To help users find more sustainable travel options, Google launched a feature Wednesday that will show a carbon-emissions estimate for almost every flight in its search results. Now, along with price and duration, travelers will be able to use environmental footprints to compare and choose flights.

James Byers, a senior product manager on the Google travel team, said the emissions estimates are based on a combination of factors, such as the distance of a trip, the number of stops, the number and class of seats on board, the type of aircraft, and data from the European Environment Agency.

The feature, which follows another eco-friendly feature for Google’s hotel searches, could be valuable in the fight against climate change, suggests Katharine Hayhoe, chief scientist for the Nature Conservancy and professor at Texas Tech University.

“I am a big fan of knowledge, and I think that simply making people aware of the amount of carbon that their trips is producing is going to be really valuable,” said Hayhoe, author of “Saving Us: A Climate Scientist’s Case for Hope and Healing in a Divided World.

In a similar way, Hayhoe points to the effect of calorie-counting, or electric bills that show a customer’s usage compared to their neighbors’. If people can see how much they’re consuming, or put their usage into context, it can “nudge” them to change their behavior, she explained.

And the transparency could nudge airlines, too.

“It is going to allow the companies that are doing the right thing — that are implementing experimental technology such as biofuels or electric planes — to highlight the benefits in a way that everybody will be able to immediately see,” Hayhoe said.

Milan Klöwer, a PhD student of climate computing at the University of Oxford, who also has side projects researching aviation’s contribution to global warming, agrees that sharing emissions data to the public is important for creating competition between airlines to improve environmental practices.

“However, using such an assessment as a choice for customers has definitely also a strong greenwashing aspect to it, because it shifts the responsibility away from the company/industry and towards individuals,” Klöwer told The Post in an email.

He added: “In that sense, great that a customer has the choice between a flight with 161 kgCO2 emissions or 191 kgCO2 emissions, but this completely obscures that an airline also has the choice whether they want to invest more into efficiency/reduced carbon emissions or not.”

Byers, the product manager, said Google has gotten a great response from the airline industry, which seems to respect the signal the tool sends, he said.

“We see emissions and a better choice by consumers to be one lens that you can look at travel through, and it tells airlines that this issue matters,” Byers said. “It matters alongside sustainable aviation fuels, alongside modern equipment, alongside good operational practices. But it’s another signal for them, and we believe they’ll value it.”

“Customers are making sustainability a priority when it comes to travel, and so are we,” Jill Blickstein, American Airlines’ managing director of environmental, social and governance, said in a statement.

Byers said the flight-emissions initiative started a few years ago as a side project among employees. But since then, he said, Google has created a team to focus solely on travel sustainability, part of its larger push to give users tools to make more eco-friendly decisions, from booking travel to shopping online.

And now that it’s hatched a model for calculating air-travel emissions, Byers said, Google wants to make wider use of it. As a new partner in the Travalyst coalition — the sustainable-travel initiative from Britain’s Prince Harry, with founding partners such as, Tripadvisor and Visa — the company will share it freely.

“We will, with Travalyst, help develop this model into a standardized way to calculate emissions that can be used across the industry,” Byers said. “We believe it’s critical that the model we build is an open model where the industry and where our travelers understand all the factors that go into it. And we hope and will seek its adoption as broadly across the industry as possible.”