As part of OnePlanet’s response to the National Emergency Briefing on Climate and Nature, this blog distils the key messages from Professor Tim Lenton’s contribution on climate tipping points. As a student of Professor Lenton at the University of Exeter, I was struck by how clearly the briefing reframed climate change, not as a gradual problem to be managed incrementally, but as a systemic risk shaped by thresholds, feedbacks and irreversibility. The reflections below draw directly on the briefing and highlight why tipping points demand urgent, coordinated action. 

Professor Tim Lenton OBE contributed to the National Emergency Briefing focussing on a concept that fundamentally challenges how we think about climate risk: Tipping Points. Not gradual change, not linear trends, but abrupt, self-propelling shifts that can radically alter the systems we depend on. 

As Tim explained, if we remain on a trajectory towards three or four degrees of global warming, the UK will not simply experience “more climate impacts”. We will be exposed to a high and growing risk of crossing climate tipping points that would make this country a profoundly different, and less habitable, place to live. 

What is a tipping point? 

A tipping point occurs when a system shifts from one stable state to another after crossing a critical threshold. A small additional pressure can trigger a large and often irreversible change, driven by internal feedbacks rather than continued external forcing. 

These dynamics are not unique to climate systems. They occur in economies, ecosystems and societies. What makes climate tipping points particularly dangerous is that they can unfold rapidly, are difficult to reverse, and can interact with one another. 

Once triggered, they do not require continued emissions to unfold, they become self-propelling. 

Cascading risks in a connected Earth system 

One of the most important messages from the briefing was that Earth’s systems are deeply interconnected. Tipping one component can increase the likelihood of tipping others, creating cascading risks. 

We are already seeing this play out. Accelerated Arctic warming is contributing to the melt of the Greenland ice sheet. Freshwater from this melt is weakening the Atlantic Ocean’s overturning circulation, a system that transports heat northwards and underpins the UK’s relatively mild climate. 

This circulation, known as the Atlantic Meridional Overturning Circulation (AMOC), has switched on and off repeatedly in Earth’s past. Climate models show that it can pass a tipping point under future warming scenarios, with severe consequences for the UK. 

A direct national risk 

If the AMOC were to collapse, the UK would not simply cool slightly. Climate models suggest winter temperatures in London could fall to minus 20°C, with several months of freezing conditions, while summers remain hotter than today due to higher global temperatures. The result would be extreme seasonality unlike anything in modern experience. 

The implications for food production, water security and infrastructure are profound. Domestic crop production could become unviable, water shortages in the southeast would intensify, and global food systems would face major disruption as viable growing regions shrink. 

This is why tipping points are not distant or abstract risks. They represent direct threats to national security, economic stability and social wellbeing. 

Risk rises with every fraction of a degree 

Crucially, tipping point risk increases sharply with both temperature and time. Every additional fraction of a degree above 1.5°C, and every year spent above it, raises the likelihood of crossing dangerous thresholds. 

This reframes climate action. It is no longer only about end-of-century targets, but about limiting peak warming and accelerating emissions reductions now. 

From peril to possibility: positive tipping points 

The briefing did not end with risk alone. Tim Lenton also highlighted the existence of positive tipping points, moments where clean technologies and behaviours become self-accelerating once certain thresholds are crossed. 

The UK power sector provides a clear example. Coal fell from 40% of electricity generation in 2012 to zero today, driven by policy signals, carbon pricing, and investment feedbacks that rapidly destabilised the fossil fuel status quo. 

Similar dynamics can be triggered in transport, heating and freight, but only if policy actively lowers the barriers between today’s fossil-fuelled systems and tomorrow’s clean alternatives. 

Mandates to phase out high-carbon technologies, combined with support for clean solutions, activate powerful amplifiers: falling costs, learning curves, infrastructure investment and shifting social norms. 

Why systems leadership matters 

Tipping points whether they are negative or positive do not respond well to fragmented action. They demand coordinated, system-level responses that align policy, investment and behaviour. 

This is where the role of Systems Connectors becomes critical. By aligning actors across siloes and scales, and by embedding long-term risk awareness into everyday decisions, leaders can help society avoid catastrophic thresholds while accelerating positive transitions. OnePlanet has built a training course for those who want to learn how to take a practical Systems Approach to complex problems. 

The message from the National Emergency Briefing is clear: incremental change is no longer enough. But neither is despair. The same dynamics that threaten stability can be harnessed to drive rapid, transformative progress, but only if we act decisively, together.