The idea that we have entered a new geological era – that the equable post-ice age Holocene is over, and has been replaced by a human-dominated era called the Anthropocene – is beginning to gain more and more currency in scientific circles. So much so, in fact, that as Nature reports this week, the question of whether or not the Holocene has ended is now being considered by the International Commission on Stratigraphy – the body that officially designates the divisions in geological time.
I cannot claim to be a neutral observer here: my upcoming book The God Species takes as a starting point the undeniable fact that humans are altering the planet in ways which are unprecedented over many millions of years, and that we need to learn to live within nine ‘planetary boundaries’ if human civilisation is to continue to flourish within the physical and biological limitations of the Earth system. (Brief aside: this does not mean we all need to go back to living in caves. I spend much of the final chapter discussing how population, consumption and our global economy can continue to grow even within these limitations.)
Also this week, some of the world’s brightest and best are meeting in Stockholm, in a conference of Nobel Laureates focusing on global sustainability, which will produce a document hopefully putting the planetary boundaries conceptual approach firmly onto the table for Rio+20 next year (the twentieth anniversary conference of the Rio Earth Summit back in 1992 that established the Climate and Biodiversity Conventions). The King of Sweden launched the meeting, which includes Nobel winners in chemistry, medicine, physics and literature, as well as government ministers and other notables. The video below of Johan Rockstrom’s opening speech (Rockstrom is the Swedish lead author of the planetary boundaries scientific paper) is well worth a watch. [Please ignore the white space underneath, which I can't figure out how to get rid of in the embed code!]
As the geologists are no doubt discussing (and in March there was a whole issue of the Philosophical Transactions of the Royal Society A journal dedicated to the Anthropocene – free introduction here), there are very strong arguments for considering the Anthropocene as a new geological era. Humans have altered the chemistry of the atmosphere (not just with a third more CO2, but also more methane, nitrous oxide, and aerosol particles, not to mention our narrowly-averted destruction of much of the stratospheric ozone layer), the temperature balance of the Earth system (because additional greenhouse gases trap heat), the chemistry of the oceans (which are getting more acidic) and the distribution of wild animals and plants.
Most of the Earth’s terrestrial surface has been transformed by human activity, whilst the majority of the oceanic continental shelves have been raked over by trawlers (in a fishing process akin, in Sylvia Earle’s memorable phrase, to “bulldozing the countryside to harvest squirrels”), and human non-biodegradeable garbage is accumulating in the oceans and on land. Humans are now a greater force of erosion and deposition than the forces of nature combined – we are very industrious animals, albeit with our fossil-fuelled machines to do most of the heavy lifting. We have also produced novel polymers and chemicals which will last for eons, and created novel radioactive elements like plutonium. Our new radionuclides – and their daughter products – will last for millions of years in a layer of human-dominated strata.
Perhaps the strongest argument for the Anthropocene is that it begins with an event which is characteristic of the accepted boundaries between earlier geological periods and eons – a mass extinction. The K-T (Cretaceous-Tertiary) boundary at 65.5 million years ago is marked with the wiping out of the dinosaurs, whilst Permian-Triassic and Triassic-Jurassic boundaries also saw the wiping out of more than half of extant species. How our end-Holocene/early Anthropocene mass extinction will play out is uncertain today, but we are clearly on the way to a Sixth Mass Extinction (Nature PDF) which rivals the previous big five in the last half-billion years of the geological record.
The ultimate challenge of the Anthropocene, to paraphrase Marx, is not just to understand it – but also to change it. Although human alteration of the planet’s bio-geochemical cycles is now so extreme as to overwhelm purely natural influences, we are only definably outside the ‘planetary boundaries’ in three out of the nine candidate areas. Plausible mitigation strategies can be designed for all of these, involving new technology and better ways of organising human society so that it begins to operate in more sustainable ways. Let us hope that the bright minds of the Nobel Prize winners can help point some of the ways ahead.