Tipping points are a huge motivating factor for many climate activists. “Cutting our emissions in half in 10 years only gives us a 50% chance of staying below 1.5C, and the risk of setting off irreversible chain reactions beyond human control,” Greta Thunberg told the 2019 UN Climate Action Summit in her famous address. “Fifty per cent may be acceptable to you. But those numbers do not include tipping points, most feedback loops, additional warming hidden by toxic air pollution or the aspects of equity and climate justice. A 50% risk is simply not acceptable to us.”

Climate tipping points are where small environmental changes – such as in the amount of Arctic sea ice or the size of the Amazonian rainforest – create knock-on environmental effects that “cascade into global consequences”, explains Tim Lenton in Positive Tipping Points. Professor of Climate Change and Earth System Science at the University of Exeter, Lenton has been at the forefront of global efforts to identify climate tipping points for decades. This new book offers his perspective on tipping points, and a snapshot of the current understanding about the risk of hitting different escalations in environmental change.

For Lenton, though, tipping points are about more than strictly environmental systems. The greater part of the book deals with tipping points technical, social and economic: “Damaging tipping points in climates, civilisation and our life-support systems are the biggest risk we face, but positive tipping points in society, technology and our relationship with nature can be our salvation.”

We hear about how social change has forced tipping points, be they moralistic anti-slavery campaigns, the organised protest of suffragettes – Lenton’s relative Lilian Lenton was a prominent suffragette – or cooperative national alliances to handle ozone levels. The historical analysis is fairly light – the role of enslaved people themselves in anti-slavery efforts, for example, is not really considered – but a range of different styles of network are covered. Lenton even touches on the role of individual billionaires seeking to use their capital and influence to tip norms – though he does recognise that “we may rightly smart at the idea that the elite who have profited most from the status quo are going to voluntarily tip us out of it”.

Technological changes are also given close attention. The introduction of the car, for example, Lenton characterises as a socio-technical tipping point that came from a tipping cascade of economies of scale in production, technological reinforcement (adoption of networks of fuel stations) and “learning-by-doing” among users and manufacturers. Lenton similarly dissects the emerging tipping point of electric vehicle and PV panel adoption. He highlights how such swings have been driven by multi-country public investment in technological development, subsidies, feed-in-tariff design and researcher training. He provides a refreshingly un-technocratic reading at each turn: “Social and technological tipping points differ from climate and ecological ones in a crucial way: the changes behind them are usually driven by human intent… A small event may occasionally precipitate a big change in worldview.”

The policy menu that Lenton ultimately espouses is one where government, the market and activism “work together towards a common goal… [activating] numerous reinforcing feedback loops that can accelerate change”. Despite many allusions to having politics that are likely shared by many tipping-point-fearing climate activists, including a scepticism of growth and capital allocation, the system Lenton presents is largely not analysed against these areas of thought. For that reason, the “positive tipping points” he chases are slightly untethered from a clear landing spot. However, there remains a lot to get into in this lively and impassioned book. It’s great to see cross-disciplinary, James Lovelock-infused environmental systems thinking alive and well.

Positive Tipping Points:How to Fix the Climate Crisis by Tim Lenton. Oxford University Press, 2025. ISBN: 9780198875789

Martha Dillon is a freelance writer specialising in the climate crisis and its links to cities, technology and housing. She writes regularly for The Architectural Review, Architects’ Journal and other publications.