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2 GLOBAL WARMING: CLIMATIC AND ATMOSPHERIC CHANGES
Natural Factors Driving
Climate Change
GREENHOUSE GASES
Recently, scientific studies conducted indicate that both natural or anthropogenic factors
are the primary cause of global warming. Greenhouse gases are also important in under-
standing earth’s climatic history. According to these studies, the greenhouse effect, the
warming of the climate as a result of heat trapped by atmospheric gases, plays a signifi-
cant role in regulating earth’s temperature (Fig. 1.1).
Over the last 600 million years, concentrations of greenhouse gases have varied
from 5000 parts per million (ppm) to less than 200 ppm owing primarily to the effects
of geologic processes and biologic interventions. Studies also have shown that there is
a direct correlation between carbon dioxide (CO ) gas and global warming. Several
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historic examples of rapid change in greenhouse gas concentrations indicate a strong
correlation with global warming during various geologic events, such as the end of the
Varangian glaciation.
According to the Intergovernmental Panel on Climate Change (IPCC) in 2007, the
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atmospheric concentration of CO in 2005 was 379 ppm , compared with preindustrial
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Figure 1.1 Greenhouse effect. Courtesy of United Nations Environmental Program/GRID-Arendal.
