What do car CO2 figures mean?
Proposed ‘feebates’ have put the focus on car CO2 figures. But they’re the same as fuel economy numbers, with the same problems, writes
The New Zealand Government’s proposal to introduce a ‘‘feebate’’ style tax on newly registered cars has thrown the spotlight on CO2 as a measurement of individual vehicles’ environmental impact.
In fact, has had a number of communications from readers asking (‘‘demanding’’ might be a better term in select cases) why we don’t give CO2 figures for vehicles that we review.
The short answer is that we haven’t in the past because it’s not something readers have expressed much interest in. At least until now.
We’ve always steered towards the official fuel consumption figures that come from mandated tests all over the world.
They’ve always seemed a bit more relatable from a consumer point of view: litres per 100km gives you an idea of how much it’s going to cost you to fuel your car and how often you’ll have to do it. It’s hard to visualise a CO2 output.
However, the feebate proposal has put more of an emphasis on environmental impact (albeit related to a different kind of potential impact on car buyers’ bank accounts) and CO2 now seems set to be a key part of consumer car conversations.
So from now on we’ll include those CO2 figures in our technical data alongside everything else. More information is better, right?
But we won’t really be telling you anything new because CO2 figures are basically the same as fuel economy figures. They’re really just different ways of expressing the same thing.
To state the obvious, a CO2 figure simply gives you the amount of greenhouse gas produced by burning fossil fuel.
For example, a Toyota Corolla – New Zealand’s best-selling passenger car – emits 138g/km from its petrol engine, according to official figures.
Those ‘‘official’’ numbers come from the same tests that give us fuel economy figures (6.0 litres per 100km in the Corolla’s case). So we wouldn’t have that CO2 figure for Corolla without the fuel economy number. You can convert from one to the
other and back again.
If you want to play at home, the Energy Efficiency and Conservation Authority (EECA) has a handy online calculator that allows you to choose a fuel and calculate its CO2 impact.
All good, but it’s important to know that those CO2 figures are subject to the same vagaries as fuel economy results.
The New European Driving Cycle (NEDC) has long been a standard for fuel consumption, although many NZ distributors also reference the closely related Australian Design Rules (ADR 81/02 if you want to be technical) test.
We’re also now in a period of transition from NEDC to the new Worldwide harmonised Light vehicle Test Procedure (WLTP) mandated in Europe, which is claimed to more accurately reflect real-world driving. In other words, the official fuel consumption figures will generally be higher under WLTP than NEDC.
The US has its own system, of course. And so on.
So there are different standards floating around out there, and CO2 results – just like fuel economy numbers – will be different under each.
So while a new focus on CO2 might seem like a one-size-fits-all measurement by which we can judge the environmental impact of a vehicle, if you’re comparing one model with another it’s still important to know which test produced the result.
One area where CO2 is a good leveller is in comparing petrol with diesel. CO2 is slightly higher for burning diesel than petrol, but of course diesel vehicles consume much less fuel for a given distance. So if CO2 really is your focus, sticking to those figures does give each fuel type a level playing field.
There’s a lot of focus on cars around climate change and rightly so; after all, there are a billion of them currently driving around the Earth.
But how do they compare with, say, air travel. According to the Air New Zealand carbon offset calculator, one person flying Auckland-Queenstown (a distance of 2050km) return generates 276kg of CO2. That’s your portion of a plane being shared with lots of other people, many of whom you probably won’t like.
Having a Corolla all to yourself for the same distance on road results in almost exactly the same CO2.
All I’m saying is, don’t feel bad about hiring a small Toyota and having a driving holiday in the South Island.