The scourge of global warming seems to be spreading. Discussion on global warming has become the in thing. In a country like India where maximum illiteracy is there, majority of people find global warming an engrossing topic to discuss. Each individual has his own perception. This year the Gangetic Plains of north India underwent a cold spell around the popular festival of Holi, and lo! It was ascribed to global warming. If a day becomes warmer global warming is declared the cause and if it becomes a trifle cool again the horror of global warming is recalled. But yes global warming is an issue that needs to be tackled very seriously and sincerely.

Everyday the media reports are full of the possible hazards and consequences of the global warming. The present is a key to the past and the past is the window for future. What were the climates of the past like has been a daunting the scientists involved with the study of the climate change.

Our planet was born after the gaseous nebula cooled down. Once it was formed, it is believed that Carbon dioxide controlled the global cooling and heating. The earliest record of an ice sheet around the globe is from 750 million years old rocks of Namibia. Imagine the impact of a complete cover of ice all around on the living being. It leads to a complete collapse of life. For millions of years all biological activity had come to a standstill, till volcanic eruptions started warming up the environment again.

Thus the earth's climate changed between the 'icehouse state' to 'greenhouse state' says R.K. Kar a palaeobotanist from the Birbal Sahni Institute of Palaeobotany, Lucknow, in one of his papers. There were several ice Ages and greenhouse stages. Of these, two episodes of greenhouse stage left their indelible mark on the flora of our planet. The first 'greenhouse state started some 500 million years ago (Ma) and lasted for about 145 Ma. In terms of geologists this is the Ordovician-Devonian global warming. The next major greenhouse state of the climate started some 203 Ma and lasted for 138 Ma, known as the Jurassic-Cretaceous global warming.

How did it happen and what were the consequences is an interesting study. It was Arrhenius (1896) who first introduced the term 'hot house' theory which later became the greenhouse theory. Greenhouse effect is a phenomenon by which carbon dioxide, water vapor, atmospheric methane, nitrous oxide, ozone and aerosol trap more solar heat within the atmosphere causing a global warming. In geological past when the earth had become a giant deep freeze, the global warming came as a relief for the fauna and the flora to regenerate and rejuvenate. The frozen life was reactivated when the gases from the sub aerial volcanic activity started to reach the atmosphere. This increased the atmospheric CO₂ content tremendously and the global warming started.

In other words the greenhouse state is associated with volcanism and sea level rise. A.E.J. Engel and C.G. Engel (1964) have shown two peaks of volcanism in the past, says Kar in his paper. The older one persisted through Late Cambrian (500 Ma) to Late Devonian (355 Ma) and the other in the Late Jurassic (135 Ma) to Cretaceous (65 Ma) periods of the earth's history. Researchers have also established that the CO₂ content of the atmosphere was very low during most of the Ice Ages.

Plant life evolved initially in the sea water. The first land plants started to appear around 450 Ma. It was during the Devonian period that is 410 to 355 Ma that plant life evolved and proliferated. It was during this period plants with naked seeds, Gymnosperms made their first appearance. The next greenhouse state of the Jurassic-Cretaceous (250 to 65 Ma) period led to the birth of Angiosperms, the flowering plants. Even after this greenhouse state, temperatures kept soaring and one episode known as Paleocene-Eocene Temperature Maxima (PETM) has been observed by the researchers in Arctic Ocean during an expedition in 2004. The scientists aboard a fleet of Icebreakers drilled into the floor of the Arctic Ocean and collected samples of past life. This was a major feat because no one had dared this kind of venture earlier.

The findings of the expedition were huge and are still being published. From the information so far been published by Matthew Huber, an Assistant Professor of Earth and Atmospheric Science in Purdue University's College of Science says "sea surface temperatures at the North Pole had soared to 23 degrees Celsius, or around 73 degrees Fahrenheit, during the Paleocene-Eocene Thermal Maximum, or the PETM, about 55 million years ago". Today's mean annual temperature around North Pole is around 20 degrees Celsius. The high temperatures of the Arctic were confirmed by the presence of an alga sensitive to temperatures, called Dinoflagellate, which is found in high temperature waters only. How such an algae was surviving in the frozen Arctic Ocean? Obviously what is frozen today must have been a huge warm water lake some 55 million years ago!

What could have been the source of heat in those pre-historic days without industries or automobiles to enrich the carbon dioxide content of the atmosphere? It is known that Clathrates or frozen Methane Hydrates are present in the ocean bed. Geological events like an earthquake or a mudslide can disturb the equilibrium and force release of methane which can break down to carbon dioxide on reaching the atmosphere. The concentration of carbon dioxide in today's atmosphere is 380 parts per million, whereas 55 million years ago it was about 2,000 parts per million.

While the plants evolved and dominated the earth during the greenhouse phases, many of the marine animals faced extinctions. Known as periods of crises for marine and land organisms coincided with periods when the plant life peaked. The sea level changes and volcanism affected the animals whereas during those turbulent millennia plants thrived.

Once again we are in the initial phase of a greenhouse state. How long it would last is anybody's guess! Though, it is more or less established that if you pump in greenhouse gases in the atmosphere the result is large scale warming. In a race for development or rather say our comforts we are trying to pump as much greenhouse gases as possible in to the atmosphere. Our future generations will face the worst of the global warming and curse us for leaving a 'hot legacy' for them.

The worst part is that if the human race survives the greenhouse state of environment, will we be able to withstand the Ice Age that normally succeeds a warm phase is a question that will also plague the future generation.