Container shipping is often said to be "dirty" but I do wonder how it compared per tonne of cargo as most of the comparisons seem to be based on distance.
Unfortunately capacity is measured differently...
Digging in:
The OOCL Hong Kong has a capacity of 21,413 TEU (plus 12 passengers) and a Deadweight of 197,317 Tonnes.
Where as a 747-8F has a lift off weight (probably the closest) 447.7Tonnes
So roughly 441 747-8 freighters to the worlds highest capacity cargo ship.
OOCL handily have a CO2 calculator based on their fleet rather than an individual ship but anyway...
Origin:
Southampton, Southampton, England, United Kingdom
Destination:
New York, New York, New York, United States
Cargo Volume:
197317 TONs
Route:
Southampton (Vessel[ATE1]) > New York
Total CO2 Emission ( MT ):
6674.2475
Total Distance ( km ):
8250
OOCL CO2 Index ( kg CO2/TON-km ):
Vessel: 0.0041
So they reckon 0.033g of CO2 per Tonne.
And..... a 747-8F operator also has a calculator
https://www.cargolux.com/eservices/Emissions-Calculatorbut it seems you have to go through Luxembourg...
John F Kennedy Intl
Luxembourg
447000Kg
6162 Km
1338.64 Tonnes
Oddly shorter
So... apparently that's
6 674 247.5Kg of CO2 for 1 massive ships maximum loading
Vs 133 864Kg of CO2 for each of 441 massive aircraft (and also apparently the least dirty) at maximum load = 59,034,024
I must have something wrong there or the protesters that keep trying to block quay sides really should be closing freight airports instead.
Although looking at that guardian article which says
Carbon emissions (according to weight of passenger)
Flight Frankfurt-Vancouver: 1.3 tonnes*
Cargo ship Hamburg-Halifax (via Antwerp & Liverpool): 5.3kg**
Trains Halifax-Vancouver: 204.2kg***
Total CO2 Hamburg to Vancouver: 209.5kg