The Island of Doubt

In "The long-term legacy of fossil fuels," (Tellus B, 59(4): 664-672, September 2007), Toby Tyrell, John Shepherd and Stephanie Castle at the National Oceanography Centre in Southampton conclude that the ocean's ability to absorb all that carbon dioxide we're pumping into the atmosphere to keep our decadent lifestyles afloat will soon hit a wall, and stop altogether. The result is, as they say, as new "post-fossil fuel long-term equilibrium state" that could last for several hundred thousand years.

Because of the residual anthropogenic CO₂, the future will not resemble past glacial-interglacial cycles and will not be predictable from comparison with them ... Our analysis clarifies how the carbonate compensation feedback should return the ocean to the pre-perturbation (pre-industrial) CaCO₃ saturation state, but in the process of so doing will shift the ocean to a new state with respect to other chemical parameters such as atmospheric CO₂.

Eventually, things will return to normal. Weathering of surface rocks and the resulting chemistry will suck all the extra carbon dioxide out of the atmosphere -- doing the work that the oceans now do on a much shorter timescale. But that will take half a million years. So between now and then, thanks to the much higher temperatures that come with extremely high (somewhere between triple and quadruple pre-industrial) levels of CO₂, no more ice ages.

This may sound like way-out, alarmist-scenario stuff, but it's actually pretty sound. Previous studies, including this one by David Archer at the University of Chicago, have come to similar conclusions.

We predict that a carbon release from fossil fuels or methane hydrate deposits of 5000 Gton C could prevent glaciation for the next 500,000 years, until after not one but two 400 kyr cycle eccentricity minima. The duration and intensity of the projected interglacial period are longer than have been seen in the last 2.6 million years.

There is an element of worst-caseness about these predictions, though. They assume we burn all the fossil fuels at our disposal, even the ridiculously hard-to-get shale oil. And I strongly doubt we're going to do that, for the simple reason that even the most expensive renewable sources of energy will be cheaper (as well as being cleaner and therefore ethically and politically more palatable).

But as Tyrell et al. point out, "even if only 1000 Gt C are eventually emitted, corresponding to about a quarter of recoverable fossil fuels, that the next glaciation is likely to be missed out altogether."

One could argue that this would be a good thing, although as Tim Lenton has calculated (Climate Dynamics DOI:10.1007/s00382-006-0109-9), the cost in terms of temperature increase will probably not be worth the convenience of skipping an ice age.

Archer told New Scientist this his findings add further reason to act now on global warming.... "People care, quite rightly, about the ultimate fate of nuclear waste that can remain radioactive for 10,000 years.... I think we should also care about global warming lasting 100,000 years." But I don't think we should be worrying about such distant futures. Our concern should be for those who will have to deal with the much close future, including possibly ourselves.

After all, you don't have to be a super techo-optimist extropian-transhumanist who thinks we'll all be cyborgs with artificial intelligence interfaces within 40 years a la Ray Kurzweil to believe that humans will be capable of incredible things 100 millennia from now. It seems likely that by then we will have mastered control of even our non-linear climate, and if we want to skip an ice age without living in a sauna, we'll make it so. We might even want to bring on an ice age or two, just to see what it's like. Who knows?

The point is, the distant future is not our concern, not when we have an increasingly good idea of just how bad things could get in the next few decades for the hundreds of millions of people living just above sea level (for now), for the hundreds of millions who depend on the seasonal Himalayan glacier melt for their drinking water (for now), the millions more who will be searching for something to replace the grains that can't grow because the prairies are too dry, and for everyone else who will have to find a place for the environmental refugees to live should we tip the planet into a new equilibrium that isn't quite as hospitable to life as we know it.