Google wants to help you 'fly greener' but is it splitting hairs with carbon-rated airfares?
From this week the search engine will provide carbon emissions in kilograms for all flight results.
When comparing fares lower emission options for a route will be highlighted in green, to help travellers pick flights that are (on paper) more carbon efficient.
Carbon estimations are made from a variety of data sources including emissions information from the European Environmental Agency, seat layout and flight times provided by airlines.
For example, searches for flights from Christchurch to Auckland show that a Jetstar service 8 per cent and 9kg more efficient than an comparable A320 service by Air New Zealand.
Combination of slightly shorter flight time and nine more seats on the Jetstar service help keep per passenger emissions down.
Air New Zealand say they are in favour of informing customers of their journey emissions but that the tool may mask overall carbon savings made on the ground or across the rest of the network.
"We are supportive of providing customers with information on the carbon impacts of their flights. It is worth noting that carbon accounting is nuanced and based on several assumptions," says Meagan Schloeffel, the airline's head of sustainability.
The calculations are more of a guideline for picking greener flights, says Google. Wind stream direction and other environmental factors are not yet taken into account, neither is whether aircraft are using alternative synthetic bio fuels.
In some parts of the world flight information may not be available or certain data missing.
More carbon conscious travellers can now use the search engine to choose flights when more energy efficient aircraft are being used for the route.
Newer aircraft, such as the A321neo, can drop the per passenger emissions even further, to around 87kg per seat.
Although whichever aircraft is used, the total carbon burned per flight is around 18.7 tonnes for the route between the two cities.
Airplanes account for a small portion of emissions that cause climate change — about 2 to 3 per cent — but their share has been growing rapidly and is expected to roughly triple by mid-century with the global growth in travel, reports the Associated Press.
The 'green flights' tool follows on the heels of a "green booking" tool for hotels and rating fuel efficiency on driving routes searched via Google Maps.
"Climate change is no longer a distant threat — it's increasingly local and personal," CEO Sundar Pichai wrote in a blog post on Wednesday. "We need urgent and meaningful solutions to address this pressing challenge."