Feb 10, 2009
Climate change threat
IF you shout “fire” in a crowded theatre, when there is none, you understand that you might be arrested for irresponsible behaviour and breach of the peace. But from today, I smell smoke, I see flames and I think it is time to shout. I don’t want you to panic, but I do think it would be a good idea to form an orderly queue to leave the building.Because in just 100 months’ time, if we are lucky, and based on a quite conservative estimate, we could reach a tipping point for the beginnings of runaway climate change. That said, among people working on global warming, there are countless models, scenarios, and different iterations of all those models and scenarios. So, let us be clear from the outset about exactly what we mean.The concentration of carbon dioxide (CO2) in the atmosphere today, the most prevalent greenhouse gas, is the highest it has been for the past 650,000 years. In the space of just 250 years, as a result of the coal-fired Industrial Revolution, and changes to land use such as the growth of cities and the felling of forests, we have released, cumulatively, more than 1,800bn tonnes of CO2 into the atmosphere.Currently, approximately 1,000 tonnes of CO2 are released into the Earth’s atmosphere every second, due to human activity. Greenhouse gases trap incoming solar radiation, warming the atmosphere. When these gases accumulate beyond a certain level — often termed a “tipping point” — global warming will accelerate, potentially beyond control.Faced with circumstances that clearly threaten human civilisation, scientists at least have the sense of humour to term what drives this process as “positive feedback”. But if translated into an office workplace environment, it’s the sort of “positive feedback” from a manager that would run along the lines of: “You’re fired, you were rubbish anyway, you have no future, your home has been demolished and I’ve killed your dog.”In climate change, a number of feedback loops amplify warming through physical processes that are either triggered by the initial warming itself, or the increase in greenhouse gases.One example is the melting of ice sheets. The loss of ice cover reduces the ability of the Earth’s surface to reflect heat and, by revealing darker surfaces, increases the amount of heat absorbed. Other dynamics include the decreasing ability of oceans to absorb CO2 due to higher wind strengths linked to climate change. This has already been observed in the Southern Ocean and North Atlantic, increasing the amount of CO2 in the atmosphere, and adding to climate change.Because of such self-reinforcing positive feedbacks (which, because of the accidental humour of science, we must remind ourselves are, in fact, negative), once a critical greenhouse concentration threshold is passed, global warming will continue even if we stop releasing additional greenhouse gases into the atmosphere.If that happens, the Earth’s climate will shift into another, more volatile state, with different ocean circulation, wind and rainfall patterns. The implications of which, according to a growing litany of research, are potentially catastrophic for life on Earth. Such a change in the state of the climate system is often referred to as irreversible climate change.So, how exactly do we arrive at the ticking clock of 100 months? We followed the latest data and trends for carbon dioxide, then made allowances for all human interferences that influence temperatures, both those with warming and cooling effects. We followed the judgments of the mainstream climate science community, represented by the Intergovernmental Panel on Climate Change (IPCC), on what it will take to retain a good chance of not crossing the critical threshold of the Earth’s average surface temperature rising by 2C above pre-industrial levels.We were cautious in several ways, optimistic even, and perhaps too much so. A rise of 2C may mask big problems that begin at a lower level of warming. For example, collapse of the Greenland ice sheet is more than likely to be triggered by a local warming of 2.7C, which could correspond to a global mean temperature increase of 2C or less. The disintegration of the Greenland ice sheet could correspond to a sea-level rise of up to 7 metres.We found that, given all of the above, 100 months from today (Aug 1) we will reach a concentration of greenhouse gases at which it is no longer “likely” that we will stay below the 2C temperature rise threshold. “Likely” in this context refers to the definition of risk used by the IPCC. But, even just before that point, there is still a one third chance of crossing the line.There is now a different clock to watch than the one on the office wall. Contrary to being a counsel of despair, it tells us that everything we do from now matters. And, possibly more so than at any other time in recent history. It tells us, for example, that only a government such as the current administration of Gordon Brown that was sleepwalking or in a chemically induced coma would countenance building a third runway at London-Heathrow airport, or a new generation of coal-fired power stations such as the proposed new plant at Kingsnorth in Kent, south-east England. Infrastructure that is fossil-fuel-dependent locks in patterns of future greenhouse gas emissions, radically reducing our ability to make the short- to medium-term cuts that are necessary.Deflecting blame and responsibility is a great skill of officialdom. On the first get-out, it is delusory to think that countries such as China, India and Brazil will fundamentally change until wealthy countries such as Britain take a lead. And it is wildly unrealistic to think that individuals alone can effect a comprehensive re-engineering of the nation’s fossil-fuel-dependent energy, food and transport systems. Governments must lead.