A few weeks ago, we wrote that videoconferencing might be the best green technology available in terms of bang for your buck, according to data culled from a green retrofit at software giant SAP.

It turns out there is something even cheaper.

White roofs cost less than conventional roofs, require almost no maintenance and can offset tremendous amounts of demand for heating and air conditioning, according to Art Rosenfeld, the former California Energy Commissioner who is also often described as "The Father of Energy Efficiency."

1,000 square feet of white roofing can offset ten tons of carbon dioxide, he told us in a recent video interview. (See segments one and two on energy efficient homes and technologies here and here.). The technology -- and bear in mind that calling changing the pigments in roofing materials a 'technology' is a bit of a stretch -- is effective in a wide range of climates, too. Installing white roofs from Chicago to Sao Paolo would offset 25 billion tons of carbon dioxide over a 20-year period, he said.

Worldwide, white roofs could eliminate 44 billion metric tons, according to a 2008 research paper from Lawrence Berkeley Labs written by Haskem Akbari and Rosenfeld. (He's in his 80s and still publishing scientific papers: one more reason Rosenfeld is in the Greentech Hall of Fame.)

California has already mandated that flat roofs like those you see on Walmart stores must be white. Aesthetics aren't really an issue. In fact, the aesthetic issues on homes can be eliminated: it just takes a little acclimation.

Happy viewing.

Back in the 1970s, Rosenfeld, a physicist at Lawrence Berkeley Lab (and Enrico Fermi's last grad student), determined that the power consumption in California and the nation would someday outstrip our ability to produce it. He kicked off a massive effort to get the state to pass efficiency regulations. Appliance makers fought vigorously, but California passed appliance and building regulations (Title 20 and Title 24) anyway. 

"They all claimed it was the [expletive] end of civilization as we knew it," he told me in 2006. "Autos were getting 14 miles a gallon. Energy efficiency wasn't part of the American ethic whatsoever."

The result? Per capita power consumption has remained relatively flat in California but nearly doubled in the rest of the country. The results can only partly be attributed to the "Rosenfeld Effect." Still, the impact has been huge. Modern refrigerators consume half or less the energy consumed by fridges back in the '70s, hold more food and cost less when adjusted for inflation. Pilot lights consumed close to 10 percent of the energy in homes. Electronic ignition has capped that work and has likely been responsible for hundreds of billions in energy savings.

The interview took place at the Emerging Technologies Summit in Sacramento for a series of videos (thanks to Jonathan Livingston for setting it up).