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ENVIRONMENT – The number of lacs on our planet is exploding. Their total area has increased by more than 46,000 km2 in 35 years, a little more than the area of Denmark. At first glance, you might think this is great news for the naturebut 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 succeeded in mapping the evolution of 3.4 million lakes over the past forty years.
The whole offers an unprecedented set of data… And a worrying discovery for the climate. “This new knowledge has allowed us to better calculate the carbon emissions of 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 considerably in recent decades, it is mainly because of the proliferation of small lakes. Problem: according to the study, these lakes of less than 1 km2 are particularly emitters of greenhouse gas.
Concretely, they produce CO2, methane, nitrous oxide… All because of the fungi and bacteria that develop there. According to the researchers’ calculations, these lakes represent 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.
Worse still, they are responsible for 45% and 59% of the increase in CO2 and methane emissions from lakes over 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 study. In total, greenhouse gas emissions from freshwater lakes are equivalent to 20% of all global CO2 emissions from fossil fuels.
Climate change in question
Why has the number of small lakes exploded? The study identifies two main reasons: human activities and climate change. The first factor concerns above all the creation of “reservoirs”, that is to say artificial lakes. The second factor relates to the disappearance of glaciers and permafrost. The more the climate deteriorates, the more these layers of ice melt, which creates many lakes, especially in the northern hemisphere.
It is then a real vicious circle: climate change creates small lakes, these release large quantities of greenhouse gases, such as carbon dioxide (CO2) for example… Which is none other than the main gas greenhouse responsible for climate deregulation.
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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