How will Earth's new lakes affect the carbon budget?

In a recent study, researchers have discovered that the number of lakes on Earth has substantially increased over the last few decades. Using high-resolution satellite imagery and artificial intelligence, the experts determined that between 1984 and 2019, the global lake surface area grew by over 46,000 km2. This is slightly larger than the surface area of Denmark. 

The team found that there has been a particular increase in small lakes. According to the researchers, the number of small lakes is especially important because they emit the most greenhouse gas in relation to their size.

“There have been major and rapid changes with lakes in recent decades that affect greenhouse gas accounts, as well as ecosystems and access to water resources. Among other things, our newfound knowledge of the extent and dynamics of lakes allows us to better calculate their potential carbon emissions,” explained study co-author Jing Tang of the University of Copenhagen.

Freshwater lakes are responsible for up to 25 percent of Earth’s CO2 emissions, and climate change is expected to make matters worse. The results of a study from the University of Cambridge suggest that emissions from freshwater lakes could double in the coming decades due to climate change.

In an effort to understand how these bodies of water are evolving over time, the researchers set out to create the most detailed map of the world’s lakes to date. 

The study revealed that over the last four decades, there has been an annual increase of CO2 emissions from lakes of 4.8 teragrams of carbon. Small lakes make up just 15 percent of the total area, yet they account for 25 percent of CO2 and 37 percent of methane emissions. 

“Small lakes emit a disproportionate amount of greenhouse gases because they typically accumulate more organic matter, which is converted into gases. And also, because they are often shallow. This makes it easier for gases to reach the surface and up into the atmosphere,” said Professor Jing Tang.

“At the same time, small lakes are much more sensitive to changes in climate and weather, as well as to human disturbances. As a result, their sizes and water chemistry fluctuate greatly. Thus, while it is important to identify and map them, it is also more demanding. Fortunately, we’ve been able to do that.”

The experts determined that climate change and human activities are the two main drivers behind Earth’s new lakes. While melting glaciers and thawing permafrost are responsible for about half of the increased lake area, man-made reservoirs make up the other half. 

The researchers noted that their new dataset offers a range of regional and global applications. “I have sent our new greenhouse gas emission estimates to the people responsible for calculating the global carbon budget, those who are behind the UN’s IPCC climate reports. I hope they include them in updating the global emission numbers,” said Professor Jing Tang.

“Furthermore, the dataset can be used to make better estimates of water resources in freshwater lakes and to better assess the risk of flooding, as well as for better lake management – because lake area impacts biodiversity too.”

The study is published in the journal Nature Communications.

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By Chrissy Sexton, Earth.com Staff Writer

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