Carl Edward Sagan (1934-1996) was an American astronomer, planetary scientist and science communicator. His notable works are Cosmos (1994). 'The dangers of climate change', is an excerpt taken from the fourth chapter of 'Cosmos', his famous book with a fine blend of science and Philosophy. Here, he discusses how both natural and human activities have shaped and will continue to shape the Earth's environment.
According to Sagan, landscapes are shaped by both gradual erosion and sudden catastrophes. He draws comparisons between Earth's environmental processes and those on other planets and moons like Venus, Mars, Ganymede and Europa. Actually the sphinx in Egypt, built over 5500 years ago, has been worn down by natural weathering processes such as sand blasting and rains. Similarly Cleopatra's Needle in New York city's central park that came from Egypt has been damaged by industrial pollution. In addition to such slow and gradual erosion, destruction also occurs through sudden catastrophes like purposeful or accidental damage done to them. It is said Mameluke Turks and Napoleonic soldiers were also behind the damage of Sphinx.
There are evidences of catastrophic destruction on the planets in the solar system. on the earth huge alluvial basins have been created by the rivers. Similar remnants of ancient rivers and by the flowing of liquid sulphur have been found on Mars and on Io, a moon of Jupiter. Internal Geological processes slowly deform the surfaces of Venus, Mars, Ganymede and Europa as well as Earth. Most of Europe was once covered with ice. A few million years ago, the present site of the city of Chicago was buried under three kilometers of frost.
The earth has a green house effect that keeps the oceans liquid and life possible. Like Venus, the earth also has about 90 atmospherel of Carbon dioxide; but it resides in the crest as limestone and other carbonoates, not in the atmosphere. If the Earth were moved a little closer to the sun, the temperature would increase. Then the hotter surface would vaporize carbonates into CO2 and generate a stronger Green house effect. Such a similar incident might have happened in the early history of Venus to create a runaway and stronger green house effect there. Since the carbon dioxide content of the Earth's atmosphere is increasing dramatically, there is a possibility of a runaway green house effect here on Earth. Even a one-or-two degree rise in the global temperature can have that catastrophic consequences.
For hundreds of thousand years human beings have been burning, cutting down forests and encouraging domestic animals to graze on and destroy grass lands. Thus the atmosphere of the earth is polluted. Like Venus, our stratosphere has a substantial mist of tiny sulfuric acid droplets. Our Earth is the only home. Venus is too hot. Mars is too cold. Unfortunately our intelligence and our technology have given us the power to affect the climate. So, Carl Sagan says that we should be aware of the dangers of climate change and help the tiny and fragile, 4.6 billion years old world not to be affected by a runaway green house effect and become a planet like Venus in the future.
-------Thulasidharan V
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