My natural gas bill arrived yesterday. On it was a note that said
"Your year-to-date gas consumption has increased by 11% compared to last year. Temperatures have been 6% colder."This confused me a bit.
First, 6% colder? What does that mean? You can't go by the usual temperature measures. Suppose last year it was 2 degrees, but this year it was only 1 degree. Is that 50% colder? (Sure wouldn't feel like it.) Or if the average this year is minus one, do you say it was 200% colder? Or if last year it was zero, and now it's –1, that must be infinity colder, right?
If I remember my grade 12 chemistry, the only scale in which you can meaningfully calculate percentage is the Kelvin scale (or the Rankine scale, for you Fahrenheit devotees). You get the Kelvin temperature by adding 273 to the Celsius temperature. If I understand it, Kelvin is a measurement of a real quantity, so that 200 actually is twice as hot as 100, in a real physical sense.
So suppose last winter the average temperature here in Ottawa was –5 Celsius (23 F). That's 268 Kelvin. Six percent colder than that is about 252 Kelvin, which is –21 Celsius (-6 F). But there's no way it was *that* cold this winter. We had a few nights of –21, but it couldn't have been the *average*.
"Temperatures have been 6% colder," then, is just plain wrong.
(Besides, temperatures can't be "colder" than each other, just "lower." That's for the same reason that $10 is "more" than $5, not "richer" than $5. But I digress.)
So what does that 6% mean, then? Maybe they mean that it was 6% colder *relative to inside*. Suppose again that last year was –5 C, and indoor temperature is 20 C (68 F). That measn the outdoors were 25 C ( 45 F) colder than indoors. So this year would be 6% more than that, or 26.5 C (47.7 F) colder than indoors, which would mean the outside temperature was –6.5 C (-20 F).
Well, that actually sounds reasonable. Maybe that's what they're talking about. But why didn't they just say so? Maybe it's too many words: "this year, the relative temperature between outdoors and indoors was 6% less." Yeah, that's kind of unwieldy. But at least it's *correct*!
Regardless, why are they telling me that in the same note that they mention my 11% increase in consumption? Are they implying that the two numbers should be the same? I don't know enough physics to comment on whether 6% more degrees should mean 6% more fuel. They probably know what they're doing, and they have physicists on staff, so probably they're right. But then, you'd think those physicists would have spotted the error in the 6% figure.
Anyway, this is more marketing than information. It does seem that the gas company is trying to hint that I'm using too much energy. Along with the bill, they sent me a bunch of coupons in the mail to use on fluorescent light bulbs (which, paradoxically, would have me use even more gas, because my incandescent bulbs give off heat and reduce my furnace usage). So I assume it's all part of a campaign to subtly encourage me to reduce my overall consumption.
If they do have ulterior motives, my skepticism is activated, and I'm not willing to trust their numbers. They're going to have to fix up their errors, and then convince me that their calculations are correct.
In short, if they want me to do more to stop global warming, they're going to have to show me their Al Gore Rythm.