A fully renewable system will probably occupy one hundred times more land than a fossil-fuel-powered one. In the case of the US, between 25 and 50 per cent of its territory, and in a cloudy, densely populated country such as the UK, all of the national territory might have to be covered in wind turbines, solar panels and biofuel crops to maintain current levels of energy production. While ongoing tinkering will improve renewable energy systems, they will never have the power densities of fossil fuels. It is land scarcity, rather than rare natural resources, that is the ultimate limit to economic growth: energy consumption must be cut.

[...] growth is not the result of a misguided cultural notion. Daly has missed the crucial insight that capitalism is a novel system, emerging only in the early modern era and pitting rival capitals against each other, such that profit-making is a structural imperative, not merely an option. Capital must complete its circuit through the commodity form greater than when it started or there will be a crisis. Profitability, not abstract measurements like GDP, is what matters. The latter’s late arrival in the history of capitalism hints that it is mere foam, while the struggle to maintain profitability goes on in the churning depths. Daly underestimates the difficulties of shackling capitalism so as to slow it down.

[...] Turning nature into ‘natural capital’ makes it easier to exploit; insisting on the non-fungibility of certain parts of nature by placing it beyond the economy’s reach is its surest defence.

Potemkin technocracies of this sort are a dead end for the environmentalist movement.

If no rapid transition away from coal, methane and petroleum is on the cards, then Artificial Geo-Engineering, a dangerous and once-ostracized technology, becomes increasingly likely. It already has the blessing of the Intergovernmental Panel on Climate Change. The probable consequences are dystopian sci-fi. ‘Solar radiation management’ will bleach the sky white, cause tens of thousands of deaths from aerosol pollution, gash the ozone layer and interrupt vital climatic systems like the monsoon and the Gulf Stream. Some of these risks are even acknowledged by its advocates; the world’s leading geo-engineer, David Keith, admits that the closest analogue to Artificial Geo-Engineering is nuclear weapons. It is appropriate that the natural habitat of this technology is in Alberta. In the 2000s, Keith was teaching at the University of Calgary, where both the institution and city have become inextricably linked to the tar-sands industry. To commodify his dangerous expertise he founded a firm, Carbon Engineering, which counts Bill Gates and tar-sands tycoon Murray Edwards as its billionaire patrons. Keith and his fellow thinkers were ostracized as dangerous quacks only a decade ago, but have become respectable through their embrace by the likes of Harvard (where Keith now teaches) and Oxford. Like nuclear waste, or the gargantuan tailings lakes of the tar-sands industry, Artificial Geo-Engineering will require millennia-long management. Should the ‘climate shield’ ever fail, if a war or some other disaster interrupts the aerosol cannons, then the world would rapidly overheat. Such an amplified geo-engineered summer could be as devastating to Earth life as a nuclear winter.

Roads and urban sprawl are leading causes of ecosystem fragmentation; a serious reduction in car use would free up huge amounts of space. In many US cities, for example, approximately 60 per cent of municipal land area is dedicated to car use in the form of roads, car parks and easements. Even if energy efficiency means that carbon pollution from oft-demonized cars is not as great as one might have expected, reducing their use is important for reasons of land scarcity. Air travel will need to be rationed, too. Although planes have doubled their fuel efficiency since 1978, flying is the fastest growing sector of transportation and, in the short term, the greenhouse-gas pollution emitted by planes has an effect 20 times greater than all the world’s cars, because of the sensitivity of the atmosphere’s upper reaches. Substitutes, such as solar-powered planes, will not be able to compete with kerosene-driven rivals for many decades. Here, there is no technological fix in sight.

The argument for half-earthing is predicated upon the clear and present danger of nuclear power, Artificial Geo-Engineering and fossil fuels. Capitalism can continue ‘business as usual’, but only at an ever greater cost to nature and the world’s poor. An effective and desirable half-Earth political economy must offer a better life for most people. If egalitarian eco-austerity is to work, resources must be rationed for the sake of fairness and efficacy; asceticism cannot be a mere ‘lifestyle choice’. An eco-austere life may mean fewer consumerist trifles and less work, but it would guarantee rights to shelter, health care, leisure and education. There is a vast literature on the uselessness of private consumption, beyond a certain point. A solution to global environmental crises requires the humbling of the global bourgeoisie, the richest several hundred million. The bourgeoisie cannot pretend that the society they have created can solve its own problems; a green veneer would signify little in a biologically impoverished world with a corporate-controlled climate. While this minority must adjust to relatively modest living standards, the very same ceiling to their consumption would imply a greatly raised floor for humanity’s majority. Most importantly, this egalitarian limit would allow the amelioration of the global climate system that everyone depends upon and the preservation of millions of other species.