Sea shipping remains the greenest mode of transportation. However, the argument that rail freight has significantly lower CO2 emissions than air freight is becoming increasingly important.
As an example to illustrate how using rail freight can have a positive impact, suppose we have a TEU-sized and 10-ton shipment from Zhengzhou, China, to Hamburg, Germany. If we use air freight, the whole shipment will generate about 50,000 kg of CO2, but using rail only generates about 3,000 kg of CO2. The two models differ by 47,000 kilograms, or about the capacity of 2,115 mature trees to absorb carbon dioxide in a year. Compared to rail, ocean shipping produces slightly less CO2, at 2,580 kilograms, but the total distance by sea is 24,452 kilometers, roughly twice the distance compared to rail freight. In the same example, intermodal transport remains the largest CO2 producer, with emissions of 64,202 kg and a distance twice as long as rail.