With climate change forecasts looking increasingly ominous and the international regulation of greenhouse gas emissions all but stalled, there has never been greater interest in geo-engineering: controlling the climate by artificial means. America's efforts to lever such mitigation strategies into the latest report by the intergovernmental panel on climate change (IPCC) were denounced as an excuse for it to go on conducting its industrial business as usual. But while climate scientists tend to regard these techno-fixes with scepticism, if not outright hostility—the IPCC called them "speculative, uncosted and with potential unknown side-effects" —there does seem to be a new willingness to give them serious consideration.
One of the earliest proposals was to increase the amount of carbon dioxide extracted from the atmosphere and "fixed" into planktonic plants in the seas. This might be done, it was said, by scattering iron into the waters: the paucity of this essential nutrient currently holds plankton growth in check. After more than a decade of research, the viability of "iron fertilisation" remains unproven. But there are ambitious alternatives. One is to erect a screen in space that would block enough sunlight to counteract greenhouse warming. A scheme worked out last year would involve a billion or so gossamer-thin mirrors being fired into space (estimated price: $5 trillion). A less technologically challenging proposal, recently discussed by the Nobel-winning atmospheric chemist Paul Crutzen, is to spray millions of tons of sulphur into the upper atmosphere, where it would form fine particles that reflect sunlight, reducing the solar heating of the planet.
We know this works in principle because nature already does it. Large volcanic eruptions throw dust and sulphur dioxide gas (which condenses into sulphurous particles) high into the atmosphere, and historical records show that this can have a temporary cooling effect. More recently, the 1991 eruption of Mount Pinatubo in the Philippines reduced average global temperatures by a few tenths of a degree—and it would have been more had El Niño not exerted a warming influence the following year.
Crutzen's proposal is not new. However, his paper drew attention because he is well known for his environmentalist leanings. If even he felt sufficiently pessimistic about the conventional solution of reducing emissions, perhaps it was time to take these more desperate measures seriously?
This is now the usual stance of scientists exploring geo-engineering: it's as well to have a last-ditch strategy if all else fails. It's in that spirit that climate modellers Ken Caldeira in the US and Damon Matthews in Canada have just carried out computer simulations of the effects of a sudden reduction in sunlight, as might be caused by a sun shield or an injection of atmospheric sulphur. The model showed that such a fix would be capable of lowering the global temperature to 1900 levels within a decade. In principle, that would allow us to go on emitting carbon dioxide unchecked, so long as we arrange the sunshade accordingly.
The bad news is that the same rapid response applies in reverse. If a sun reflection system were to fail for any reason, the suppressed warming that has meanwhile accumulated appears all at once, with catastrophic warming rates of up to 4 0C per decade—not quite The Day After Tomorrow, but not far off. There is also the fact that even without warming, rising CO2 levels could still devastate marine ecosystems because of the consequent acidification of the oceans. So things would need to get pretty grim before this risk seems warranted.
China's wacky buildings
Whatever the 2008 Olympics might do for China's international prestige or its human rights, they are already a bonanza for architects. New materials and computer-aided design and manufacturing tools are everywhere revolutionising the notion of what a building may look like; but in China, unhampered by stringent planning regulations and with a limitless workforce, anything seems possible. The new national stadium in Beijing is a bird's nest of high-performance steel girders, 11,200 tons of which hang self-supported atop the building's superskeleton. Predicting the stresses in this highly irregular grid, which cannot afford to slump by more than a few inches without danger of cracking, was a technical tour de force of computer modelling and on-site monitoring.
Even more innovative is the swimming stadium, dubbed the Water Cube, the walls and ceiling of which are based on the structure of soap foam. About 90km of steel struts form a framework of polyhedral cells boxed in by transparent plastic sheeting, making the building translucent enough to cut lighting costs by 50 per cent. The resulting mesh looks irregular but is in fact modelled on an "ideal" mathematical foam discovered in 1993, which contains less bubble-wall surface area than any other such structure. That putative economy is more than offset by the complexity of design and fabrication, but the result is an enclosure with an organic feel, rather like being inside a glass honeycomb made from bees on acid.
