Technological breakthroughs and policy measures targeting energy efficiency and clean energy alone will not suffice to deliver Paris Agreement-compliant greenhouse gas emissions trajectories in the next decades. Strong cases have recently been made for acknowledging the decarbonisation potential lying in transforming linear economic models into closed-loop industrial ecosystems and in shifting lifestyle patterns towards this direction. This perspective highlights the research capacity needed to inform on the role and potential of the circular economy for climate change mitigation and to enhance the scientific capabilities to quantitatively explore their synergies and trade-offs. This begins with establishing conceptual and methodological bridges amongst the relevant and currently fragmented research communities, thereby allowing an interdisciplinary integration and assessment of circularity, decarbonisation, and sustainable development. Following similar calls for science in support of climate action, a transdisciplinary scientific agenda is needed to co-create the goals and scientific processes underpinning the transition pathways towards a circular, net-zero economy with representatives from policy, industry, and civil society. Here, it is argued that such integration of disciplines, methods, and communities can then lead to new and/or structurally enhanced quantitative systems models that better represent critical industrial value chains, consumption patterns, and mitigation technologies. This will be a crucial advancement towards assessing the material implications of, and the contribution of enhanced circularity performance to, mitigation pathways that are compatible with the temperature goals of the Paris Agreement and the transition to a circular economy.
A sectoral perspective can help the Global Stocktake (GST) to effectively achieve its objective to inform Parties' in enhancing subsequent NDCs and in enhancing international cooperation. Specifically, granular and actionable sectoral lessons, grounded in country-driven assessments, should be identified and elaborated. To be effective, conversations on sectoral transformations need to synthesise key challenges and opportunities identified in the national analyses and link them to international enablers; focus on systemic interdependencies, involve diverse actors, and be thoroughly prepared including by pre-scoping points of convergences and divergence across transformations. We specifically recommend that:
the co-facilitators of the Technical Dialogue use their (limited) mandate to facilitate an effective conversationon sectoral transformations e.g. by organising dedicated informal seminars in between formal negotiation sessions;
key systemic transformations necessary toachieve net-zero by mid-century should be spelled out and included in the final decision or political declaration of the GST; and
the political outcome of the GST should mandate follow-up processes at the regional level and encourage national-level conversations to translate the collective messages from GST into actionable and sector-specific policy recommendations.
Charting future emissions pathways is a central tenet of IPCC assessment reports (AR), yet it is unclear how underlying drivers (including around policy and technology) have influenced the evolution of emissions pathways. Here we compare scenarios in AR5 and AR6 and find that scenarios without specific climate policies enforced have shifted lower in each scenario generation, owing to falling low-carbon technology costs and reduced expectations for economic growth, reducing fossil-fuel shares in energy and industry. Mitigation pathways consistent with 1.5-2 °C have seen increasing electrification rates and higher shares of variable renewables in electricity in more recent scenario generations, implying reduced reliance on coal, nuclear, bioenergy and carbon capture and storage, reflecting changing costs. Despite the shrinking carbon budget due to insufficient recent climate action, mitigation costs have not increased given more optimistic low-carbon technology cost projections. Moving forward, scenario producers must continually recalibrate to keep abreast of technology, policy and societal developments to remain policy relevant.
