Founder of Forum for the Future
Copenhagen could turn out to be a real success story (if not a resounding triumph). It's astonishing how little attention is being paid to the new commitments made by China, India, Indonesia, Brazil, Mexico – and even the US – over the past year or so. But to secure that success, the conference needs to land three big things.
Recover lost ground by powerfully reasserting the scientific consensus delivered by the Intergovernmental Panel on Climate Change in its fourth assessment report. Stay open to legitimate scepticism; nail the crazy stuff.
Go big on new jobs, technology breakthroughs, innovation, massive efficiency and productivity gains (available at zero cost), improved health and quality of life. See off the critics who bang on about "hair shirt policies", sacrifice costs and so on.
Sign off on the strongest possible political agreement. Get every country in the world to commit to getting a legally binding treaty in place by the end of next year, based on deep cuts in the rich world and much more ambitious reductions in CO2 intensity in developing and emerging economies. Agree an emergency funding package to help to prevent further deforestation as part and parcel of a much bigger financing agreement.
And spice all that up with a few hard-edged decisions, confirming the agreement of the last G20 meeting to eliminate all government subsidies for fossil fuels.
Leader of the Green Party
To have even a 50/50 chance of keeping the global temperature rise below C, industrialised countries need to adopt binding targets to reduce emissions by at least 40 per cent by 2020, based on 1990 levels. Importantly, these should be domestic reductions – not "outsourced" to poorer countries.
Governments need to recognise that investing in alternatives to polluting, finite fossil fuels, together with a shift to a more sustainable economic model, will actually benefit society and the economy.
The Copenhagen summit can be judged a real success only if it reaches a binding agreement in line with keeping global warming below the C threshold. The EU can show political leadership and hopefully win a positive result in Copenhagen by committing to ambitious policies now. I take heart from the millions of people campaigning for their governments to act urgently. I very much hope that the politicians at Copenhagen will listen.
Energy and climate change minister
We need developed countries, which have contributed the lion's share of emissions in the past, to agree to significant specific emissions cuts by 2020. But developing countries must also commit to taking action, because on current trajectories about 90 per cent of future emissions growth would come from the developing world.
We need solutions to the problem of forestry, which emits more carbon than every car, boat, train and plane on the planet combined. People living in forested areas need alternative livelihoods if they are to refrain from destroying the world's great carbon stores.
We need finance and international co-operation to support technological innovation. And, because it is too late to avoid some serious effects of climate change, we need finance to help developing countries to adapt to risks of flooding and drought.
Inventor of the Gaia theory
I don't think there's a lot one can do seriously to tackle climate change. The most important thing we all can do is to prepare the infrastructure of the various nations that we inhabit to cope with the more probable climate change. I mean the obvious things – you've got to make sure that the Thames barrier really works, and nobody ought to cut back on a thing like that just because there's a recession on. It's that kind of preparing ahead that I think is the most vital thing we can do. To blazes with vain attempts to stop global warming by various renewable energy proposals. I think those are pipe dreams, but also very profitable pipe dreams.
We all do our bit. We've been running low-energy bulbs now for 30 years; we run a small car. I think everybody's got to do their best that way, but don't bust a gut trying to do it because they are not sure.
I think what needs to happen is for people to be more ready to accept rather unpleasant changes at some time in the future, and the catch is we just don't know when it will happen. It could be next year but it might delay as much as 100 or even 1,000 years, so there's no great certainty. All we know is that the changes that have been made, like the increase of CO2, or the change of land usage, are so great that there's no going back.
Chair of the Government's Climate Change Committee
The target should be a 50 per cent cut in greenhouse gas emissions by 2050. That will not prevent global warming. But it will limit the extent to which warming exceeds C and make a rise above 4C very unlikely. That matters because the likely adverse impacts grow dramatically as the temperature increase exceeds C, and could be catastrophic at 4C or more.
A 50 per cent global cut implies average 2050 emissions of about two tons CO2 per capita. The US emits 24 tons per capita, the EU about 11, China between five and six, India about one. The good news is that low-carbon energy sources, energy efficiency improvements and moderate lifestyle changes make about two tons per capita achievable with only a small sacrifice of economic growth. The challenge is to agree a fair allocation of effort, rapidly reducing developed country emissions, containing and reversing China's emissions growth, ensuring that India seizes the chance to grow in a low-carbon way.
The UK is committed to cutting our emissions to about two tons per capita in 2050, with the Committee on Climate Change responsible for ensuring steady progress to that goal. Whatever the outcome of Copenhagen, sticking to that path will be a fair contribution to the global effort.
Professor Brendan Mackey
Chair of the International Union on the Conservation of Nature Task Force on Climate Change
We must seek to solve the problem through mitigation: achieve deep cuts in fossil fuel emissions and emissions from the clearing and degradation of carbon stocks in natural ecosystems, especially forests and wetlands. There are around 2,400 billion tons of carbon in the world's terrestrial ecosystems – about three times that in the atmosphere. Reducing emissions from both sources is now essential to have any hope of stabilising atmospheric greenhouse gas concentrations at a safe level.
Furthermore, deep cuts in emissions from both sources must be achieved in developed and developing countries. The atmosphere does not care about the GDP of the emitting country. Carbon emitted from degraded Russian and Canadian forests and wetlands is as potent a greenhouse gas as those emitted from Brazil or Gabon.
Secretary for State for Energy and Climate Change
There is undoubtedly a positive momentum; you can see the fact that in the past 10 days or so the US, Brazil, China and India have all put numbers on the table as a sign that the deadline is working.
There is a real sense that we need to get a deal done at Copenhagen. The question is not just deal or no deal; it is what kind of deal we get. I think we need to push for the highest-ambition deal we can get, including with the EU's position, which is that we all go to 30 per cent, as part of a high-ambition deal.
It is very important that Copenhagen sets a deadline for a legally binding treaty, and I think that deadline should be within months of a political agreement.
Given the urgency of the situation I think it is right to say we need a political agreement in December because the alternative course, which is letting the 176 pages of negotiating text just run on, was a recipe for inaction.
As part of a deal we've said we will do a 34 per cent reduction by 2020, compared with 1990, unilaterally.
There has to be a significant financial contribution (for developing countries) covering adaptation, mitigation and forestry.
We need to take advantage of this moment. I think this is the best chance we have of getting a high-ambition agreement because the world is watching. The single most important thing we can get out of Copenhagen is a peaking of global emissions by 2020.
We will have taken action which will safeguard the world and that our kids will inherit from us. The stakes are high and the longer we leave it, the more the cost will rise of action and the more dangers we store up for future generations.
Professor Hans Schellnhuber
Director of the Potsdam Institute for Climate Impact Research
The Herculean task ahead is to decarbonise the global energy system over the coming decades while addressing the development needs of a growing population. Despite all previous mitigation efforts, global carbon dioxide emissions have risen by about 40 per cent over their 1990 levels, and recent scientific results indicate that climate change is happening faster than previously predicted. Therefore, if they want to avert dangerous levels of warming, world leaders in Copenhagen should act in time and agree on three milestones. First, the C limit of a global mean temperature rise over pre-industrial times is adopted as legally binding in international law. Second, a global emissions budget up to 2050 is defined that needs to be divided in an equitable manner among all nations. This budget must not exceed 750 gigatons of CO2 for the next 40 years. Third, the worldwide emissions peak needs to occur in about 2015 to maintain a realistic chance of reaching the long-term decarbonisation objectives. It is time for genuine leadership at the highest political level to demonstrate that the world is prepared to take responsibility on behalf of current and future generations.
Chair of the 1997 Kyoto climate change talks
In order to organise the international community to answer climate change, we need to have a solid political compromise. It seems the possibility to reach complete agreement on emissions is not realistic now. Since the US has not yet decided on the level of compromise it's going to take, others aren't in a position to compromise themselves because these kind of commitments relate directly to the ways and means of consumption and will affect the competitiveness of the different parties involved. This has been the problem from the very beginning and this is still the problem.
The focus now should be on the political understanding, and that includes the need to have the US in the game and also to have big developing countries which are relevant from the point of view of emissions, such as China, Brazil, India, Indonesia, Mexico, and South Korea. They need to have clear commitments to mitigate and to adapt. Some of them will need financial resources to do so.
Starting tomorrow, you have two weeks – it's enough time to get people together and steer the process for a solely political understanding, not to have the details.
Time is very short; there is no reason to postpone rational measures that could be adopted even before the agreement is adopted. If you could reduce emissions right now, why not do that?
Founder of the Global Warming Policy Foundation
The countries will have to realise that this is a blind alley because there is no basis for agreement between the big developing countries like India and China and the developed world. The reason why there is this row between developed and developing countries is over burden-sharing, and the burden is such a huge one.
The only sensible approach is that if there is any warming, and to the extent that there is any warming, then we have to adapt. We have to develop technology further so that we can adapt more effectively.
There are very, very poor countries that might find it difficult, and we should help them. I think that would cost only a fraction of what it is being suggested we should spend. It is sensible to develop, over a longer timescale, economically effective alternative sources of energy, but that won't happen overnight.
There are two great uncertainties. One is the extent to which CO2 concentrations have a warming effect; I think most people agree that they have some warming effect. How big is a matter of great dispute. And there are all the natural factors that affect the climate. These, including the science of clouds, are very imperfectly understood.
Professor Bob Watson
Defra's chief scientific adviser and former head of the Intergovernmental Panel on Climate Change
Governments around the world, working with the private sector, have to double and redouble their efforts to find approaches to low-carbon production of energy and low-carbon use of energy. We also need to make sure we've got technology – more efficient cars, more efficient houses. Government, working with the private sector, has to drive the low-carbon economy; in parallel to that, as individuals we have to analyse how we can reduce our carbon footprint. We need to try to use more renewable energy; we need carbon capture and storage on the production side and, in many countries, we need nuclear.
The first priority would be for the industrialised countries to put some strong commitments on the table. We also need to work with India, China and Brazil, and the other major emitters from the emerging economies will start a process of decarbonisation themselves. Obviously the developing countries will need to have differentiated responsibilities: I would not expect them to be as stringent as the developed world, and they will need assistance both in technology and finance.
We need Europe to work with Japan; to work with the US; to show real leadership; to decarbonise. So we need to reduce our emissions both in energy production and use. We also need to reduce emissions from agriculture and forestry.
Everybody has given up on the chance of a legally binding agreement and therefore what we have to hope for is a strong politically binding agreement with a short time-frame – six months to a year – to convert it into a legally binding framework.
Clapham, south London
I'm 15, so I should be really worried about global warming. But the truth is, I'm not half as worried as I think I should be. We "do" global warming at school – I did some coursework on it recently as part of my geography GCSE. Maybe that's the problem: it's on the curriculum, so it's like any other subject, something you do at school. But global warming isn't just any old subject – it could change my life, and it is changing the world. Perhaps schools need to rethink the way they teach us about it, because it's a lot more relevant than most of the work we do at school, and I think they could encourage us to make that connection.
I know I should do more to cut down my carbon footprint. I've just asked my friends and most of them feel, like me, that they don't do enough. Only one of my friends, Hetty, is really interested in global warming. She's a vegetarian and she never uses plastic bags when she goes shopping. But she's the only one, out of six of us.
The meeting in Copenhagen sounds boring to me – a bunch of adults sitting around having talks. But what they decide will affect my future and my children's future. Lots of the predictions about the bad stuff that could happen centres on 2050. By then I'll be 56, and my children will probably be in their mid-twenties. I hope we won't be saying: "If only they'd acted at Copenhagen, we wouldn't be facing world disaster." The trouble is, I think we might be.