Climate change is changing the colors of our planet (literally)

Climate change affects all regions of the world. This is a very serious threat, and its consequences impact many different aspects of our lives. Now, a new study warns about the health of ecosystems through the change in color of lakes.

Blue lakes around the world (such as Frase Island’s Lake McKenzie, Iceland’s Blue Lagoon, New Zealand’s Blue Lake, and Oregon’s Crater Lake) could lose their beautiful, crystal-clear blue hue because of rising of global temperatures, which are turning blue lakes into cloudy green-brown bodies of water.

The scourge of climate change

A team of scientists from the University of North Carolina at Chapel Hill has examined 5.14 million satellite images of freshwater reservoirs taken between 2013 and 2020. They represent 85,360 lakes and reservoirs scattered around the world. The main objective was to find out the dominant color of the water. Scientists looked at more than 5 million Landsat-8 satellite images by closely watching their color changes. It turned out that the pure blue color is already present in less than a third of them. Thus, 69 percent of all lakes on Earth have a greenish-brown color.

The new study has shown that it is not sediment and algae transport that determine whether the lake remains blue for most of the year or takes on a less pleasing color as the months go by. Satellite images have proven that the main factors to take into account are: air temperature, precipitation, altitude above sea level and the depth of the reservoir.

“No one has ever studied the color of lakes on a global scale,” says Xiao Yang, a remote sensing hydrologist at Southern Methodist University and co-author of the study published in the journal Geophysical Research Letters. “There have been previous studies of maybe 200 lakes around the world, but the scale we’re trying here is much, much larger in terms of the number of lakes and also the coverage of small lakes. Although we’re not studying every existing lake in the Earth, we’re trying to cover a large, representative sample of the lakes that we have .”

The algae problem

The bluer lakes tend to be deeper and are found in cooler, high-latitude regions with high rainfall and winter ice cover, while the greenish-brown lakes are found in drier, continental interior regions and along the coasts. costs.

Climate change is transforming these blue lakes making them increasingly rare. The researchers modeled the different warming scenarios, concluding that, firstly, lakes located at high latitudes, such as those in Canada, northern Europe and New Zealand, could stop being blue. In fact, microscopic algae already exist in all of these lakes. If the air begins to heat up more, they will also “bloom” and it will be impossible to fight them.

“Warmer water, which produces more algal blooms, will tend to change lake colors toward green,” said Catherine O’Reilly, an aquatic ecologist at Illinois State University and a co-author of the study. ” There are many examples of researchers actually seeing this happen when studying an individual lake .”

The blue lakes are in decline. But cosmetic changes are only the beginning of the problem. The color change is also an indication of how drastically these ecosystems are mutating, which will affect the wildlife and humans that depend on them.

“If you’re using lakes for fishing or livelihood or drinking water, the changes in water quality that are likely to occur as lakes become greener will likely mean that it will be more expensive to treat that water. There may be periods when the water is not usable and fish species are no longer present, so we wo n’t get essentially the same ecosystem services from those lakes when they go from blue to green,” the researchers conclude.

Referencia: Xiao Yang, Catherine M. O’Reilly, John R. Gardner, Matthew R. V. Ross, Simon N. Topp, Jida Wang, Tamlin M. Pavelsky. The Color of Earth’s Lakes. Geophysical Research Letters, 2022; 49 (18) DOI: 10.1029/2022GL098925