This is a guest post from John Polkinghorne
There’s a difference between “pollutants” and “greenhouse gases”. Cars put out a few pollutants, such as nitrogen oxides, carbon monoxide, sulphur dioxide and particulate matter – which means unburnt carbon (soot) and worse. These contribute to localised air pollution and health issues. In terms of these pollutants, though, cars today are much cleaner than they were a few decades ago.
Greenhouse gases are another story. In the car engine, petrol or diesel is combusted with oxygen, to produce energy and carbon dioxide (CO2). This chemical reaction is what makes your car move, and CO2 is the inevitable product. This is different from the other nasty stuff above, where the pollutants are byproducts and can be reduced through higher-quality fuels, better filters etc.
CO2 is of course a greenhouse gas, contributing to global warming. Cars may become more efficient in the future – in fact, new cars could become 20% to 40% more efficient over the next 20+ years – but CO2 will always be generated, as it’s the main product of the chemical reaction which powers the car. And it will always be created in proportion to the amount of fuel used, so saying a car is “low emissions” is the exact same thing as saying it is “fuel efficient”. As I showed in a previous post, our fuel efficiency doesn’t seem to have improved in the last few decades.
CO2 is sometimes referred to as a pollutant, and the US Environmental Protection Agency has now classified it as such, but it’s quite different from nitrogen oxides, soot and those other grimy things. It doesn’t have much of a local effect, but it contributes majorly to global warming.
How much CO2 do our cars produce?
According to the Ministry for the Environment (New Zealand’s Greenhouse Gas Inventory 1990–2010), the road transport sector accounted for 12,514.1 gigagrams of CO2-equivalent emissions in 2010. This is a rather silly unit in my opinion – although Quagmire from Family Guy might disagree – so let’s convert it to tonnes instead. With that cleared up, road transport accounted for 12.5 million tonnes of CO2-equivalent emissions in 2010.
New Zealand’s total ‘net’ emissions (after accounting for forestry, which removes CO2 from the air) were 51.7 million tonnes. So, road transport makes up 24.2% of our net emissions. But this includes freight and other non-passenger uses. We’ve got to dig a little deeper to find how much is generated by cars. For this, I turn to the very interesting Annual Fleet Statistics published by the Ministry of Transport. Figure 1.10 shows that 65.2% of road transport emissions come from the “light passenger fleet”, which includes passenger cars and vans.
So, this suggests that cars (and vans, let’s not forget the vans, although it’s only passenger vans and not goods vans and I really can’t imagine they make up a big chunk of this) are producing 65.2% x 12.5 million tonnes = 8.15 million tonnes of CO2-equivalent emissions in New Zealand each year.
That’s a little under two tonnes per man, woman or child in the country. It’s more than your car weighs, and it’s about 15.8% of our country’s net emissions total.
What does this mean for you?
The average NZ car uses 10 litres of fuel to drive 100 kilometres, although this can be quite a bit higher or lower depending on the car, the driver and the traffic. Petrol produces around 2.3 kilograms of CO2-equivalent emissions for every litre – which is about three times as much as the petrol itself weighs, incidentally.
Every 100 kilometres you drive, then, you’re producing 23 kilograms of CO2. The average car drives some 12,000 km a year, producing 2.8 tonnes of CO2.
As consumers, the best thing we can do to reduce our contribution to global warming is to change our transport habits. Better driving makes a small difference, more efficient cars can make a bigger difference. Carpooling is better still, and public transport is much better than that. I’ll look at public transport emissions in my next post.