Global Warming: Hot Air Is Not Enough

President George W. Bush averted a nasty rift when he agreed in the final hours of the recent G8 summit to "consider seriously" the need to halve the world's emissions of global-warming gases by 2050. Canada, the European Union and Japan had already embraced that goal, leaving America the dirty stand-out. The deeper truth is that these eight industrial countries control

Only part of the world's emissions, and the industrial activities that cause emissions are slow to change. Coal will be the hardest to tame because it is so cheap and abundant. Many coal-power plants coming online today will still be in service by 2050, and advanced plants that store effluent safely underground won't be used widely for many more decades. The geopolitical hurdles are also high. The plan introduced with much fanfare earlier this month by China, which next year will become the world's top emitter of greenhouse gases, contains nothing beyond what Beijing already had in place. The world, therefore, is in for some warming.

Pessimism about stopping global warming is leading some scientists to wonder out loud if it is possible through "geoengineering" to force the Earth to cool. The idea is not entirely new and is fraught with dangers, but it is likely to get more attention in coming years. At least since the 1950s, weather makers have dreamed of steering clouds and rain to crops (though they failed in practice). From there it was a small step to dreaming on the global scale. Indeed, when the thesis of global warming was first proposed a few decades ago, some analysts envisioned putting mirrors in space or on deserts to deflect a small fraction of sunlight—just enough to offset, crudely, the buildup of warming gases in the atmosphere. These premature plans were wildly costly and faltered also because climate is sensitive to a lot more than just the gross amount of sunlight that warms the planet.

Today's plans are looking more practical, though still fraught with danger. One would spread iron, a nutrient for algae, in the ocean to stimulate photosynthesis, a natural process in which plants absorb carbon dioxide. Injecting iron in parts of the ocean where it is scarce could trigger algal blooms and help remove even more CO2. Experimental "iron fertilization," as well as careful measurement around natural iron sources, offers tantalizing support for the theory, though nobody knows what biological horrors might follow from messing with the ocean ecosystem on a large scale. Nobel laureate Paul Crutzen helped touch off the current pondering about geoengineering with an editorial in the August 2006 issue of the scientific journal Climatic Change. He revived a Russian idea from the 1970s to inject sulfur particles into the stratosphere with balloons, artillery guns or jumbo jets. (Full disclosure: I am on the journal's board of editors.) Sulfur, in turn, can produce aerosols (particulates) and clouds that reflect some sunlight back to space.

The plan has some drawbacks. Nasty chemistry, including that which caused the hole in the ozone layer, might follow—nobody is sure. Sulfur can also cause acid rain and respiratory diseases. But such ideas are worth a close look, says Crutzen, because unchecked changes in climate might be even worse. And nature already does this—through volcanoes such as Mount Pinatubo, which cooled the planet for a while after it erupted in 1991. None of this is ready for prime time, and the mere mention causes environmentalists to shudder because it distracts from the urgent need to reduce emissions. But it will get more attention as the difficulties in making deep cuts in emissions and adapting to climate change become more apparent.

Geoengineering will raise at least two awkward questions. First, it turns the geopolitics of global warming on its head. Cutting emissions requires many nations to cooperate. Geoengineering can be done by just a few, or even one. Who will determine if geoengineering is safe, and what if the rest of us don't like the consequences? The second is humanity's relationship to nature. Climate warming is already causing stress on natural ecosystems, and it is a small step to imagine engineering rare and special ecosystems to help protect them. But if mankind extends management to the whole planet, do we, in effect, turn Earth into a zoo?