Earth-system science
Hothouse Earth
Definition
Hothouse Earth is a trajectory of the Earth System, proposed by Steffen and colleagues in 2018, in which human emissions and biosphere degradation push the planet toward a threshold — possibly around 2°C of warming — beyond which intrinsic biogeophysical feedbacks (such as permafrost carbon release and forest dieback) take over and drive further warming even if human emissions fall, leading to temperatures and sea levels far outside the Holocene range.
References
Supports definition and framing.
Overview
What it means
The paper's unsettling contribution is that meeting the Paris target might not exclude the risk: a cascade of tipping elements could lock in a pathway that human action can no longer steer. Its counterpoint is "Stabilized Earth" — deliberate stewardship of the whole Earth System to hold the planet in a habitable, interglacial-like state.
The hypothesis reframed mitigation from an optimisation problem into a systemic-risk problem.
How it is used
The concept is cited in tipping-points research, planetary-boundaries debates, and communications on why the 1. 5–2°C range carries non-linear risk.
Why it matters
It gave scientific form to the deepest climate fear — that warming could become self-sustaining — and sharpened the case for precautionary ambition.