ImageAfter two weeks of largely fruitless climate negotiations at the UNFCCC meeting in Bonn/Germany, the world is one step closer to miss the overarching target of international climate policy: limiting the mean temperature increase to 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels.

Since it is politically unrealistic to stick to a target that is obviously unattainable, there will be attempts to modify the 2 degrees target in the near future. Basically, there are three options to change the primary target of international climate policy. World leaders could either allow the 2 degrees target to become a benchmark that can be temporarily overshot, accept a less stringent target or give up on a climate stabilization objective altogether.

Applying one of these options would mean to renegotiate a quantified limit that was meant to be non-negotiable, the threshold to "dangerous climate change." This would result in the end of “science-based” climate policy as we knew it. Neither the European Union, nor Environmental NGOs or mainstream climate science would like to see that happen. And there is one way to avoid this: the more or less deliberate modification of assumptions in climate economics.

Modifying assumptions in climate economics

Eventually, it’s all about adjusting the global carbon budget derived from the 2 degrees target. Carbon budgets were originally calculated to make climate policy goals more accurate than would be possible using simple end point emissions reduction targets. This approach was also intended to create a sense of urgency for short- to medium-term action, above all through the formulation of a last possible peak year and a maximum emissions level for 2020.

But sufficient momentum for urgent action never picked up; global emissions are still rising and the widely accepted maximum levels set for 2020 have already been exceeded (50 Gigatonnes CO2e in 2010 compared to 44 Gt in 2020, according to UNEP's annual “Emissions Gap Report”). Therefore, if central assumptions of climate economics remain unchanged, climate science will soon be forced to conclusively reject the feasibility of the 2 degrees target.

Changing specific assumptions and boundary conditions is not in itself illegitimate; it is a constitutive element of advances in scientific knowledge. But if assumptions were deliberately changed in order to maintain the 2 degree target, this would certainly be motivated by climate-policy considerations. This process would take place, however, entirely within the domain of climate science or scientific policy advice.

These modifications would not be seen as politically driven, and in fact such interventions would not even be noticed by most climate policy actors. The knowledge base of climate science offers multiple starting points for such an approach, some of which have already been used in the recent past, because, as Celine Guivarch and Stephane Hallegatte put it in their excellent paper 2C or not 2C,

“often the policy demand for evaluations of the 2°C target has pushed modelers toward imple­menting more optimistic assumptions for their mitigation portfolios.”

Different options

An increase in the maximum reduction rates after 2020 would have no impact on the overall size of an emissions budget up to 2050. By going significantly beyond the usually assumed—but already quite optimistic—feasibility limit of a global 3 percent emissions reduction per year, the models would be able to capture anticipated delays in reaching the emissions peak. This would also make it possible either to increase the maximum emissions level for 2020 in a gradual manner, or to do with­out such a figure altogether.

Delaying the last possible peak year - the central “make-or-break” point for climate policy in the carbon budget approach - could also be enabled by reducing the“acceptable” probability of staying below the 2 degrees limit from the approximately 67 percent currently favored by scientific policy advisors to 50 percent, which would extend the remaining emis­sions budget considerably.

The same effect could be achieved by increasing negative emissions in the second half of the twenty-first century. Most studies on the feasibility of the 2 degree target now assume that we have to be able to significantly reduce the net amount of greenhouse gases in the atmosphere within a few decades, mainly through the combustion of fast-growing biomass in power plants and the subsequent capture and underground storage of the resulting CO2(BECCS). The assumed amount of negative emissions could be raised gradually to compensate for emissions in excess of budgets during the first half of the century.

Sustaining the top-down paradigm

The main result of such interventions, which may also be combined in various ways, would be to enable climate policy to maintain the 2 degrees target for several years longer than originally calculated, despite rising global emissions. The conditions that underpin the EU’s leadership role in international climate policy would remain intact, and the 2 degrees target would continue to function as a central reference point for climate policy. The idea that there is a clear boundary separating “dangerous climate change” from “non-dangerous climate change” could be maintained because the political and economic restrictions that such a boundary would impose would be somewhat relaxed.

In a nutshell: the largely ineffective top-down paradigm that has been dominating international climate policy since 1992 could be sustained for some more years.