The Third Pole climate evolution study

Studies show that the uplift of the Third Pole has intensified the Indian monsoon (Kearey et al., 2009).So far, various proxies have been used to infer the uplift history and process of the Third Pole. Studies with the composition of oxygen isotopes in rocks and lake sediments show that various areas of the Tibetan Plateau were at elevations of over 4000 m about 11–35 million years ago (DeCelles et al., 2007; Garzione et al., 2000; Rowley and Currie, 2006). The shape and size of fossil leaves also help to shed light on the uplift history of the Tibetan Plateau that, about 15 million years ago the elevation of southern plateau was more than 4600 m (Spicer et al., 2003).

The elevated topography of the Third Pole not only acts as a barrier to the mid-latitude westerlies, but also triggers strong dynamical and thermo-dynamical impacts, thus contributing greatly to global circulation as well as regional and hemispherical environmental changes (Bothe et al., 2011). The Third Pole also plays a prominent role in the evolution of the Asian monsoon system, which is critical for the moisture fluxes and precipitation patterns in the region (An et al., 2001).

Third Pole affect the atmospheric circulation patterns in Eurasia and thus significantly influence the climate system in the northern hemisphere. The winter Eurasian snow cover south of 52N was found to show a significant correlation with the following Indian summer monsoon by Hahn and Manabe (1975). Further study showed that heavysnowfall over the Tibetan Plateau can both weaken and prolong the duration of the summer monsoon system in the region (Liu et al., 2004).

• Cryosphere study under global warming

The Third Pole shows a large-scale warming trend that began in the mid-1950s. The temperature rise of up to 0.3 C per decade has been going on for last fifty years, which is approximately three times the global warming rate (Qiu, 2008). The air temperature increases more significantly in the central, eastern, and northwestern parts of the TP (Liu and Chen, 2000). The warming trend in the cold season is greater than that in the warm season. The cause of increases in temperature in TP is due to increase in greenhouse gas emissions, changes in cloud cover, and snow-albedo feedback, the Asian brown clouds and land use changes can be found in various studies (Duan et al., 2006; Frauenfeld et al., 2005; Liu et al., 2006; Qiu, 2008).

• Glacier study

The Third Pole contains glaciers with a total area of 100,000 km2. Since the 1990s, most of the glaciers in the region have undergone considerable retreat though the extent in retreat varies geographically (Kang et al., 2010). The central part of the Third Pole exhibits the least extent of glacial retreat, while the southeast part under the influence of a maritime climate has the greatest extent in retreat (Pu et al., 2004). The glaciers retreat information can be found in various studies (Menon et al., 2009; Kang et al., 2007)

• Snow cover and Permafrost degradation: snow cover and permafrost degradation will likely cause a drier ground surface (Cheng and Wu, 2007) and significantly affect soil properties (Wang et al., 2006).

• Land use land cover (LULC) change:  Grassland occupies an area of about 1.5 million km2 (Cui and Graf, 2009). Significantly decrease in grasslands approximately 14–16% of total grassland area is reported on the plateau region of TP by Wang et al. (2006).  Study shows that the main reasons for degrading in grassland are warmer temperature, changes in combination of temperature and precipitation, decreasing glaciers, melting frozen soil, overgrazing and rat damages (Shang and Long, 2007). Due to unsustainable logging practices, agricultural use and urbanization, deforestation on the Third Pole began in the 1950s and accelerated in the 1960s (Houghton and Hackler, 2003; Liu et al., 2005; Studley, 1999), which may impair forest functions of safeguarding watersheds and river flow (Houghton and Hackler, 2003).

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