Centuries-long cooling after achieving net-zero greenhouse gas emissions

Reaching net-zero CO₂ emissions is widely expected to stop global warming, but the fate of temperatures long after the last tonne of greenhouse gas is emitted is less clear. Climate models do not agree on what happens in the centuries that follow. Some simulations suggest additional multi-century warming even after emissions cease, a behavior that complicates long-term planning and risk assessments.

Now, researchers have provided an analytical estimate of this post-cessation shift, called the zero emissions commitment (ZEC). ZEC describes the temperature change that unfolds long after CO₂ emissions stop, driven by how long CO₂ remains in the atmosphere and by the physical characteristics of Earth’s climate system.

The team links ZEC to three core climate metrics: the airborne fraction of cumulative CO₂ emissions, transient climate response, and equilibrium climate sensitivity. By constraining these parameters using historical CO₂ information, they derive a near-zero multi-century ZEC for idealized, perfect CO₂ cessation—implying that, under those assumptions, long-term additional warming would be minimal.

But net-zero policies are not the same as “turning off” fossil CO₂. Real strategies target the combined effect of multiple greenhouse gases and depend on carbon dioxide removal (CDR) to offset residual emissions. Because these policy pathways differ from an idealized stop to CO₂ alone, the long-term climate response may also differ.

To capture these policy-relevant effects, the authors introduce the net-zero emissions commitment (Net-ZEC). Net-ZEC quantifies temperature outcomes after net-zero GHG emissions, accounting for the aggregate cooling and warming contributions across gases and for how offsets are represented in practice.

Across scenarios and across multiple offset conventions, Net-ZEC implies a multi-century cooling that is not negligible: at least 0.6 °C following net-zero greenhouse gas emissions. In other words, even when targets are framed as “stopping warming,” the long-tail climate outcome could tilt toward cooling over subsequent centuries.

The result is particularly notable because it points to a directionally consistent response rather than a wide model spread. It also suggests that the climate system’s slow processes—ocean heat uptake and the persistence of greenhouse forcing—may amplify the effects of removal-based strategies.

For policymakers, the finding reframes net-zero as more than a stabilization goal. If the analysis holds across broader assumptions, net-zero could eventually produce sustained temperature reductions beyond what a simple “halt warming” narrative implies.