A Precarious Puzzle of Expanding Deserts: How arid Asia has varied over time and the confusion over recent desertification

Written by Jane Baldwin

Inner Mongolia (Nei MengGu in Mandarin Chinese) lies right at the border of the nation of Mongolia within mainland China (see Figure 1). Pictures of yurts, traditional pony races, Mongolian wrestlers, and most of all rolling grasslands attract many Chinese tourists to this region each year (see Figure 2). In summer 2009, while I was an undergraduate studying Mandarin Chinese in Beijing, I also became enticed to this region. Tasked by my program to use my newly polished Mandarin to conduct a “social study” in an area outside Beijing, Inner Mongolia seemed both a very foreign and fascinating locale to investigate.

Jane Fig 1
Figure 1. Inner Mongolia, a Chinese province, lies just south of the nation of Mongolia. It is part of the arid lands that stretch across interior Asia. Source: adapted from Nasurt, 2011.

A group of my classmates and I took an overnight train from Beijing to Hohhot, and then a bus far into the countryside to our first yurt encampment. As expected, the great expanse of the scenery was stunning—the landscape stretched out before us only punctuated by occasional small hills, yurts, and sheep. However, we were shocked to discover the lush grasses in pictures were reduced to dry scrub only an inch or two high (see Figure 3).

Jane Fig 2
Figure 2. The Inner Mongolian pastoral ideal branded by Chinese tourist agencies. Source: http://www.chinadaily.com.cn/m/innermongolia/2015-04/10/content_20401697.htm
Jane Fig 3
Figure 3. The state that many grasslands in Inner Mongolia are currently in or approaching following recent desertification. Source: http://www.theguardian.com/world/2015/apr/10/inner-mongolia-pollution-grasslands-herders

I was concerned by this difference, and decided to focus my interviews with the local people on these environmental changes. The local nomadic herders informed me that desertification (or shamohua in Mandarin—literally translated as “change into desert”) had become a serious issue in this region over the past 20 years or so. One herder I interviewed recalled that as a teenager, the grasses had reached as high as his horse’s flank, while now they extended no higher than his horse’s hoof. These observations led me to wonder many questions which did not yield firm answers through my interviews: What was the cause of these dramatic changes? Were the local people responsible for the degradation? Or was it caused by larger scale climate variations outside of their control? And what would be the appropriate policy response to deal with the degradation and still respect the people who had lived there for generations?

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Since that summer, this suite of questions around deserts and desertification has inspired much of my study and research, both as an undergraduate and now a PhD candidate in Atmospheric and Oceanic Sciences. My PhD research focuses broadly on understanding the climate of arid and semi-arid regions across Asia that define the margins of these grasslands (see Figure 1). As the largest deserts outside the tropics, this region presents a number of interesting climate dynamics questions. However, through research, classwork, and personal reading I have also sought to understand this region from a variety of angles beyond climatological, in particular geological, historical, and political. While spiraling in towards the desertification question, I have developed a mental narrative for this region, and its changes and controls of its climate over different periods of time.

Observing sediments and fossils, geologists have pieced together a record of arid Asia that shows this region to have varied greatly over the long geological timescales of millions of years. 50 Ma (million years ago), what is now Central and northern East Asia was covered in warm, damp forest populated by ancient horses, and rhino ancestors larger than modern elephants. A few theories exist for what spurred the relatively rapid (few million year-long) transition to the cool, dry climate we know today. Around this time India’s collision with the Eurasian subcontinent was creating the colossal Tibetan Plateau and Himalayas. The longest running theory for the formation of these deserts is that this newly risen topography blocked moisture from reaching Central and northern East Asia, drying this region. Climate modeling studies have indeed indicated that the Tibetan Plateau creates significant aridity outside the tropics in Asia . However, new research presents an alternative theory for the formation of this region. A large inland sea on the western margin of Central Asia, called the Paratethys, was recently found to have retreated just prior to the transition of this region to an arid environment; the migration of this moisture source may have played a dominant role in drying Central Asia. Which of these mechanisms (Tibetan Plateau uplift or the retreating Paratethys) was most important for the drying of Asia, and whether they might be linked, are both still open and actively researched questions.

More recent environmental history (i.e. the past few thousand years) is recorded in tree rings. When trees are water-stressed, how much their trunks grow radially depends in large part on how much rainfall there is. Widths of tree rings thus provide a proxy for historical drought/wet periods. The dry climate of this region over the past few thousand years, and its variations in precipitation recorded in these tree rings are hypothesized to have played key roles in human history, with the most dramatic example being the expansion of the Mongol Empire. Genghis Khan and the nomadic steppe tribes allied with him relied on horses for travel, sustenance, and warfare. Tree rings suggest that during the 13th century when the Mongol Empire expanded to cover China, Central Asia, and parts of the Middle East and Europe, the region was warm and persistently wet; these climatic conditions favored high grassland productivity, supporting Mongol political and military power during this critical period. This is but one example of how climatic and historical changes link tightly in this water-stressed region.

Over the past hundred years, the clearest climatic trend on the global scale has been warming caused by anthropogenic carbon emissions, primarily CO2 released from burning fossil fuels. How this global signal will translate to the regional scale is still a topic of active research in the climate science community. The most recent UN Intergovernmental Panel on Climate Change (IPCC) report shows that warming is clearly predicted over Asia as carbon emissions continue to increase. However, there is little consensus among climate modeling studies regarding how precipitation will change over arid Asia. This uncertainty is concerning for an environment that is already exhibiting symptoms of increasing water-stress. Desertification or land degradation has occurred across the margins of arid Asia over the past few decades, including places as diverse as the former Soviet countries that exist in the Aral Sea drainage basin, Qinghai Province on the Tibetan Plateau, and of course Inner Mongolia. While the UN Convention to Combat Desertification has motivated countries to submit plans to fight this degradation, on-the-ground action has been slow and limited. Facing the double threat of ill-planned development and global warming, these delicate regions on the border of Asia’s great deserts are currently in a precarious position.

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While my understanding of arid environments and particularly their variability has increased significantly since I first visited Inner Mongolia in the summer of 2009, the recent desertification of this region is still a puzzle for me and for the scientific community at large. Over the past decade, the Chinese government has tried a number of strategies to deal with the desertification in Inner Mongolia. Citing overgrazing as the cause of the increased aridity, the government has resettled pastoralist nomads into cities—nomads who have grazed the steppe for thousands of years. Since 2003, the total number of urban resettlements in Inner Mongolia is 450,000. Meanwhile, in the tradition of the great engineering emperors of yore, the Chinese government is supporting a “Great Green Wall” of trees planted to halt the expanding desert and decrease dust transport. By the project’s planned end in 2050, it is intended to stretch 4,500km (2,800 miles) along the edge of China’s Northern deserts, covering 405 million hectares—a truly massive endeavor.

Unfortunately, without knowing the root cause of the desertification or how this region will respond to ongoing global warming, it is difficult to predict whether these policies are appropriate. While the Chinese government points its finger at overgrazing, some experts believe that it was the government’s prior actions in this region (fencing land and supporting agriculture over pastoralism) and ongoing mining pollution that has pushed this region away from a sustainable equilibrium and towards desertification. Adding flame to the fire, ecologists and hydrologists wonder whether the Great Green Wall’s trees will grow successfully or just deplete the water supply further. Meanwhile, recent climate studies provide an alternative explanation to these land-use centric arguments, suggesting that non-local climatic causes such as global warming and decreasing East Asian monsoon strength may explain the increasing aridity.

In this quagmire of rapid environmental change and scientific uncertainty one thing is clear: it is critical for there to be a robust dialogue between scientists and policy makers for Inner Mongolia, and the dry climates in Asia at large, to have a chance at developing sustainably.

 

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Jane is a PhD candidate in Princeton’s Atmospheric and Oceanic Sciences program in joint with NOAA’s Geophysical Fluid Dynamics Laboratory, where she is advised by Dr. Gabriel Vecchi. Her research employs a combination of dynamical climate models and earth observations to elucidate the ties between global and regional climate, and move towards useful predictions of climate change at regional levels. 

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