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When I travel, I try to limit my environmental impact. I don't want to refrain from travelling completely, but when I do travel, I tend to favour ground-level transportation over air-transportation, if distances are not too large (e.g., if traveling over-land would take more than three days, I might fly anyway.

A well-filled train usually has a much lower ecological footprint per traveller-kilometer than an æroplane, particularly if the train is hydro-electrical, such as in Sweden. High speed trains and diesel trains are already worse, but still considerably better than flying. But what about ferries? Fuel used by (fast) ferries can be quite dirty. On the other hand, ferries may carry over a thousand travellers, sometimes several thousands.

How does the ecological footprint per traveller of a typical, well-filled ferry compare to the ecological footprint per traveller of an æroplane? For the sake of this question, I'm interested in ferries going out on the open ocean on routes that potentially compete with airplanes, not in local ferries crossing a river, a lake, a fjord, or a small sound (there's probably no mode of transportation spanning as many orders of magnitude in size as a boat).

For example, travelling from Stockholm to Warsaw, one might identify four alternatives with a somewhat similar travel class, where all day trains are 2nd class and all overnight accommodation (train or ferry) is with a bed/berth in a shared cabin.

  • flying in an ordinary economy seat
  • by train+ferry via Nynäshamn–Gdańsk
  • by train (almost) all the way via Copenhagen, Hamburg, Berlin (a considerable detour)
  • (only part of the year) by train-on-ferry via Malmö and Berlin (Berlin Night Express)

Which one is the most ecological?

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  • Personally I would like to have the comparable data of any available classes, so I can make a choice and see the difference between them.
    – Alendri
    Oct 7, 2012 at 13:13

5 Answers 5

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Emissions figures for ferries are surprisingly hard to find compared to those for cars, trains, and aircraft. The best source I've found for ferries is this report:

Åkerman, Jonas (2008). Klimatpåverkan från utrikes resor ["Climate effects from foreign travel"]. Report TRITA-INFRA-FMS 2008:7. Stockholm: Royal Institute of Technology.

Åkerman looks at foreign travel by residents of Sweden. He sources ferry emissions figures from public environmental impact reports and personal communications from Silja Line and Viking Line, the main operators of ferries between Sweden and Finland. These are the final figures he arrives at for ferries and other major modes of transport:

Mode of transport Average greenhouse emissions (kg CO₂-equiv. / passenger-km)
Air 0.24
Car 0.09
Ferry 0.17
Bus 0.02
Rail 0.04

There are caveats and significant uncertainties attached to all these figures, but even taking them as order-of-magnitude estimates indicates that the train produces far fewer greenhouse emissions than the ferry.

Estimating the relevant distances for your Stockholm-Warsaw trip with Google Maps gives me:

Route Distance (km) Emissions (kg CO₂-equiv. / passenger)
Air, direct 800 192
Ferry + Rail via Gdańsk 570 + 350 97 + 14 = 111
Rail via Hamburg 1800 72

I didn't do the maths for "Berlin Night Express" route, but I imagine it would be similar to the train-only route since the Trelleborg-Sassnitz crossing is a short one.

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    Interesting! As a side note, I'm surprised by the bus vs. rail figure, considering that rail is often electric and electric rail may be nuclear or renewable, whereas buses are essentially always diesel.
    – gerrit
    Jun 14, 2019 at 12:20
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    It would also be interesting to see how the emissions of ferries are divided between foot passengers, car passengers, and freight sharing a ferry
    – Chris H - UK
    Jun 14, 2019 at 12:26
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    @gerrit Yes, that surprised me too. My guess is that it's skewed by the restriction to international travel, which in the case of buses often means pre-booked charter coaches with high occupancy ratios. Åkerman assumes 70% occupancy for buses which is probably reasonable in this case, but would probably be unrealistically high for a lot of local/regional bus services.
    – Pont
    Jun 14, 2019 at 12:55
  • I suspect part of the issue is that most ferries are car ferries, so the ferry has to lug around not only the passengers but also their cars.
    – Peter Green
    Feb 17 at 20:22
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Comparing aeroplanes and trains shows that aeroplanes are very much the least ecologically friendly mode of transport. As an example from http://www.seat61.com/CO2flights.htm:

enter image description here

A site which has some limited data comparing plane, train and car+ferry gives us the following data, but I would assume that the car emissions skew the numbers somewhat, which leads me to believe that the ferry could be the lowest impact:

enter image description here

Caveat: these only take CO2 into account, and there are many other ways transport impacts the environment.

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It's worth pointing out that most figures for ferries assume you are taking a car.

Most of the answers already given use such figures. However, there is also the important case to consider of foot passengers. According to Seat61, the UK's DEFRA uses a nominal figure of 22.54 grams of CO2 per foot passenger kilometre, which would put ferries within the same order of magnitude as trains and buses.

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    If anyone can find a primary source for this DEFRA figure I'd much appreciate it, I had a quick Google and couldn't spot one
    – Muzer
    Feb 17 at 13:38
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    Huh, this is interesting! The same order as trains, despite trains being largely electric and ferries using some quite dirty fuel? Passengers also have a lot more space per person on ferries, and water has quite high resistance. I agree that a primary source would be very nice to have here.
    – gerrit
    Feb 17 at 14:15
  • I suspect the main factor there is that trains go much, much faster than ferries. I could be wrong though!
    – Muzer
    Feb 17 at 14:20
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    @Muzer Depends. Some modern RORO-ferries like the MS Color Fantasy get quite close to cruise ships IMO, whereas others like MS Wawel are much more basic. Small cable ferries might even be human powered (but are not the scope of the question).
    – gerrit
    Feb 17 at 16:31
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    @gerrit, ships, even ships burning the dirtiest bunker oil available, are phenomenally efficient -- a cargo ship is nearly an order of magnitude more efficient than a train for moving goods. The thing that hampers ferries is the low load factor: even a fully-loaded ferry is sparsely loaded compared to a passenger train.
    – Mark
    Feb 18 at 4:33
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Ecopassenger provides a search engine comparing the environmental impact of various travel options. They're focussed on trains, planes, and automobiles, but some train routes include ferries. Comparing only trains shows, as expected, that trains are by far the most environmentally friendly in all aspects:

Hamburg - München
Searching for Hamburg – München

One ferry included in train search engines is Stockholm - Turku. Searching for Stockholm - Helsinki includes this ferry, and shows very bad news for ferries (at least this particular ferry):

Stockholm - Helsinki
Searching for Stockholm - Helsinki

This seems confusing, because the methodology states about ferries:

For several relations ferries are part of the journey. In this version of EcoPassenger it was not possible to estimate the energy consumption and emissions for ferries because the timetable data of Merits (see the following section) did not allow identifying ferries as separate transport mode. Thus the distance for the ferry transport with train and car is considered, but no separate energy and emission values.

which makes me wonder what the big orange bar is about. I have asked the UIC (which hosts Ecopassenger) if this result really means what it seems, because it would seem to indicate flying is much cleaner than train+ferry, which is very different from what I thought or from other estimates.

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In the EU, there is the THETIS law, mandating publicisation of CO2 emission by ferries.

However, this data is not very useful in itself and a lot of factors have to be taken into account for a fair per passenger calc (Writeup (in French), study)

From the site made from the above writeup futur.eco, a comparaison between plane and ferry would be as such for a leg between Marseille and Bastia in Corsica

Mode Distance (km) Emissions per passenger (kg)
Plane 361 43
Ferry 338 124

The ferry calculation is as follow :

  • Travel duration : 18:45 - 08:00 (N+1)
  • Cabin : yes
  • Consumption of services : no
  • Car : no
  • Nb. of passengers : 1

The Plane calculation is from IATA CO2 Connect from MRS-BIA in economy using the A320ceo as this is the most used plane on that route

I haven't had the time to make other comparaisons but if the data from THETIS and the parsing from futur.eco is to be believed, taking the ferry has an extremely larger footprint than flying

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