With Speed and Violence: Why Scientists Fear Tipping Points in Climate Change (34 page)

I am sorry if you have got this far hoping for a definitive prognosis for our planet. Right now, the only such prognosis is uncertainty. The Earth system seems chaotic, with the potential to head off in many different directions. If there is order, we don't yet know where it lies. No scenario has the ring of certainty. No part of the planet has yet been identified as holding an exclusive key to our future. No feedback is predestined to prevail. On past evidence, some areas may continue to matter more than others. But "the story of abrupt climate change will become more complicated before it is finished," as Alley puts it. "We have to go looking for dangerous thresholds, wherever they may be."

For now, we have checklists of concerns. Melting Arctic ice, whether at sea or on land, could have huge impacts, both by raising sea levels and by amplifying global warming. Glaciological "monsters" could be lurking in Pine Island Bay or the Totten glacier. The whole West Antarctic ice sheet could just fall apart one day. El Nino may get stuck on or off, triggering megadroughts or superhurricanes. The Amazon rainforest may be close to disappearing in a rage of drought and fire that would impact weather systems around the world. The oceans may turn into a giant lifeless acid bath. Smog may cripple the hydroxyl cleaning service or shut down the Asian monsoon. And the stratosphere may contain yet more surprises.

Methane is always lurking in the background, ready to repeat the great fart of 55 million years ago, if we allow it out of its various lairs. And the North Atlantic seems to hold a particular fascination. I keep coming back to Alley's disturbingly simple choice for the Gulf Stream as it surges north: sink or freeze? And to Peter Wadhams's lonely chimney, stuck out off Greenland somewhere northeast of Scoresby Sound, endlessly delivering water to the ocean floor. Until it stops. Who knows when? And who knows what will follow?

Quite a lot of this book has been taken up with climatic history. This is deliberate. The past shows more clearly than any computer model how the climate system works. It works not, generally, through gradual change but through periods of stability broken by sudden drunken lurches. And the past operation of the climate system reveals in their fully conscious state the monsters we may be in danger of waking.

But past climate does not provide a blueprint for the future. There are no easy analogues out there. We have already strayed too far from the tracks created by Bond's solar cycles and the other natural oscillations of the Earth system. Greenhouse gas concentrations are already probably at their high est level in millions of years; temperatures will soon join them. But the distinctive nature of our predicament goes a long way beyond that. Give or take the occasional asteroid impact, past changes have almost all been driven by changes in solar radiation, beamed down to us through the stratosphere. Earthly feedbacks such as biological pumps and spreading ice sheets, and threshold changes to marine currents and terrestrial vegetation, followed on the solar signal. This time, we are starting from the ground up, with a bonfire of fossil fuels that has shaken the carbon cycle to its core. Not only that: we are simultaneously filling the atmosphere with aerosols and assaulting key planetary features like the rainforests and the ozone layer. There can be no certainty about how the monsters of the Earth system will respond. We can still learn from the past, but we cannot expect the past to repeat itself.

When I first wrote at length about climate change, back in 1989, in a book called Turning Up the Heat, I warned that we passengers on Spaceship Earth could no longer sit back for the ride. We needed to get hold of the controls or risk disaster. But it was at heart an optimistic book. I figured that if Homo sapiens had come through the last ice age as a mere novice on the planet, then we could make it this time, too. We had the technology; and the economics of solving the problems wouldn't be crippling. I compared the task to getting rid of the old London pea-soupers of half a century ago. Once the decision was taken to act, the delivery would be relatively easy. We'd soon be wondering why we had dawdled for so long.

Fifteen years on, the urgency of the climate crisis is much clearer, even if the story has grown a little more complicated. But we are showing no signs yet of acting on the scale necessary. The technology is still straightforward, and the economics is only easier, but we can't get the politics right. Even at this late hour, I do believe we have it in our power to set Spaceship Earth back on the right course. But time is short. The ship is already starting to spin out of control. We may soon lose all chance of grabbing the wheel.

Humanity faces a genuinely new situation. It is not an environmental crisis in the accepted sense. It is a crisis for the entire life-support system of our civilization and our species. During the past io,ooo years, since the close of the last ice age, human civilizations have plundered and destroyed their local environments, wrecking the natural fecundity of sizable areas of the planet. Nevertheless, the planet's life-support system as a whole has until now remained stable. As one civilization fell, another rose. But the rules of the game have changed. In the Anthropocene, human influences on planetary systems are global and pervasive.

In the past, if we got things wrong and wrecked our environment, we could pack up and move somewhere else. Migration has always been one of our species' great survival strategies. Now we have nowhere else to go. No new frontier. We have only one atmosphere; only one planet.

APPENDIX: THE TRILLION-TON CHALLENGE

Ali the world's governments are committed to preventing "dangerous" climate change. They made that pledge at the Earth Summit in Rio de Janeiro in 1992. (The signatories included the U.S. and Australia, which both refused to ratify the subsequent Kyoto Protocol and its national targets for emissions reductions.) But what constitutes dangerous climate change? And how, in practice, can we prevent it?

For some people, dangerous climate change is already a reality. Many victims of recent hurricanes, floods, and droughts blame climate change. Such claims are usually impossible to prove. But that doesn't mean that our weather is not changing, says Myles Allen, of Oxford University. In essence, climate change is loading the dice in favor of weird and dangerous weather. "The danger zone is not something we are going to reach in the middle of this century," Allen says. "We are in it now." The 35,000 Europeans who died in the heat wave of 2003 were victims of an event that would almost certainly not have happened without the insidious increase in background temperatures that turned a warm summer into a killer.

But, despite such local disasters, most would argue that the critical aim in the quest to prevent dangerous climate change is to avoid crossing thresholds in the climate system where irreversible global changes occurespecially changes that themselves trigger further warming. There is no certainty about where such "tipping points" lie. But there is a growing consensus, especially in Europe, that the world should try to prevent global average temperatures from rising by more than 3.6'F above pre-industrial levels, or about 2.5 degrees above current levels.

Unfortunately, there is no certainty either about what limits on green house gases will achieve that temperature target. We don't yet know how sensitive the climate system is. Current estimates suggest that to stack the odds in favor of staying below a 3.6-degree warming, we probably need to keep concentrations of man-made greenhouse gases below the heating equivalent of 450 parts per million of carbon dioxide. In practice, that probably means keeping carbon dioxide levels themselves below about 400 ppm. Let's call this the "safety-first" option.

Forgive me if I now abandon this language of parts per million. I find it an irritating and unnecessary abstraction. It seems to me much more sensible to talk in terms of tons of carbon instead. Then we can establish how much there is in the atmosphere and see more clearly how much we can afford to add before the climate goes pear-shaped.

The simple figures are these. At the depths of the last ice age, there were about 44o billion tons of carbon dioxide in the atmosphere. As the ice age closed, some 22o billion tons switched from the oceans to the atmosphere, raising the level there to about 66o billion tons. That's where things rested at the start of the Industrial Revolution, when humans began the largescale burning of carbon fuels. Today, after a couple of centuries of rising emissions, we have added another 22o billion tons to the atmospheric burden, making it about 88o billion tons. If we want to keep below the safetyfirst concentration, we have to keep below 935 billion tons. So we have only about another 5 5 billion tons to go.

Currently, we pour about 8.2 billion tons of carbon into the atmosphere annually. Of this, a bit over 40 percent is quickly taken up by the oceans and by vegetation on land. The rest stays in the air, where its life expectancy is more than a century. So, for practical purposes, we are adding about 4.4 billion tons of carbon dioxide a year to the atmosphere. Even at current rates of emissions, that means that we will be above our 935billion-ton safety-first target before 2020; and assuming that emissions continue to rise at the current rate, we will be there in less than a decade. Frankly, barring some global economic meltdown, there is now very little prospect of not exceeding 935 billion tons. If we had acted quickly after 1992, we could have done it. But the world failed.

If we are lucky-if climate sensitivity turns out to be a little lower than the gloomier predictions suggest-the 3.6-degree target may still be achieved while we allow carbon dioxide levels to rise significantly above 935 billion tons. We cannot be sure. There is already about i degree of warming "in the pipeline" that we can no longer prevent. But if we are feeling lucky-and with a nod to both round numbers and political reality-we might allow ourselves a ceiling of a trillion tons. Some would call that a "realistic" target, though others would brand it a foolish bet on a climate system we know little about.

The "trillion-ton challenge" is still a tough call. Literally, whatever target we set will require drastic cuts in emissions. Nature will probably continue to remove a certain amount of our emissions. But experts on the carbon cycle say that we must reduce emissions to around a quarter of today's levels before nature can remove what we add each year. Only then will atmospheric levels stabilize; only then will climate start to stabilize. The quicker we can do it, the lower the level at which carbon concentrations in the air will flatten out. Reaching the safety-first target of 935 billion tons of carbon dioxide would require an immediate and dramatic ditching of business as usual in the energy industry worldwide. Global emissions would need to peak within five years or so, to fall by at least 50 percent within the next half century, and to carry on down after that. A trillionton target could be achieved with more modest early cuts and greater reductions later.

Another consideration is the danger posed by the sheer speed of warming. Many climate scientists say that rapid warming may be more destabilizing to vulnerable systems like carbon stores and ice caps than slower warming. For this reason, it could be important to take some urgent steps to limit short-term warming while we get carbon dioxide emissions under control. And there is a way to do that-through a concerted assault on emissions of gases other than carbon dioxide that have a big short-term "hit" on climate.

Let me explain. Different greenhouse gases have different lifetimes in the atmosphere, ranging from thousands of years to less than a decade. For convenience, climate scientists usually assess their warming impact as if it operated over a century-carbon dioxide's average lifetime in the atmosphere. But this is rather arbitrary. And it has the effect of "tuning" the cal culations to make carbon dioxide seem more important, and other gases less so. Most significant here is methane, which, however you measure it, is the second most important man-made greenhouse gas after carbon dioxide. Measured over a century, the warming caused by a molecule of methane is about twenty times as great as that caused by a molecule of carbon dioxide. But methane does most of its warming in the first decade, its typical lifetime in the atmosphere. It has a quick hit. Measured over the first decade after its release, a molecule of methane causes a hundred times as much warming as a molecule of carbon dioxide.

By following the scientists' conventional time frame, Kyoto Protocol emissions targets have underplayed the potential short-term benefits of tackling methane emissions. It is unlikely that the politicians who signed the protocol were even aware of this.

But underplaying the benefits has had an important effect on policy priorities. To take one example, if the British government decided today to eliminate all methane emissions from landfill sites, it would meet only a fraction of the country's Kyoto targets, because the Kyoto rules measure the impact of foregone emissions over the whole of the coming century. If the initiative were measured instead on its impact over the first decade, the benefits would be five times as great. The methane specialist Euan Nisbet, of London's Royal Holloway College, reckons that the short-term hit would be almost as great as banning all cars on the streets of Britain. And, if the rules had been drawn up differently, it would have been enough to entirely meet Britain's Kyoto target.

If the world is mainly concerned about the effect of greenhouse gases in fifty to a hundred years' time, then we should probably stick with the existing formula. But if we are also concerned about quickly reducing global warming to stave off more immediate disaster, then there is a strong case for coming down hard on methane now-on leaks from landfills, gas pipelines, coal mines, the guts of ruminants, and much else. "Cutting carbon dioxide emissions is essential, but we have neglected methane and the near-term benefits [acting on] it could bring," says Nisbet. He wants the Kyoto Protocol rules narrowed to a twenty-year time horizon. Jim Hansen takes a similar view. "It makes a lot of sense to try to reduce methane, because in some ways it's easier," he says.