Why Greenland’s crystal blue lakes have turned brown, and why you should worry

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More than 7,500 lakes in western Greenland have turned brown, begun emitting carbon, and suffered a drop in water quality due to extreme weather events that took place in 2022, according to a new study.

These lakes, which were once crystal blue, provide drinking water to locals, feature rich biodiversity, and sequester atmospheric carbon.

The study, ‘Abrupt transformation of west Greenland lakes following compound climate extremes associated with atmospheric rivers’, was published in the journal Proceedings of the National Academy of Sciences last week.

The analysis also revealed that the lakes underwent the transformation at a breakneck speed. Typically, such changes take place over centuries, but in this case, they happened within months after the extreme weather events occurred.

Jasmine Saros, a professor at the University of Maine (United States) and lead author of the study, told Earth.com, “The magnitude of this [change in the lakes] and the rate of change were unprecedented.”

What happened?

Greenland usually experiences snowfall during the fall season, from late August to late September. However, in 2022, due to warmer temperatures, the snow turned into rain. The heat also caused permafrost — frozen ground that often contains a significant amount of organic carbon — to thaw, leading to the release of carbon, iron, magnesium, and other elements. As the record level of rain poured on the region, these elements were washed into the lakes, resulting in their transformation.

According to the study, the increase in temperatures and precipitation was driven by several atmospheric rivers. The National Oceanic and Atmospheric Administration (NOAA) defines atmospheric rivers as: “Relatively long, narrow regions in the atmosphere — like rivers in the sky — that transport most of the water vapour outside of the tropics”.

Although these “rivers in the sky” bring much-needed precipitation and contribute to annual freshwater supplies, strong atmospheric rivers can lead to disastrous flooding and bring in heat. Studies have shown that with rising global temperatures, atmospheric rivers are expected to become more intense — they will be significantly longer and wider than the ones we observe today, according to a 2018 study by the National Aeronautics and Space Administration (NASA).

Existing climate models show that by the end of the 21st century, atmospheric rivers will become 50–290% more frequent in Greenland, western North America, east Asia, western Europe and Antarctica, a report by Phys.com said.

What was the impact?

As organic carbon and other elements washed into the lakes, their physical, chemical, and biological properties changed. The study said that the impact of the 2022 extreme weather events was visible by July 2023, meaning the lakes’ colour, odour, and taste had dramatically altered.

As a result, the water quality of these lakes was adversely affected. Soros told Earth.com, “The increased dissolved organic material can interact with drinking water treatment processes to produce chlorination byproducts called trihalomethanes, which may be carcinogenic.”

Besides, the colour change also meant that less sunlight was able to penetrate the lakes, which, in turn, impacted the phytoplankton living in the water. Phytoplankton consume carbon dioxide on a scale equivalent to forests and other land plants through photosynthesis. However, reduced light in the lakes hindered this process, reducing the absorption of carbon dioxide. Meanwhile, the breakdown of organic matter by other organisms in the lakes increased.

This transformed the lakes from carbon sinks into significant sources of carbon dioxide, with emissions rising by 350%, according to the study.

Saros told Earth.com, “Because the lakes turned so brown, it reduced the light coming into the system, which tends to favour organisms that use organic carbon pathways instead of photosynthesis”.

Why is this significant?

The findings have come just three months after a different study revealed that the amount of carbon absorbed by land has temporarily collapsed. It had concluded that forest, plants and soil – as a net category – absorbed removed only 0.23 to 0.65 gigatonnes of carbon in 2023. This was the lowest amount since 2003 and more than three times lower than the average over the past decade.

Notably, Earth’s oceans, forests, soils and other natural carbon sinks absorb about half of all human emissions. As these carbon sinks either stop to absorb carbon or become carbon sources, the levels of atmospheric carbon are expected to skyrocket.

The planet is already emitting unprecedented amounts of heat-trapping greenhouse gases into the atmosphere, especially through burning fossil fuels. The Global Carbon Budget report, published in November last year, said global carbon dioxide emissions were set to reach 41.6 billion metric tonnes in 2024, up from 40.6 billion tons in 2023.

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