The shipping industry does contribute to CO2 emissions just as the aviation industry does. It's significant but not the largest pollution source on the planet.

What is VERY significant about the shipping industry is the type of fuel they use. Up until the middle of the last decade (2015) they were using diesel with a very high sulfur content. Because it's the cheapest.

This generates a LOT of small particulate sulfate emissions. These do two things:

they kill a few million people a year through lung disease

they change the albedo of the planet and make it more reflective

The reality is the emissions from the shipping industry are actually a "geoengineering" program that has been cooling the planet for decades. When the UN attempted to clean up the industry in 2015 by requiring them to switch to low sulfur fuels it had consequences.

There are several papers arguing that the reduction of reflective sulfates caused by this change has caused a 0.2C spike in the global temperature in the last 5 years.

Keep in mind that the total amount of warming that is currently being masked by sulfate particulates is estimated to be around 0.7C. If we stop polluting that's the temperature spike we get within 3-5 years as the particulates wash out of the atmosphere.

This is the "geoengineering trap" that I have written about. If we stop dumping sulfates into the air (which kills about 8 million per year globally) we take a huge temperature spike. A spike that would cause possibly hundreds of millions to die all at once.

What would you do?