For the past 40 years, environmental protection has been an important and indispensable part of Sino-US ties. One can say without doubt that the world's environmental problems will not get solved without the cooperation of these two great nations.

Since environmental cooperation was covered by the 1979 Sino-US science communique, environmental studies became a popular subject of academic exchange for overseas students pursuing advanced degrees. In the early 1980s, one of my professors at Tsinghua University got his PhD in air pollution control from Cincinnati University, which later became the alma mater for many of his fellow students.

My professor later became a "godfather" in this field and many of his students and the students of his students are now playing key roles in the on-going "war on air pollution". They are also making significant contribution to environmental advancement in China.

In 1992, I helped found and managed the first professional joint-venture environmental consulting firm in China and later on served as China program adviser for the Air and Waste Management Association, implementing the government-sponsored but privately run Sino-US environmental cooperation project in the field of cleaner production from 1997 to 1999.

Corporate environmental practice was transferred to China through investment activities, primarily through Sino-US joint ventures. It also became a golden era for US environmental technology and service providers because of the increased awareness of both the government and public.

Since 1999, I have joined the Environmental Defense Fund, a US environmental NGO helping implement the first official US-China joint environmental cooperation project between the two environmental ministries: the US Environmental Protection Agency and China's Ministry of Ecology and Environment.

In the presence of then Chinese premier Zhu Rongji and then US vice-president Al Gore, China and the United States signed a letter of intent on a feasibility study on reducing sulfur dioxide emissions through market mechanism in China, opening a new era of official cooperation between the two countries.

This marked the beginning of the long standing cooperation between the two countries, which later became the Joint Committee on Environmental Cooperation. Innumerable activities have taken place under the committee's umbrella and the cooperation continues.

Climate change became a global focus during the eight years of the Barack Obama administration. The US and China put their other differences aside and joined hands to take on this global challenge.

Climate change was not only featured in every strategic and economic dialogue, but also occupied a major part of the three "joint presidential statements".

Cooperation between the US and China led to carbon mitigation commitments by both countries, serving as the keystone for the Paris Agreement. It also enabled both countries to step up ways to achieve higher ambitions. The US started to enforce regulations on methane, a powerful global warming gas, and China announced it would launch the largest carbon market in the world by 2020.

The Environmental Defense Fund and myself have been fortunate to have participated in this process and played a key role on different occasions.

But multinational cooperation for an eco-friendly planet has become increasingly challenging since the US withdrew from the Paris Agreement and other international mechanisms in the past two years.

It is undeniable that the US used to be the world leader in responding to climate change and will continue to play an important role in the fight, since dozens of its states and cities have promised to reduce greenhouse gas emissions at local levels. The good news is, China and the US are still working together to some extent: in December last year, the two parties held a high-level regional dialogue on climate change, while Chinese and US business communities - who are highly sensitive to market variations - maintained cooperation in energy innovation.

As the Convention on Biological Diversity 15, with the theme Ecological Civilization - Building a Shared Future for All Life on Earth, is coming up in Southwest China's Yunnan province next year, the world may take another step forward.

For the past decades, I have witnessed the ups and downs in Sino-US relations but there have always been the "ups" in environmental cooperation, except in the past two years. However, I still believe the two countries will find their global positions to help shape the world for the better in the decades to come, because there is only one Earth and because I am just one of many in both the US and China who believe in environment and are willing to devote themselves to the cause while putting other differences aside.

The author is founder, chief representative and vice-president of the Environmental Defense Fund's China Program. His areas of expertise include emissions trading, green supply chains, environmental enforcement, Chinese environmental and climate policy, and green finance.

The author contributed this article to China Watch exclusively. The views expressed do not necessarily reflect those of China Watch.

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