Heat Waves and Droughts Unseen in 100 Years Become the Norm... Eurasian Steppe Climate Shifts Rapidly [Reading Science]

Seoul National University Identifies Rapid Drying Since the 1990s... Temperature Rise Twice the Northern Hemisphere Average
Declining Soil Moisture Intensifies Heat Waves... Shrinking Grasslands and Expanding Bare Land Threaten Food Security

The Eurasian steppe, stretching from southern Ukraine through southern Russia to western Kazakhstan, has shifted to hotter and drier conditions not seen in the past 100 years. It began drying rapidly in the early 1990s, and since the 2000s, conditions have persisted beyond the range of past natural climate variability. The analysis found that a vicious cycle in which increasingly dry land intensifies heat waves and rising temperatures further worsen drought has accelerated climate change.

Seoul National University said on October 27 that a research team led by Professor Jong-Seong Kug of its Department of Earth and Environmental Sciences, in an international collaboration, had identified a rapid “climate regime shift” in the West Eurasian steppe region. The findings were published in the international journal Nature Geoscience.

The mid-latitudes of the Northern Hemisphere and the steppes of western Eurasia have dried rapidly since the early 1990s. Since the 2000s, dry conditions beyond the range of past natural variability have persisted. Provided by the research team.

The research team analyzed climate data from 1901 to 2024 and large-scale simulations from several climate models. The results showed that in recent decades, the West Eurasian steppe region has experienced the most severe summer drying in the mid-latitudes of the Northern Hemisphere.

In particular, summer temperatures in the region rose by about 0.63°C per decade from 1992 to 2010, roughly twice the 0.32°C-per-decade average increase over Northern Hemisphere land during the same period. Drying accelerated around 1992-1993, and a statistically distinct shift in climate conditions was also identified around 2006. No clear signs of a return to past climate conditions had emerged by 2024.

As Land Dried, Heat Waves Intensified... Temperature Rise Amplified by Up to 44%

One of the key factors driving the rapid climate change was the interaction between soil and the atmosphere.

When soil contains sufficient moisture, water evaporates and absorbs heat from its surroundings, cooling the land surface. This works much like sweating, which lowers the human body's temperature. But when drought dries out the soil, the cooling effect of evaporation weakens. More of the energy received from the sun is then used to heat the land surface and the atmosphere, intensifying heat waves.

Higher temperatures increase the atmosphere's demand for evaporation, drying the soil further. This creates a recurring vicious cycle: drought intensifies heat waves, and heat waves, in turn, worsen drought.

To assess these effects, the research team compared climate models that suppressed soil-atmosphere interactions with models that included them. In five of the seven models used in the analysis, removing these interactions substantially weakened warming and drying.

Since the 1990s, declining soil moisture has weakened the land surface's cooling effect, creating a vicious cycle in which heat waves and droughts intensify each other. As a result, vegetation productivity in croplands and grasslands is also declining. Provided by the research team.

In those models, soil-atmosphere interactions contributed about 24-44% of the temperature rise trend and about 37-68% of the increase in potential evapotranspiration. This means that declining soil moisture did not merely result from drought; it also acted as a factor amplifying climate change.

Global warming caused by human activities and natural changes in atmospheric circulation also played a combined role. The research team found that while warming driven by factors such as rising greenhouse gas emissions set the stage for hotter and drier conditions, changes in atmospheric circulation extending from Europe to East Asia since the 1990s further reduced precipitation and raised temperatures.

Grassland Area Down 5%, Bare Land Up 26%... Warning for Grain Production

The effects of the climate regime shift were also evident in actual ecosystems.

Satellite observations showed that from 2021 to 2023, the area of grassland in the West Eurasian steppe region was about 5% smaller than the average before 2010. By contrast, the area of bare land without vegetation increased by about 26%. Gross primary production (GPP) in farmland and grasslands also declined, indicating weakened plant photosynthesis and carbon absorption capacity.

The region is a major center for grain cultivation and livestock farming. If heat waves and droughts persist over the long term, agricultural production could become more uncertain and the degradation of grassland ecosystems could worsen. This is a potential risk for South Korea, which relies on international grain markets.

However, this study did not directly analyze the effects on actual grain production or international grain prices. The findings suggest that a climate regime shift in major agricultural regions could increase risks to food supply chains.

The research team projected that continued warming could further intensify drying in the West Eurasian steppe region. Even with active greenhouse gas reductions, the region is unlikely to return to its past, wetter climate conditions in the short term.

“This study shows that global warming does not necessarily manifest only as gradual climate change,” said Jong-Seong Kug, a professor in Seoul National University's Department of Earth and Environmental Sciences. “It is important to recognize that a region's climate can change rapidly as drying soil intensifies heat waves, which then further worsen drought.”

He added, “Since this kind of climate regime shift could also occur in other semi-arid regions, assessments of future climate risks should consider not only average warming but also the possibility of abrupt changes and compound disasters.”

This content was produced with the assistance of AI translation services.