When Presidents Xi Jinping and Barack Obama signed a new climate agreement in September, they took a critical step in bilateral cooperation to combat global climate change. The two of us were recently invited to China to share experiences—in the United States and Holland, respectively—in cleaning up air pollution at ports and reducing greenhouse gas emissions in the shipping industry, while maintaining growth.

Our trip to China took place at a particularly opportune moment. The National People’s Congress in August adopted a number of amendments to China’s Air Pollution Prevention and Control Law, providing a clear legal foundation for the government to tackle air pollution and GHG emissions from ships. The law grants the country’s Ministry of Transport the authority to designate emission control areas for ships operating along China’s coast. Shortly after, the Ministry of Transport issued a comprehensive 5-year action plan that proposes, among other progressive measures, to set up ECAs in China’s three key port regions. The Ministry plans to release a detailed plan for implementing these emission control areas before the end of this year.

Shipping emissions are virtually unregulated in China. With many of its major ports located in cities with poor air quality, China’s actions and plans represent major steps forward in addressing its need to clean the air. As the world’s largest manufacturing hub and home to the world’s eight biggest ports, China’s initiatives also contribute to greening the global supply chain. We applaud China for taking these important steps.

In the United States and Holland, we face similar challenges, because of the global nature of shipping. Having worked to address these challenges, we would like to offer some specific recommendations for China’s consideration.

First, China is considering, initially, an option of requiring ships to burn low sulfur fuel, but only when vessels are berthed in port. Data on world ports indicate that emissions from the movement of vessels are substantial, often exceeding emissions while they are at rest at a port. This suggests that China could deliver the greatest air and health benefits by drawing its boundaries for ECAs at the outer boundary of its territorial waters (12 nautical miles)—and beyond, if necessary—and requiring all vessels moving within those ECAs to use cleaner fuel.

Second, all of China's major ports should be included in the ECA to avoid cargo diversion to the least-regulated ports. The U.S. faced a similar challenge in 2006, when the San Pedro Bay Clean Air Action Plan was developed. The Ports of Los Angeles and Long Beach had to work together. But the threat of ships diverting their cargos to other west coast ports remained until the North America ECA was established in 2012. That set a uniform standard for all ports in the United States. Similarly, when Europe introduced a sulfur ECA, leveling the playing field was a key issue.

Third, enforcement is critical for keeping the playing field level among ocean carriers, and making sure an ECA program delivers the expected air improvement benefits. After the much stricter 0.1 percent fuel sulfur ECA requirement came into effect this year, both the U.S. and EU have worked to develop and improve ship and fuel inspections. High quality enforcement on a global scale is essential. A regime to ensure sufficient fuel testing is imperative, and all countries can benefit from cooperating with each other.

We are encouraged by China’s commitment to develop a clean and sustainable port and shipping industry. Its plans to take action, including its ECAs—if properly designed and enforced—could meet the public’s demand for cleaner air. We, as partners in the world’s port community, hope to provide support to this important endeavor.