we know why the lakes are less and less blue

Blue lakes like the ocean are a dream and we admire them all the more because they are not the majority on earth. Researchers from the American Geophysical Union analyzed more than five million satellite images representing more than 85,000 lakes and water bodies around the world. They scrutinized its color for seven years between 2013 and 2020 and calculated that 30% – only – of the world’s lakes are blue. They are generally mountain lakes and the blue color is explained by a context of cooler temperatures and higher precipitation.

Global warming influences the color of lakes because the rise in temperature influences their ecosystem and in particular the presence of algae or sediment. According to these researchers, with a 3°C increase in air temperature in the middle of summer, 14% of blue lakes could turn green or brown due to the proliferation of certain algae.

These scientists have therefore drawn up a map of the current blue lakes in order to be able to follow their evolution: these blue lakes are currently located in northern Europe, mainly in the Alps, and the Scandinavian countries but also on the Tibetan plateau, in the north of the United States, in the rocky mountains of northeastern Canada, as well as in Patagonia, or in New Zealand. But in the years to come, their color is likely to approach the green of the lakes found at low altitudes, near the coasts or in drier regions.

Next to less blue lakes there are also less white mountains, therefore also greener. A new study published last month by Italian researchers confirms this: in winter, snow remains on the ground on average 15 days less than 30 years ago. This varies according to the regions of the world of course, but the French Alps are in this average of 15 days less snow. In the Pyrenees, it is more like 10 days, while the mountains of Canada have downright one month less snow compared to the 1980s.