the number of small lakes on Earth is increasing, and this is not good news

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ENVIRONMENT – The number of lakes on our planet is exploding. Their total area has increased by more than 46,000 km2 in 35 years, slightly more than the area of ​​Denmark. At first glance, this may seem like good news for nature, but the reality is quite different.

This is explained by researchers from the University of Copenhagen in a study published in the scientific journal Nature. By combining high-resolution satellite images with artificial intelligence, they have managed to map the evolution of 3.4 million lakes over the past forty years.

It all offers an unprecedented data set… And a worrying discovery for the climate. “This new knowledge has enabled us to better calculate the carbon emissions from the lakes”, explains Jing Tang, assistant professor in the Department of Biology and co-author of the study. That’s where the whole problem comes from.

“These lakes act as greenhouse gas factories”

If the number of lakes on our planet has increased significantly in recent decades, it is mainly due to the proliferation of small lakes. Problem: according to the study, these lakes of less than 1 km2 emit especially greenhouse gases.

Specifically, they produce CO2, methane, nitrous oxide… All because of the fungi and bacteria that develop there. According to the researchers’ calculations, these lakes make up only 15% of the total area of ​​the lakes. Yet they are responsible for 25% of CO2 emissions and 37% of methane emissions from lakes worldwide.

Even worse, they are responsible for 45% and 59% of the increase in CO2 and methane emissions from lakes in the period 1984-2019. “Small lakes emit a disproportionate amount of greenhouse gases because they generally accumulate more organic matter, which turns into gas. And also because they are often shallow. It is therefore easier for gases to reach the surface and rise into the atmosphere.”explains Jing Tang, co-author of the study.

“These lakes act as greenhouse gas factories” concludes the investigation. In total, greenhouse gas emissions from freshwater lakes correspond to 20% of all global CO2 emissions from fossil fuels.

It is about climate change

Why has the number of small lakes exploded? The study identifies two main causes: human activities and climate change. The first factor concerns above all the creation of “reservoirs”, i.e. artificial lakes. The second factor concerns the disappearance of glaciers and permafrost. The more the climate deteriorates, the more these ice sheets melt, creating many lakes, especially in the Northern Hemisphere.

It is then a real vicious circle: climate change creates small lakes, these release large amounts of greenhouse gases, such as carbon dioxide (CO2) for example… Which is none other than the main greenhouse effect responsible for climate change.

The study also points to the drying up of many lakes due to high temperatures, drought and human consumption of water resources. This trend is particularly marked for lakes observed in the western United States, central Asia, northern China, and southern Australia.

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