Sustainability Language

Climate & Greenhouse Gas Emissions

Climate sensitivity

The amount of global surface warming expected from a doubling of atmospheric carbon dioxide, central to projecting future climate change.

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Definition

Climate sensitivity quantifies how strongly the global climate responds to rising greenhouse gas concentrations. Equilibrium climate sensitivity (ECS) is the long-term warming once the climate system fully adjusts to doubled CO2; the IPCC Sixth Assessment Report assesses a best estimate of 3°C, a likely range of 2.5–4°C, and a very likely range of 2–5°C.

References

Overview

What it means

It converts emissions into expected warming, so it anchors carbon budgets, mitigation targets and scenario projections.

How it is used

Estimated from climate models, the instrumental record and palaeoclimate evidence; the related transient climate response (TCR) measures warming at the moment of doubling under a gradual increase.

Why it matters

The remaining uncertainty — especially the upper tail — directly affects how quickly emissions must fall to meet Paris Agreement goals. - **Note:** Values above 5°C cannot yet be ruled out; the very-likely upper bound carries only medium confidence in IPCC terminology, and recent high-sensitivity studies (e. g. Hansen et al. 2023) remain contested.

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