Did you read this when I posted it?
I know, it's a lot to read, but here's a choice bit:
>> The report found that in 2001, heavy-duty diesel trucks,
>> buses and cars burned more than a billion metric tons of
>> fuel, and emitted 2.2 million metric tons of sulfur oxide.
>> The same year, ocean-going vessels burned 280 million tons
>> of fuel, far less, but emitted 3.4 million metric tons
>> of sulfur oxide, about 17% of the global total.
So I say: forget about planes (and frankly, SUVs) for now, let's work on the ships a bit.
http://mailman.lbo-talk.org/pipermail/lbo-talk/Week-of-Mon-20070319/005659.html