I think this is looking at the wrong number. The atmosphere "cares" about emissions in absolute terms, not in terms of who or what put them there per unit of utility gained by their presence.
The fuel used in these container ships is truly nasty stuff, with marine shipping being solely responsible for double-digit percentages of certain greenhouse gases.
Of which greenhouse gases?
I skimmed through the linked section and https://en.wikipedia.org/wiki/Initial_IMO_Strategy_on_the_re... , without spotting a double-digit number that turned out to be a %-of-global-GHG-emissions.
Or are you referring to all-time emissions? That would seem more probable, given the long history of coal-fired ships.
Per the linked Guardian article from 2009, shipping is responsible for 18-30% of all the world's nitrogen oxide (NOx) pollution and 9% of the global sulphur oxide (SOx) pollution.
Yeah, technically those are indirectly greenhouse gases, but just to note, the article linked points out that "Maritime transport accounts for 3.5% to 4%".
It's double-digit percentages of some pollutants that are very bad for human health, but relatively minor in terms of climate change.
EDIT: I take it back. NOx is significant. SOx not so much.
The fuel used in these container ships is truly nasty stuff, with marine shipping being solely responsible for double-digit percentages of certain greenhouse gases.
[1]: https://en.wikipedia.org/wiki/Environmental_effects_of_shipp...