The environmental effects of shipping include air pollution, water pollution, acoustic, and oil pollution. Ships are responsible for more than 18% of nitrogen oxides pollution, and 3% of greenhouse gas emissions.
Although ships are the most energy-efficient method to move a given mass of cargo a given distance, the sheer size of the industry means that it has a significant effect on the environment. The annual increasing amount of shipping overwhelms gains in efficiency, such as from slow-steaming. The growth in tonne-kilometers of sea shipment has averaged 4 percent yearly since the 1990s, and it has grown by a factor of 5 since the 1970s.
The fact that shipping enjoys substantial tax privileges has contributed to the growing emissions.
Ballast water discharge and the environment
Ballast water discharges by ships can have a negative impact on the marine environment.