Knowledge about environmental issues is increasing. Yet there is insufficient progress regarding the internationally agreed goals of the Paris climate treaty, the global SDGs or the Aichi agreement on biodiversity. National and international inaction or disputes in environmental governance are to a considerable extent based on conflicting economic interests, but also on more fundamental value disagreement. These divergent normative viewpoints cannot be easily reconciled, particularly in the context of increasing political divisions due to the rise of populist parties in Western democracies, making the question about legitimacy even more timely.
Early social choice approaches building on normative individualism or Bentham’s utilitarianism failed to identify real and stable preferences; begged the question about value commensurability; and aggregation was subject to methodological and normative challenges. This called into question their legitimacy. Moreover, empirical studies suggest that overly simple calls for more dialogue between decision-makers are often insufficient to reconcile divergent normative viewpoints, since remaining power imbalances may threaten legitimacy, and polarization can even increase. Divergent normative viewpoints thus persist in sustainability debates – and are frequently intermingled with scientific debates in light of complexity and uncertainty. For an overview of currently predominant approaches in global environmental assessments see Kowarsch et al., 2017. This raises a fundamental question: What are legitimate responses at the sustainability science-policy interface?
It seems we have three options: one can either love, leave or change the divergent normative viewpoints.
1. Promising types of “love” responses involve: embracing the diversity of values in sustainability assessments and noting excluded values in existing research. This may include a wider framing of legitimate value perspectives for sustainability governance in terms of, e.g., diverse goals, metrics and indicators, compared to current practices. If corresponding policy pathways are explored in assessment processes, such assessments may facilitate clarification of normative standpoints, later political compromise, or sometimes even the identification of common ground between divergent values in terms of viable policy options. The latter can be supported by directly reframing existing policy proposals in terms of alternative values. But a worry with such responses is that policy overlap seems rare and mere transparency of alternative normative viewpoints – if feasible at all – does not necessarily facilitate a good compromise in pluralist societies.
2. Given these concerns, another category of potentially legitimate response options is about simply “leaving” the divergent normative viewpoints to public politics by exclusively focusing on facts, e.g. possible technologies and pathways, in scientific assessments. While this decisionist model remains widely supported by politicians and experts alike, it is misleading since facts and values are inevitably intertwined in the science and economics of climate change and sustainable development. This makes decisionist approaches problematic from the standpoint of legitimacy.
3. More ambitious approaches therefore aim to “change”, i.e. revise, existing normative viewpoints of particular actors in environmental governance, e.g. short-term thinking or powerful entrenched interests in sustainability governance. While legitimacy concerns are particularly salient here, promising ways to achieve this may include, for instance: nudging for behaviour and preference change; the development of enhanced narratives; stronger philosophical arguments in favour of a particular set of values; and platforms for democratic deliberation and social learning. The latter assume prospects for preference change and higher acceptance of alternative values (e.g., by allowing ‘incipient’ qualities of citizens to become manifest, cf. Niemeyer 2014) through extensive and structured, democratic and participatory deliberation processes. However, there is still little evidence for more fundamental value change in deliberation processes. Moreover, nudging may be paternalistic and requires support from existing governments. Instead, arguments on environmental justice and ethics usually remain disputed and sometimes overly abstract.
Thus, divergent normative viewpoints at the science-policy interface are challenging for sustainability governance.
 For a definition of values see Dietz et al. 2005: “Environmental Values” in Annual Review of Environment and Resources. The seminal research by Schwartz et al. also implies that contemporary political conflicts concerning the role of the state and contested visions of liberty, identity, or (intra- and intergenerational) equality go well beyond mere economic interests. Moreover, Dryzek (“The Politics of the Earth”) et al. shed light on the different, value-laden discourses and (meta-)narratives about sustainability.