In 2017, I attended the first Shipping and Environment conference, hold in Gothenburg. After presenting our work on shipping emission and impacts (Liu et al, 2016 in Nature Climate Change), I raised a question for myself. What is the driving force for shipping activities? Can I provide a better tool to assess the maritime emissions through international trade perspective? I kept thinking these questions until dinner. I told a friend at dinner that I would link shipping emissions to driving force. As he is American and I am Chinese, so I said I will start from the bilateral trade between US and China.   

It’s hard to chase after a word. This work is much more complicated than expected. Beginning with exhaustive bottom-up analysis, trade database, including the value, weight and details for a total of 12,346 subcategories for US and China bilateral trade in 2016, were linked to 4,482 vessel calls identified by the automatic identification system signals. We also need to update our previous shipping emission inventory model to evaluate trade embodied seaborne transport emissions. By analyzing the vessel emissions with a chemical transport model, we tracked the globally distributed impacts on ambient pollutant concentrations from shipping emissions related to US-China trade. The health consequences were afterwards evaluated based on exposure level. The scale of “responsibility” was enlarged from traditional CO₂ emissions to both CO₂ emissions and air quality/health impacts.   

Finally, we accomplished this work before I visited Gothenburg again for the second Shipping and Environment conference. I met that friend and told him: “The idea I told you two years ago was realized finally, but it took me two years long”. He said: “I have some good ideas twenty years ago, but I can’t finish them.” So, I am not that slow.   

All this is due to my very supportive students. Zhihang Meng, Xiaotong Wang and Zhaofeng Lv always respond to my requests very quickly. At the final stage of this work, Zhihang, Xiaotong and I squeezed in a small office and worked until midnight every day. I remember the beautiful night view of campus and the cool, fresh air when riding bike home. Zhihang lost 5 kg weight in that month. He is a master student and could not have to bear so much pressure. We enjoy working on this issue. We work for dreams.   

The completion of this research improved our understanding of the world. I often discuss with my students, what do we want from this study? One student (Zichen Guo, an undergraduate student from School of Economy, involved in our discussion) wrote down the following words, shining some lights on this question.   

“The past 40 years have witnessed the tremendous development opportunities and the improvement of people’s well-being brought about by trade liberalization. As a low-cost, high-volume transport method, maritime transport can carry commodities and semi-finished products between different countries at low economic and environmental costs, playing an invaluable role in promoting the integration of China with the world. The advancement of globalization will continue to be a major trend in the world, in which trading will be the driving force for the refinement of the global division of labor. At the same time, it will also increase economic efficiency and generate huge benefits. An important issue to be declared is that although we’re assessing the pollution scale of maritime transport, we by no means oppose trading activities. Our only goal is to refine the assessment of the environmental influence of maritime transport. Seaborne pollution caused by trading is a global problem, but it can hardly be regarded as a regional problem. Firstly, because trade is still the driving force of globalization, any alterations would affect all of the economies which are linked together as a complicated network. Any unexpected trade reduction between countries will have an impact on the other economies that coexist in the network as much as that on the previous countries themselves. Secondly, because seaborne pollution spreads across the entire route of transportation, it is difficult to assign that impact to a specific area. The problem is obviously global, and only through international cooperation can the pollution be effectively controlled. Based on these two reasons, the role of maritime transport in promoting regional development (in the sense of economic development) is far greater than the resulting regional environmental burden.”

Full text is available at: https://www.nature.com/articles/s41893-019-0414-z

Visit Huan Liu’s homepage for more information:

https://www.tsinghua.edu.cn/publish/enven/6309/2012/20120613085639880749805/20120613085639880749805_.html