Because I'm not reflexively opposed to geoengineering research, and because I increasingly suspect that some level of albedo-management geoengineering will be necessary simply due to climate disruption happening faster than previously expected, some people tend to assume that I'm a geoengineering advocate. I'm not -- but as I've noted before, I do believe that it would be less disastrous than climate-driven depopulation. Nonetheless, geoengineering is all-but-certain to have undesirable consequences, both politically (see next post) and environmentally.
This week we got an excellent example of the latter.
Using well-established data on the light-diffusing effects of aerosol particles, Daniel Murphy [at the National Oceanic and Atmospheric Administration's (NOAA's) Earth System Research Lab] calculated that the geoengineering scheme currently envisioned could reduce incoming sunlight by about 3%. That squares with data from the Mount Pinatubo eruption.
The geoengineering scheme would also mean 3% less sunlight reaching flat photovoltaic collectors that generate electricity. But the aerosols would cut the available solar radiation even more to dish- and tube-shaped collectors that use mirrors to concentrate sunlight. Murphy's research shows that for every watt per square meter of sunlight diffused by the aerosols, as much as 5 watts per square meter would be made unavailable to mirrored collectors on the ground.
This is a problem, but not a fatal one. Commercially-available photovoltaic cells remain painfully inefficient, so one of the best ways to increase the energy returned from a solar array is to use concentration. High-atmosphere particles tend to scatter light, however, and diffuse light doesn't concentrate as well as direct sunlight.
There are a few caveats:
Solar, concentrated or otherwise, isn't likely to be a critical energy source at the poles, so the reduction in solar efficiency resulting from stratospheric sulphate geo would be less important if the geo focuses on polar regions.
Even if this turns out to be a minor drawback, it's an important indicator that no one response to global warming is perfect. Even carbon emission reduction has negative repercussions -- up-front expense in some cases, time required in others, and even the possibility of a short-term increase in warming due to the removal of atmospheric particulates (shutting down coal plants means more than reducing CO2, it also reduces soot and other pollutants -- yay for our lungs, but clearer skies mean warmer Earth). Still, geoengineering, because of its scale and the complexity of its subject, is highly likely to offer up more of these dilemmas.