At its conception, the Copenhagen climate summit was intended to be the birthplace of a global, legally binding treaty on climate change that would ultimately replace the Kyoto Protocol when its second commitment phase expires at the end of 2012. In the months and weeks leading up to the summit, however, hopes faded that two weeks of talks in the Danish capital would result in a treaty. With most of the world in a recession and the United States lacking domestic climate legislation, expectations shifted to reaching a political agreement in Copenhagen that could later be strengthened into a legal treaty.

But the eventual outcome, known as the Copenhagen Accord, was neither a legal document nor a statement unanimously agreed by UN member states. And after two weeks of painstaking talks, nations walked away with a promise to meet again in 12 months in Mexico, but without clear milestones in place for making further progress on a climate deal. Nonetheless, not all have deemed Copenhagen a failure. After all, the accord for the first time made 2 °C a global temperature guardrail, rather than an EU aspiration. It also put in place a commitment to significant funding for developing nations to adapt to climate change, and included aspirational targets from all of the major emitters, including emerging economies.

Symbolically, the Copenhagen Accord has gone some way towards bridging the divide between rich and poor nations that has dogged climate negotiations, but it does little to prevent dangerous climate change, which is the core objective of the UN Framework Convention on Climate Change (UNFCCC). Nature Reports Climate Change asked several experts who watched the negotiations closely for their take on the Copenhagen Accord and on the next milestones for climate policy.

Mike Hulme, University of East Anglia, UK

Credit: MIKE HULME

The Copenhagen Accord is neither one thing nor the other; it's not a document that fits easily within any understanding of UN multilateralism. So it's moving [us] into new territory because of the way it was agreed and the formal status it has, and also because its ownership is less than ideal. This kind of agreement reflects a new political reality [where] politics and power will win out. My view is that this was a good outcome from Copenhagen. I think that people may well now see that there is more progress to be made by pursuing options outside of the formal structure of the UN.

It's better to be pragmatic than to be overly aspirational — surely the lessons of the 12 years since Kyoto tell us that?

Clearly the emerging economies have now found their voices on climate change, and one could make a strong case that the Major Economies Forum is a good place to drive this forward. But I would also like to see more radical thinking. Different climate forcing agents might be best attended to in different ways. One could have two separate treaties: one controlling short-lived agents such as black soot and methane, and one concerned solely with carbon dioxide.

I don't hold out a great deal of optimism that market-based mechanisms — especially with [only] a proportion being auctioned — provide a strong enough downward pressure on emissions. For that reason, I wouldn't mind too much if [the climate bill] doesn't get through the Senate if it forces other types of thinking. I've come around to the view that we need to set near-term targets that are pragmatic and technology-based, and they should be achievable on the basis of credible social, technical and economic analysis, not aspirational targets driven by IPCC [Intergovernmental Panel on Climate Change] science. It's better to be pragmatic than to be overly aspirational; surely the lessons of the 12 years since Kyoto tell us that?

Jonathan Lash, president of the World Resources Institute, Washington DC

A binding legal agreement, hopefully delivered in Mexico, is the ultimate goal.

Credit: WORLD RESOURCES INSTITUTE

The Copenhagen Accord is a much bigger — and better — deal than many people realize. Yes, the failure of 192 nations to emerge from two weeks of gruelling talks with a binding legal agreement was disappointing. Yes, the commitments made are not (yet) enough to halt the build-up of greenhouse gases at a level that would prevent temperatures rising more than 2 °C, the danger threshold set by scientists. But the accord breaks new ground in several ways. First, it includes quantitative commitments by all major emitters. Second, it provides for verification that these commitments are carried out — a contentious issue, and a line in the sand for the United States. Third, it reflects a serious commitment to countering the climate threat by heads of states, who took unprecedented action to prevent a dysfunctional UN process and a small minority of nations from blocking action.

Since 1992, the Conference of the Parties to the UNFCCC, which passes decisions by unanimous consent, has been the vehicle for international climate negotiations. In the run-up to the Copenhagen summit, it had become increasingly clear that this model was not working. But a binding legal agreement, hopefully delivered in Mexico, is the ultimate goal. There will be key indicators of progress along the way. The first is the 31 January deadline by which the Accord says countries must submit their commitments to reduce greenhouse gases. Another indicator will be the contents of China's twelfth Five-Year Plan, due out this spring; [and] of course the passage of US climate legislation.

David G. Victor, Stanford University, California

The underlying cause is a basic lack of public interest in addressing the problem.

Credit: DAVID G. VICTOR, UNIVERSITY OF CALIFORNIA, SAN DIEGO

Copenhagen was a non-event: neither a success nor a colossal failure. The biggest problem with the acrimonious end to the Copenhagen conference is that it leaves neither a clear milestone nor any strong compass for the next rounds of diplomatic efforts. Mexico City will probably come and go without a clear outcome. The next definitive milestone is the expiration of the Kyoto treaty in 2012. At a minimum, governments will scramble to find some kind of replacement treaty so that systems put into place under the Kyoto Protocol — such as the Clean Development Mechanism — do not become mired in disarray. Already, the credibility of those systems has been undermined by the inconclusive outcome in Copenhagen. It will be impossible to make much of a dent in world emissions without a central role for the private sector, and private-sector investors are a lot more skittish about the wisdom of low-carbon investments given the inability of governments to agree on a game plan in Copenhagen.

The single most important international activity after Copenhagen will be to find an acceptable path that works for the small number of countries that really matter — starting with the United States and China. [But] the fact is that the world is in for some serious warming. If 'dangerous' is 2 °C, then I suspect we are toast. A lot of people will lament that, but one has to wonder whether this is not a failure of governments but rather a failure of people. So far, very few people are willing to pay substantial amounts of money to avoid uncertain and distant global warming, and government policy reflects that reality. Governments, to be sure, have made this even worse through their inability to reach even basic effective agreements — as was evident in Copenhagen. But the underlying cause is a basic lack of public interest in addressing the problem.

John Schellnhuber, climate advisor to the German government and director of the Potsdam Institute for Climate Research, Germany

Credit: DEUTSCHE BUNDESSTIFTUNG UMWELT

Copenhagen was a landmark event for at least two reasons. First, the global policymaking elite assembled there confirmed that the scientific evidence on global warming is the frame of reference for all climate-protection strategies. Second, after almost 20 years of lofty announcements and sustainability kitsch, the meeting made brutally clear how little the respective sovereign states are willing to contribute, for the time being, to the welfare of humankind.

The UN meeting in Bonn this summer will provide the crucial test-bed for avenues beyond the Copenhagen quagmire.

Since the Copenhagen summit simply extended all existing negotiating mandates, a lot of bilateral and multilateral activities will unfold when the various parties recover from the self-afflicted shock. The [UN] meeting in Bonn this summer will probably provide the crucial test-bed for avenues beyond the Copenhagen quagmire. If there is such a thing as an international, legally binding and effective climate agreement, it has to [put in place] an extremely convincing concept that is considered tolerable, if not fair, by practically everybody. I think there is still time to replace the climate-policy-as-usual agony with such a vision. In my view, the many small countries were not the problem in Copenhagen; [the problem was] primarily the United States and China. If those two were willing to cooperate on climate protection then the UN system would also work fine.

Bill McKibben, founder of 350.org

Credit: © NANCIE BATTAGLIA

I think [the Copenhagen Accord] pretty clearly failed to take account of the latest science. Almost two-thirds of countries endorsed a target of [limiting atmospheric carbon dioxide concentrations to] 350 parts per million (p.p.m.) — but it was the wrong two-thirds, the poor and vulnerable nations.

The US and China, having broken the UN process, also bought it.

The next important milestone is seeing whether civil society, globally and in the United States, manages to rise to the occasion and build the kind of pressure that can achieve some political successes. But agreement isn't really the point — meeting the bottom line set by physics and chemistry is. There was real and powerful demand for meeting that bottom line from the 112 nations that endorsed a 350-p.p.m. target in Copenhagen — they'd understood the science, and they'd understood that their futures were at stake.

The US and China decided they didn't want these pesky nations burdening the talks with their unreasonable demands for survival, so they cut their own pact. But in some sense, the US and China, having broken the UN process, also bought it. That is, success and failure are increasingly on their shoulders. We in civil society need to figure out how to highlight that.

Roger Pielke Jr, University of Colorado, Boulder

Credit: UNIVERSITY OF COLORADO, BOULDER

The outcome of the Copenhagen meeting should be obvious: there is simply no way that the world is going to coordinate efforts to stabilize concentrations of carbon dioxide and other greenhouse gases through a mechanism focused on binding targets and timetables for emissions reductions. It is often said that the definition of insanity is doing the same thing and expecting different results. [Yet] many in the climate debate seem ready to put the Copenhagen experience out of their minds and gear up for doing it all over again in Mexico City. Insane!

Perhaps we should do away with the unhelpful idea that there is a threshold that somehow separates a dangerous climate from a safe climate.

Perhaps we should do away with the unhelpful idea that there is a threshold that somehow separates a dangerous climate from a safe climate. Climate is already dangerous for many people. Further, regardless of the stabilization target chosen — 450 p.p.m. or 350 p.p.m. or whatever — the policy implications are largely the same, necessitating never-before-experienced improvements in efficiency and a massive expansion of low-carbon energy supply. The pace at which we will achieve those goals will be determined not by any sort of derivation from a fairly meaningless global temperature target, [but] by technology, innovation and economics.

It is time to focus much more directly on the decarbonization of the global economy. This means improving energy efficiency and expanding low-carbon energy supply. These actions will result not from treaties but from processes of innovation implemented over many, many decades in a frustrating and incremental process. These goals are largely, but not always, compatible with policies focused on improving energy security — in places as varied as the United Kingdom and Pakistan — and expanding energy access for the 1.5 billion people without reliable access to electricity. It would be interesting to see countries negotiating an upstream carbon tax and a mechanism for its proceeds to be used to support decarbonization, energy security and enhanced access to electricity. Such negotiations [would] still be very complicated and political.