The uproar over Superfreakonomics has led to a lot of smart posts being written on the pitfalls associated with "geoengineering" as a response to global warming. Now, as I've mentioned before, "geoengineering" is often used as a catch-all term for a wide variety of schemes to artificially reduce the temperature of the earth, but Nate Silver homes in on the two most audacious ideas out there:

-- Finding some mechanism to shoot sulfur into the atmosphere -- this is the approach that Levitt and Dubner concentrate on in SuperFreakonomics. Sulfur has a cooling effect, as can be observed, for instance, when there is a large volcanic eruption -- volcanoes emit lots of sulfur and when Mount Pinatubo erupted in 1991 it cooled the planet's temperatures by approximately 0.9° F for several months.

-- Creating artificial cloudcover. Or to be more precise, modifying clouds to be more reflective, which would modify the earth's albedo and cause more sunlight to be bounced back into space. This is the approach pursued by Dr. John Latham, a seventysomething British scientist employed by the National Center for Atmospheric Research in Boulder, Colorado, whom I spoke with on the phone several weeks ago.

A couple points about this. First, if, like Dubner and Levitt, you're skeptical about the omniscience of climate models—and, while I think modern climate models are pretty good, it is true that there's a fair bit of uncertainty still—then you should be skeptical of geoengineering, too. Trying to spray sulfates or other aerosols into the air to reflect sunlight and cool down the planet could have a lot of unintended side effects that are, at present, difficult to model. Whenever I ask climate scientists what they wish they still understood better, aerosols are often at the top of the list. And the consequences could be dramatic: Two University of Colorado researchers recently found that the sulfur scheme could wreak havoc on global rainfall patterns. A lot more research is needed on this subject, and Dubner and Levitt are way too glib about the risks.

Second, as Ryan Avent points out, geoengineering is likely to create as many headaches over international coordination as a treaty to reduce carbon emissions will. Who controls the sulfur spray? What if one country gets drought as a result of geoengineering and wants to adjust the mechanism at the expense of another country? What if some countries decide unilaterally to fiddle with their own cloud cover? Who compensates the losers? This isn't necessarily any easier than a carbon treaty.

Third, most people who work on geoengineering will tell you that we should be looking into it as a complement to efforts to reduce carbon emissions, not as a substitute. One important thing to note, which Nate Silver does, is that spraying sulfur in the air to try to cool the Earth without reducing emissions would do nothing to prevent the build-up of carbon that's rapidly acidifying the ocean. Ocean acidification is a big deal—it's already wreaking havoc on coral reefs, it could seriously disrupt the ocean food chain, and it could conceivably alter the climate in ways we don't quite understand.

In many ways, the uncertainty around climate projections always struck me as a good argument for reducing emissions and trying to interfere with the Earth's climate as little as possible. Yes, it's possible that climate modelers are overstating how hot the Earth will get if we keep pumping CO2 into the air. It's also very possible that they're understating things. (If forced to bet, I'd stick with the IPCC "consensus" estimate that a doubling of CO2 in the air will raise global average temperatures about 3°C, but as the IPCC will be the first to concede, "values substantially higher than 4.5°C cannot be excluded.") Uncertainty is not our friend. It's risky business to keep fiddling with atmospheric chemistry and assuming everything will turn out okay.*

* I guess one counterargument here is to say: "Sure, but isn't it also risky business to try to revamp the world's energy economy and assume everything will turn out okay, given the (even greater) uncertainty in economic modeling?" That's a fair point, and I guess I'd respond by saying a) trying to cap carbon and shift away from fossil fuels seems like the more reversible move: If, for some reason, the costs of moving away from burning fossil fuels turn out to be absolutely intolerable, we can quickly go back to using them; that may not be true if the climate hits certain tipping points where, say, Siberian bogs start decaying, methane in the ocean is bubbling up, and we can no longer control the rate of warming; and b) from past experience, every time we've put a price on an externality or capped a seemingly "indispensable" pollutant (lead, CFCs, sulfur-dioxide), the economy has survived just fine. In the face of uncertainty, shifting away from fossil fuels looks like the far less risky venture.