The Zero Emissions Commitment and climate stabilization

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?

Reply on RC2

“…Potential feedbacks such as thawing permafrost (MacDougall and Friedlingstein, 2015;MacDougall et al, 2015;Burke et al, 2017;Gasser et al, 2018;Lowe and Bernie, 2018;MacDougall, 2021), peat land area and carbon evolution (Müller and Joos, 2021), ocean circulation changes due to ice melt from Greenland or Antarctica (Bronselaer et al, 2018;Lago and England, 2019;Li et al, 2023), feedbacks between warming, nitrous oxide and methane (Stocker et al, 2013;Battaglia and Joos, 2018;IPCC, 2021), and, on longer timescales than considered in this study, feedbacks associated with the potential melting and disintegration of polar ice sheets are currently missing from most ESMs. These feedbacks would potentially reduce the emission budget over time and potentially make negative emissions over long time periods necessary to maintain a stable temperature (Palazzo Corner et al, 2023).…”

Dependence of Climate and Carbon Cycle Response in Net Zero Emission Pathways on the Magnitude and Duration of Positive and Negative Emission Pulses

“…The change in SAT after the cessation of positive emissions is known as zero emission commitment (ZEC; Cao & Caldeira, 2010;Jones et al, 2016;MacDougall et al, 2020). Previous studies indicate large uncertainty in the sign and magnitude of ZEC because of the differences in the representation of processes in models (MacDougall et al, 2020;Palazzo Corner et al, 2023). Borowiak et al (2024) show that the global mean SAT changes after immediate cessation of anthropogenic CO 2 emissions are larger than natural variability in most models.…”