If you're certain that daylight-saving time is good for the planet, put your hands up. Now put your hands down, because a recent study of more than 7 million residential meter readings over a three-year period shows what many of us have believed anecdotally for years. Electric bills go up when we switch to daylight-saving time.

How much more? Between 1% and 4%. And that's not counting collateral costs such as increased emissions.

As the Wall Street Journal reports, University of California economics professor Matthew Kotchen and a colleague concluded that

"... the reduced cost of lighting in afternoons during daylight-saving time is more than offset by the higher air-conditioning costs on hot afternoons and increased heating costs on cool mornings. 'I've never had a paper with such a clear and unambiguous finding as this,' says Mr. Kotchen, who presented the paper at a National Bureau of Economic Research conference this month."

Kotchen's work amplifies what researchers Ryan Kellogg and Hendrik Wolff found in 2007 when they sought to determine whether an extension of DST could save energy.

Based on analysis of data related to an extension of DST to accommodate the Olympic Games in 2000, and on examination of prior DST studies, Kellogg and Wolff concluded that "current plans and proposals to extend DST will fail to conserve energy."

Opinions about DST are strong on both sides, and on Slashdot, the commentary is lively as ever.

For an amusing and revealing look at the crackpot scientific theorizing behind the social phenomenon and government policy, see Michael Downing's Spring Forward: The Annual Madness of Daylight Saving.

You'll end up with your head in your hands, wondering exactly how it was that lawmakers voted to extend DST by four weeks beginning in 2007. The intention was to reduce electricity consumption by 1%. But as Downing puts it, "Congress didn't do its math homework."