CO2 study: planes may be less efficient

Increased leg room that passengers enjoy on long flights could be driving up carbon emissions in air travel, despite efficiencies touted by the industry.

University of Otago researchers analysed commercially sensitive fuel sale data in order to update a 2007 estimate of international aviation emissions associated with New Zealand.

As more people are travelling and more goods are being freighted into and out of the country, an increase in carbon emissions was expected from the 5.5 million metric tonnes of carbon dioxide (MtCO2) estimated more than a decade ago.

However, the increase the researchers uncovered outpaced their expectations.

The way airlines were operating appeared to be a factor, and researchers believe providing more space for passengers and therefore having fewer people on board could be a factor.

Using updated fuel sale data from a decade later, the researchers re-created the 2007 study, which was completed in 2011.

The leader of the research team, department of physics senior lecturer and He Kaupapa Hononga: Otago’s Climate Change Research Network co-director Dr Inga Smith said it was now estimated that the country’s 2017 international aviation CO2 emissions were a surprising 8.4MtCO2 in total.

"That’s a big number because it is not counted in New Zealand’s domestic emissions.

"If you were counting all of that, it would be about an extra 10% on top of what does count in our greenhouse gas inventory.

"We expected the emissions to go up in total, because we knew there were more people flying and, it turned out, slightly more cargo as well.

"We thought that it would go up, but maybe it would be a little less ... because maybe the planes are more efficient — that’s what we always hear. We didn’t find that at all.

"When [lead author assistant research fellow Anna Tarr] first came to me, I said ‘that can’t be right’."

Yet, the numbers were confirmed.

International visitors’ emissions increased 48% over the decade and New Zealand residents’ increased 86%, Dr Smith said.

In total, emissions from passenger travel to and from New Zealand increased by 60% over the decade.

This increase was despite the fact that passenger numbers and the distance they travelled only increased by 46%.

Emissions from short-haul flights stayed relatively the same, but long-haul flight emissions increased by 14%.

While it was outside the scope of their study, the researchers were left to believe that the way aeroplanes were operated was a deciding factor.

"We’d heard that aircraft were getting more efficient over time.

"This apparent decrease in the efficiency of aeroplanes servicing New Zealand, across 21 airlines, seems to be due to operational factors such as seating density," Dr Smith said.

The University of Otago study was published in open-access environmental science journal Environmental Research Communications last month.