ネットゼロ後も温暖化が続くリスクを考慮した排出計画が必要(Emissions plans must consider risk of global warming continuing after net zero)

2023-11-14 インペリアル・カレッジ・ロンドン(ICL)

＜関連情報＞

• https://www.imperial.ac.uk/news/249475/emissions-plans-must-consider-risk-global/
• https://www.frontiersin.org/journals/science/articles/10.3389/fsci.2023.1170744/full

ゼロ・エミッションの約束と気候安定化 The Zero Emissions Commitment and climate stabilization

Sofia Palazzo Corner,Martin Siegert,Paulo Ceppi,Baylor Fox-Kemper,Thomas L. Frölicher,Angela Gallego-Sala,Joanna Haigh,Gabriele C. Hegerl,Chris D. Jones,Reto Knutti,Charles D. Koven,Andrew H. MacDougall,Malte Meinshausen,Zebedee Nicholls,Jean Baptiste Sallée,Benjamin M. Sanderson,Roland Séférian,Merritt Turetsky,Richard G. Williams,Sönke Zaehle,Joeri Rogelj
Frontiers  Publised:14 Nov 2023
DOI:https://doi.org/10.3389/fsci.2023.1170744

Abstract

How do we halt global warming? Reaching net zero carbon dioxide (CO₂) emissions is understood to be a key milestone on the path to a safer planet. But how confident are we that when we stop carbon emissions, we also stop global warming? The Zero Emissions Commitment (ZEC) quantifies how much warming or cooling we can expect following a complete cessation of anthropogenic CO₂ emissions. To date, the best estimate by the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report is zero change, though with substantial uncertainty. In this article, we present an overview of the changes expected in major Earth system processes after net zero and their potential impact on global surface temperature, providing an outlook toward building a more confident assessment of ZEC in the decades to come. We propose a structure to guide research into ZEC and associated changes in the climate, separating the impacts expected over decades, centuries, and millennia. As we look ahead at the century billed to mark the end of net anthropogenic CO₂ emissions, we ask: what is the prospect of a stable climate in a post-net zero world?

Key points

• Substantial uncertainty remains in both the sign and magnitude of the Zero Emissions Commitment (ZEC): the expected additional change in global surface temperature once we achieve net zero CO₂ emissions.
• Uncertainty in ZEC has implications for the remaining carbon budget to stay below the temperature limits of the Paris Agreement: a positive ZEC reduces the remaining budget; a negative ZEC opens the door for more ambitious targets or more time to reach net zero.
• The prospect of additional warming after net zero is both plausible and significant, with a chance that ZEC could exceed 15% of total global warming.
• While a ZEC of 0 means no further change to global surface temperatures, other aspects of the Earth system, such as sea levels, will continue to change in a net zero world due to warming realized previously. These changes should be factored into the assessment of safe warming limits and adaptation plans.
• Current climate models do not adequately represent the full scope of complex and interdependent Earth system processes that determine ZEC. We present a structure for quantifying uncertainty in ZEC and propose a roadmap for future research into quantifying ZEC and reducing its uncertainties.