If you are planning a trip, but you want to check the climate impact before choosing how to get there, then beware. Google has been seriously underestimating the carbon footprint of plane flights, and overestimating that of some train journeys. And its calculations don’t just appear in its search results, but also feed the sites of more and more online booking companies, like Skyscanner and Booking.com. To be fair, carbon footprints are actually very hard to get right, as the BBC’s Climate Editor, Justin Rowlatt, discovers on his own trip to Rotterdam. On the way out, he takes the Eurostar high-speed train, whose carbon emissions depend on the weather over the North Sea that day. On the way back he catches a plane, whose climate impact… also depends on the day’s weather conditions over the North Sea. So what is Google doing to fix its methodology and can we trust carbon footprint calculations at all? And do passengers even really care that much about the environmental impact of their journey, or should they be made to pay for it directly? Presenter Justin Rowlatt is joined by: Doug Parr, chief scientist and policy director at Greenpeace UK Dr Feijia Yin, assistant professor for the climate effects of aviation at Delft University of Technology Andrew Murphy, head of sustainability at Eurostar Sola Zheng, aviation researcher at the International Council on Clean Transportation Email us: theclimatequestion@bbc.com Producer: Laurence Knight Production Coordinators: Sophie Hill and Debbie Richford Series Producer: Alex Lewis Editor: China Collins Sound Engineer: Tom Brignell