Climate
Tipping Points
Some parts of the Earth's climate system can reach critical thresholds where small additional changes trigger large, self-sustaining and potentially irreversible transformations.
- Tipping elements
- 16+
- At risk near
- 1.5 °C
- Nature
- Nonlinear
Identified in Earth's climate system
Several thresholds may be crossed
Feedback-driven, often irreversible
What is a climate tipping point?
A tipping point is a threshold in a part of the Earth system beyond which a small nudge causes a large, self-sustaining and often irreversible change. Gradual warming can produce abrupt outcomes because the underlying system is nonlinear — dominated by feedback loops that amplify their own change.
Nonlinear response
Most of us intuitively expect linear change — twice the forcing, twice the response. Earth systems don't always behave that way. A small additional warming can push a system past a hidden threshold where the response becomes disproportionate.
Self-reinforcing feedbacks
Once past the threshold, feedback loops — melting ice exposing dark ocean, thawing permafrost releasing methane, dying forests emitting stored carbon — sustain and amplify the change without further external forcing.
Effectively irreversible
On human timescales, some transitions cannot be undone. An ice sheet that collapses will not simply refreeze if temperatures fall again. A rainforest that becomes savanna may not return to forest for millennia.
A simple picture of a threshold
Imagine a ball resting in a valley. Push it gently and it rolls back. Push it hard enough to cross the ridge and it accelerates down the other side into a new, deeper valley. Returning to the original state now requires far more effort than the original nudge — and sometimes it is simply not possible.
- Stable state: small perturbations decay away.
- Approaching threshold: recovery slows, variability grows.
- Past threshold: the system reorganises into a new state.
Watch Professor Tim Lenton explain
Professor Tim Lenton, Director of the Global Systems Institute at the University of Exeter, has been one of the world's leading researchers on climate tipping points for nearly two decades. His work has fundamentally changed our understanding of how the Earth system responds to warming — and why avoiding critical thresholds is one of humanity's greatest scientific and societal challenges.
Lenton's 2008 paper in PNAS introduced the modern concept of "tipping elements" in the Earth's climate system. His 2019 Nature commentary, Climate tipping points — too risky to bet against, warned that several may already be nearer than assumed. He co-led the 2023 and 2025 Global Tipping Points Reports — the most comprehensive synthesis to date.
Global tipping elements
Select a region to explore the science behind each major Earth-system tipping element — what it is, how close it may be, and what its transition could mean for the wider climate system.
Tipping element
Greenland Ice Sheet
- Estimated threshold
- ≈ 1.5 °C global warming (best estimate)
- Explanation
- Sustained surface melt lowers the ice sheet's surface into warmer air, accelerating further melt in a self-reinforcing loop.
- Current evidence
- Greenland has lost mass every year since 1998; melt-elevation feedback is well documented in ice-core and altimetry data.
- Possible consequences
- Complete loss would raise global sea level by ~7 metres over centuries to millennia.
Threshold estimates draw on Armstrong McKay et al. (Science, 2022) and the Global Tipping Points Report (2023). Uncertainties are large; values are best current estimates, not fixed dates.
Cascading tipping points
Tipping elements are not independent. Crossing one threshold can raise the probability of crossing others through shared feedbacks — a cascade in which change in one system propagates through the wider Earth system.
Step 1
Arctic ice loss
Sea ice and Greenland melt expose darker surfaces.
Step 2
Lower albedo
Dark ocean and land absorb more solar energy.
Step 3
More absorbed energy
The Arctic warms three to four times faster than the global average.
Step 4
Permafrost thaw
Frozen soils release methane and CO₂ that had been locked away for millennia.
Step 5
Further global warming
Additional greenhouse gases amplify warming everywhere.
Step 6
Amazon stress
Warmer, drier conditions weaken the forest's water recycling.
Step 7
Carbon release from forests
Dieback and fire flip biosphere sinks toward net carbon sources.
Step 8
More warming, greater risk of cascades
Higher temperatures raise the probability of other elements crossing thresholds.
Every arrow above represents a physical feedback in the Earth system, not a forecast. The purpose of the diagram is to show how transitions could reinforce one another — and why even modest additional warming carries systemic risk.
Why Earth's energy imbalance matters
The Earth continues to accumulate excess heat because more solar energy is entering the climate system than is leaving it. This persistent energy imbalance is the fundamental driver behind approaching tipping thresholds.
The imbalance drives the risk
The longer Earth's energy imbalance persists, the more heat accumulates in the ocean, cryosphere and land — and the closer key tipping elements come to their thresholds. Recent measurements suggest the imbalance is now roughly 1.0 W/m² and has grown over the past two decades.
Every extra joule stored in the climate system raises the probability that some changes become self-sustaining and irreversible on human timescales.
Two complementary responses
Reducing risk requires rapid and sustained cuts in greenhouse gas emissions — addressing the cause of the imbalance. Alongside this essential work, research communities are exploring approaches that could help reduce the amount of solar energy absorbed at the surface.
MEER's work on brightening surfaces is one example of research examining how increasing reflectivity might complement — never replace — emissions reductions.
Key scientific papers
A curated selection of the most influential publications shaping our understanding of climate tipping points. Links go to the original publisher or report.
PNAS · 2008
Tipping elements in the Earth's climate system
Lenton, Held, Kriegler, Hall, Lucht, Rahmstorf, Schellnhuber
Why it matters. The paper that introduced the concept of tipping elements and mapped the major candidates. It became the foundation of a new field of Earth-system science.
Nature (Comment) · 2019
Climate tipping points — too risky to bet against
Lenton, Rockström, Gaffney, Rahmstorf, Richardson, Steffen, Schellnhuber
Why it matters. A widely-cited call showing that several tipping elements appear to be closer than previously thought, and that cascading transitions cannot be ruled out.
Nature Climate Change · 2011
Early warning of climate tipping points
Lenton
Why it matters. Introduced statistical indicators — such as slowing recovery from perturbations — that may signal a system approaching a tipping point.
Science · 2022
Exceeding 1.5 °C global warming could trigger multiple climate tipping points
Armstrong McKay et al.
Why it matters. The most comprehensive re-assessment of tipping-element thresholds since 2008, and the source of many of the temperature estimates now widely cited.
University of Exeter / Systems Change Lab · 2023
Global Tipping Points Report 2023
Lenton et al.
Why it matters. A synthesis of over 200 authors on the state of tipping-point science, negative tipping points (positive social change) and policy implications.
University of Exeter · 2025
Global Tipping Points Report 2025
Lenton et al.
Why it matters. Updated assessment of Earth-system and positive social tipping points, produced ahead of COP30, incorporating the latest observational evidence.
Frequently asked questions
Common questions from teachers, students, journalists and the general public — answered with reference to current science.
Related science
These pages form a continuous educational journey through the science of climate change and surface cooling.
Planetary Boundaries
The safe operating space for humanity.
Earth's Energy Balance
The underlying imbalance driving warming.
The Greenhouse Effect
The physics behind climate change.
Understanding Albedo
How reflectivity shapes Earth's temperature.
Surface Reflection
Practical approaches to increasing reflectivity.
Radiative Cooling
How materials cool by emitting heat to space.
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Related glossary terms
- Climate Resilience→
A community's ability to withstand, recover from and continue functioning through climate stress.
- Adaptive Mitigation→
Interventions that adapt to warming today and reduce warming tomorrow.
- UHI→
The phenomenon where cities are noticeably hotter than the surrounding countryside.
- Passive Cooling→
Cooling a surface, building or space using materials and design instead of electricity.
- Solar Reflectance→
The fraction of incoming solar energy a surface reflects across the sun's spectrum.
- Reflective Cooling→
Cooling by bouncing sunlight away from a surface before it can be absorbed as heat.