe that the scientific evidence is beyond reasonable doubt. Public support for domestic climate change policies will perhaps provide the strongest impetus for political leaders ahead of Copenhagen. They are no doubt aware that a low-carbon economy would provide many new opportunities and benefits, without suffering the crippling economic and social consequences of climate change from current emissions.

But they also recognise that changing our current high-carbon economy will involve initial costs and difficult choices for taxpayers and consumers. There is a danger that the small but vocal minority, who perceive their short-term vested interests to be best served by maintaining the high-carbon status quo, will frame the public debate only in terms of these initial costs.

Instead we need a strong and vigorous public discussion about how best to promote future prosperity and well-being, not just for us now, but for our children and future generations as well.

If the leaders of developed nations such as the UK can make strong and credible commitments on climate change, based on well-informed domestic policies with solid public backing, then there is a very good chance of success in Copenhagen. A huge show of popular support, together with vigorous public action in cutting emissions, should empower our political leaders to reach a wise and visionary agreement.

• Bob Ward is policy and communications director at the Grantham Research Institute on Climate Change and the Environment at London School of Economics and Political Science.

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