Southend to Melbourne without flying...

[Cudzoziemiec]

Yes. ^ And I'd expect a cargo ship to be more efficient still.

[FifeingEejit]

The IMO have been interested in the others long enough for new ships to have Exhaust Scrubbers dealing with the sulphur to an extent.

...sometimes by dumping it in the sea.

aye that's the extent!

It's one of the reasons for the push to LNG.
Though that seems a little short sighted