Researchers at Eötvös Loránd University (ELTE) have reconstructed approximately 16,000 years of summer temperature changes from sediments collected at Lake Prokoško in Bosnia and Herzegovina. The findings show how the Western Balkans responded to rapid climate changes at the end of the last glacial period, how warmer and cooler phases unfolded during the Holocene, and how the impact of human land use became increasingly pronounced.
The research was led by Enikő Magyari, a researcher at the Department of Environmental and Landscape Geography, ELTE Faculty of Science, and head of the DOMINO-CLIMATE Élvonal project.
Lake Prokoško, covering just 4.8 hectares, lies at an elevation of 1,670 metres in the Vranica Mountains, part of the Dinaric Alps. Over thousands of years, remains from the surrounding landscape and the lake's own ecosystem accumulated in its bottom sediments, making it possible to reconstruct the region's environmental and climatic history in detail.
Two studies by ELTE researchers published in 2026 examined different periods represented in the same sediment sequence. Enikő Magyari , head of the Institute of Geography and Earth Sciences at ELTE, doctoral researcher Eszter Tombor, and their colleagues analysed the rapid changes that occurred approximately 16,000–10,000 years ago, during the Late Glacial period and the beginning of the Holocene. Their findings were published in the prestigious journal Palaeogeography, Palaeoclimatology, Palaeoecology.
In a separate study published in Quaternary Science Reviews, Enikő Magyari's research group traced the history of the Holocene, with contributions from their Czech colleague Aneta Formáčková, among others. Together, the two studies provide a continuous picture of how summers in the Western Balkans have changed from the end of the last glacial period to the present day.
Tiny Insects as Climate Thermometers
Chironomids played a key role in reconstructing past temperatures. Their larvae live on lake beds, and different species prefer different water temperatures, oxygen levels and nutrient conditions. After moulting, their chitinous head capsules sink to the lake bed, where they can remain preserved in the sediment for tens of thousands of years.
By examining the chironomids’ head capsules recovered from the sediments, the researchers identified the species that inhabited the lake during different periods. Comparing these findings with faunal and climate data from hundreds of modern European lakes made it possible to estimate past mean July temperatures.
In addition to chironomids, the researchers analysed pollen, sediment particles, organic matter and geochemical elements. This enabled them to track not only temperature changes but also changes in forests, soil erosion and the condition of the lake.
Temperatures Changed by Several Degrees Within a Few Centuries
The oldest layers examined reflect the cold conditions prevailing towards the end of the last glacial period. Around 14,600 years ago, mean July temperatures around the lake were below 8°C. They then rose by approximately 2.6°C in a short period, reaching around 10.2°C. As temperatures increased, biological activity in the lake intensified, vegetation spread and conditions in the catchment became more stable.
However, this warming came to an abrupt end. Around 12,900 years ago, the Younger Dryas began, marking the last major cooling event at the end of the last glacial period. At Lake Prokoško, mean July temperatures fell by approximately 2.3°C, to around 7.9°C. Cold-water chironomid species became more abundant again, while increased erosion brought more clastic material into the lake.
The Lake Prokoško study also showed that the same large-scale climate change affected different parts of Europe to varying degrees. In many Alpine lakes, summer cooling of 3–4°C has been reconstructed, whereas in the Eastern and Southern Carpathians, the cooling was generally less than 1°C. The 2.3°C decrease recorded at Lake Prokoško falls between these two extremes.
This reveals a west-to-east trend: cooling was more pronounced in the west and weakened towards the east. The researchers link this pattern to oceanic and atmospheric changes in the North Atlantic region. The findings are particularly relevant to the Carpathian Basin, demonstrating that the same climatic event can have different effects in Western, Central and Eastern Europe.
Summers During the Holocene Were Sometimes Warmer Than Today
Another period of rapid warming began at the end of the Younger Dryas. Between approximately 11,800 and 11,400 years ago, mean July temperatures rose by around 2.9°C. By 10,500 years ago, they may already have reached approximately 12.6°C. The lake became more productive, the ice-free season grew longer, and the development of closed-canopy forests in the catchment reduced erosion.
Summer temperatures did not remain constant throughout the Holocene, however. Around 6,800 years ago, reconstructed mean July temperatures may have reached approximately 14°C, meaning that some summers around Lake Prokoško were warmer than those experienced today.
This does not mean that the warming then and now has the same cause. Warm summers during the Middle Holocene were driven primarily by gradual changes in Earth's orbital parameters, which led to stronger summer insolation in the Northern Hemisphere. This was mainly a seasonal phenomenon. In contrast, the warming occurring today is global and year-round, is progressing more rapidly, and is primarily associated with human-caused greenhouse gas emissions.
Human Impact Became Apparent 6,000 Years Ago
Around 6,000–5,500 years ago, a significant cooling trend began. Reconstructed mean July temperatures fell from approximately 14°C to around 12.8°C, and then to 11.8°C by about 5,670 years ago. This formed part of the so-called Neoglacial transition towards the cooler Late Holocene.
At the same time, evidence of human presence became increasingly apparent. Pollen data indicate that people had begun to alter the landscape around the lake by the end of the Neolithic, approximately 6,000 years ago. Plants associated with grazing and open habitats became more common, followed later by more intensive forest use and the expansion of open areas.
Around 3,000 years ago, another significant cooling began, with mean summer temperatures falling from approximately 14.7°C to 12°C. Around 2,000 years ago, temperatures rose again during the Roman Warm Period, reaching approximately 13.3°C.
Climate Change and Tourism Both Leave Their Mark
Over the past millennium, the chironomid community has reflected not only temperature changes. Centuries of alpine grazing opened up the landscape and increased the nutrient load entering the lake. Around 700 years ago, the midge community changed significantly, and over the past 500 years, species that prefer more nutrient-rich waters have become increasingly common.
Today, Lake Prokoško is no longer an untouched alpine lake. The surrounding area is a popular summer destination, and intensive use of spring water, together with nutrient inputs and wastewater pollution, affects both the lake's water balance and its ecosystem. The youngest sediment layers show increasing eutrophication, the spread of aquatic vegetation and worsening oxygen depletion in deeper waters.
The lake's sediments therefore preserve not only the history of natural climate change but also the history of human-driven landscape transformation.
At the Boundary Between Three Climatic Worlds
One of the key conclusions of the two studies is that the same climate change can vary in intensity across different parts of Europe. During the Younger Dryas, summer cooling reached 3–4°C in the Alps, approximately 2.3°C in the Western Balkans, and less than 1°C in the Eastern Carpathians. The Bosnian site thus represents an important climatic transition zone between Western, Central and Eastern Europe.
The research also demonstrates that alpine lakes respond sensitively even to relatively small temperature changes. The duration of ice cover, water stratification, oxygen content and biological activity can all change. These lakes are therefore particularly sensitive indicators of environmental and climatic change.
Palaeogeography Palaeoclimatology Palaeoecology
Chironomid-based Late Glacial and Early Holocene summer temperature variability in Lake Prokoško (Western-Balkan region)
13-Aug-2026