[Note to readers: Ever the editor, I have taken the liberty of updating this blog and tightening its arguments since first posting it last weekend. — John Osborn]

If you were among those who attended one of the seven Live Earth concerts held around the world on 7/7/07, or tuned in via MSN or NBC, you were asked to commit yourself to six steps, the last of which entailed adding your name to a seven point “Live Earth pledge”, making for a total of thirteen environmentally friendly acts. Of these, according to event organizer Al Gore in a pre-show interview, the first of the Live Earth pledges is by far the most important. It reads:

“[I pledge] to demand that my country join an international treaty within the next two years that cuts global warming pollution by 90% in developed countries and by more than half worldwide in time for the next generation to inherit a healthy earth.”

By Sunday afternoon, July 8, when I wrote this this entry, roughly 163,000 souls worldwide had signed up, yet I’d wager that few even remotely understand what is being asked. Which pollutants are we talking about, for example, and why is a fifty percent worldwide reduction the right number? What do we mean by “in time for the next generation?” And are the seven actions on the list sufficient (the first clearly is not) or merely representative?

Answering these reasonable questions — something I could not have done a week ago — requires a quick tour of current climate science and a look at a useful tool — “stability wedges” — devised by two Princeton scientists at the Carbon Mitigation Institute. And a good place to start is with “Field Notes from a Catastrophe”, an exemplary 200-page piece of reporting and science writing by New Yorker staff writer Elizabeth Kolbert, which I read on two steamy New England afternoons over the July Fourth weekend.

If you supplement Field Notes with two or three of the scientific papers and essays she cites as well as the three recent working group reports of the U.N. Intergovernmental Panel on Climate Change (IPCC), you’ll know as much as any informed citizen can be expected to know about the science behind the Live Earth pledges, and can decide for yourself whether you wish to sign on. In the meantime, here’s a summary of what I learned.

Carbon dioxide is the primary engine of global warming

First, to the question of “pollution.” The key villain in our climate crisis –whether you believe it’s here or in the future — is carbon dioxide. That’s the gas that climate scientists and policy-makers typically single out for their greatest attention, though methane, nitrous oxide and soot also play important roles and will have to be dealt with. Reducing carbon dioxide is a good place to start. Here’s why.

Average carbon dioxide concentration in our atmosphere reached 378 parts per million (ppm) in 2005, well above the 299 ppm reached 350,000 years ago, , according to paleontologists, and last equaled 3.5 million years ago. Some scientists believe that carbon dioxide concentrations haven’t been this high since the Eocene period, fifty million years ago, when, as Kolbert puts it, “crocodiles roamed Colorado and sea levels were nearly three hundred feet higher than they are today.” And of course, because we continue to pour more of the gas into the atmosphere, concentrations will continue to rise through the end of century, with various models predicting levels of 549, 717, 856 and even 970 ppm by 2100.

High concentrations of carbon dioxide are of concern because the gas traps heat, and plays a leading role in driving global warming. There seems to be broad agreement that temperatures today are on average a half-degree higher than they were at the start of the 20th century (1900) and that the many observable changes to our natural environment and climate, which we’re hearing more and more about on the nightly news, are due to that seemingly small increase. The half degree rise in temperature has closely followed the explosive rise in carbon dioxide. Even if we were to somehow stabilize carbon dioxide concentration at 450, 500 or 550 ppm, average temperatures are still likely — according to the IPCC and nearly everyone else — to rise another degree or two by 2100, if not more. No one really knows what the consequences are likely to be, whether some gotcha — or as climate scientists call it, a “disastrous anthropogenic interference (DAI)” — lies in wait, such as the melting of the Greenland ice sheet or a dramatic slowing down of the circulation responsible for the Gulf Stream.

How much carbon dioxide is too much?

Many scientists seem to have settled on 500 (+/-50) ppm as an objective point of danger for carbon dioxide concentration. Five hundred ppm is roughly double that of preindustrial levels, though, as Kolbert points out, “this figure has at least as much to do with what appears to be socially feasible as with what has been scientifically demonstrated.” Some scientists think 450 ppm is a threshold, while others argue that it’s likely to be 400 ppm or lower. An influential paper by James Hansen of NASA says 475 ppm may be too much. The truth is that no one really knows.

Cutting current carbon dioxide concentration in half over a generation (say twenty years), if that’s what the Live Earth organizers are proposing, would be a challenge, to put it mildly. Carbon dioxide in the atmosphere lasts for roughly 100 years, so to cut the current concentrations in half anytime in the next century would mean stopping all man-made carbon dioxide emissions today, tantamount to shutting down the world economy. Even stabilizing carbon dioxide concentrations within a generation at 500 ppm — the consensus danger point — looks beyond reach, unless, as two Princeton scientists, Robert Socolow and Stephen Pacala, wrote in an influential 2004 paper, we find a way to hold constant the number of tons of carbon dioxide we add to the atmosphere annually.

Mankind is adding roughly 7 gigatons (7 billion tons or 7 Gt) of carbon dioxide to the atmosphere per year (7 GtC/yr), and under Socolow and Pacala’s 2004 “business as usual (BUA)” scenario, that amount will grow to 14 GtC/yr (or more) by 2054. To stabilize carbon dioxide concentrations at 500 ppm over that period of time, they wrote, we need to find ways to run our world without letting our output of carbon dioxide rise any further. Can it be done?

Socolow and Pacala say yes. But the problem is huge. How can the world economy continue to operate (and grow in places like India and China) without adding more and more gas to the atmosphere. Socolow and Pacala proposed breaking the problem into segments, or “wedges”. What we need they wrote, are at least seven major initiatives, each of which is capable of preventing one billion tons of new carbon output from being emitted by 2054. Here’s a visualization of the problem and its solution.

In fact, Socolow and Pacala managed to come up with 15 initiatives — “wedges” — each capable of keeping one gigaton of carbon dioxide out of the atmosphere over the next 50 years and each possible with current technologies. Among the wedges they proposed were a doubling of nuclear power capacity, the mandating of carbon capture and storage for all new coal burning plants, exchanging biomass fuel for fossil fuel, reduced use of vehicles, and so on. The numbers involved are huge, and the U.S. and China, in particular, will have to be on board for most of the initiatives to work. For that reason, the Live Earth organizers suggestion that 90% of the reduction in climate changing pollution needs to come from the developed countries of the world is probably not correct. Each “wedge” needs its own analysis and plan of action, and for any one option, a developed region may or may not have the greatest role to play.

Pick a wedge, one for now another for later; we’ll need more than one

For more details, take a look at the list of fifteen wedges posted at the Princeton-based Carbon Mitigation Institute (CMI) website. You’ll find that several shed light on one or more of the seven Live Earth pledges. For example, there’s Live Earth Pledge #6: plant new trees and join with others in preserving and protecting forests. Socolow and Pacala propose that one-half wedge can be created by reducing the clear cutting of tropical forests over fifty years to zero and another one-half wedge added by planting 741 million acres of new trees (I’ll leave it as an exercise to figure how many states that’s equivalent to). Clearly the numbers required are huge, well beyond anything attempted to date.

Or take Live Earth Pledge #4: work for a dramatic increase in the energy efficiency of, among other things, our means of transportation. Socolow and Pacala create one wedge by increasing the fuel efficiency of the two billion cars they expect to be in use by 2054 from 30 mpg to 60 mpg. They can create a second wedge if everyone in the world drives on average 5,000 miles per year instead of a predicted 10,000 miles per year. But wait, are we even at a fleet average of 30 mpg? Watching the current struggle in Congress over fuel efficiency standards for U.S. automakers does not raise one’s confidence. And the increased miles U.S. commuters are driving — in he country with the most cars — makes the second wedge look equally daunting.

So, it’s conceivable that seven wedges aren’t enough. What if, for all sorts of reasons, some are unable to deliver their one GtC/year of carbon dioxide savings or are simply beyond the will of our institutions? What if carbon dioxide output rises faster than the currently projected rate? At least we have 15 wedges to choose from. But Martin Hoffert, an emeritus NYU physics professor, argues that we’ll need more to get to where we need to be. In a much discussed 2002 report that preceded the helpful notion of “wedges”, Hoffert advocated for research and investment in a number of futuristic technologies that have the potential to provide us with additional options for the second half of this century, when we may need them desperately. Unlike the CMI wedges, those on Hoffert’s list are carbon free. They include fusion, space-based solar power, wind turbines suspended in the jet stream, a Buckminster Fulleresque world-uniting power grid and much more.

Taking the pledge

Such thinking takes us a long way from the Live Earth pledges, but also suggests how big the problem is and how enormous the scale of solutions required.. We’re the ones who are going to have to start the work and pay for it. Sacrifices lie ahead, even if we can’t fully predict yet what they’ll be or who will have to bear them. Sure we can kick them down the road, but then we’ll be leaving our children and grandchildren with an even bigger problem. The next generation could find itself dealing with carbon dioxide concentrations of 600, 650 or 700 ppm and mitigation will seem even more impossible.

At least the science now provides us with numbers that we can use to create a kind of global dashboard. On the one-hand, 500 ppm seems like a number we don’t want to exceed if we’re to limit the amount of warming that occurs over the next hundred years to one degree Celsius or so and if we’re to avoid potential DAI events whose triggers are seemingly unknowable until they occur. On the other hand, the notion that we can approach the problem in terms of a series of “stabilization wedges” — some for now, others for later — gives us a tool we can use to create solutions of appropriate size (and seriousness) and to measure progress.

Will we do it? There’s no evidence we will. At present there are few incentives to implement any of the wedges that have been proposed. No carbon taxes, no carbon caps, no worldwide treaty, no strong signals from the marketplace. So it can’t hurt to take the Live Earth pledge, but we need to understand what we’re signing up for. If we’re agreeing to fight for a 90% decrease in our own production of carbon dioxide, or even a 50% decrease in worldwide growth (7 GtC/yr versus 14 GtC/yr), then we need to be prepared for changes that will be a lot less fun than a rock concert.

In her book, Kolbert lists a number of natural feedback loops that threaten to amplify the environmental changes already underway, in the absence of collective action. But, she concludes:

“Perhaps the most unpredicatable feedback of all is the human one. With six billion people on the the planet, the risks are everywhere apparent. A disruption in monsoon patterns, a shift in ocean current, a major drought — any one of these could easily produce streams of refugees numbering in the millions. As the effects of global warming become more and more difficult to ignore, will we react be finally fashioning a global response? Or will we retreat into ever narrower and more destructive forms of self-interest? It may seem impossible to imagine that a technologically advanced society could, in essence, choose to destroy itself, but that is what we are now in the process of doing.”