Lambin begins with a quick glance over some of the unprecedentedly rapid changes that have occurred, such as global warming, the Aral Sea, and mass extinctions. And he surveys different ways of looking at the relationship of humanity to its environment: early scientific ideas, analogies with biology, modern economics, systems theory, coevolution and complex systems, and sustainability.
There are many different models for the mechanisms of environmental degradation. Here Lambin considers concepts of capital, carrying factors, the environmental Kuznets curve (the idea that environmental impact peaks at intermediate incomes), diminishing returns, the tragedy of the commons, stability and resilience, and vulnerability. And the causes that drive these include resource scarcity, loss of resilience, expansion of economic activity, demographic shifts, unintended policy consequences, interconnectedness of syndromes, interplay between different levels, globalization and consumption.
As case studies in choices between degradation and restoration, Lambin considers the collapse of Mayan Civilization and the 19th century reforestation of Europe. And as an illustration of how difficult understanding the mechanisms of environmental change can be, he looks at desertification in the Sahel.
Lambin concludes with an outline of the different schools of thought on solutions, which he labels "fewer mouths to feed", "bigger pie", "return to the candle", "smaller portions", "equal shares", "tend the garden" and "privatize the pie". Some of the approaches that will play a role include ecoefficiency, decarbonization, dematerialization, pollution reduction, and restoration and repair. And these will involve institutions, markets, international agreements, and cultural changes.
Covering such a broad range of material in so limited a space means staying at an extremely high level of generality. And this sometimes leaves gaps: it is suggested but not argued or explained, for example, that moving some taxes to resources and pollution instead of labour and capital would increase employment. The case studies do offer a bit more depth, however, and the sweeping view of The Middle Path may bring readers into touch with new ideas or connections.