Wetlands are known for sequestering carbon dioxide and stocking carbon in the soil. However, they are also a prominent source of methane that has much higher warming potential than carbon dioxide. The balance between these two gasses primarily determines if a wetland is a greenhouse gas source (warming effect) or sink (cooling effect).

China owns the fourth largest area of natural wetlands in the world. Since 1950, half of the wetlands in China have been lost. After China acceded to the Ramsar Convention, new policies for wetland restoration were put into practice to recognize the ecological benefits, e.g., zoological, ecological, botanical and hydrological services provided by wetlands. If wetland restoration can result in a net greenhouse gas sink, then it theoretically serves as a natural solution to climate change. A new study closely examines such climate impacts of wetland restoration in China.

“The ecosystem services of wetland restoration have often been evaluated, but the potential as a natural climate solution is poorly understood,” said first author Professor Tingting Li, a scientist at the Institute of Atmospheric Physics, Chinese Academy of Sciences.

Li and her colleagues assessed methane emissions and carbon dioxide sequestration from wetlands restoration in China, using a combination of climate and ecosystem data and models, “We set four wetland management scenarios with increasing levels of wetland restoration under three climate scenarios and tried to find the best climate-management providing greatest cooling effect in modern climate.” Li said.

They found that the medium levels of restoration under strong climate mitigation pathway will provide the highest climate cooling effect. The cumulative Global Warming Potential will be -3.2 petagram carbon dioxide equivalent (2020 – 2100), attributed to higher carbon dioxide sequestration, more than offsetting increased methane emissions.

“The medium restoration management includes large area of grassland restored to wetland in the Qinghai-Tibet Plateau, where cold climate and the hummock–hollow terrain constrains methane emissions but the high latitude induces high carbon sequestration,” Professor Zhangcai Qin, the corresponding author and Deputy Director of the Future Earth China Hub said. “This eventually results in the greatest cooling effect.” 

China plans to restore wetlands of 14,040 square kilometers (5,420 square miles) from 2004 to 2030, of which 40% have already been restored. From now to 2030, about 800 square kilometers (308 square miles) need to be restored each year to reach the restoration target.

“An appropriate management could minimize net greenhouse gas emissions, and potentially complement Nationally Determined Contributions that aim to limit global temperature rise,” pointed out by co-author Professor Panmao Zhai, the Co-Chair of Working Group I of the Intergovernmental Panel on Climate Change Sixth Assessment Report. 

“In addition to gaining the many hydrological and biodiversity benefits from increasing the area of wetland ecosystems, the restoration planning and policy should holistically consider the location, pre-land-use, wetland type and rewetting measures to balance the trade-offs between carbon sequestration and methane emissions in order to maximize the climate benefits of wetland restoration,” added co-author Professor Pep Canadell, the executive director of the Global Carbon Project, a Global Research Network of Future Earth.

Li, T., Canadell J.G., Yang, X., Zhai, P., Chao, Q., Lu, Y., Huang, D., Sun,W., Qin, Z., 2022. Methane emissions from wetlands in China and their climate feedbacks in the 21st century. Environmental Science & Technology. https://doi.org/10.1021/acs.est.2c01575