I have experience teaching and have found that people learn much better when they do the research themselves. But if it must be provided...
In 2016, U.S. greenhouse gas emissions totaled
6,511 million metric tons of carbon dioxide equivalents.
28% came from the transportation sector.
And of that,
60% was from light-duty vehicles and 23% was from medium- and heavy-duty trucks.
From these numbers we can calculate that in 2016 US cars and trucks amounted for 1,513,156,400 metric tons of CO2. That was 4,142,796 metric tons of CO2 per day.
Here's the math:
6,511,000,000 * .28 * .83 = 1,513,156,400
1,513,156,400 / 365.25 = 4,142,796
How does a cargo ship compare? Here's some
academic analysis. It's from 2009, and recent measures have reduced cargo ship pollution, but since the industry is slow to change let's assume things haven't improved much. I've used the paper for my next calculations.
How much greenhouse gases a ship emits depends on the ship.
In general, and in absolute numbers, the bigger the ship the more greenhouse gases it produces.
Post-Panamax is the biggest class of container ship. Each can carry more than 4400 20-foot shipping containers and they are too wide to pass through the Panama Canal. On average a Post-Panamax ship emits 110,360,000 metric tons of C02 per year. That's 302,149 metric tons per day. And that's disgusting.
It's worth nothing that in 2009 Post-Panamax ships represented only 1.6% of the total international shipping fleet. No other class of ship emits even half as much in absolute numbers.
Panamax ships are the next biggest class. Each can carry 3000-4400 20-foot shipping containers, and they are the largest class that can pass through the Panama Canal. One of those emits on average 53,680,000 metric tons of CO2 per year, or 146,967 per day.
We agree: The pollution is far too much.
And you are partly right: The "
bunker fuel" cargo ships run on is of a very low grade variety. Much of it is "
vacuum resid" — the heavy residual by-product of the petroleum refining process. But it's not crude, it's actually worse — especially for its sulphur. And it's not correct to say the fuel ships use is unfiltered. Law restricts its sulfur content in a variety of areas, including everywhere within 200 nautical miles of North America. To meet that standard ships typically use refined Marine Gasoil or Marine Diesel in those areas instead.
Back to your example: Cars and trucks in the US emit far more CO2 than a container ship, even if the ship is among the worst polluters. At least 34 times as much. More often at least 70.
Besides, when we measure how much CO2 is produced per metric ton of cargo carries, ships are the most efficient mode of transportation: Post-Panamax ships emitted on average 10.8 grams of CO2 per metric ton-km of cargo. Trucks the same year emitted on average more than
80 grams of CO2 per metric ton-km of cargo.
In other words, the same amount of goods could travel one day on a truck or over a week on a Post-Panamax ship for the same CO2 cost. Given the choice to travel 21 days on a Post-Panamax container ship or three days on a truck, the journey by ship would emit less CO2.
We agree shipping causes terrible pollution, and maritime shipping, in particular, uses low quality fuel. We agree it is more environmentally responsible to buy goods that are produced locally. But you are prone to inaccuracy and exaggeration. Please get your facts straight when you argue your positions.
By the way,
here's an article about how the International Maritime Organization has imposed significant new air quality regulations. They are due to take effect in 2020. It also discusses how some ships are using liquefied natural gas as a much cleaner alternative to heavy bunker fuel.
Maybe you'll find it interesting.