Conservationists do not need to exaggerate the crisis facing the world’s biodiversity (Costello 2019).

Almost 30,000, out of 100,000 species assessed, are threatened with extinction (IUCN Red List 2019). This is far too many and a crisis. Helpfully, we know what threatens each species and there are many examples of conservation success in preventing extinctions.

Claims that one million species are threatened, and that present extinction rates are many times higher than for tens of millions of years, attract media attention (Diaz et al. 2019). However, they do not help because they do not tell us what species are threatened. Worse, they may be counterproductive because they contribute to “compassion fatigue” where people respond less to hopeless situations (Markowitz et al. 2013); and if not supported by unequivocal evidence, they may undermine the credibility of the message.

The one million hyper-estimate was based on two assumptions: (1) that there may be eight million species on Earth, when it is more likely to be two million (Costello and Chaudhary 2017), and (2) that the species not assessed for extinction risk are equally threatened as those that have been; also debatable (Costello et al. 2013a, b).

Neither is it reasonable to compare the recent global extinctions of almost 900 species, largely due to predation by people and predators we introduced to islands, to the numbers of extinctions tens of millions of years ago of different animals due to different causes (which were disturbingly similar to climate change). The causes, kinds of animals and time-scales are completely different.

Instead, conservationists should realise that expert-curated databases of almost all named species are freely available online (Roskov et al. 2019). These databases provide a starting point for assessing species extinction risk. Rather than dramatizing the problems, we should be making best use of databases and expert communities to work collaboratively to identify which of the over one million yet to be assessed species are most threatened, by what, and where they are.

This article (Costello 2019)  was discussed on Radio New Zealand on 26 July 2019. Feedback to the radio station included “I agree – otherwise it feels overwhelming and hopeless so we give up! We need hope, we need to hear about more successes, that is empowering.” and “In the end, the number is a distraction, the point is that the impact of people on nature and the consequential impact on us is crucial to pay attention to and change our behaviour.


Costello, M.J. 2019. Unhelpful inflation of threatened species. Science 365 (6451), 332-333. DOI: 10.1126/science.aay3467

Costello MJ, Chaudhary C. 2017. Marine biodiversity, biogeography, deep-sea gradients, and conservation. Current Biology 27, R511–R527.

Costello M.J., R.M. May, N.E. Stork. 2013a. Can we name Earth’s species before they go extinct? Science 339, 413-416.

Costello M.J., R.M. May, N.E. Stork. 2013b. Response to Comments on “Can we name Earth’s species before they go extinct?” Science 341, 237.

Diaz et al. “Summary for policymakers of the global assessment report on biodiversity and ecosystem services of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services”, 39 pp. Accessed (2019)

IUCN Red List of Threatened Species,, accessed 27th May 2019.

Markowitz M., P. Slovic, D. Vastfjall, S.D. Hodges, 2013. Compassion fade and the challenge of environmental conservation. Judgment and Decision Making 8 (4), 397–406.

Roskov Y., et al. Species 2000 & ITIS Catalogue of Life, 2019 Annual Checklist. Digital resource at Species 2000, Naturalis, Leiden, The Netherlands.

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