Go Before You Go?

This again?

Hi,
Some of these numbers seem doubtful to me:
"Flight for family of 4 creates more CO2 than the family would generate at home for a year"
Four passengers on a 1000 mile flight result in about 500 lbs each of CO2, or about 1 ton.
A family of 4 in the US generates about 60 tons a year of CO2 emission.
http://www.infinitepower.org/calc_carbon.htm
The fuel used is about the same as if they drove.
http://silentaircraft.org/efficiency/

Energy cost per flush:
Once at alttitude, the toilets are flushed using the differential pressure between the cabin and the outside. And, since fresh air has to be brought into the airplane all the time anyway, I would think the energy per flush would be near zero.

Just ot reassure people, all of the toilet flush products are held in a tank and emptied on the ground.

Gary

How is CO2 released per flush? Just based on the power required for the sucking action?

The waste from airline toliets is treated in someway prior to discharge, at least in the US.

I see this as a push from Southern China Airlines to control thier disposal costs, using the disguise of CO2 emmisions.

I'm skeptical too. I'd ask Boeing and Airbus before taking this too seriously. I mean, it's possible, but I don't see how right now.

I'm beginning to think that maybe it's really a weight issue.

If 300 passengers do their thing before boarding, the plane will weigh a bit less. 200 pounds?

Plus the number of flushes would be less: more pounds.

In a long-haul flight, those pounds mean fuel.

Let's take a look at another number provided by Captain Liu in that article you referenced.

"Citing a survey by the company's logistics department, Liu said carrying one kilogram of items such as blankets and pillows by air for one hour uses 0.2 kilograms of fuel oil."

So what that tells us is the estimated fuel consumption from an additional unit of weight.

Conceptually, we tend to rely on averages for certain things. But in reality, the tangible effect of an action, in terms of marginal resource use, is far different than what a simple average would indicate.

I don't have greenhouse gas emissions statistics for China, so I'll US numbers to illustrate why the following claim is inaccurate:
"a flight for a family of four already creates more CO2 than that family would generate at home in an entire year"

"At home" is a bit vague and misleading. Is that the amount of fuel and electricity used to power, heat, and cool a residence? Does that include the energy used in daily transportation? Or is that total national greenhouse gas emissions divided by the number of households? Also, does that actually factor in that people who fly tend to be wealthier and therefore use more energy than an average person in general - especially in a country like China?

The radiative forcing concept is also not well-established, nor has it been studied in many areas outside of aviation, so relying on that to come up with a final number is speculative, to say the least.

Regardless, let's take a look at how much CO2 is emitted by a family of four, first using basic energy intensity averages (BTU/passenger-mile), then also using that figure provided by Captain Liu to estimate the actual CO2 emissions attributable to a family of four flying on a plane instead of there being 4 empty seats.

With the first one, the average energy instensity of a domestic flight in the US is 3,189 BTU/passenger-mile. The average length of haul for a domestic flight is 842 miles, so an average round trip flight is 1,684 miles. That means four people would account for 21,481,104 BTU for a round trip flight. The emissions coefficient for jet fuel is 156.258 pounds per million BTU, so the CO2 attributable to four people using the energy intensity model is 3,357 pounds.

By comparison, Captian Liu's numbers indicate that an additional kilogram of weight increases fuel consumption by 0.2 kilograms of fuel per hour. A round trip, non-stop flight of 1,684 miles will take a scheduled 4.81 hours. Actual flying time is almost certainly less than that, but we'll use that number to be conservative with respect to this marginal fuel consumption model.

Assume a family of four to be an adult male, an adult female, a 9 year old girl, and a 7 year old boy. The 50th percentile weight target in the US is 157, 128, 64, and 51 pounds respectively, for a total of 400 pounds, or 181 kilograms. New federal guidelines have passenger-with-baggage assumptions that are obviously higher than that - 202.5, 181.5, 84.5, and 84.5 pounds respectively, for a total of 553 pounds, or 250.8 kg. Let's use the latter figure, as again it's the conservative number (ie, doesn't favor the marginal fuel consumption model).

Take 250.8 kg for 4.81 hours times 0.2 kg of (jet) fuel per hour, and that comes to 241.4 kg of fuel. Jet fuel is 3.1 kg per gallon, and a gallon of jet fuel emits 21.1 pounds of CO2. Do the numbers, and that comes to 1,641 pounds of CO2 -- roughly half the amount using the average energy intensity model.

Per capita annual greenhouse gas emissions in the US are 53,066 pounds CO2 equivalent, so 4 people would, on average, be responsible for 212,263 pounds CO2 equivalent. Per day, that comes to 581.1 pounds. So a round trip flight, using the marginal fuel consumption model, is equivalent to only 2.8 days of average greenhouse gas emissions. If one uses the speculative radiative forcing multiplier, that number goes up to 7.6 days. If one uses the energy intensity model plus the radiative forcing assumption, it goes up to 15.6 days.

Going back to the original claim that one round trip by airplane will put out more CO2 than (over) a year's worth of home energy consumption, and using that last number from the energy intensity and radiative forcing model, it would mean that residential energy consumption only accounts for roughly 4% of a country's total energy consumption, when in reality it's about 22%.

No matter how it's sliced, a family of four flying on a plane does nowhere near the global warming damage claimed in the post.

Another interesting thing one finds from Captain Liu's number and the marginal fuel burden model is that one adult male with baggage puts out the same amount of CO2, mile-for-mile, as someone driving a gasoline-powered vehicle that gets 55 mpg (the EPA combined rating of a Prius).

Anonymous: Actually, nowhere in the People's Daily article is it stated that "a flight for a family of four already creates more CO2 than that family would generate at home in an entire year." It wasn't quoted from Captain Liu.

Captain Liu's number and the marginal fuel burden don't say that flying is like driving a Prius, they indicate that filling an empty seat on a plane that is already flying is equal to getting into a Prius and driving solo. Your body-weight in a plane is equal to you plus a car on the road. But your ticket money edges up the chances some tiny bit that another plane will fly, and the average fuel used per person is worse than a solo-Prius.