That appears to be a widespread consensus. “Jim’s analysis is very shrewd,” says Michael Oppenheimer, a professor of geosciences and international affairs at Princeton University. “It’s something we all should be thinking about, but the uncertainties are so large that it’s a weak point.” Schneider, too, offers praise overall but caution about specifics. “Jim’s doing great work,” he says, “but I wish he’d get off absolute numbers. It’s not as though the world is okay with 1.8 degrees of warming but turns into a pumpkin at 2.2 or something.”
Seeking a Workable Solution
Indeed, although few climate scientists are ready to buy Hansen’s argument in detail, they agree that the changes already observed are ominous. “Where I’ve come down on this,” says Fred Krupp, president of the Environmental Defense Fund, “not sparked by Jim Hansen but by watching coral reefs die and Antarctic ice sheets break off sooner than we ever expected, is that we need to stabilize CO2 at current levels or below.”
Lurking behind this general tone of caution is the sense that reducing the growth of CO2 emissions is a daunting enough prospect by itself, given that the world’s population continues to grow and that countries such as India and China are determined to catch up to the developed world economically. Halting that growth entirely would be even more difficult, and actually drawing down the amount of CO2 in the atmosphere seems largely inconceivable. Nevertheless, Hansen and his co-authors lay out a possible strategy. “The only way I can see of doing it,” Hansen says, “is, first of all, to cut off emissions from coal entirely by 2030.” Coal, he points out, is the single biggest fossil-fuel reservoir of carbon, and because it is only burned in power plants, not as transportation fuel, “it can be captured at just a few sources rather than millions of tailpipes.”
To push coal-based carbon emissions down to zero, he and his colleagues suggest, the world has to agree that, starting right away, no new plants will be built unless they have the capability to capture waste CO2 before it leaves the smokestack. At the same time, existing plants will either have to be retrofitted with capture technology or phased out by 2030.
A second major effort, the authors say, would involve massive reforestation of areas that have been denuded of trees. “Deforestation contributed a net emission of 60 ± 30 ppm over the past few hundred years,” they write, “of which ~20 ppm CO2 remains in the air today.” Regrowing forests, they argue, could absorb all of that excess and more. And finally, they favor the use of “biochar,” or charcoal made from agricultural waste and other biomass. If burned or left to decay, this biomass releases CO2. When converted to charcoal and tilled into the soil, it does two things. First, it is exceptionally stable, so it keeps carbon sequestered for centuries, at least. Second, it increases soil fertility, because it adsorbs nutrients and keeps them available for new crops. “Replacing slash-and-burn agriculture with slash-and-char,” they write, “could provide a CO2 drawdown of ~8 ppm in half a century.” More speculative technologies might also eventually be able to draw CO2 out of the atmosphere and lock it up in minerals, although their potential scale and expense are still guesswork.
But possibility and plausibility are two different things. Hansen and his colleagues have produced a road map; getting all the biggest carbon emitters to go along will be tough. The scheme would take decades to implement even if every nation agreed to it today. The task, the scientists admit, “is Herculean yet feasible when compared with the efforts that went into World War II.” Schneider, though just as concerned as Hansen about the dangers posed by increasing atmospheric carbon, has a less optimistic view. “It has no chance in hell,” he says. “None. Zero. The best thing we can do is to overshoot, reach 450 or 550 parts per million, then come back as quickly as possible on the back end.” And even that, given the political barriers to quick and effective action, will be difficult.