Half the planet's wetlands are dried out or degraded, and rewetting them could limit more greenhouse gas emissions this century.
James Dinneen is a writer.
Wetlands in the United Kingdom.
The title is Shutterstock/steved.
About a tenth of all expected human-caused emissions over the same period could be avoided if wetlands are restored.
Wetlands emit greenhouse gases if there is enough water in them. Wetlands emit a lot of methane when they are covered in water. Wetlands emit less methane when they are dry but the dead plants and other organisms release carbon dioxide and nitrous oxide.
Zhenzhong Zeng and his colleagues at the Southern University of Science and Technology in China calculated the exact water level at which wetlands produce the least net emissions.
Records of water levels and emissions from wetlands around the world were considered by the researchers.
When the water level was a few centimetres below the surface, the amount of carbon stored in wetlands offset the methane emissions. Emissions were the lowest in tropical wetlands.
By the end of the century, restoring the more than 4 million square kilometers of degraded wetlands to an ideal water level would prevent between 100 and 400 gigatonnes of carbon-equivalent emissions, a greater reduction than all the forest restoration projects that countries have committed to around the world, according to
An additional 150 to 650 billion tonnes of emissions will be avoided by the end of the century if wetlands are not degraded. The countries with the greatest potential for emissions reductions are Siberia, Canada, Brazil and Indonesia.
Even if we don't fully restore a wetlands, we can make some progress in raising the water level. Peatland has more carbon than all the world's forests.
Wetlands are usually drained by agriculture and urban development. Zeng says that long periods of dry weather can affect wetlands.
Chris Evans at the UK Centre for Ecology and Hydrology said that restoring wetlands competes with other uses. A project in Europe is trying to figure out how to restore wetlands without taking away from agriculture. More than half of China's wetlands will be protected by the law in the next decade. Wetlands in the US are being rewet by the help of beavers.
The journal is called Nature Geoscience.
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