Comparing flying with driving

Out of curiosity about greenhouse gas emission claims about airlines, I decided to use official NZ Government figures about carbon emissions from aircraft and cars to compare a Boeing 737 flight on a typical NZ short haul flight. Our short hauls are much shorter than European or American routes.

I learned that an average emission rate for a single 737 flight was already worked out by an agency called NIWA. NIWA stands for National Institute for Weather and Atmospheric research.

For a typical NZ short haul journey the average was 3,860kg of CO2. The route between Auckland and Wellington is one of the shortest jet flights in New Zealand so is perhaps less than average but let’s stick with 3,860kg of Carbon.

I then compared one car traveling Auckland to Wellington by great circle distance (not by the greater road distance) at 297.5 grammes of CO2 per kilometre for 630 km (340nm) It works out that one car will burn 187.43 kg of CO2.

Being generous and assuming for every two passengers on a 114 seat aircraft they might double up and share a car ride, I worked out that 57 pax (half of 114 pax) sharing a car will emit a whopping 10,683kg of CO2, driving from Auckland to Wellington.

If the same 57 couples flew, they would each only cause 33.86kg of CO2 emissions per person or 67.72 per couple. That means flying is 33.86kg per person and driving (car sharing) is 93.5kg.


Using Trains between Wellington and Auckland

Our most common locomotives in New Zealand are GE diesel-electric engines of 1650 hp (DC class loco) hauling 740 ton freight trains, or in the case of pax services on the Auckland Wellington route, 247 pax capacity passenger carriages. patronage is only around 60%.

I if you crunch the numbers, on the same journey from Wellington to Auckland as the jet flight mentioned above a typical NZ diesel loco burns 7,581 US Gals, and emits 3.188kg of CO2 per kg of diesel fuel. So for that journey a passenger train emits 24.169 tonnes of CO2 or 53,165lb of CO2.

Per pax on a 247 pax train that amounts to 97.85 kg of CO2 per person (215 lb). Trains are efficient for hauling heavy cargo loads, but not for passenger journeys.

Remember on the same route per person by car (sharing as couples) each person will emit 93.5kg of CO2 and flying by Boeing 737 around 33.4kg of CO2. By train it is 97.85kg per person.

Flying in an airliner seems about as clean and green as one can get. Put another way boys and girls, if you want to destroy the environment with CO2 emissions, don't fly.

Aviation only accounts for 2% of the world's emissions apparently. Private cars account for around 30% of emissions. Cars are the area in which we can most easily change Carbon emission behaviours with hybrid cars and biofuels.

Airliners are unable at the moment to utilise biofuels. Even though gas turbine (jet) engines will operate on soya bean oil and probably various other vegetable oils, no biofuel has yet been able to be certified for flight in very cold conditions found at high altitudes, where jet engines are most fuel efficient. That was the sole reason why airlines were exempted from the Kyoto Accords.

People who vilify the airline industry for Carbon emissions need to examine the facts and be fair. The behaviour most easily changed is the type of fuel we all use in private cars.