The number of lakes on Earth has increased substantially in recent decades, according to a unique global survey that found 3.4 million lakes. There has been a certain increase in the number of small bodies of water emitting large amounts of greenhouse gases. The study is critical for the planet’s carbon account, global ecosystems and human access to water resources, say scientists from the University of Copenhagen and other institutions of higher learning who have prepared more accurate and detailed maps.

Bacteria and fungi that feed on dead plants and animals at the bottom of the lake emit large amounts of carbon dioxide, methane, nitrous oxide and other gases. Some of it ends up in the atmosphere. This mechanism makes these bodies act as greenhouse gas factories.

In fact, the researchers said in a statement, fresh water may account for 20 percent of all global emissions of carbon dioxide from fossil fuels to the atmosphere. Forecasts indicate that climate change will cause the lake to emit an increasing proportion of greenhouse gases.

Between 1984 and 2019, the surface of the world’s lakes grew by more than 46 thousand square kilometers, similar to that of Denmark, which increased the emission of these gases.

That’s just one of the reasons why it’s important to know how many and how big these lakes are, and how they develop. Until now this information is unknown.

The researchers created maps using high-resolution satellite imagery combined with artificial intelligence.

“Among other things, our new knowledge of the area and dynamics of lakes allows us to better estimate their potential carbon emissions,” explained Jing Tang, an assistant professor in the Department of Biology and one of the authors of the study, which was published in Nature Communications.

According to the study, the annual increase in carbon dioxide emissions from the lake during this period was 4.8 teragrams (10 to the power of 12 trillion) of carbon, which is equivalent to the increase in UK emissions in 2012.

Since 1984 more and more small lakes have appeared. This number is very important according to the researchers, because they emit the largest amount of greenhouse gases in relation to their size. Although small lakes represent only 15 percent of the total area of ​​lakes, they contribute 25 percent of carbon dioxide and 37 percent of methane emissions. In addition, they also contributed 45 percent and 59 percent respectively to the net increase in carbon dioxide and methane emissions from lakes during 1984-2019.

“Small bodies of water emit a disproportionate amount of greenhouse gases, because they usually accumulate more organic matter, and also because they tend to be shallow. This makes it easier for them to ascend into the atmosphere,” added Jing Tang.

“At the same time, they are much more sensitive to climate change and weather, as well as human disturbance. As a result, the size and chemical properties of the water fluctuate greatly.”

The mapping also revealed that there are two main reasons for many of the new lakes on Earth: climate change and human activity. Reservoirs account for more than half of the increase in the area of ​​lakes, i.e. artificial lakes. The other half is created primarily by melting glaciers or melting permafrost.

According to the researchers, the new data set offers a wide range of regional and global applications.

“I am sending our new estimates to the people responsible for calculating the global carbon budget, the people behind the UN Intergovernmental Panel on Climate Change report,” Jing Tang concludes.