In international climate-policy circles, there is broad consensus on the target of limiting global warming to a maximum of 2 C above pre-industrial levels. Still, barring a breakthrough in United Nations negotiations in the near future and a reversal in current emission trends, meeting that 2-degree target is well nigh impossible.

But if world leaders abandon this target, they will have to make a fundamental strategic decision on the structure and stringency levels of a new climate goal. So international climate policy needs a paradigm shift.

The science-based approach of translating a global temperature cap into precise national emission budgets is politically unfeasible. Instead, countries with a strong climate-policy agenda should advocate dynamic formulas for setting targets.

The 2-degree target is the primary point of reference for today's climate debate. A corresponding rise in the global mean temperature is usually seen as the limit beyond which the effects of climate change could become dangerous. But, contrary to widespread belief, the last assessment report of the UN's Intergovernmental Panel on Climate Change did not call for the 2-degree target, which, since the mid-1990s, has acted as a catchy symbol and point of orientation for an ambitious but realistic global climate agenda.

The European Union (EU) was the primary force pushing for the 2-degree target internationally. Environment ministers of EU member states have been advocates of the target since 1996. Ahead of the UN Climate Change Conference in Copenhagen at the end of 2009, the EU succeeded in getting all relevant partners in the negotiations - including even China, India, Russia, and the United States - to commit to the 2-degree target.

In the "Copenhagen Accord", the UN finally recognized the target, though without any binding measures for achieving it. There is little hope that this will be rectified at the next climate change conference in Cancn, Mexico, from Nov 29 to Dec 10.

Since the volume of greenhouse gases (GHGs) emitted thus far will raise temperatures by 1.5 C compared with pre-industrial times, major political decisions are needed to ensure compliance with the 2-degree target. Climate science assumes that the global emissions peak must occur within the next several years. Currently, however, there is little to suggest that a reversal of today's trends will even be visible on the horizon by then.

So at some point in the near future, a growing number of voices from the climate-science community must definitively reject the possibility of holding on to the 2-degree target. When that happens, simply championing a softer target, most probably 2.5 C or 3 C, will not suffice.

According to the current paradigm, the global target is defined within scientific categories and understood as an absolute upper limit. Given this top-down approach, all initial efforts have been focused on creating a global climate treaty, leading to a heavy focus on global negotiations while neglecting concrete de-carbonization efforts by developed and developing nations.

This has resulted in stalemate, because one government can always blame failure on the inaction of others. Even the EU has used this argument to justify its refusal to increase its target for GHG reduction for 2020 from 20 percent to 30 percent, although this would be an equitable burden for Europe to bear on the path towards meeting the 2-degree target. An alternative paradigm would have to combine realism with a positive global vision. One possibility is to establish "climate neutrality" as a long-term global objective, that is, work to reduce net emissions of GHGs to zero. Even if this objective were to be initially linked with a broadly defined timescale, it would establish the standard for action according to which all countries would have to be measured.

Within such a framework, an ambitious climate-policy actor such as the EU, Switzerland or Japan would face the task of committing to exacting de-carbonization measures. They would need to muster evidence that the transition to a low-carbon economy is both technically feasible and profitable, yielding positive effects not only for the climate, but also for energy prices and security of supply. Success would spur other G20 countries, acting out of self-interest, to follow in the climate leaders' footsteps.

This type of bottom-up approach would lead to significant reduction in emissions. To be sure, it would be impossible to predict, under the currently favored top-down principle, how much temperature increase the world would have to bear. But it is questionable whether the increase would be any different. Given that clinging to a strict temperature limit is not a politically viable option, focusing climate policy on flexible benchmarks such as "climate neutrality" would be more effective over the short term and more promising over the long term.

The author is a senior research fellow at SWP, Germany's largest foreign and security policy think tank.

Project Syndicate.