[morsch]

I wonder. From first principles, I don't quite understand how cruise ships can be that bad.

It's not obvious to me how tourists on a ship can use much more energy than of they were in a land based resort. Yes, they're moving, but ships move very efficiently, which is why it's used for bulk transport. And tourists on land also move, often by car. Or are cruise ships more comparable to cars than cargo ships in terms of movement?

The facilities themselves, pools, rides, restaurants, A/C, theatres, are all also used on land and I don't the why they would be less efficient on a ship. Unless being on a ship results in trade-offs that impact efficiency, e.g. less insulation requires more A/C. I'd kind of expect the opposite, with everything from cabins to restaurants being comparatively cramped. Maybe energy is just being wasted, what with the power plant being right there.

Obviously the power generation is 100% fossil, but the power on land is also generated somewhere, and it's usually not green -- though this is increasingly an argument.

The crude oil is bad, yes, but also used by cargo ships which must dwarf cruise ships by a ludicrous amount.

The raw sewage is specific to cruises, admittedly, though I'm sure plenty of raw sewage and worse is dumped into our oceans by land dwellers. But that is no defense.

Don't get me wrong, I have no desire to go on a cruise, it sounds like hell to me. I'm perfectly willing to believe they're inefficient, I just don't quite understand why.

The linked study is pretty bad. It seems to get it's data from https://seattlecruisecontrol.org/learn/greenhouse-gas-emissi... which itself is based on website CO2 calculators. That's not exactly science.

Also, a third of the CO2 attributed to the cruise ship vacation is the flight there and back. Which is fair enough if you ask me, just noteworthy and is gonna vary a lot depending on how far people have to fly to get there.

[bergie]

> I wonder. From first principles, I don't quite understand how cruise ships can be that bad.

Because of tragedy of commons. There is very little environmental regulation affecting shipping. And cruise ships can utilise flags of convenience to skirt the little that there is.

You could totally make them more efficient and less harmful, but that would cost money, and hence hurt shareholder value.

For example, we've been cruising on a sailboat since last April. Germany - Scotland - Madeira - Canary Islands. All areas also frequented by cruise ships. Almost all of our electricity (~1.4kWh per day) comes from solar and wind. We do burn some fuel when becalmed or doing harbour manouvers. Since mid-July we burned 140l of diesel, which comes to 380kg of CO2. Not nothing, but also not terrible. On top of that we burn about 1l of ethanol per week for cooking purposes. Building the sailboat of course caused a lot of emissions, but amortised over the 45 years this boat has been sailing, probably aren't too bad. And equipment like sails and ropes are mostly made of recycled plastics, and last many years.

But of course we lack some luxuries that the cruising customers expect. There's no AC, and the only swimming pool available is the sea. Showers are on deck and require boiling some hot water. And worse of all, we don't have the energy budget to run Starlink 24/7, so there's only couple of hours of Internet per day.

[leoedin]

Thanks for applying scepticism to the claim! Yes, cruise ships are bad for all sorts of reasons - but from an absolute energy consumption point of view there’s no way they’re as bad as people are making out.

Just as high density apartment living is the most efficient way to live on land, there must be similar benefits in a ship. I’d be surprised if the energy consumption per person was much higher than that of a land based resort.

The ships engine will be less efficient than a modern power station, and there’s no zero carbon generation on a ship. That might account for 4x CO2 per kWh. Anything more seems suspect.

[mmooss]

> there’s no way

If the evidence doesn't match your theory, you need either more evidence or a new theory.

[mrguyorama]

>I don't quite understand how cruise ships can be that bad.

Many many reasons. Cruise ships use some of the worst, most polluting fuel in general. They are barely a step above floating coal power plants. They also have significantly fewer systems to "filter" the exhaust compared to a power plant. Despite that, they have insane energy needs.

Medium cruise ships are capable of over 50 Megawatts of power generation. They usually have about 10 megawatts of constant "hotel" load. These ships are air conditioning a huge volume, extremely leaky in terms of insulation, and are constantly in the hot and humid tropics. They also have to "generate", ie boil and condense, tens of gallons of water per person, per day. 10 Megawatts for about 3500 people is not great. A megawatt can conservatively power 500 homes. They also rarely use power hookups in port, so they will be running that 10 megawatts of diesel output even in port.

Cruise ships also do not steam for efficiency the way most merchant vessels do, but rather to meet a strict timetable like an airline. The same medium cruise ship will spend about 30 megawatts to go 25 knots from port to port.

[morsch]

Many of those things also seem to apply to large hotel and leisure resorts -- huge volume, leaky construction, hot environment. I wonder how much power they allocate per guest.

The points regarding energy intensive water treatment and less efficient movement are well taken, though.

[mschuster91]

> The crude oil is bad, yes, but also used by cargo ships which must dwarf cruise ships by a ludicrous amount.

Cargo ships don't need much power output in port. The main power plants are shut down, usually it's only the (tiny) auxiliary generator unit in use.

A cruise ship however? That one runs orders of magnitude more electrical stuff all the time, and that's a loooot of fuel consumed.

[gus_massa]

>>> The average EU citizen living in "centuries old city centers" emits ~5.66 tCO2eq/year

As the GP said, that excludes the flight to get there. Also it does not include going to a swimming pool everyday, and probably not crazy 15°C/60°F AC [1]. It's not a good comparison of old style turism with crouse turism.

[1] At home I use the AC at 26°C/79°F. It's insane to use a wool pullover in summer just because someone likes the AC at 15°C/60°F.