95 right? More likely wrong.

The conversation after Sunday lunch somehow migrated to the topic of octane in petrol. A woman was complaining that her husband makes her buy premium 95 petrol even though it costs more. The husband, who drives a Prius, was defending the extra expense on the grounds that the extra octane makes the engine run more efficiently, reducing carbon dioxide emissions.

I had never heard this before, and any idea that might reduce C0₂ emissions catches my ear. Was I unwittingly damaging the atmosphere by my frugal habit of buying the cheaper petrol? I had to look into this.

One of the best sources of information available was an Engen FAQ on octane, which confirmed, as I had suspected, that we cheapskates are right. “The great majority of vehicles inland . . .  are satisfied by 93 octane,” the website explains. “The use of octane grades higher than your vehicle actually requires will cost you more, cost the country more and have a negative environmental impact.”

The FAQ explains that this is because:

“There will be no additional benefit to driveability or performance of your vehicle if you use a higher grade than it requires. Petrol with a higher octane requires more severe refining and greater energy use in the production process. If not offset by greater fuel efficiency of the vehicle using the fuel, this extra energy use is wasted energy. This wastage results in higher emissions of greenhouse gas (carbon dioxide), which harm our environment.”

What the Engen website did not explain is the relationship between octane and altitude. Octane is purely a measure of how petrol reacts to pressure. Higher octane fuels will not ignite prematurely under higher pressure, which could cause engine knocking. But the Highveld altitude has a low ambient air pressure, which reduces the pressure inside most engines and thus reduces the need for octane. I spoke to John Fitton, an independent petroleum industry consultant, who said that most engines requiring 95 octane at the coast—as is recommended in the manual for my Honda Jazz—only need 91 octane in the Highveld.

South African regulations allow for three grades: 91, 93 and 95. At low altitude, 95 is the only grade available. Highveld petrol stations offer 93 and 95, but 91 isn’t sold at all in South Africa. Fitton told me that this is only because the petrol retailers are trying to satsify ill-informed customers. “Consumers think octane is power,” he said.

Fitton pointed out that the lower octane requirements at higher altitude do not apply to turbocharged engines and a minority of newer engines with gasoline direct injection. (These engines are sold under a variety of brand names such as Mercedes-Benz’s Charged Gasoline Injection, VW’s FSI and Ford’s EcoBoost.) Owners of these cars should obey the instructions in the car manual whether they are in Lesotho or Lambert’s Bay. For the rest, Fitton said, “There’s no advantage to using the higher octane; you’re just going to spend more money and emit more C0₂.”

At 75 rand per gram above 120 g/km, the tax can add up. So check the website of the National Association of Automobile Manufacturers of South Africa for the carbon emission of the vehicles on your list before you head to the showroom. Despite the howls of protestation from the auto industry, I found a surprising number of cars that will attract no tax. Here’s the list:

Audi A4 2.0 TDi 100kW, Citroen C1 1.0i and C3 1.6 HDi, Daihatsu Charade 1.0, Fiat 500 1.2, Ford Fiesta 1.6 DV6, Honda CR-Z  Hybrid, (as well as the anticipated hybrid Jazz), Peugeot 107 and 207 1.6 HDi, Smart fortwo, Toyota Prius (the cleanest of the lot) and the VW Golf 6 1.6 TDi, Polo 1.6 TDi, and CrossPolo 1.6 TDi. BMW’s 320d Dsl comes so close to the mark that the tax will have no noticeable impact on the sticker price.

And in case you missed the latest Star Motoring, here are my thoughts on the tax:

The “debate” over the carbon tax on new cars is hardly a debate at all. The Retail Motor Industry’s opposition to a tax based on vehicle carbon dioxide emissions receives plenty of publicity, and the government fails to rise to the defense of the new tax, due to be implemented in September.

But there are plenty of good arguments for taxing CO₂ in the car showroom that are not being heard. The decision made at the point of sale is a fateful one, and not just for the new owner of the car. Should the buyer naively choose a thirsty vehicle without calculating the lifetime fuel costs in advance—a common occurrence—the environment will lose regardless of what happens after he drives away from the dealer.

We do not live in Japan. Cars do not head for the scrapheap after 100,000 kms. They are passed down the economic ladder to poorer and poorer drivers until they literally fall apart. So if the new owner of this vehicle suddenly turns green or tires of paying dearly at the pump, he will sell it on to someone else to do the polluting for him.

Similarly, if he decides to drive less to compensate for his fuelish vehicle—the alternative suggested by the motor industry—the car will last longer. He may be delaying its ultimate output of CO₂, but if the car will last 300,000 kms and emits 200 grams of CO₂ per kilometre, it will eventually send 60 tons of carbon dioxide into the atmosphere.

If, however, the new tax prods him to save R5250 by purchasing a vehicle that emits 130 grams/km instead, the planet will be spared 21 tons of CO₂ in that single decision.

The auto retailers do have some reasonable proposals to protect the environment. They are correct that a carbon tax on fuel gives drivers of both new and used vehicles a flexible incentive to save by driving less. They argue convincingly for stricter fuel guidelines that will give South Africans access to the cleanest new engines and improve the emissions of existing cars as well.

But global warming will not be stopped by drivers cutting back on kilometres. It will not go away because our fuel is cleaner. Nor will it be fixed by a carbon tax on inefficient new cars. It will take all of these approaches in combination and many more.

Many eminent scientists believe that to keep the earth from warming into the danger zone of higher than 2 degrees above pre-industrial levels, greenhouse gases will have to cut by 80 or even 90 percent in the developed world. We don’t need to choose the single best solution among many; we need to adopt all reasonable solutions.

The carbon tax on new vehicles is not perfect. It addresses only one facet of the problem, and the tax is calculated into the sticker prices instead of staring consumers in the face. But we consider it entirely acceptable to fund the government with imperfect taxes on such virtues as saving (interest tax), earning wages (income tax) spending (VAT) and running a successful business (corporate profits tax). Compared to these, a tax on the polluting capacity of new vehicles smells like a rose.