Melting of major Glaciers in the western Himalayas: evidence of climatic changes from long term MSU derived tropospheric temperature trend (1979–2008)

摘要

Global warming or the increase of the surface and atmospheric temperaturesof the Earth, is increasingly discernible in the polar, sub-polar and majorland glacial areas. The Himalayan and Tibetan Plateau Glaciers, which arethe largest glaciers outside of the Polar Regions, are showing a large-scaledecrease of snow cover and an extensive glacial retreat. These glaciers suchas Siachen and Gangotri are a major water resource for Asia as they feedmajor rivers such as the Indus, Ganga and Brahmaputra. Due to scarcity ofground measuring stations, the long-term observations of atmospherictemperatures acquired from the Microwave Sounding Unit (MSU) since 1979–2008is highly useful. The lower and middle tropospheric temperature trend basedon 30 years of MSU data shows warming of the Northern Hemisphere'smid-latitude regions. The mean month-to-month warming (up to 0.048±0.026°K/year or 1.44°Kover 30 years) of the mid troposphere (nearsurface over the high altitude Himalayas and Tibetan Plateau) is prominentand statistically significant at a 95% confidence interval. Though themean annual warming trend over the Himalayas (0.016±0.005°K/year),and Tibetan Plateau (0.008±0.006°K/year) is positive, the month tomonth warming trend is higher (by 2–3 times, positive and significant) onlyover a period of six months (December to May). The factors responsible forthe reversal of this trend from June to November are discussed here. Theinequality in the magnitude of the warming trends of the troposphere betweenthe western and eastern Himalayas and the IG (Indo-Gangetic) plains isattributed to the differences in increased aerosol loading (due to duststorms) over these regions. The monthly mean lower-tropospheric MSU-derivedtemperature trend over the IG plains (dust sink region; up to 0.032±0.027°K/year) and dust source regions (Sahara desert, Middle East,Arabian region, Afghanistan-Iran-Pakistan and Thar Desert regions; up to0.068±0.033°K/year) also shows a similar pattern of month-to-monthoscillation and six months of enhanced and a statistically significantwarming trend. The enhanced warming trend during the winter and pre-monsoonmonths (December–May) may accelerate glacial melt. The unequal distributionof the warming trend over the year is discussed in this study and ispartially attributed to a number of controlling factors such as sunlightduration, CO₂ trends over the region (2003–2008), water vapor andaerosol distribution.