Consumers, shipping, and our carbon footprint

Do you ever wonder about the carbon footprint of the goods that you purchase from overseas? Well, we at the ICCT definitely do wonder about these things, and it turns out that the carbon footprint can vary quite widely. And it doesn’t just depend on how far away the goods came from, but also on the particular ship the goods are carried on.

Most goods in the world travel by ship and by truck before they reach their ultimate consumers. But when summing up the goods carried times the distance traveled, more than half of all global freight, in cargo times distance traveled, moves on ships (most of the rest is by truck and by rail). To better understand shipping efficiency, the ICCT collaborated with researchers at University College London, to analyze the variation in the shipping fleet’s efficiency. The work by UCL is very cutting edge, utilizing a novel approach with global satellite data on the ocean-going shipping fleet. We then assessed this work in context of the future shipping fleet moving toward the lowest carbon technologies and practices in a recently released report, which suggests that the fleet could save 2 million barrels of oil per day—or 300 million metric tons of carbon dioxide per year—in the 2030 timeframe.

Most of the goods that we purchase at retail and grocery stores are moved on container ships. The container ship fleet has an enormous range of energy efficiency. As shown in figure below from the ICCT report, this translates to a broad range of low-to-very-high carbon intensity in carrying this freight. Average container ship carbon intensities are about 150 grams of carbon dioxide per twenty-foot-equivalent unit carried a nautical mile (gCO2/TEU-nm). However, the difference between the leaders and the laggards is quite large; laggard ships, at over 200 gCO2/TEU-nm, are more than twice as high in carbon footprint as the leaders, for a given amount of cargo carried a given distance. To achieve these efficiency improvements, typically the industry leaders are embracing new efficiency technologies (like advanced engine controls), slowing down the ship speed (to cut down aerodynamic an hydrodynamic losses), and embracing newer larger ship designs.

Container ships’ new ship design efficiency (horizontal axis) and in-use efficiency incorporating real-world speed differences (vertical axis)

Because we also study cars at the ICCT, we also pulled the data on the international shipping of cars on “pure car carrier” ships from the global 2011 ship database. To ship a two-ton vehicle—say a mid-size crossover sport utility vehicle—from Asia to North America or Europe, an industry-leading ship might emit about 200 kg of CO2 and an industry laggard would emit 600 kg CO2 for the same journey. To put this upstream carbon in perspective of your own carbon footprint, if your new car arrived on the industry laggard ship (instead of the industry leader), that would add equivalent of more than 1000 extra miles of driving in an average world car to your carbon footprint (or over 2000 miles in a Toyota Prius…) before you even took your first drive. And there are about 3 million vehicles imported to the US, excluding Mexico and North America, so all these extra miles really add up. In other words, consumers and shippers tend to have little awareness or ability to pick the ship on which their goods are shipped, but there is, nonetheless, a 3x difference depending on what ships the goods are placed on. In fact, we find that a 2.5x to 5x disparity in ship carbon intensity is common between leaders and laggards for the major ship types as well.

How ships are designed, how slow steaming is managed, and how well ships are maintained (like how propellers and hulls are polished) are all largely invisible to the public. But in an era of increased information, and increased awareness and concern over the climate implications of our consumption, paying a little closer attention to our ships’ would be a good idea. And the data are now at hand to make sure this information helps bring about a low carbon goods movement.