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East Asia may be permanently locked into hotter and drier climate

An abrupt shift in the climate over inner East Asia may lead to a tipping point that pushes Mongolia into a permanently dry and barren region. Researchers at Utah State University warn that heatwaves and concurrent droughts have increased significantly during the past two decades in a “vicious cycle,” where a lack of soil moisture produces more heatwaves.

The scientists used tree ring data to examine the past climate from before weather conditions were documented. The researchers acquired heatwave and soil moisture records, which indicate that the recent back-to-back years of record high temperatures and droughts are unparalleled in more than 250 years.

According to the study, soil drying has contributed to record high temperatures in the region, and the compounding effects are intensifying a lack of soil moisture. “The result is more heatwaves, which means more soil water losses, which means more heatwaves – and where this might end, we cannot say,” said Deliang Chen.

When soil contains moisture, evaporation cools the air at the surface. But when the soil is dry, heat is directly transferred into the air.

The study authors said that in the past 260 years, only recent decades “show significant anticorrelation between heatwave frequency and soil moisture, alongside a radical decline in soil moisture fluctuation.” 

According to the experts, a series of recent heatwaves in Europe and North America indicate that the semi-arid climate of this region has now entered a new regime. 

Lakes across the Mongolian Plateau are rapidly shrinking and disappearing. By 2014, Chinese researchers had documented a 26-percent decrease in the number of lakes greater than one square kilometer in size, and they found an even larger decline in the size of the region’s largest lakes.

“Now we are seeing that it isn’t just large bodies of water that are disappearing,” said study co-author Jee-Hoon Jeong of Chonnam National University in South Korea. “The water in the soil is vanishing, too.”

“This may be devastating for the region’s ecosystem which is critical for the large herbivores, like wild sheep, antelope and camels. These amazing animals already live on the edge, and these impacts of climate change may push them over,” explained study lead author Peng Zhang of the University of Gothenburg.

Daniel Griffin is an expert in the Department of Geography, Environment, and Society at the University of Minnesota. Upon reviewing the study, he said that the long-term perspective from these tree-ring records illustrates a nuanced picture of the changing climate that is now afflicting large swaths of the inner East Asia region.

“It is one thing to recognize that the ‘normal’ climate conditions are changing. However, what concerns me the most is thinking about the extreme events of the future: how severe might those become?”

“And if the ‘new normal’ is extremely hot and dry by historical standards, then future extremes may well be unlike anything previously witnessed,” said Griffin.

The warming trends in Mongolia and its surrounding countries are particularly interesting to climate scientists because this region of East Asia is directly linked to global atmospheric circulations.

“Summer atmospheric waves tend to create a high-pressure ridge pattern around Mongolia that can persist for weeks, triggering heatwaves,” explained Simon Wang of Utah State University. “The warming climate is amplifying these atmospheric waves, increasing the chance of prolonged or intensified high-pressure to occur over Mongolia and this can also have ramifications across the Northern hemisphere.”

“Such large-scale atmospheric force is further amplified by local interactions with the land surface,” said Hyungjun Kim of the University of Tokyo. “An even worse problem may have already occurred in which an irreversible feedback loop is triggered and is accelerating the region toward a hotter and drier future.”

The study is published in the journal Science.

By Chrissy Sexton, Staff Writer

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