It’s been an exciting news month for the polar ice sheets. A study published on May 28th in the journal Nature indicated that, fourteen thousand six hundred years ago, the rapid shedding of Antarctic icebergs raised the world’s median ocean levels by six and a half feet in a little more than a hundred years. That bit of paleoclimatology comes on the heels of a pair of studies, published two weeks ago, concluding that glaciers in the West Antarctic have passed a tipping point and are now doomed to disintegrate and melt. Sea levels will rise by four feet, and up to ten feet if the rest of the West Antarctic ice sheet follows. A third study concluded that parts of Greenland’s ice cap will be eaten away from below, since it is piled atop newly discovered canyons, which will allow warm ocean water to encroach inland for up to sixty-five miles. The rising waters won’t be witnessed by anyone reading this post, as the really big effects lie hundreds of years in the future. But, if the predictions are correct, all of Florida south of Fort Lauderdale will eventually drown. So will broad swaths of the coastal countries bordering the Indian Ocean.
The distant future—that is, the one that lies beyond the lifespans of today’s youngest children—has been largely absent from public discussions of climate change. Perhaps that should be reconsidered. The International Panel on Climate Change (I.P.C.C.), which largely defines the public discussion on climate change, looks out until the year 2100, and no further. Its fifth assessment report, to be published in final form this fall, anticipates a maximum sea-level rise of only three feet by the year 2100. Some scientists have argued that this is a low-ball number—though it’s dire enough if you live in Far Rockaway—but there hasn’t been much debate about timescale. Once exception came last December, in a paper published in the online journal PlosOne. The lead author was James Hansen, the former head of the NASA Goddard Institute for Space Studies, who has studied global warming since the nineteen-seventies. “Focus on a single date … encourages people to take the estimated result as an indication of what humanity faces, thus failing to emphasize that the likely rate of sea level rise immediately after 2100 will be much larger than within the 21st century, especially if CO2 emissions continue to increase,” the study says.
The biggest unknown in climate modelling is how long carbon emissions will continue, and at what pace. The I.P.C.C. estimates that to keep total warming to two degrees Celsius, which has become a benchmark by international consensus, we must generate less than a trillion metric tons of carbon-dioxide emissions in total. We’re already most of the way there. As Peter Kelemen, a geochemist at Columbia University, told me in a phone interview, energy companies have identified more than enough economically recoverable fossil-fuel reserves to reach those levels. “I emphasize the uncertainties of those estimates, but there is more fuel in the ground and burnable than is considered safe. It’s almost inevitable that we’ll blow past the nominally safe CO2 levels in the air,” he said.
Future generations may be forced to spend large amounts of money to remove carbon dioxide from the air. Theoretically, there are a few ways to do this: we can grow pools of algae, which will pull in carbon dioxide, then turn the organic matter into biofuels and capture and store the carbon when it’s burned, or we can build towers dangling shreds of plastic that have been infused with carbon-absorbing chemicals. Kelemen is exploring a third method: using peridotite bedrock, which is found throughout the world. The idea is to flush huge quantities of seawater through the holes bored into the ground, speeding up the process of mineral carbonation that the rock undergoes naturally.
Kelemen has rough calculations of how much it might cost to pull carbon dioxide out of the air. The arithmetic depends on how much is to be removed, and the cost per ton to do that. Say, for instance, that a lack of effective limits on emissions allow carbon dioxide levels to reach 550 parts per million. That’s a ghastly figure, and a future society might decide to lower the concentration to 450 ppm, which is deemed to be at the upper limit for a sustainable climate by some scientists. (Current CO2 concentrations recently cracked 400 ppm.) According to Kelemen, the project would require the removal of about 1.5 trillion tons of CO2 from the atmosphere. It could, perhaps, be done at a cost of three trillion dollars a year for twenty-five years—assuming that one or more of today’s incipient technologies pans out. In the middle of this century, that sum will probably represent a small but measurable percentage of global G.D.P.
The world could instead choose to spend the money now to severely curtail carbon emissions. This seems even more speculative than the idea of carbon-air removal, given the lack of progress so far. But maybe not. There’s a story that Kelemen likes to tell about the London sewer system. In the early nineteenth century, when London became the largest city in the world, it was awash in human waste, which ran in the streets or into neighborhood cesspits that frequently overflowed. During the Great Stink of 1858, when the weather was unusually hot and dry, the stench became overpowering, prompting fears of another in a series of cholera outbreaks that had plagued the city. Parliament voted to rip up London’s streets, and in the course of the next ten years the country built its capital a sewer system that cost millions of pounds. It was an expenditure but, suddenly, it seemed worthwhile. Kelemen says, “When people think that putting CO2 in the air is like throwing poop in the street, it will seem affordable to take care of this garbage. But until people think that CO2 management is a necessity, any negative impact, any cost, any downside of any kind, will seem to be too much.”
Photograph by Robert Harding/Corbis.
