Overall I agree with its program but it has some major shortcomings. The book is uneven and each chapter warrants attention in turn:

Chapter 1 makes an argument for 'ecological humility' on the grounds that we don't understand ecology nearly as well as we like to think. From this, two conclusions: 1) geoengineering (e.g. solar radiation management) is extremely dangerous and 2) the neoliberal argument that the economy is too mysterious to control is subverted by the higher-order mysteriousness of life. If we have to regulate one, let it be the economy. 'Ecological humility' is set against Marxist prometheanism and right-wing Malthusianism, and attention is drawn to holistic concerns of mass extinction and zoonotic disease alongside climate change. The rejection of Malthusianism isn't very clear and probably should have been developed more.

Chapter 2 takes aim at 'demi-utopias' proposed for managing the environmental crisis with minimal social change (e.g. carbon capture, nuclear energy, colonial conservation). Ultimately, the argument is made for socialist implementation of massive rewilding, veganism, energy quotas and solar/wind power. Lots of people have attacked them over stuff they wrote here but IMO none of it is as essential or interesting as the material in Ch 1 and 3

Chapter 3 shifts to a discussion of economic planning with Otto Neurath, Leonid Kantorovich, and Cybersyn as primary touchstones. Being a math nerd, I wish they had delved deeper in to the specifics, but the main takeaways are: 1) there exist mathematical techniques for optimizing supply chains and production without the need for monetary price signals, 2) advances in down-scaling and up-scaling complex meteorological models used for studying climate change could provide a framework for multi-scale democratic planning that preserves regional autonomy.Chapter 4 is a fictional short story riffing on William Morris' News From Nowhere in which a young man in 2023 awakens in an eco-socialist 2047. It's true leftist literature: tedious and didactic. There's an element of 'doth protest too much' in that all the characters seem overly happy about their intensely energy-restricted lives spent tilling bean fields and sharing washing machines; the only character to complain about not eating meat is dismissed as a grouchy crank. I share the authors belief that the grotesque energy consumption of a modern American upper-middle-class consumer is not necessary for a 'good life', but their presentation of socialism feels like being toured around North Korea or something. Despite citing Ursula K. LeGuin as an inspiration, they missed the part in The Dispossessed where she honestly portrayed the complaints of communal life .In general, I found Chapters 1 and 3 the most rewarding and original. The ecological humility argument in Ch. 1 is a strong case against certain strains of optimistic prometheanism, and I love that it also provides a basis for rejecting neoliberalism. I wish Chapter 3 was its own book, because it was provocative and inspiring and made me want to study in-natura economic modeling.The weakness of the book comes through in Chapters 2 and 4, which oddly work at cross-purposes with 1 and 3. The thrust of 1 and 3 is something like: "we're up against hard ecological limits and need a non-Malthusian way to constrain human economic activity (ch 1) and we have powerful tools for managing human activity by democratically choosing between many different planning scenarios at different scales (ch 3)". There's an open-endedness here where the planning tools enable optimizing for many different concerns. But then Chapters 2 and 4 veer off by promoting a highly specific (and unpopular!) program. In particular, the authors have taken a lot of criticism about their anti-nuclear stance (something I'm currently agnostic about) and their commitment to specifically ethical veganism (something I'm loosely sympathetic to but do not share). These dogmas muddle the really interesting contributions in HES.