Irreversible Hotter and Drier Climate Over Inner East Asia

Heat waves are bringing Mongolia’s climate to a turning point

According to an international group of climate researchers, the semi-arid plateau of Mongolia could soon become as sterile as parts of the American Southwest due to a “vicious circle” of heat waves that exacerbates soil drying and ultimately creates more heat waves.

Write in the diary scienceThe researchers warn that heat waves and concurrent droughts have increased significantly over the past two decades, with worrying implications for the future. Using tree ring data, which provides insight into regional climates prior to modern weather logs, researchers developed heatwave and soil moisture records, suggesting record temperatures and droughts in more than 250 years have been unprecedented in recent years.

According to the results of the study, the record temperatures in the region are being accelerated by soil drying, and together these changes are exacerbating the decline in soil water. “The result,” said co-author Deliang Chen of the Swedish University of Gothenburg, “is more heat waves, which means more soil water losses, which means more heat waves – and we cannot say where this might end.”

When the soil is wet, the evaporation cools the air on the surface. However, when the soil runs out of moisture, the heat is transferred directly to the air. In their work Abrupt Shift to a Hotter and Drier Climate over East-East Asia beyond the turning point, the authors state that in the last 260 years only the last few decades “in addition to a radical decline in the soil have a significant anti-correlation between heat wave frequency and soil moisture fluctuations. “The scientists note that a number of recent heat waves in Europe and North America have shown the connection with near-surface air and soil moisture and that” the semi-arid climate of this region has entered a new regime in which soil moisture no longer exists abnormally decreases high air temperature. ”

The lakes on the Mongolian plateau have already seen a rapid decline. By 2014, researchers from China had documented a 26 percent decline in the number of lakes by more than a square kilometer, with the region’s largest lakes being even smaller on average.

“Now we see that not only large bodies of water are disappearing,” said author Jee-Hoon Jeong of Chonnam National University in South Korea. “Even the water in the ground disappears.”

“This can be devastating to the region’s ecosystem, which is vital for the large herbivores such as wild sheep, antelopes and camels,” said Peng Zhang, lead author of the study and researcher at Gothenburg University. “These amazing animals are already living on the fringes, and these effects of climate change can rush them.”

Co-author Jin-Ho Yoon of the Gwangju Institute of Science and Technology in South Korea noted that the centuries-old tree ring dates make it clear that the confluence of increased summer heat waves and severe droughts is unique in the context of the past 260 years. Co-author Hans Linderholm from the University of Gothenburg said the trees used in the analysis seem to “feel” the heat waves throughout their lives.

“The conifers react strongly to unusually high temperatures,” said Linderholm. “If we examine their growth rings, we can see their response to recent heat waves, and we can see that they don’t seem to have experienced anything like it in their very long life.”

The tree rings examined in the study were mainly collected from the Mongolian plateau, suggesting that the increasing heat affects plants even at high altitudes.

Daniel Griffin, of the University of Minnesota Department of Geography, Environment, and Society, who was not involved in this study but reviewed the paper, said the long-term perspective from these tree ring records illustrates a nuanced picture of the changing climate now affects large chunks the region of East East Asia.

“It’s one thing to recognize that“ normal ”climatic conditions are changing. However, what preoccupies me most is thinking about the extreme events of the future: how difficult could they get? Griffin asked. “And if the ‘new normal’ is extremely hot and dry by historical standards, future extremes may be different from anything previously observed.”

While warmer and drier trends can be observed in Europe and Asia, Mongolia and its surrounding countries are of particular interest to climate researchers, as this region in East-East Asia has a very direct relationship to global atmospheric circulation.

“Summer atmospheric waves tend to create a high pressure crest pattern in Mongolia that can last for weeks and trigger heat waves,” said co-author Simon Wang of Utah State University. “The warming climate amplifies these atmospheric waves and increases the likelihood of sustained or increased high pressure over Mongolia. This can also affect the northern hemisphere.”

“This large-scale atmospheric force is further intensified by local interactions with the land surface,” emphasized co-author Hyungjun Kim from the University of Tokyo in Japan. “Perhaps a worse problem has already arisen, creating an irreversible feedback loop and accelerating the region towards a hotter, drier future.”

In fact, the researchers have observed that the recent heat waves under the reinforced high pressure ridge have even drier and hotter air than the heat waves of the past.

The research team found that the combination of warming and drying appears to be nearing a “turning point” and is potentially irreversible, which could put Mongolia in a permanent state of drought.

Reference: “Abrupt shift to a hotter and drier climate across East Asia beyond the turning point” by Zhang, P., J.-H. Jeong, J.-H. Yoon, H. Kim, S.-Y. Wang, HW Linderholm, K. Fang, X. Wu, D. Chen, November 27, 2020, science.