Imagine a world where 50% of natural habitat was protected for nature. No deforestation, no overexploitation, no pollution. Sound good? Well, according to a recent study, conserving 50% of the planet for nature could be a feasible solution to the biodiversity crisis of the Anthropocene 2. 50% protection by 2050 entails massive benefits for the environment; mitigation of climate change, conservation of global heritage and a halt to species extinction2,3,5.

Decisions over how much land to conserve have often erred on the side of what is palatable to policy-makers and society2,3,4. Recall the 10-12% terrestrial protection goal included by the United Nations in the Brundtland Report of 19883. Subsequently the 17% terrestrial and inland water, 10% marine protected areas by 2020 set by the Convention on Biological Diversity in Aichi Target 11 (Japan, 2012)2.

Whilst the importance of biodiversity conservation is clearly recognised by policy-makers, protection goals to date consistently fall short. Protection of 50% of natural habitat by 2050 is an ambitious but realistic conservation target. Set as a midpoint between the region-dependent 25-75% of protected land necessary to stabilise the environment4. This estimate is based on empirical data and expert analyses.

The Design

The Convention on Biological Diversity updated its definition of a protected area in the mid-2000s: “A specifically delineated area designated and managed to achieve the conservation of nature and the maintenance of associated ecosystem services and cultural values through legal or other effective means.” A consensus of 1500 scientists suggests that protected areas should fulfil a remit of four main goals3:

  1. All native ecosystem types must be represented.
  2. Natural patterns of abundance and distribution must be maintained for native species.
  3. To maintain ecological processes, e.g. carbon storage.
  4. To maintain short and long-term resilience to environmental change.

By dividing the planet into 846 ecoregions within 14 biomes, the level of current protected areas can be assessed into four categories: Half Protected (HP), Nature Could Reach Half (NCRH), Nature Could Recover (NCR) and Nature Imperilled (NI)2. Figure 1 shows how these four categories are represented across the world. Ecoregions are placed into a category depending on the following criteria:

  • HP: at least 50% of any given ecoregion is currently formally protected.
  • NCRH: less than half of the ecoregion is currently protected but that the sum of protected and un-protected natural habitat remaining is at least 50%.
  • NCR: the sum of protected and un-protected natural habitat is less than 50% but more than 20%.
  • NI: where the sum of natural remaining habitat is less than or equal to 20%.

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Figure 1: World map of ecoregions classified by protection status. Half Protected (dark green), Nature Could Reach Half (light green), Nature Could Recover (orange), Nature Imperilled (red) (ECOREGIONS 2017 ©Resolve).

See the planet divided into biomes and ecoregions here:

Informing Conservation Strategy

Comprising 37% of ecoregions, NCRH represents all 14 biomes. Amongst the tropical and sub-tropical moist broadleaf forest ecoregions, more than 50% are currently half protected or NCRH2. These ecoregions cover around 14% of the Earth’s land and support at least 50% of all species2. NCRH provides the greatest opportunity for conservation, proving very attractive to governments and potential donors.

Tropical and sub-tropical grasslands, savannahs and shrubland, Mediterranean forest, woodland and scrub, and tropical moist and dry forests comprise higher endemism and beta diversity level than any other biome2. They are also the most vulnerable and present the biggest challenge to governments and conservationists. Figure 2 outlines the proportion of ecoregions in each category.

Nature Imperilled ecoregions often represent significant biodiversity. The tropical and sub-tropical dry broadleaf forest is the most endangered biome, with 26 out of 56 ecoregions classified as NI and only 2 half-protected2. Effort in these areas may seem less attractive to governments, they must be careful not to write off NI regions as ‘beyond hope’.

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Figure 2: Proportion of ecoregions classified by protection status out of total 846 ecoregions. Half Protected (HP), Nature Could Reach Half (NCRH), Nature Could Recover (NCR) and Nature Imperilled (NI).

Is it possible?

Achieving a ‘Half Earth’ is a mammoth task. So far, only 11% of ecoregions have published plans to address all four of the conservation targets outlined above in the Boreal Scientist’s Letter2. The IUCN reports that protected areas currently make up around 15.4% of terrestrial land and 2.18% of Oceans worldwide1, 4.

Nature Needs Half (NNH) has come under scrutiny for failing to address the social impact, such as community displacement and redistribution of resources1. Neither does it include plans to address the fundamental processes driving the degradation of natural habitat, such as industrialisation and intensive agriculture – How will we make the ‘other 50%’ sustainable?1. For more information on NNH:

However, there are already examples of countries where NNH is thriving. In Namibia 47% of the country is made up of ‘communal conservancies’ where local people protect their environment and generate sustainable income; Nepal has seen a rise in tiger and rhino numbers as a result of community forest management and Bhutan, which ranks amongst the lowest GDP per capita, protects 51% of its’ land in national parks and forest corridors2.

In North America too: Haida Gwaii, British Columbia, half for nature is culturally important to the indigenous population3. Whilst Massachusetts, Vermont and Quebec are making great strides by re-foresting marginal land, an innovative solution to protecting nature whilst retaining valuable agricultural resources4.

A Goal:

Protecting half of the Earth is a precautionary value, dependent on connected areas to maintain gene flow within species and allow distributional shift in response to climate change3, 4. It is estimated that saving 50% of natural habitats would stabilise around 80% of species5. Perhaps 50% for nature represents a moral obligation too, for humankind’s ingrained ‘pro-growth’ attitude has undoubtedly contributed to the state of the Earth today5.

Community schemes and redistribution of natural resources hold great promise for achieving a Half Earth. Education is key – innovative schemes that engage society to enjoy and value nature such as ‘America’s Great Outdoors Initiative’4 and those lead by the National Trust in the UK.

Half for nature provides an opportunity: a new way of thinking for scientists, policy-makers and the public alike. Ultimately, the idea that Nature Needs Half gives humans the opportunity to preserve and restore the Natural World – enriching our lives and feeding our souls.

An article by Alicia Thew

Link to Dinerstein et al. (2017):


  1. Büscher, B., Feltcher, R., Brockington, D., Sandbrook, C., Adams, W., Campbell, L., Corson, C. et al. (2017). Half-Earth or Whole Earth? Radical ideas for conservation, and their implications. Oryx 51:407-410.
  2. Dinerstein, E., Olson, D., Joshi, A., Vynne, C., Burgess, N.D., Wikramanayake, E., Hahn, N. et al. (2017). An ecoregion-based approach to protecting half the terrestrial realm. BioScience 67: 534-545.
  3. Locke, H. (2013). Nature Needs Half: A necessary and hopeful new agenda for protected areas. Parks 19:9-18.
  4. Noss, R.F., Dobson, A.P., Baldwin, R., Beier, P., Davis, C.R., Dellasala, D.A., Nowak, K. et al. (2012). Bolder thinking for conservation. Conservation Biology26:1-4.
  5. Wilson, E.O. (2016). Half-Earth: Our Planet’s Fight For Life. 1st New York. Liveright Publishing Corporation.

Photo by Mikael Castro, credit to Namibia Tourism Board

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