Freighters are Okay After All

Keywords: greenhouse gas; Derek Paul; cargo ship; Kyoto; jet airplane; hydrogen-oxygen fuel; bunker oil

I’ve been fretting in a public way lately about my inability to determine whether traveling by ship actually emits less greenhouse gas (ghg) than flying. I even got into a bit of an argument by e-mail with a physicist friend, Derek Paul, who thought it was easier than I claimed to find data about the emissions of ships. To my great relief, Derek has answered my questions in a way that I find convincing. He doesn’t have CO2 data but he makes reasonable inferences on other grounds. I feel satisfied enough to go ahead and look for a cargo ship (see photo) going to Europe this spring. From anywhere in Europe it’s easy to take a train to Moscow.

Because I may have aroused anxiety about this subject in some of you dear readers, I will present Derek’s letter here. I hope that it convinces you too, if you’re worried about such matters. (Fortunately, I think I’m actually influencing a few people to cut back on their own fossil fuel-driven travel, so I have a special responsibility to tell the truth.) Here’s Derek’s letter:

Dear Metta,
Thanks for this reply. Far from suggesting that individuals can do nothing, it was I who suggested to you that having families (and you are a family of one) halve their greenhouse gas emissions as a way forward that didn't depend on governments. I said that

a) Shirley and I have roughly halved our ghg emissions these last three years (except for air travel), and we also have now given up air travel), and

b) that if we could persuade two other families to do the same, and if they in turn would each persuade two more families, and so on, there would then develop an exponential in the ghg reductions on the domestic front. In seven years, I estimated, it could have the effect of bringing Canada to within its Kyoto target, only two years behind the specified date, 2012.

It is after 1 a.m., so I am going to answer only one other point in your letter. One really needs to reduce all the kind of information you have come up with to ghg emissions per person per km. If you want to compare transatlantic crossing by air and by ship, you need figures for the total expenditure of fuel and figures for the numbers of passengers carried, as well as information on how those numbers vary with the speeds of travel. You can get incredibly many more people on a QEII than you can on a Boeing 747, and the QEII would be much more economical at 12 knots than at 28. Yes, economical sea travel will always be slow. We need a graph that shows consumption as a function of speed. However, if the QEII is nearly empty, it will use a substantial fraction of the fuel required by a fully loaded QEII. Note my reference to cargo ships earlier. Adding a few passengers makes almost no difference to the fuel expended.

Fuel economy is a steeper function of load for aircraft. A fully loaded jet aircraft requires a great deal of fuel to attain a 10,000m elevation, but from then on its fuel consumption is a matter of speed much more than load. I discussed that a bit in my last email.

The trend in the aircraft industry is to go for larger airbuses, such as can carry 800 passengers. Fitted with hydrogen-burning engines, such craft would produce no carbon dioxide. However, ALL air-burning engines produce oxides of nitrogen -- it has nothing to do with bunker oil, it has to do with the temperature of the combustion. With a hydrogen-oxygen system, engines would be essentially nonpolluting, because there would be no nitrogen, and no carbon dioxide. Burning bunker oil in oxygen would also not produce oxides of nitrogen, of course.

When all is said, however, since sea freight is much cheaper than air freight, it would thus appear that, per km of load, the present slow travel across the oceans easily beats air travel in fuel consumption. Much of the cost of air freight is for fuel, so there must be much less CO2 produced per kg per km across the oceans by slow freighter.

I am glad you are asking friends to make a similar pledge to yours.
Derek