Avoiding mass extinction

Photo by Graham Watkins

Time is short to avoid a new mass extinction of species

The Red List of threatened species is sad reading (report, 13 September), but it uses only named species for which enough information is available. The vast majority of species in the world are unknown.

Wild species aren’t evenly distributed, and about 70 per cent of the land-dwelling ones are concentrated in 34 “biodiversity hotspots”. These once occupied about 15.7 per cent of the planet’s land area. But 86 per cent of this habitat has already been destroyed, mostly since 1950, and the remnants now occupy only 2.3 per cent of the Earth’s land surface.

It isn’t possible to slash and burn 86 per cent of the habitats of tens of millions of species without at least half of them going extinct. Not necessarily at once, but committed to extinction they will be, because of the reduction and fragmentation of their populations and habitats, and factors like the deaths of partner species, such as their pollinators and seed-dispersers. This process seems set to peak in the period 2000-2025, when half of the world’s species are likely to be lost, at a rate of about a million a year. The continuing growth in demand for farmland, timber and minerals is a major factor, but another is climate change. This is being caused partly by ecosystem damage that releases vast clouds of greenhouse gases, and partly by the burning of fossil fuels, which does the same even faster.

The extreme rate at which species are dying out now will appear in the fossil record of the future as a mass extinction. This will be clearly understood, if a successor species exists that’s able to understand at all, as having had a completely new cause: humanity. There’ll be an extremely thin layer of rock dividing deeper levels full of diverse fossils from shallower levels with hardly any. The marker layer will contain abundant plastic polymer molecules, radioactive decay products from artificial nuclear fusion, and distinctive concentrations of metals.

To change this outcome will require much more determined action than we’ve been able to muster so far.

Julian Caldecott, published in The Independent, 25 September 2007.