Google has changed the way it calculates the climate impact of air travel in a way that dramatically undercounts key factors in aviation's contribution to climate change.
That might not sound like a big change, but as a result, estimates of carbon emissions per passenger are now drastically lower than they were before the change. That's because non-carbon dioxide emissions and effects like contrail formation contribute to more than half of the real impact of flying on the climate. Google itself acknowledged the issue when it quietly announced the change on GitHub last month, saying that non-carbon dioxide "factors are critical to include in the model, given the emphasis on them" in the latest Intergovernmental Panel on Climate Change report.
"Google has airbrushed a huge chunk of the aviation industry's climate impacts from its pages" Doug Parr, chief scientist of Greenpeace, told the BBC.
Contrails are the wisps of ice crystals that form in the wake of a plane. They're also a huge contributor to the climate impact of flying and are responsible for more than half of flights’ climate impact and up to 2% of total global warming. That's a big number, and one that academics and some in the aviation industry are working on cutting down.
Being able to accurately estimate and predict the climate impact of contrails is still a difficult task given the time of day, temperature and altitude of a flight can all play a role in how severe the impact is. Yet Google has chosen to exclude the factor entirely from its flight emissions calculator.
Public knowledge of the climate impact of contrails is already low. But the new changes by Google to its flight calculator put them further out of sight, out of mind. The calculator's reach spreads beyond Google's pages; the BBC notes that it's used by Skyscanner, Expedia and other major travel sites.
The decision to remove contrails from Google's calculations is particularly worrisome for the climate because, unlike reducing carbon dioxide emissions, cutting down on contrails and their warming impact could have immediate benefits. That's because while carbon dioxide stays in the atmosphere for centuries, contrails' warming impact is fairly short term. Reducing them would cut down on climate damage in the near term, even as the aviation industry works to cut carbon emissions over the long haul.
Sources familiar with the company's work told Protocol in April that Google was working with industry experts on better integrating contrails into its carbon calculator. As recently as last October, the page stated that Google Flight's emissions estimates include both carbon dioxide emissions and non-carbon dioxide effects, including contrails, using estimates based on "lower bounds from scientific research," citing a 2018 Nature paper.
Any mention of contrails has since been removed from the page. In last month's GitHub announcement, Google said it's working with researchers and other partners to improve modeling non-carbon dioxide factors, and that it would be "sharing updates at a later date."
"We strongly believe that non-CO2 effects should be included in the model, but not at the expense of accuracy for individual flight estimates," a Google spokesperson said in an email noting that the company is working "on soon-to-be-published research" on the topic.
Update: A comment from Google was added to this story on Aug. 25, 2022.