There is a new call to extend conservation frontiers as an ultimate attempt to save global biodiversity. Under the slogan ‘nature needs half’ (Nature Needs Half, 2016) and spearheaded by leading conservation scientists, including Wilson (Reference Wilson2016), Noss et al. (Reference Noss, Dobson, Baldwin, Beier, Davis and Dellasala2012) and Wuerthner et al. (Reference Wuerthner, Crist and Butler2015), a vision has been formulated to turn half of the Earth into a series of interconnected protected areas. This radical plan for conservation seeks to expand and strengthen the world's current network of protected areas to create a patchwork grid of reserves encompassing at least half the world's surface and hence ‘about 85%’ of remaining biodiversity (Wilson, Reference Wilson2016, p. 186). We wish to open up debate about this idea. While it could be interpreted as simply a rhetorical challenge to provoke greater conservation effort, it is proposed by senior scientific figures and is being widely discussed and supported, including for example at the recent World Conservation Congress, where E.O. Wilson promoted the idea. Critical reflection about this proposal is thus important.

The plan proposed is staggering in scale: protected areas, according to the IUCN, currently incorporate c. 15.4% of the Earth's terrestrial areas and 3.4% of its oceans. They would thus need to more than triple in extent on land and by more than ten-fold in the oceans. Not only would this include the Earth's currently still relatively intact ecosystems and natural habitats, it would also necessarily entail an active programme of restoration and rewilding to return larger areas to a more pristine pre-human baseline (Donlan et al., Reference Donlan, Greene, Berger, Bock, Bock and Burney2005; Noss et al., Reference Noss, Dobson, Baldwin, Beier, Davis and Dellasala2012; Wilson, Reference Wilson2016). E.O. Wilson is arguably most explicit in his recent book Half-Earth: Our Planet's Fight for Life, stating that ‘only by setting aside half the planet in reserve, or more, can we save the living part of the environment and achieve the stabilization required for our own survival’ (Wilson, Reference Wilson2016, p. 3). Other conservationists agree that such a goal is the ‘only defensible target’ from a ‘strictly scientific point of view’ to allow for a sustainable future (Wuerthner et al., Reference Wuerthner, Crist and Butler2015, p. 18).

These proposals seem to be driven by the credo desperate times call for desperate measures. We agree with E.O. Wilson and other conservationists that biodiversity is being lost at an unprecedented rate as a result of human activity, and that there is an urgent need for action to address this. Desperate times, however, demand careful decisions. We argue that the Half-Earth idea does not get to the root of the problems it seeks to address, and would have serious negative impacts both on people (particularly poor people) and probably also on biodiversity. If the current environmental crisis calls for radical thinking there are different and, we believe, better possibilities that should be taken seriously by conservationists and others.

Firstly, the most basic problem with the Half-Earth proposal is that it ignores the powerful engines of resource extraction and consumption that are the main drivers of biodiversity loss globally (Wells & McShane, Reference Wells and McShane2004; Vandermeer & Perfecto, Reference Vandermeer and Perfecto2005; CBD, 2014). A plan for the future of biodiversity that does nothing to address the overconsumption of resources in industrialized and emerging economies makes unrealistic assumptions about the extent to which nature's half can be managed in isolation. Even if one could separate humanity from nature on half of the Earth the activities of the human half (especially fossil fuel use) will need to be addressed fully to ensure the survival of biodiversity. The way the human half is managed will continue to have major consequences not just for biodiversity in nature's half, but across the entire planet.

Secondly, the nature needs half plan would have a significant social impact. What sort of protected area is entailed in this vision? The more restrictive, which place most limits on human activity, have often created significant challenges of physical and economic displacement (West & Brockington, Reference West and Brockington2006; Oldekop et al., Reference Oldekop, Holmes, Harris and Evans2016). It is therefore inconceivable that strict protected areas (IUCN Category I or II) could expand to 50% of the Earth without considerable social impacts. Many strict protected areas are already embroiled in myriad social conflicts (Duffy, Reference Duffy2014) and the nature needs half proposal is therefore likely to fuel even more conflict and violence. Perhaps the vision could become more palatable if the half is achieved primarily through the expansion of other kinds of protected area categories that explicitly link with social justice, sustainable use and related concerns, for example through indigenous peoples’ and community conserved territories and areas. This point is explicitly left open by Nature Needs Half (2016), which emphasizes the importance of all categories of protected areas, not just strict reserves. An increase of the amount of land in which people can live and work, but which is off limits to resource extraction and drastic land use change, could be progressive. But it is doubtful that this is the vision that excites the Half-Earth movement.

Thirdly, the question of who controls protected areas (who creates them and dictates what may be done there) raises another major concern with the proposal. Where will the new protected areas be located? How will the burden of creating more protected areas be shared globally? Many current conservation efforts focus on the biodiversity-rich tropics, and hence on low-income countries with major problems of poverty, and a lack of infrastructure, industry and employment. If Half-Earth advocates take the same focus (and as biodiversity scientists it would be strange if they did not), the removal of land from non-conservation use will impact most on those communities that are poorest and least responsible for our current environmental predicament. These problems are predictable, but Half-Earth discussions hardly mention them, nor suggest how they might be addressed.

A fourth problem is that Half-Earth advocacy ignores decades of thinking about building relationships between protected areas and human societies. Since the World Parks Congress in Bali in 1973 it has been shown that protected areas work best if they are supported by local people. A recent study that examined 165 protected areas globally found that protected areas ‘that explicitly integrated local people as stakeholders tended to be more effective at achieving joint biological conservation and socioeconomic development outcomes’ (Oldekop et al., Reference Oldekop, Holmes, Harris and Evans2016, p. 133). Studies of forestry management have reached the same conclusions (Persha et al., Reference Persha, Agrawal and Chhatre2011). Yet advocates of dramatic spatial expansion of protected areas say little about how these areas can be sustained socially and politically (Wuerthner et al., Reference Wuerthner, Crist and Butler2015; Wilson, Reference Wilson2016).

A fifth and final problem is that the Half-Earth idea offers no agenda for the biodiversity in a human half of Earth. What will this enclave of industrial and urban humanity be like? Will there be any non-human nature at all? Will this half be restricted merely to glimpsing the Earth's saved biodiversity virtually, via hidden micro-cameras, as Wilson (Reference Wilson2016, p. 192) recommends (cf. Adams, Reference Adams2010)? Will only the managers of nature's half be allowed behind the curtain? This, we fear, would be a recipe for a dystopian world, where the vast majority of humanity is prevented from experiencing the very biodiversity many of them will have been displaced to save.

The Half-Earth proposal, in short, is infeasible, and will have dangerous and counter-effective consequences if implemented. The only logical conclusion of the Half-Earth proposal would be injustice on a large scale without effectively addressing the actual roots of the ecological crisis.

We can do better than this. If we have license to think freely and radically about stopping biodiversity loss, there are other more promising prospects that build on sound research and are already being developed and tested. Firstly, conservation strategies need to focus directly on drivers of biodiversity loss by addressing how the global economy works, especially with respect to resource extraction and consumption, to decrease pressure on nature (Wells & McShane, Reference Wells and McShane2004; Vandermeer & Perfecto, Reference Vandermeer and Perfecto2005). We need to recognize that it is ultimately economic growth itself that is the root cause of biodiversity loss (Fletcher, Reference Fletcher2012), and hence to take the possibilities of degrowth economics seriously (D'Alisa et al., Reference D'Alisa, Demaria and Kallis2010; Kallis, Reference Kallis2015). Consequently, we cannot rely on free markets, economic valuation, and corporate social responsibility to fund our goals, as advocated both by E.O. Wilson and, curiously, a group of so-called Anthropocene conservationists (Kareiva et al., Reference Kareiva, Marvier and Lalasz2012) to which E.O. Wilson otherwise sees his proposal as starkly opposed. Instead, we must promote concerted and widespread programmes of regulation and redistribution to equalize use and control of our remaining natural resources. This proposal is sometimes mistaken for a return to failed socialist and communist experiments, with coercive resource allocation determined by experts and bureaucrats. But this is not the case. Expert and bureaucratic resource allocation is more characteristic of the Half-Earth vision. Our suggestion is that natural resources and ecosystems become global public goods that are at the same time governed in local or bioregional economies focused on socio-ecological justice (Scott Cato, Reference Scott Cato2013; Martin et al., Reference Martin, Akol and Gross-Camp2015).

Secondly, conservation strategies must support measures that address inequality. Inequality harms the environment as well as health and human well-being (Holland et al., Reference Holland, Peterson and Gonzalez2009; Wilkinson & Pickett, Reference Wilkinson and Pickett2010; Hicks et al., Reference Hicks, Levine, Agrawal, Basurto, Breslow and Carothers2016). A half-conserved Earth that leaves the majority of people in chronic poverty would not only be unjust, it also could not be sustained. Whereas Half-Earth proponents focus mostly on the effects of aggregate population increases in poor areas, we believe that a focus on the effects of the relative impacts of consumption and resource use is not only more realistic, it is also more just. It means focusing on those segments of the global population that consume the most, and who encourage rather than prevent further aggregate consumption and resource use. This latter focus is crucial: instead of encouraging further aggregate consumption and resource use, longer-term equality can only be achieved within a broader political–economic framework focused on ensuring that all human beings can live prosperous lives within local and global ecological boundaries. In short, cutting inequality in half would do more for conservation than attempting to protect half of the Earth from humanity (Mikkelson et al., Reference Mikkelson, Gonzalez and Peterson2007; Holland et al., Reference Holland, Peterson and Gonzalez2009). Pursuing economic growth alone would undermine this goal and hence accomplishing effective conservation would require dramatically redistributing existing wealth (Kallis, Reference Kallis2015).

These measures are intended to bring about a radical shift from an economic focus on the magnitude of growth to the socio-ecological quality of life. They are drastic proposals, with far-reaching consequences. But that is precisely why we propose them. They are, we argue, a far more realistic and fair way of sustaining biodiversity and people than the idea of a Half-Earth. They focus on tackling the root causes of environmental degradation and will be far less harmful—even beneficial—for people. To the extent that such a programme of radical conservation would bring unwelcome change, it would be to those who have historically contributed and continue to contribute most to the ecological crisis.

It is crucial, therefore, to turn away from attempts to increase polarization between people and nature, and to rethink and nurture already existing and freshly emerging alternative conservation movements that are more democratic, equitable and humane. These movements see people as part of nature rather than separate from it, and seek healthy environments across the whole Earth. They are not content to leave half the Earth behind.