“It has an accelerating effect on global warming,” explains one of the study’s authors.

Lakes are sinks of greenhouse gases. Explains Friday, May 19 in franceinfo Jean-François Creteau, CNES engineer and scientific director of the Swot mission. “When it dries up, it can in turn generate significant re-emissions of greenhouse gases. So that has an accelerating effect on global warming.”adds the co-author of a study published in the journal science, which reveals that more than half of all lakes and reservoirs lose water. The main drawback is global warming and the excessive use of this water by man.

franceinfo: Why is this remark so troubling?

Jean-François Creteau: Because we have seen a decrease over the last 30 years in the water in the Great Lakes. In this study, we worked on approximately 2,000 lakes, 1,000 natural lakes, and 900 artificial lakes. We’re seeing a very significant decline, especially in arid regions. This will lead to a number of problems, both in terms of the amount of water available to humans, and the effects on climate change. Because lakes also play a role in reducing greenhouse gases.

Does this mean that there is a snowball as large lakes and reservoirs dry up?

Yes, because lakes are sinks of greenhouse gases, especially methane. And when it dries up, just as it does with thawing permafrost, it can in turn generate significant re-emissions of greenhouse gases. Therefore, it has an accelerating effect on global warming.

Have you identified the affected sites in France?

Not in this study, because we worked on the 2,000 largest lakes in the world. On the other hand, we have a satellite mission launched by CNES and NASA three months ago, called Swot, which makes it possible to work in 2 to 6 million lakes. This could help to see what role lakes in France play in global warming and how they will evolve over time.

Fresh water is a vital resource. Could its scarcity cause, or is already causing, global population displacement?

Yes she can. There is the issue of scarcity which will lead to economic loss, especially for those who live off agriculture and are forced to move. We experienced this in Central Asia or in the Sahel. But in others, on the contrary, there is a rather strong rise in the level of lakes due to increased precipitation, which leads to devastating floods. We have the city of Bujumbura around Lake Tanganyika in Burundi, which has been hit by severe flooding in recent years.

The conclusions of this study are entirely fatalistic or, on the contrary, do they tell us that there is still time to work for our water resources?

The purpose of the study is to make an observation, rather than to say whether or not it is possible to act. We have a water resource that we can hardly control, and it is linked to natural events. We can control it, because it is linked to climate change. But above all we will say: be careful, this water is limited and we need it. So it may be necessary to change or manage the uses intelligently. But our study exists above all to say: This is what happens.