THE RISE OF the Tibetan Plateau in western China caused a major worldwide climate shift. As the highest region on Earth, this area became the world’s third major weather-maker, after the polar regions, and gave rise to the South Asia Monsoon about 8 million years ago. The growth of the plateau also set the stage for the ice ages that began approximately 2.5 million years ago. Glacial deposits, lake strand-lines, paleo-biologic studies, and ice core records now available from the Tibetan Plateau are filling a critical gap in comparing the Asian mid-latitude climate record with the more extensive records from other continents and the polar regions.
During historic times, China has undergone significant climate shifts, some natural, others most likely anthropogenic. Although desertification has been ongoing in China for perhaps 3,000 years, at least some of this has been attributed to human activities. The recent rapid retreat of China’s glaciers appears to be linked to global warming. Although the Chinese government places its highest priority on economic growth, it also appears to be taking anthropogenic climate change very seriously.
IMPACT OF THE TIBETAN PLATEAU
Rapid uplift during the late Cenozoic has shaped the landscape of the Tibetan Plateau and has drastically changed China’s climate. Regional differences in geo-morphology and local precipitation can result in different timing of glacial advances around the world. Currently, the Pacific Ocean monsoon dominates east China, while both the South Asia Monsoon and the mid-latitude Westerlies control the weather of the Himalaya and western China. The South Asia Monsoon dominates the southern part of Tibet, while the mid-latitude Westerlies dominate the northern part. These different climatic regimes have had important influences on the Quaternary glaciations.
The rise of the Himalayan Mountains and plateaus significantly increased worldwide erosion rates. Silicate weathering provides one of the major natural processes that remove CO2 from the atmosphere, in the process forming carbonates. Hence, the rise of the Himalaya and Tibetan Plateau could have contributed to the onset of Pleistocene glaciation by depleting atmospheric CO2, the most abundant greenhouse gas.
The Tibetan Plateau contains the largest ice mass on the Earth outside the polar regions. The Tibetan Plateau holds almost 37,000 catalogued glaciers, with a combined area of nearly 50,000 km2. These glaciers owe their existence to the rise of the Tibetan Plateau. They extend north into the arid and desert regions, feeding the Yellow and Yangtze rivers, which provide the main water resource for arid central Asia, and northeastern China. They also extend south into the warmer, wetter forests and concentrate around the Brahmaputra, Mekong, and Salween rivers, which provide needed water to both local residents and much of southeast Asia.
Coastal areas of China could suffer from sea-level rise due to melting of polar ice caps. On the Tibetan Plateau, however, the immediate response to the accelerating glacial retreat could be villages displaced as a consequence of lake expansion and disasters related to glacial lake outbursts and other floods. Severe water shortages may follow once the reservoir of glacial ice is depleted.
PALEOCLIMATE RECORDS
Until recently, researchers have found it difficult to compare the relative ages of China’s Quaternary glaciations with each other, let alone with global ice ages. However, absolute numerical dating now allows China’s glaciations to be placed into the pre-existing worldwide framework. Based on these new dating results, Yi Chaolu and others have determined that most Asian Quaternary glaciations in the last 100,000 years were synchronous with global glacial events. One glacial advance between 44,000 and 54,000 years ago in southeastern Tibet was not synchronous with global cooling, and might have been caused by greater precipitation during a locally colder period. Chinese researchers have identified more Quaternary glacial periods before the Wisconsin Glaciation than have been identified in other regions of the world. The uplift of Tibet during the Cenozoic could be responsible for these differences.
As one of the thickest ice caps in central Asia, the Guliya Ice Cap, on the crest of the Kun Lun Mountains, provides valuable information for this critical region about the past climatic and environmental changes. Yang Meixue and others report that the Guliya ice core demonstrates periodic oscillations of the temperature and precipitation over the past 1,700 years. The results show various oscillations in the ice core records, with multiple timescales (200, 150, 70, 40, and 20 years). Their amplitude, phase, and frequency vary with time. Temperatures recorded since 1700 c.E. show that precipitation correlates well with temperature in this region.
Yao Tandong and others used data from an ice core from the Puruogangri Icefield on the central Tibetan Plateau to construct a temperature history for the region based on the temperature proxy, 51sO. Reconstructing temperatures back to 1000 c.E. shows changes on the plateau generally similar to those in other parts of the Northern Hemisphere on a multi-decadal timescale. These data indicate that the 20th century warming in China was abrupt and exceptional, and that the 20th century was warmer than any time during the past 1,000 years.
The impressive Tibetan Plateau contains the largest ice mass on Earth outside the polar regions, with almost 37,000 catalogued glaciers that have a combined area of nearly 50,000 km2.
Unlike much of the Northern Hemisphere, temperatures throughout the Tibetan Plateau showed no widespread cooling trend from 1000 c.E. to the late 19th century. They show, instead, slightly increasing temperatures. For the northern portion of the plateau, however, temperatures exhibited a very slight cooling trend from 1000 c.E. to the late 19th century. This reconstruction confirms the existence of the Medieval Warm Period and the Little Ice Age in China. However, the Little Ice Age was not as relatively cold as in other regions of the Northern Hemisphere.
RECENT CLIMATE CHANGE
China is experiencing a well-documented, widespread warming. The glaciers on the Tibetan Plateau are retreating rapidly, and permafrost is melting. This rate has accelerated in the early 21st century under the impact of an intensified South Asia Monsoon, which is likely a consequence of global warming.
Yao Tandong and others trace the glacial retreat in China to the termination of the Little Ice Age, around the beginning of the 20th century. Since then, the glacial retreat can be divided into several stages. The first half of the 20th century was characterized by shifting from glacial advances to retreats. Between the 1950s and the 1960s, the glaciers began extensive retreat, with over half of the studied glaciers retreating, about 30 percent advancing, and the others stable. In a short period from the late 1960s to the late 1970s, advancing glaciers increased again and the percentage of retreating glaciers decreased to less than half. Starting in the 1980s, glacier retreat intensified again, with 90 percent of the studied glaciers retreating. Since the 1990s, glacial retreat has been accelerating, with 95 percent of the studied glaciers now retreating.
The magnitude of glacial retreat is less on the northern Tibetan Plateau, and more at the margins; the greatest retreats are on the southeast plateau. The rate of glacial retreat reached 213 ft. (65 m.) per year on the southeast plateau, where the South Asia Monsoon prevails. The smallest glacial retreat appears on the central plateau, where a continental climate dominates.
Monsoons and the Westerlies affect the dominant patterns of glacial retreat on the Tibetan Plateau. The monsoon water vapor flows through the lower reaches of the Brahmaputra River valley toward the interior of the plateau, which results in the development of the largest glaciers. With global warming, the Southeast Asia Monsoon is intensifying, which causes more precipitation on the southeastern plateau. The increased precipitation there comes mostly as rainfall, as opposed to the situation in the mountains influenced by the Westerlies, where increased precipitation on high elevation glaciers falls mostly as snow. Trends showed strong increases for spring and winter precipitation from 1961 to 2001.
Over the last decade, many lakes in highly glaciated regions have expanded. Yao Tandong and others assessed size changes of lakes greater than 3.7 sq. mi. (10 sq. km.) and discovered that over 70 percent of the lakes evaluated expanded by at least 12 percent, since the 1990s. Glaciological observations in the region suggest that intensified glacial melting in response to the current warming is the principal driver, not precipitation patterns over the plateau.
Lake expansion will most likely modify the hydro-logic cycle over the Tibetan Plateau. Grassland destruction and resultant reduction of livestock grazing is now occurring near Lhasa. (Higher CO2 concentrations also favor woody plants over grasslands.) Furthermore, the potential for glacial lake outburst flooding is also increasing, which could cause serious damage in south Asian countries such as India, Nepal, and Bhutan.
The southern limits of China’s permafrost appear to be moving northward at over .93 mi. (1.5 km.) per year. The area of permafrost is expected to decline by 30-50 percent during this century. Permafrost collapse tends to cause slumping of the soil surface and flooding, followed by a complete change in vegetation, soil structure, and many other important aspects of these ecosystems. Melting permafrost causes concern, because frozen ground stores huge quantities of carbon as methane and CO2.
Recent studies show that initial flooding caused by melting boosts plant productivity, sequestering more carbon from the atmosphere in plant biomass. Hence, permafrost degradation may initially increase soil carbon sequestration, rather than release large amounts of carbon into the atmosphere, as originally predicted. But over time, the greenhouse effect of high methane emissions will outweigh the reduction of carbon in the atmosphere.
Chinese scientists conclude that human activities have accelerated the desertification process and have driven the north China deserts southward by approximately 186 mi. (300 km.) over the past 3,000 years. A growing population, intensive agricultural activities, excessive tree-cutting, and frequent warfare have damaged the natural vegetation, caused soil erosion, and intensified desertification. Reforestation projects and greater rainfall from changes in the East Asia Monsoon patterns currently affecting the semi-arid to arid areas in this region are likely to help prevent and reverse desertification. However, water shortages will persist, due to lack of glacier storage and the current heavy mining of ground water.
Most recently, both the International Energy Agency and the Netherlands Assessment Agency say that China became the world’s leading source of greenhouse gas emissions in 2007. According to the World Bank, Chinese industry uses 4-10 times more water per unit of production than the average in industrialized nations. China ratified the Kyoto Protocol in 2002, but as a developing nation was not held to specific emissions targets. China’s emissions of sulfur dioxide and particulates that act contrary to greenhouse gases (decreasing radiative heating in the lower atmosphere) are increasing even faster than China’s economic growth. Their control may exacerbate the warming.
The China Daily recently reported that over 400 sq. mi. (644 sq. km.) of land in southern China would be flooded by 2050 as sea levels rise due to global warming. The Pearl River Delta area, a leading manufacturing hub, will be hard hit by climate change in the coming decades. The cities of Guangzhou, Zhuhai, and Foshan are expected to be the worst hit as sea levels rise by at least 11.8 in. (30 cm.) by 2050. Climate change will thus likely depress economic development of this province, which is currently one of the biggest consumers of energy and producers of greenhouse gases.
CLIMATE CHANGE POLICY
Although China’s leaders recognize that they must deal with emissions of climate and health-related pollutants, economic growth remains the country’s highest priority. The state is a partner in most energy, and many industrial, enterprises, as well as the regulator of environmental issues. As a result, environmental controls are weak, and enforcement of standards and laws lacks uniformity. China’s central Energy Bureau has only 100 full-time staff (compared to the U.S. Department of Energy’s 110,000). Another result of the economic system has been to allow low-efficiency energy use with little, if any, economic penalty.
China depends heavily (about 70 percent) on coal for its energy. With energy demands rising, more coal production is planned at least until 2020. China produces about 35 percent of the world’s steel, 50 percent of the world’s cement and flat glass, and about 33 percent of the world’s aluminum—all very energy-intensive industries. In 2007, China was the second largest producer of cars (passing Japan), next to the United States. On average, China uses 20 percent more energy per ton of steel and 45 percent more per unit of cement than the international averages. Because of the international nature of their market, China’s leaders argue that pollution originating from these global industries should not be attributed strictly to China, but that end users are partners in degrading the environment.
The Chinese leadership has issued numerous statements recognizing the need for a change in course. Recent actions include the passage of the Renewable Energy Law (endorsing expanded use of renewables), the phasing out of export subsides for polluting industries, and the closing of illegal coal mines and some heavily polluting factories. Targets for energy efficiency have been established, but have so far gone unmet. The government has been unwilling to use significant financial tools to implement climate-related goals. The government controls the rates for commodities such as electricity, fuel oil, gasoline, and water, which all remain relatively inexpensive. Officials have rejected proposals to introduce surcharges on electricity and coal to reflect the true cost to the environment. China has also declined to institute other tax policies or market-based incentives or to accept mandatory limits on its CO2 emissions.
The per capita use of energy in China still falls far below that of most of the industrialized world; only about 15 percent of that in the United States. As citizens of China achieve the level of affluence of the industrialized world, they will invariably desire more amenities. Private cars, for instance, are increasingly common. To achieve parity in standard of living without greatly increasing their energy use and greenhouse gas emissions will be a daunting challenge.
