It is not possible to overestimate the global significance of the next two weeks of intense negotiation. Copenhagen is unprecedented; it is not an updated Kyoto and even Bretton Woods is little more than a footnote when compared to the magnitude and urgency of the challenge we now collectively face.
Given the uncomfortable repercussions associated with the scale of emissions reductions necessary to avoid "dangerous climate change", it is not surprising that the build-up to Copenhagen has triggered a co-ordinated backlash attempting to undermine the science of climate change.
However, whilst important questions have been raised about "process" and "communication", the validity of the science itself has emerged unscathed and, I believe, strengthened. Despite the best attempts of often well-funded "sceptics" picking over the minutiae of the science, the principal objections have been about the alleged behaviour of individual scientists rather than the science itself – a distinction overlooked in much of the reporting on the issue.
Away from this distraction, the real issues of how the global community can respond to the magnitude and urgency of the challenge remain both unchanged and central to the Copenhagen process.
Whilst the next fortnight of discussions in the Danish capital is pivotal to thrashing out the scope and structure of any meaningful agreement, stringent targets and detailed national commitments are unlikely to be forthcoming at this stage. Consequently, Copenhagen must be seen not as the last battle, but as a kick-start to an intense international process culminating, within a year, in detailed national commitments informed by the science of climate change.
Anything short of this will mean knowingly bequeathing to future generations a life of hardship and uncertainty at best and social and environmental collapse at worst. Moreover, our failure to act now condemns many millions of the world's poorest citizens to the additional ravages and instability of a rapidly changing climate.
So what is the scale of the challenge, why is it fundamentally different from what has gone before, and what do targets from the Copenhagen process need to look like? In 1992, the Earth Summit in Rio thrust what had hitherto been a scientific issue – climate change – into the political arena. However, whilst precedents existed for similar transitions in the guise of acid rain and ozone depletion, in reality these are wholly inadequate analogues for this new challenge.
Unlike sulphur or chlorofluorocarbons (responsible for acid rain and the ozone depletion respectively) carbon is ubiquitous, so whether it's the energy we consume, the production of fertiliser, the food we eat or the cement we manufacture, greenhouse gas emissions are implicated. Certainly substitutes exist for all of these. But with a growing population and all current models of development and industrialisation premised on cheap and abundant hydrocarbons, the challenge of a wholesale transition of contemporary society to low or zero carbon in little more than a couple of decades is unprecedented.
In recent weeks we've seen provisional commitments from several major emitting nations to achieve either absolute reductions in emissions (US) or lower the emissions per unit of economic growth (China and India) by 2020. These transitions should be welcomed. But they are little more than token gestures when compared with the scale of what the science concludes is necessary to give even a 50:50 chance of avoiding "dangerous climate change".
Unfortunately, and in complete contrast to what the sceptics would have us all believe, scientists have repeatedly underplayed or at least remained quiet as to the scale of the disjuncture between the science and politics of climate change. For example, the Stern and Committee on Climate Change reports are premised on global emissions reaching their highest levels by 2015 and 2016 respectively, before beginning a process of year-on-year reductions.
But amongst those working on climate change there is near-universal acknowledgment that such early peaking years are politically unacceptable – yet the Stern and the CCC analyses remain pivotal in the formation of emission-reduction policy. Statements by the US, China and India, allied with commitments from other nations, suggest peaking global emissions between 2020 and 2030 is about as hard as the economic and political orthodoxy is prepared to push.
Consequently, if Copenhagen is to have any chance of kick-starting a global movement to stay below the 2C characterisation of dangerous climate change, it must inspire and instigate a rapid shift away from the current political and economic consensus. If peaking global emissions between 2020 and 2030 are left unquestioned, the cumulative quantity of greenhouse gases emitted will be sufficient to put temperatures on a 4C or higher trajectory. Accordingly, the first challenge for Copenhagen is to get political buy-in to what the science is saying in relation to, at least, a 50:50 chance of not exceeding 2C.
In brief, wealthy (OECD) nations need to peak emissions by around 2012, achieve at least a 60 per cent reduction in emissions from energy by 2020, and fully decarbonise their energy systems by 2030 at the latest. Alongside this, the "industrialising" nations (non-OECD) need to peak their collective emissions by around 2025 and fully decarbonise their energy systems by 2050. This scale of reductions is presently far removed from that which the negotiators in Copenhagen are intending to consider.
The second challenge for Copenhagen, therefore, is to make a clear and explicit decision to do all that is necessary to put global emissions on a C pathway, even if this requires a temporary cessation in economic growth amongst the wealthy OECD nations.
An alternative, but equally honest, response would be to acknowledge that we lack the necessary moral fibre to make the requisite short-term reductions and openly accept our inaction will lead to high levels of "dangerous climate change" with all that entails for the poorer communities around the globe and also for future generations. Either way, as a minimum, any output from the Copenhagen process needs to be upfront, honest and direct.
Professor Kevin Anderson is director of the Tyndall Energy Programme at the Universities of Manchester and East Anglia