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