It's simply not true. It started out as a factoid, but got jumbled into nonsense by a game of telephone:

1. True: 16 of the world’s largest ships produce as much _sulfur_ pollution as all the world’s cars.[1]

2. False: "How 16 ships create as much pollution as all the cars in the world", headline from Daily Mail.[2]

3. False: "world's 6 largest shipping tankers produce more CO2 than all the world's personal vehicles combined", from OP.

While SOx and NOx pollution is extremely bad, they're not as culpable in causing respiratory diseases and climate change, and that's why legislative action has been slow coming.

[1] https://www.lngtransfer.com/news/the-16-biggest-ships-produc...

[2] https://www.dailymail.co.uk/sciencetech/article-1229857/How-...

> Separate studies suggest that maritime carbon dioxide emissions are not only higher than previously thought, but could rise by as much as 75% in the next 15 to 20 years if world trade continues to grow and no action is taken. The figures from the oil giant BP, which owns 50 tankers, and researchers at the Institute for Physics and Atmosphere in Wessling, Germany reveal that annual emissions from shipping range between 600 and 800m tonnes of carbon dioxide, or up to 5% of the global total. This is nearly double Britain's total emissions and more than all African countries combined.[1]

> Passenger Cars: 749.4[2]

[1] https://www.theguardian.com/environment/2007/mar/03/travelse...

[2] https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100USI5.pdf

According to the data it appears I am not completely wrong. The maritime transportation sector is of roughly equal CO2 contribution to the US passenger vehicle fleet in 2007. According to the trend indicated by The Guardian in the next 15-20 years (from a 12 year old article, which would be a few years from now) maritime transportation emissions could rise by 75% while the US passenger auto fleet emissions remain flat thereby indicating a slice of tankers contribute more CO2 emissions than passenger vehicles.

These sources weren't hard to find or read, so I am not sure why you think my statement is false.

Your statement was not that the maritime transportation sector is roughly equal to the US passenger vehicle fleet. Your statement was that "The world's 6 largest shipping tankers produce more CO2 than all the world's personal vehicles combined." Those two statements are several orders of magnitude apart, and the second one more than qualifies as "completely wrong."

Before you wrote the world's passenger vehicles, not the US'.

I am visiting Tauranga for couple of days - a big port here in NZ. I can smell sulphur quite often around city. Reminds me my childhood when playing with chemicals.

Similarly I can smell NOx out of some modern diesels. Reminds me a jar of nitric acid I used to keep under my desk, until the lid rusted thru...

I think it’s because once they are in international waters, they use extremely dirty burning bunker fuel.

I think it's because they use cheap oil that tends to be really, really dirty when burned.

I don't think that could be a full explanation. Perfectly clean burning turns all of the carbon atoms in the fuel into carbon dioxide.

[hydrocarbons] + O2 -> CO2 + H2O

"Dirtier" burning would result in less CO2 emission.

The problem is that you are assuming that what these ships are burning is [hydrocarbons] when it’s much more than just that. There are various impurities including sulphur, which lead to extremely dirty emissions such as SO2.

The OP is misinformed with regards to the “6 largest ships” claim and the “CO2” claim — as covered elsewhere in comments on this article.

There are worse things in cigarettes than nicotine. In a similar way there are worse things in bunker fuel than hydrocarbons.