Over the weekend, the Washington Post ran an important front-page story on the global warming debate: "Now that most scientists agree human activity is causing Earth to warm, the debate has shifted to whether climate change is progressing so rapidly that, within decades, humans may be helpless to slow or reverse the trend." Right. A few months ago, I wrote an article on this very subject for QED that isn't fully online, but here are some basic numbers from the piece and reasons for serious pessimism that humans really can slow or reverse the trend at this point. Basically, the goal looks attainable in theory, but in practice may be far out of reach.

The UN's Intergovernmental Panel on Climate Change has argued that to avert catastrophic global warming, the world will, at the very least, need to keep the amount of CO2 it emits into the atmosphere stabilized under a "red line" of 550 parts per million by mid-century. (The Pew Center on Global Climate Change says that even that level will lead to significant global warming, and suggest 450 ppm as a safer, though unrealistic, goal.) Hopefully meeting that goal will stave off the climate change-associated death, destruction and mayhem that is predicted by, say, the Pentagon. But unless the world starts changing its mix of energy sources, and soon, we won't even come close to meeting the IPCC goal: at the current rate, atmospheric concentrations of CO2 will reach 1,100 ppm by 2100.

Okay, so to avoid that fate, roughly two-thirds of the world's power must come from carbon-free sources by 2050, given current growth rates. (These numbers come from interviews with Nathan Lewis of Caltech, along with, among other things, his presentation here.) That's 20 TW of power coming from carbon-free sources by mid-century; to put that in perspective, much more than the total amount of power produced by all sources globally, at present. It's an unimaginable amount of carbon-free power that needs to be generated, and fast.

So where are we going to find those 20 terrawatts? Well, nuclear power alone can't do it—to produce even 10 TW of nuclear power by 2050 would mean building 10,000 new plants: one every other day for 50 years. Realistic? No. And that's ignoring the fact that the world's uranium deposits will run out in about 45 years, unless fast-breeder reactors somehow become more feasible. Biomass alone can't do it either. It would take all of the farmable land on earth that isn't being used for growing food to produce 7-12 terawatts of power; and there likely isn't enough freshwater on the earth for those farms anyway. Hydropower, meanwhile, would give us, at most, 1.5 TW—which is five times the present amount—and poses more than a few environmental hurdles in setting up new dams.

Two other popular solutions: Carbon sequestration—pumping carbon into the ocean or geological reservoirs—shows a lot of promise, but the hurdles are very real. How, for instance, will the carbon waste get transported from power plants to sequestration sites? Can we ensure that the carbon won't leak back out of the ground? And what happens if the carbon that's been sequestered in the water starts raising the pH levels of the oceans dramatically? It's a promising idea, but still shaky. Meanwhile, conventional estimates put the maximum total potential for wind power sites around the world at about 1.6-2 terawatts, total (although two Stanford researchers have very recently suggested a much higher figure; jury's still out though, from what I gather).

Just looking at the math here, the only source that could even conceivably provide enough power to avert catastrophic global warming is solar power. The potential value for practical sites around the world is about 600 terawatts, and with solar farms running at 10 percent efficiency, that would yield 60 terawatts, more than enough to provide the carbon-free energy necessary.

So that's all very well and good, but—and this is what the article was about—there are still so many hurdles standing between where the solar industry is today, and where it would have to be to help the world achieve 550 ppm by mid-century, that it would require a radical shift in thinking on the part of world leaders to get there. More radical, certainly, than anything now being contemplated by politicians in this country.

Even ambitious mainstream liberal ideas for weaning the United States off carbon sources, such as those from the Apollo Alliance or the Solar High-Impact National Energy Project (SHINE) fall short, although they're decent steps. The SHINE proposal, for instance, is billed as a "man-on-the-moon" solar initiative, but aims for solar to generate a relatively scant 9 percent of electricity needs in the United States alone by 2025. That's certainly far more than the projected 1 percent under current trends, but it probably wouldn't meet the more important goal of having 20TW of the world's power coming from carbon-free sources by 2050. The scale of the problem here is really overwhelming.