A climate change laboratory
The Kolsai Lakes are a system of three alpine lakes in the Kungey Alatau range, a part of the Northern Tian Shan mountains in Kazakhstan. The lakes sit at ascending altitudes of 1,800, 2,250, and 2,700 meters above sea level. Their brilliant turquoise water, a result of suspended glacial sediment, gives them the name "Pearls of the Northern Tian Shan". These lakes are fed by the Kolsai River, which originates from glaciers on the surrounding peaks. This direct link makes the entire lake system records climate change, as the health of the lakes is tied to the mass of the glaciers above them.
Systematic glaciological research in this region began during the International Geophysical Year of 1957-58. One of the most important monitoring sites in the Northern Tian Shan is the Tuyuksu glacier, which has one of the longest continuous mass balance records in the world. This long-term data provides a clear picture of glacial decline. Studies in the peripheral ranges of the Northern Tian Shan, such as the Ile and Kungey Alatau where the Kolsai Lakes are located, show a particularly rapid reduction in glacier area. For the period of 1955–1999, the glacier reduction speed was measured at 0.73% per year.
Measuring the melt
The glaciers of the Tian Shan are in a state of negative mass balance, meaning they are losing more ice through melting than they gain from snowfall. Data from the nearby Tuyuksu group of glaciers, an important reference site, shows a mean surface lowering of 23.2 meters between 1958 and 2016. This equates to a mass balance loss of -0.35 meter water equivalent per year for that period. The overall glacier retreat rate in the Northern/Western Tian Shan has accelerated, increasing from 0.87% per year to 1.49% per year after 2011.
This accelerated melting has direct consequences for the Kolsai Lakes and the entire region's water supply. Increased meltwater can raise river and lake levels. As glacier volume continues to decrease, this effect will reverse, leading to diminished water resources for downstream communities and ecosystems. The formation of new and expanding glacial lakes is another consequence of the melt. These new lakes can be unstable, often dammed by loose rock and ice, posing a risk of glacial lake outburst floods (GLOFs).
The sustained increase in summer temperatures is the primary driver of this accelerated glacial retreat. Projections indicate that on mountain ridges below 4,500 meters in the Tian Shan, many glaciers may disappear entirely, with a potential reduction of up to 70% in some areas by the 2050s-2070s.