Zero Emissions Commitment depends on warming level

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Abstract
When anthropogenic CO2 emissions cease, global temperature does not stabilise immediately. The resulting global temperature change, the Zero Emissions Commitment (ZEC), is central to carbon budget assessments and understanding reversibility of global warming, yet its dependence on prior warming levels remains unclear. Here we show, using zero-emission simulations with the UK Earth System Model (UKESM1.2) across global warming levels of 1.5–6K, that ZEC stays near-zero up to 2K, but becomes positive at higher warming levels, reaching 0.2–0.6K after ~150 years. This dependence indicates that stabilising or reversing warming becomes progressively more difficult as peak temperature rises. We identify the mechanism behind this behaviour: stronger warming from higher radiative disequilibrium and weakening carbon sinks, driven by saturated land carbon uptake and the reduced radiative impact of further CO2 drawdown. Higher peak warming therefore commits the planet to additional warming, limiting temperature-overshoot reversibility.

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