Matthew J. Kotchen and Laura E. Grant, NY Times - Why do we - along with
75 other countries - alternate between standard time and daylight time?
Although many people believe it has an agricultural provenance, daylight
time has always been a policy meant to save energy. As Benjamin Franklin
argued, if people moved up their summer schedules by an hour, they could
live by "sunshine rather than candles" in the evenings.
Energy conservation was the motivation for daylight time during World Wars
I and II and the oil embargo of the 1970s, and it remains so today - even
though there has been little scientific evidence to suggest daylight time
actually helps us cut back on electricity use.
Recently, however, we were able to conduct a study in Indiana, where
daylight time was instituted statewide only in 2006. Before that year,
daylight time was in effect in just a handful of counties. This change of
policy offered a unique, natural experiment to measure the overall effect
on residential electricity consumption. We could compare the amount of
energy used by households in the late-adopting counties during the two
years before they switched to daylight time with the amounts they used
during the year afterward - while using counties that always practiced
daylight time as a control group.
We found that daylight time caused a 1 percent overall increase in
residential electricity use, though the effect varied from month to month.
. . Daylight time costs Indiana households an average of $3.29 a year in
higher electricity bills, or about $9 million for the whole state. We also
calculated the health and other social costs of increased pollution
emissions at $1.7 million to $5.5 million per year.
What explains this unexpected result? While daylight time reduces demand
for household lighting, it increases demand for heating in the early
spring and late fall (in the mornings) and, even more important, for
cooling on summer evenings. Benjamin Franklin was right about candles, in
other words, but he did not consider air-conditioners.