An important new book considers the long-term implications of our relationship with carbon dioxide, writes Tim Flannery
EARLIER this year, the members of the Royal Geological Society met in London to consider whether a new division of the geological time scale should be recognised. Such divisions mark periods of profound planetary change, such as the Cambrian explosion and the extinction of the dinosaurs.
The proposed new division, known as the Anthropocene, will mark the moment when humans began to exert pervasive influence on the earth. Reaching a decision may take years, but if the proposal is accepted, the beginning of the Anthropocene will be signified by a ‘‘ golden spike’’, driven into the rocks that mark the period’s dawn.
But where should the golden spike be placed? In rocks tens of thousands of years old, dating to when humans began exterminating the megafauna? Or in sediments dating to 1945, when the dawn of the atomic age left its indelible mark on the planet? Wherever its chosen starting point, it’s indisputable that humans have long exerted considerable influence on the earth.
Given our ever-more capable technology, it seems that our actions so far are just the beginning. Yet as American ecologist and paleoclimatologist Curt Stager points out in Deep Future, already these are sufficient to influence the earth for thousands of years to come.
Stager begins this extraordinary book by tackling a misconception of the scientists’ own making. The projections of the Intergovernmental Panel on Climate Change generally only extend to 2100, which in Stager’s view misleads many to imagine that the influence of the human-produced greenhouse gases will somehow cease at that point. The reality, he tells us, is that ‘‘ shockingly long-term climatic changes await us as a result of modern human activity’’.
Just how long term is spelled out by the work of David Archer, an oceanographer who has developed computer models that run forward in time for hundreds of thousands of years. According to one of Archer’s colleagues, quoted by Stager, the reason that effects will be so long-lived is: ‘‘ Our carbon emissions won’t be gone nearly as quickly as we once thought. In fact, they’ll stick around pretty much forever.’’
The precise longevity and impact of the carbon pollution being produced this century depends on how much we emit. The IPCC has modelled a low-growth emissions scenario known as B1. It envisages that humans will act aggressively to limit carbon pollution, so that the concentration of CO in the atmosphere remains below 600 parts per million (up from 391 parts per million today). If such a course is followed, global emissions must peak in the next couple of decades.
col- leagues estimate that if this occurs temperatures will peak in 200 to 300 years, at 2C to 4C higher than present, and sea levels will stop rising several centuries to several millennia from now, having peaked at 6m to 7m above present levels.
But the big surprise is what happens to the CO . Because the oceans and land have a finite capacity to absorb CO , about onequarter of what we have emitted by 2100 ‘‘ lasts essentially forever’’. Indeed, even 50,000 years from now, that residual carbon pollution will be acting to keep earth’s temperature above its pre-industrial level.
The consequences of a business-as-usual approach would see at least five times more carbon pollution reaching the atmosphere. In this scenario, emissions would not peak for more than a century and atmospheric concentrations of CO would peak at 2000 parts per million three centuries from now. As a result, the entire ocean would be acidified, becoming ‘‘ a corrosive solvent to shell-bearing sea-creatures’’, and temperatures would not peak for about a 1000 years, having reached 5C to 9C higher than today.
But again the astonishing thing is the longevity of the impact, with full recovery taking a half-million years. Such long-term effects would completely disrupt the natural cycle of ice ages that have characterised earth for the past several million years, with no new ice age occurring for hundreds of thousands of years.
Despite the long-term effects that Stager sees from our present pollution, he’s no catastrophist. Future rises in sea level are believed by some, such as climate scientist James Hansen, to be profoundly disruptive. Stager finds no evidence in the fossil record