Politically informed advice for climate action

Upward estimates for carbon budgets are unlikely to lead to action-focused climate policy. Climate researchers need to understand processes and incentives in policymaking and politics to communicate effectively.

Climate policymakers unexpectedly received an extension by about 500 Gt in the remaining budget of carbon dioxide emissions for ambitious temperature targets, as a recalculated 1.5 °C budget was published1 in September 2017, and the approach later confirmed2,3. That the previous estimate — introduced in the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC) — is in need of an update that could lead to larger carbon budgets is now broadly accepted4,5. Nevertheless, the specifics of the recalculation, and consequently the magnitude of the extension, have been controversial within the climate community.

Equally controversial has been the assumed effect of the initial publication1 on policymakers. The core author team not only discussed potential implications for climate policy in the paper but, even more importantly, also pursued a dedicated communication strategy that led to global high-level media coverage — and immediate dissatisfaction among colleagues, voiced in scientific blogs, on Twitter and, informally, in tea kitchens and corridors.

Millar and colleagues have highlighted that meeting the 1.5 °C target is geophysically still possible without consideration of solar geoengineering. On the other hand, climate scientists critical of their approach are concerned about politically problematic messages that such a large adjustment might send. They note that climate change deniers immediately exploited the correction as ‘proof that climate science had it wrong’ in overestimating warming trends. They also fear that questioning one of the core outcomes of the IPCC AR5 might foster uncertainty among policymakers and potentially undermine the political utility of the carbon budget concept.

I argue that both Millar et al. and their critics within climate science gravely misconceive the relevance of the size of the remaining carbon budgets for mitigation action. When thinking about the policy relevance of their work, climate researchers tend to address imagined rather than actual policymakers6. They mistakenly assume a high degree of problem-solving orientation and a strive for consistency between talk, decisions and action. By contrast, most policymakers and political leaders are not keen to reduce uncertainties and overcome ambiguities — these are a source of political flexibility.

Policymakers cannot be expected to take a sudden carbon budget extension as a welcome opportunity to step up mitigation efforts, only because meeting 1.5 °C now seems a little less unrealistic. Rather, such an extension reinforces their long-held belief that it will always be ‘five minutes to midnight’, although global emissions are still not decreasing — something they already experienced with shifting benchmarks in the annual United Nations Environment Programme (UNEP) Emissions Gap Report (see Fig. 1). In that sense, the recent carbon budget extensions allow for ‘more of the same’, not least because the approach of Millar et al. will affect any temperature-related carbon budget, regardless of the target. This holds even though Millar et al. chose not to give a revised budget for 2 °C, which is still the more relevant target for policymakers in industrialized countries. Therefore, to open a new chapter in climate policy, we need an approach that avoids reassuring policymakers that all is still well.

Fig. 1: Shifting benchmarks.
Fig. 1

a, Maximum greenhouse gas emissions (expressed as CO2 equivalents) compatible with a 2 °C trajectory in 2020, 2025 and 2030, as given by the UNEP Emissions Gap Reports23,24. b, Benchmark values in the 2015 edition are about 20% higher than in the 2013 edition. This shift was a result of the introduction of a new scenario category — “limited action until 2020” — in the face of insufficient mitigation and slightly increasing global greenhouse gas emissions, resulting in widening emission gaps. The benchmark for 2020 (52 Gt) has been kept stable in the 2016 edition, whereas the 2017 edition does not contain a benchmark for 2020 anymore. Panel b courtesy of UN Environment Programme.

If the IPCC’s aim of striving for ‘policy relevance’ means supporting stringent action on mitigation, then climate researchers will not only have to get a much better understanding of policymaking and politics, they also need to shift the ways in which they communicate their results.

Deliberate inconsistency

Although the carbon budget concept has become increasingly popular since 2009, it has only been able to influence international climate policy talk — but not decisions, or actions. Contrary to climate scientists’ expectations at the time of introduction of carbon budgets in the months before the Copenhagen climate summit7,8,9, diplomats never seriously tried to create a policy framework under the United Nations Framework Convention on Climate Change (UNFCCC) that aimed at avoiding dangerous anthropogenic interference on the basis of total allowable emissions. Framing climate change as a stock problem is more accurate than focusing on end-point reduction targets for 2030, 2050 or 2100. But the UNFCCC’s reluctance to decide on a global carbon budget, let alone to act on it, eventually led to a problematic extension of the concept — a debt mechanism where deployment of carbon dioxide removal from the atmosphere later in the century allows for an initial budget overshoot10,11. With this extension, climate researchers adopted the standard approach pursued by most governments instead of disciplining them: run huge deficits, betting on payback by future generations.

Looking at 25 years of the UNFCCC process, the assumption that climate policymakers might strive for consistency seems far-fetched. It also feeds a somewhat patronizing discourse on science advice for policy, built on the idea that governments — although trying to deliver on their promises — do not manage to do so, and need a helping hand. Instead, I suggest that governments and supranational institutions keep asking for ambitious mitigation pathways without implementing the knowledge presented, because they have an interest in continuing inconsistency. In real-world policymaking, talk, decisions and actions are not consistently derived from agreed descriptions of a given problem, because policymakers are always are confronted with overall inconsistent demands from different stakeholders. From their perspective, the most efficient way of dealing with these tensions is to address some stakeholder groups through talk, some through decisions, and some through actions. Usually, this is done by different ministries or agencies12.

Since aiming for ambitious temperature targets is only possible with a complete overhaul of the global economy, climate researchers and advisers have to move beyond their natural allies in the ministries of environment or research and equally deal with all branches of government. If they do so, they will find it harder to imagine a policy design to manage carbon budget uncertainties based on a transparent methodology that creates the conditions for countries to adapt their commitments to the evolving signal of human-induced climate change, as suggested by Millar and colleagues1,13.

Climate scientists tend to expect that policymakers might want to define core elements of their objectives more clearly (for example, the pre-industrial temperature baseline5,14 or the temperature overshoot option15), but governments know the practical value of imprecision. The more precisely a policy objective is defined, the greater its risk of failure. Conversely, constructive ambiguity helps with concluding intergovernmental negotiations10, and an uncertain knowledge base calls for more studies and permits a broader set of interpretations.

Failure or success

Acknowledging inconsistency as the modus operandi of policymaking is not to say that governments are willingly and indifferently moving towards climate catastrophe. They simply have a more complex set of criteria for success — criteria that have more to do with politics than policy. Advisors from the realm of science tend to neglect this dimension16. Political organizations, including ministries and government agencies, strive to enhance legitimacy and external support. Parties and politicians need to compete in elections, and to achieve success — not simply for their own well-being but also to be able to shape policies. Thus, success and failure are important political categories. With a policy objective to avoid “dangerous anthropogenic interference with the climate system” (as stated in Article 2, UNFCCC), the primary concern is how to avoid failure or at least successfully shift the blame17.

In this respect, a major change in estimates of the remaining carbon budget is of high political significance, because it potentially shifts the odds for success and failure. Since remaining budgets are already very tight and depend on large amounts of assumed carbon dioxide removal, every downward change could spell the end of ambitious climate targets. As such, it would highlight the failure of more than 20 years of UN climate negotiations.

Policymakers cannot afford to pursue objectives that scientists have declared to be unachievable or to work on obviously unsolvable problems. They would therefore be forced to renegotiate threshold levels or to modify the exact meaning of temperature targets18, for example, from not-to-exceed to deliberate overshoot15. In contrast, a significant extension of the carbon budget results in avoiding such a dilemma, and helps to stabilize the long-established climate policy storyline that ‘it is five minutes to midnight, but we can still make it if we start to act now’.

For policymakers and even more so for high-level politicians, it does not matter what the reasons behind resetting the doomsday clock are. What matters is that a declaration of ultimate failure has been avoided. Scientists who advise on climate policy might think that it does not make much of a difference if the ‘make-or-break’ point gets shifted one or two decades into the future. But they underestimate the effects of fluid participation in policymaking and decisionmakers’ ability to diffuse responsibility12. For ministers now involved in negotiating the consequences of the Paris Agreement, 10 to 20 additional years make all the difference; and their successors in 2030 will certainly not be willing to take the blame for opportunities missed by previous governments in the crucial years after Paris.

Change of framing

Researchers are not in a position to change core features of the policymaking process that limit the use of evidence, such as time constraints, path dependencies, limited capacity to digest new information, industries exerting their influence, and competing values. And scientific advisers will not be able to force policymakers to overcome inconsistency between talk, decisions and actions. But they can play their part in hedging inconsistency in climate policy.

Consider the following thought experiment: assume that during the course of the IPCC Sixth Assessment Cycle, the research community adopts standards for assessing the achievability of climate stabilization targets more realistically19, and, for instance, communicates its findings in a slightly different way. Instead of saying “yes, meeting the 1.5 °C target is still feasible, but only if A, B and C happens”, the core message would be “no, meeting the 1.5 °C target is currently not plausible, unless governments implement A, B and C”.

The difference in wording is small, and scientifically, both versions are probably equally valid. But the climate policy perspective changes considerably. In the first case, policymakers can focus on the ‘big prize’, the cherished long-term target that is still in sight, and achievement of the target is already assumed. This is a common way of exploiting the future for today’s political gains12, because governments are quite lenient when it comes to delivering the appropriate action. In the second case, instead of handing over the ‘big prize’ to policymakers early on, climate researchers hold it back, but define clear requirements for bringing it again into play, based on the latest scientific findings.

Such a communication would help to shift everybody’s attention, from talk and decisions to actions, and from the far-away future to the next 5 to 10 years20. Shifting the communication from a “yes, if…” to a “no, unless…” frame would prevent climate research and advice from resetting the clock time and again. Instead it puts the pressure where it belongs — on governments.

Politically informed advice

The concept of a global carbon budget has been shaping how the broader climate community looks at the core of the climate mitigation problem today. But carbon budgets have only been able to influence climate policy talk, not decisions, let alone actions. In other words, the concept is not particularly ‘actionable’, similar to global temperature targets21.

The IPCC describes its main goal as “providing policy-relevant but not policy-prescriptive information”22, but in the face of a looming global climate crisis, the relevance of scientific expertise should go beyond merely affecting policy talk. This will only be possible if climate researchers, including the majority of social scientists, learn more about real-world policymaking processes, and take this knowledge into account when advising policymakers.

Evidence-based policymaking in a strict sense will remain an illusion, but in order to make evidence-informed policymaking a reality, we need politically informed advice16. This is not to be confused with ‘playing politics’ or acting as ‘policy entrepreneurs’, quite the contrary. Science is based on the principle of intellectual consistency, and climate researchers should do everything to preserve this foundation of their work.

Politically informed advice can be an effective approach to hedge inconsistency — by communicating the evidence in a way that makes it harder for climate policymakers to evade the practical consequences of the knowledge base they already accept.


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The author would like to thank F. Schenuit for his support in tracing benchmark shifts in UNEP Emissions Gap Reports 2010–2017.

Author information


  1. The Ocean in the Earth System, Max Planck Institute for Meteorology, Hamburg, Germany

    • Oliver Geden
  2. Centre for Globalisation and Governance, University of Hamburg, Hamburg, Germany

    • Oliver Geden
  3. EU/Europe Research Division, German Institute for International and Security Affairs, Berlin, Germany

    • Oliver Geden


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Corresponding author

Correspondence to Oliver Geden.