A blog written for the Guardian’s Travel website about a new price-comparison website that compares the environmental impact of flights as well as their price…

Price comparison sites now play such a major role in our travel choices that it’s hard to think of a time without them. They’ve helped to pull the rug out from under travel agents who used to be our only conduit to finding the best prices. It feels as if we’ve booted them out of their swivel chairs and taken their place at the bookings terminal instead.

It’s largely an illusion, of course. How do we really know that all the prices have been accurately and fairly compared? After all, the travel sector is notorious for its price volatility, where the cost of a flight or hotel can change by the minute. And how many sites are being compared when you make a search? Have any of them paid to be among the sites being compared? Have any been left out, as a result? The next logical leap will be a comparison site comparing price comparison sites. Don’t tell me, there’s one already out there.

You’re more than welcome to use this blog to list your favourite price comparison sites, or list your gripes, but that isn’t the purpose of this blog. Rather, it is to discuss the arrival of a new price comparison site – one that, yes, compares prices, but also compares the carbon footprint of the various airlines it lists when you make a search.

The Carbon Friendly Flight Finder is collaborative effort by The Carbon Consultancy, Global Travel Market and FlySmart.org and when I had a little play with it this morning it seemed to do pretty much what it says on the label. Type in a search for a return flight from, say, London Heathrow to New York JFK leaving this Saturday and returning a week later and it tells you that Opodo is currently offering the best deal with an Air France flight priced at £270. (The most expensive option is an Aeroflot flight offered by Travelocity priced at £2,807. The mind boggles.)

However, it also tells you that the Air France flight has a “carbon ranking” of “3”, compared to, say, KLM (“7) or Virgin Atlantic (“1”), with “1” being the best and “10” the worst. The Carbon Consultancy says that the carbon rankings for each airline are not based on the actual emissions of that particular flight, but on an assessment based on a wide range of factors. You can read its a detailed explanation. But I’ll save you the hassle: all it is saying that the carbon ranking it gives to each airline is little more than an educated guestimate.

I welcome seeing this additional information published right next to the price, but in reality we’re talking about very small differences in fuel efficiencies between the airlines, especially when comparing them over long-haul routes. The variables that make the real difference over the same distance are whether the flight is direct or has to first go via a hub (which the Carbon Friendly Flight Finder does factor in), or whether, if it’s short haul, you are travelling on a jet or a turboprop plane.

Rather than being given a rather vague ranking out of 10, I would prefer to see the actual listings of grams of CO2 per passenger kilometre travelled. And, further still, see this compared against, where they exist, other travel options such as trains, ferries, and coaches. (See Fred Pearce’s recent Greenwash column for a discussion about making just such comparisons.) I would also like to see the airline’s carbon rankings accurately reflect the fact that the carbon dioxide they emit is done at high altitude which has a significantly greater impact on the climate – the so-called radiative forcing multiplier – than emissions down on the ground. It is only by making such comparisons that an accurate picture can be painted of the various “carbon rankings” of the choices that lay before us.

There’s a danger of losing perspective of the fact that by far the best option is to reduce the amount of flying you do, wherever possible, rather than fretting about whether or not flying with British Airways is a little bit better in terms of emissions than, say, flying with Virgin Atlantic. Flying London to New York with either of them will still result in well over a tonne of carbon dioxide entering the atmosphere per passenger. And if you want one extra comparison, that’s broadly equal to one month’s worth of emissions resulting from the (non-flying) lifestyle of an average Briton.

As is the case with carbon offsetting (which The Carbon Consultancy promotes), I fear that such initiatives only ever really end up providing a comfort blanket for those who don’t wish to engage with the hard-edged environmental realities that now circle over our holidaying habits. Do they really offer anything more than the dangerous illusion of “job done”?