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Relation Between Global Warming and Atmospheric CO2 Level: Evidence from Vegetational Change in NW Himalaya, India

Seema Singh, Arun K. Awasthi, and Brahm Parkash
Earth Sciences, I.I.T.,Roorkee, India, Roorkee, India

Global warming is a specific example of climate change. We seek to better understand levels of atmospheric CO2 and associated climate change through C-isotope data obtained from pedogenic carbonates over past 35Ma of Cenozoic strata in NW Himalaya. It is a common belief that CO2 is largely responsible for global warming. But geological evidence indicates that atmospheric CO2 levels have been declining over past 65Ma. Especially important insights are gleaned from the Himalayan system. We attempt to demonstrate the decline of CO2 levels by studying vegetational change during the last 35Ma in NW Himalaya. This is considered because physiological studies of plants show that C3 plants become increasingly less efficient under low atmospheric CO2 levels leading to conditions where C4 plants have higher efficiency than C3 plants. Stable isotope studies of pedogenic carbonates from palaeosols in NW Himalaya reveal that sediments from 35 - 18Ma, 18 - 10Ma, 10 - 7Ma, 7- 5.5Ma and 5.5 - 0.5Ma have C13 values between -10.33 to -18.52 ‰, -9.21 to -12.59‰, -7.8 to -12.9 ‰, -12.2 to -4.56 ‰ and -5.84 to +2.12 ‰ respectively. These C13 values show that between 35 - 7Ma there was dominance of C3 plants, between 7 - 5.5Ma there was mixed vegetation of C3 and C4 plants and after 5.5Ma there was complete dominance of C4 plants and even today. This corroborates well with the decline of atmospheric CO2 levels. Similar trends were found in America, Africa, Asia and Europe. Then if there is decline in CO2 level, then why do we correlate it with global warming. Does it mean that global warming is dependant on other factors like solar cycle variations, earth’s orbit, volcanoes etc. To know the exact reason there is a need of more indepth and thorough study. But the above discussion surely indicates that atmospheric CO2 level is not a major cause of global warming.

Presentation GEO India Expo XXI, Noida, New Delhi, India 2008©AAPG Search and Discovery