Paul Weisz considers transforming America’s energy economy using approximately 1000 square meters of solar cells per capita. That amounts to macroengineering; covering roughly 2.7% of the nation’s area would alter radiative equilibrium and could effect climate change.
Earth’s albedo is modest, but efficient solar cells reflect even less solar energy than the land they shade, a radiative forcing that can amount to hundreds of watts per square meter. Many cell designs also retard nighttime cooling. Weisz proposes 650 000 km2 of photovoltaics in 11 nations alone. Add the rest, and the total is millions. Multiplying hundreds of watts per square meter over millions of square kilometers yields approximately 1014 W, rivaling the present anthropogenic CO2 forcing.
This dark side of solar power competes with local efforts, like Los Angeles’s Cool Cities Initiative, to limit the heat island effect of simmering expanses of asphalt by making sunlit surfaces lighter, not darker. Pale paving and roofing grow attractively cheaper as oil, electricity, and asphalt prices rise. Few Americans can swing a mortgage on 1000 m2 of silicon, but whitewash is universally affordable. Even Senator John Kerry parks his sport utility vehicle on a brilliant white-shell Nantucket driveway, admirably offsetting the albedo deficit of the solar cells atop his yacht.
