Dear Science,
When all those people avoided driving on I-5 two months ago, did
that have any noticeable effect on the climate?
Choked
Yes, actually.
Which isn’t surprising. When all airliners were grounded after the
September 11 attacks, nighttime temperatures dropped—particularly
near major airports. Without planes in the sky, a major source of
emissions disappeared. Emissions from airplanes cause our nights
to be warmer.
To answer your question, I could compare the number of cars on the
road any given day with how hot it gets and look for a correlation. As
everyone knows, correlation is not causation; a hotter day with more
traffic doesn’t tell us what causes what. But rarely are we given an
opportunity like the major construction project that occurred from
August 10 to 25. It’s not every day you can simply shut down a large
chunk of a local freeway and see how the climate responds.
What happened to the local climate when drivers were instructed to
cut back on unnecessary trips, carpool, take the bus or train,
telecommute, walk, or ride a bicycle? Science sat down for an edifying
evening with Excel, the National Weather Service, and R (a free
statistical package) to find out. On the weekdays between August 10 and
25, not much changed. But on both weekends, something interesting
happened. The average and maximum daily temperatures were lower, below
historical averages, and statistically significantly below those of all
the other nonconstruction weekends (by a two-tailed Student’s t-test with unequal variance) from August of this and last year. The changes
were modest, the data sets tiny, and the data subject to the variation
of the climate. (In other words, do I believe the change? Maybe. Maybe
not.) Still, it appears reducing car capacity, given adequate warning,
might actually cause the weekends to be cooler.
As much as the commutes to and from work, it’s the little
trips—to the grocery store, to the bank, to the movie-rental
place, to the library, to the amateur porn festivals on Lower Queen
Anne—that bloat local traffic. It’s unreasonable to expect
everyone to live within walking distance of work. But we should at
least plan communities where these little tasks, these “unnecessary
trips” that presumably vaporized on those construction weekends in
August, do not require a car.
As any local skier or boarder can tell you, a few degrees makes the
difference between epic snow or a slushy rain in the mountains. Might
the Saturday drive to the slopes create the slush? Maintaining
or expanding car capacity might come with an unexpected cost; we may
lose our snowpack.
Warmly Yours, Science
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