A world whose atmosphere is loaded with carbon dioxide, on the one hand, and sulfur dioxide [to counter the warming effects of CO2], on the other, would be a fundamentally different place from the earth as we know it.
From Elizabeth Kolbert’s review of SuperFreakonomics. She continues:
Among the many likely consequences of shooting SO2 above the clouds would be new regional weather patterns (after major volcanic eruptions, Asia and Africa have a nasty tendency to experience drought), ozone depletion, and increased acid rain. Meanwhile, as long as the concentration of atmospheric CO2 continued to rise, more and more sulfur dioxide would have to be pumped into the air to counteract it. The amount of direct sunlight reaching the earth would fall, even as the oceans became increasingly acidic. There are eminent scientists—among them the Nobel Prize-winning chemist Paul Crutzen—who argue that geoengineering should be seriously studied, but only with the understanding that it represents a risky, last-ditch attempt to avert catastrophe.
This is a basic truth of geo-engineering that is irresponsible to ignore as Levitt and Dubner.