Achieving net zero emissions has rapidly become the dominant long-term objective guiding national climate policies. At the end of 2018, only 24 countries were considering or had adopted long-term net zero targets. By the end of 2021, this had climbed to almost 150 countries, covering 89 per cent of global carbon emissions. In this article, we trace the origins and diffusion of net zero pledges through the lens of international norm theory. Drawing on a newly compiled database of national net zero targets, our analysis highlights the critical role played by climate scientists, transnational advocacy networks, and norm entrepreneurs in articulating the norm of net zero emissions. The IPCC's fifth assessment report was foundational, by introducing the concept of a cumulative carbon budget, allowing translation of abstract temperature goals into more actionable net zero targets. The norm of net zero has been institutionalised at the global political level in the period 2015–2018 and cascaded through the international system in 2019–2020. Yet, it remains subject to various forms of contestation, most notably regarding validity, fairness, scope, and implementation. The norm is now at a critical stage in its lifecycle that will decide whether it gets institutionalised or suffers backsliding and even erosion.
- With almost 150 countries and an even larger number of non-state actors adopting net zero pledges, net zero has rapidly become a global norm, increasing the social costs (to reputation, status, etc.) on holdouts that have not yet adopted the norm. Each country, company, or other entity not adopting the norm will face increasing pressure to justify its position.
- The scientific community and, more specifically, the IPCC can successfully articulate new global norms, rooted in an evolving scientific understanding of a global problem. These norms are more likely to diffuse through the international system with support from transnational advocacy groups.
- Countries have adopted net zero pledges with different motivations, ranging from persuasion (being convinced that net zero is the right thing to do) to mere virtue signalling (only backing the idea to look good to others). Even so, net zero now provides a focal point around which civil society and other actors can mobilise. Those countries that are merely ‘posing’ can find themselves rhetorically entrapped in their own pledges.
- Now that a critical mass of states has rallied behind the global norm of net zero, the focus of policy-makers and campaigners should turn to norm implementation and compliance. This requires the development of national roadmaps that, at a minimum, set intermediary targets, identify concrete policy measures, and establish monitoring and review systems.
- Like many other global norms, net zero remains subject to contestation, notably regarding its validity and fairness. There is a serious risk of norm erosion or backsliding if these issues remain unresolved. To achieve successful institutionalisation and implementation, major developed economies should take the lead in acting on their net zero pledges in a rigorous, transparent and resolute way.
Photo by Miguel Á. Padriñán