Global Warming Ecosystems

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Chapter- 4


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Global warming/ enhanced greenhouse effect and the loss of biodiversity are the major environmental issues around the world. The greatest part of the world’s population lives in the tropical regions. Mountainous regions in many cases provide favourable conditions for water supply due to orographically enhanced convective precipitation. Earth scientists are examining ancient periods of extreme warmth, such as the Miocene climatic optimum of about 14.5-17 million years ago. Fossil floral and faunal evidences indicate that this was the warmest time of the past 35 million years; a mid-latitude temperature was as much as 60C higher than the present one. Many workers believe that high carbon dioxide levels, in combination with oceanographic changes, caused Miocene global warming by the green house effect. Pagani et al. (1999) present evidence for surprisingly low carbon dioxide levels of about 180-290ppm by volume throughout the early to late Miocene (9-25 million years). They concluded that green house warming by carbon dioxide couldn’t explain Miocene warmth and other mechanism must have had a greater influence.

Carbon dioxide is a trace gas in the Earth’s atmosphere, which exchanges between carbon reservoirs in particularly the oceans and the biosphere. Consequently atmospheric concentration shows temporal, local and regional fluctuations. Since the beginning of industrialization, its atmospheric concentration has increased. The 1974 mean concentration of atmospheric CO2 was about 330 μmol mol-1 (Baes et. al., 1976), which is equivalent to 2574 x 1015 g CO2 702.4 x 1015 C assuming 5.14 x 1021 g as the mass of the atmosphere. This value is significantly higher than the amount of atmospheric CO2 in 1860 that was about 290 μmol mol-1 (617.2 x 1015 g). Precise measurements of the atmospheric CO2 concentration started in 1957 at the South Pole, Antarctica (Brown and Keeling, 1965) and in 1958 at Mauna Loa, Hawaii (Pales and Keeling, 1965). Records from Mauna Loa show that the concentration of CO2 in the atmosphere has risen since 1958, from 315 mmol mol-1 to approximately 360 315 mmol mol-1 in 1963 (Boden et al., 1994). From these records and other measurements that began more recently, it is clear that the present rate of CO2 increase ranges between 1.5 and 2.5 mmol mol-1 per annum. In the context of the Indian Himalayan region, the effect of warming is apparent on the recession of glaciers (Valdiya, 1988), which is one of the climatic sensitive environmental indicators, and serves as a measure of the natural variability of climate of mountains over long time scales (Beniston et al., 1997). However no comprehensive long-term data on CO2 levels are available. The consumption of CO2 by photosynthesis on land is about 120 x 1015 g dry organic matter/year, which is equivalent to about 54 x 1015gC/yr (Leith and Whittaker,

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