The way Google calculates the climate impact of your flights has changed, the BBC has discovered.
Flights now appear to have much less impact on the environment than before.
That's because the world's biggest search engine has taken a key driver of global warming out of its online carbon flight calculator.
"Google has airbrushed a huge chunk of the aviation industry's climate impacts from its pages" says Dr Doug Parr, chief scientist of Greenpeace.
With Google hosting nine out of every 10 online searches, this could have wide repercussions for people's travel decisions.
The company said it made the change following consultations with its "industry partners".
It affects the carbon calculator embedded in the company's "Google Flights" search tool.
If you have ever tried to find a flight on Google, you will have come across Google Flights.
It appears towards the top of search results and allows you to scour the web for flights and fares.
It also offers to calculate the emissions generated by your journey.
Google says this feature is designed "to help you make more sustainable travel choices".
Yet in July, Google decided to exclude all the global warming impacts of flying except CO2.
Some experts say Google's calculations now represent just over half of the real impact on the climate of flights.
"It now significantly understates the global impact of aviation on the climate", says Professor David Lee of Manchester Metropolitan University, the author of the most comprehensive scientific assessment of the contribution of air travel to global warming.
Flying affects the climate in lots of ways in addition to the CO2 produced by burning aviation fuel.
These include the creation of long thin clouds high up in the atmosphere - known as contrails - which trap heat radiated by the Earth, leading to a net warming effect on our planet.
These additional warming impacts mean that although aviation is only responsible for around 2% of global CO2 emissions, the sector is actually responsible for around 3.5% of the warming caused by human activity.
And it is a sector that is only going to get bigger.
Since 2000 emissions have risen by 50%, and the industry is expected to grow by more than 4% every year for the next two decades, according to the International Energy Agency (IEA).
Google is open about its calculations for the tool - posting the methodology on a US software website called GitHub.
The BBC was alerted to the fact that it had posted a note saying it was changing how it assesses the impact of aviation.
It is a curious document.
Google begins saying it has made the change following "recent discussions with academic and industry partners".
It acknowledges these factors are "critical to include in the model" and cites the emphasis given to them in the latest report by the UN's climate science body, the IPCC.
Google reiterated this point when approached by the BBC, saying it "strongly believes" that non-CO2 effects of aviation should be included in its calculations.
Yet on Github Google says: "the details of how and when to include these factors requires more input from our stakeholders".
The reason for this, Google said in reply to a request for comment, was that the company's priority was the "accuracy of the individual flight estimates" it provides to its consumers.
It says it is working with academics to better understand how contrails and other warming impacts affect specific flights.
Why do aircraft leave contrails in the sky?
The UK government takes a different approach.
It recommends companies reflect the additional impacts of flying by multiplying the CO2 emissions a flight generates by a factor of 1.9 - effectively doubling their impact.
In its guidance to companies, the UK's Department for Business, Energy & Industrial Strategy warns the value of this multiplier is "subject to significant uncertainty", but says "there is currently no better way of taking these effects into account".
Transport and Environment, a group campaigning to reduce the environmental impact of travel, agrees.
"Current scientific knowledge is sufficient to state that non-CO2 effects represent two thirds of the total climate impact of aviation", it says.
"The industry has hidden this problem for decades... Google should show customers the non-CO2 effects for each flight, as the European Parliament has proposed to do."
Google's changes are likely to have far-reaching effects.
The company's carbon calculation methodology is widely recognised as the industry standard in aviation.
It is used by Skyscanner, one of the biggest online travel agencies in the world with more than 100 million visitors a month.
A number of other major online travel businesses including Booking.com, Expedia, Tripadvisor and Visa have said they intend to use it too.
Google's chief sustainability officer, Kate Brandt, has said the company aims to "build tools that enable travellers and business around the world to prioritise sustainability".
Industry experts say the decision to change its methodology will have the opposite effect.
"I worry the impact of the equivalent of hundreds of millions of tonnes of CO2 will be ignored because it has become invisible to customers," says Kit Brennan, a founder of Thrust Carbon, a UK company specialising in helping businesses reduce the effect their travel has on the climate.
He fears consumers could come to believe that non-CO2 impacts on the climate are not relevant in the longer-term, despite the science that contradicts this view.
That would mean up to 1.5% of the warming caused by human activity would be being ignored and the pressure on airlines to reduce their emissions would be cut accordingly.
This article orignially appeared on BBC News