There were several ice Ages and greenhouse conditions. Of these, two episodes of greenhouse conditions 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. 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 CO₂content of the atmosphere was very low during most of the Ice Ages. However, in contradiction to this find a very recent study carried out by Thomas Marchitto and Scott Lehman of CU-Boulder's Institute of Arctic and Alpine Research, it has been found that the carbon build up in the oceans during the past millennia was released in two big pulses 18, 000 year and 13, 000 years ago. Their results were published in Science Daily of 11 May, 2007.

Scientists have been aware that nearly 600 billion metric tons of carbon was released in to the atmosphere after the last ice age. Half of it was absorbed by the oceans. The recent study will for the first time help the climatologists and environmentalists to trace the nature's processes of release of carbon dioxide in the atmosphere and may be also help to find the actual impact of carbon dioxide released through anthropogenic activities! Using Carbon 14 isotopes to trace and track the carbon content of deep and surface ocean waters and the atmosphere, they established that carbon added to the upper atmosphere at the end of the last ice age was 'very old'. Thus suggesting it had been stored in deep oceans and isolated from the atmosphere. Hot oceanic currents were responsible for release of this carbon from the vaults of ocean in two major 'burps' 18000 and 13000 years ago. 

Carbon dioxide is one of the most abundant Green House Gases (GHG) that is rapidly dragging our planet towards a Global warming. World over efforts are on to overcome the problem of GHGs. The industrial revolution of 1850 set the ball rolling for augmentation of GHGs in the atmosphere. Rapid strides in technology brought automobiles on the road; generation of electricity from coal became the in thing.

Thermal power plants are one of the worst atmospheric polluters. A study carried out in USA says that a 500 megawatt coal powered plant produces 3.5 kilowatt-hours per year electricity, enough for a city of 140, 000 people. The process requires burning of 1,430,000 tone of coal, consumes 2.2 billion gallons of water and 146, 000 tons of limestone.

Such a plant releases 3.7 million tons of Carbon dioxide (CO₂), a leading GHG and main cause of global warming. This was just one example. In addition there are scores of other processes that keep on unleashing CO₂ in the atmosphere. Trees (forests) and water bodies particularly the oceans are the sinks of CO₂. Heavy pollution of the oceans and massive deforestation has made these ineffective.

The scientists world over have been tinkering with various ideas of disposal of CO₂. V.K. Sibal, Director General of Hydrocarbons, Government of India and his team had published a paper in Current Science, proposing dumping CO₂ in the coal mines.

Coal Bed Methane (CBM) is now considered a major source of gas supplementing the production of hydrocarbon gas from petroleum sources, says Sibal. At present the government has given on contract 16 blocks of CBM to various agencies for exploration and exploitation. Total CBM resources in these blocks are estimated to be of the order of 820 billion cubic meters. It is also estimated that these blocks will produce 20-22 million cubic meters of CBM per day for 20 years.

The contemporary commercial production of CBM depends exclusively on reservoir pressure depletion. CBM stored in the depths and cracks and crevices of coal seams is pushed up due to pressure from the reservoir. As the pressure depletes the recovery of CBM is affected. The method, says Sibal is simple but ineffective because the total recovery is generally less than 50% of the gas available.

Sequestration of CO₂ of generated from combustion of fossil fuel has been proposed as a safe method of enhanced recovery of CBM and also a significant tool to divert the harmful GHG to the deep vaults of the earth.

Actually the idea has emerged from the fact that the subsurface formations retaining hydrocarbons have substantial capacity to store CO₂. In fact oil and gas reservoirs not being tapped further can also become potent producers of CBM, if CO₂ is pumped in. The process, feel Sibal and his colleagues will have double benefit. On one hand it will be goodbye to CO₂ and on the other the productivity of hitherto considered uneconomic petroleum//gas wells or coal mines would become economic with the availability of CBM.

The concept sounds wonderful, but two issues, namely, avoiding risks and the cost of collection, transportation and sequestration of CO₂ need to be addressed. Carbon capture and storage are in fact a burning topic amongst the scientists. In January, 2007 the Department of Science and Technology (DST), Government of India jointly National Geophysical Research Institute, Hyderabad organized an international workshop at Hyderabad, on R&D Challenges in Carbon Capture and Storage Technology for Sustainable Energy Future. Dr.(Mrs.) Malti Goel, Adviser with DST and Co-Chair of the Workshop in her presentation laid emphasis on pre-combustion carbon capture, terrestrial and geological sequestration modeling studies and monitoring and measuring techniques of CO₂ sequestered. Such workshops are of importance and significance, because the brainstorming therein leads to cost effective innovations. 

The rapid pace of development across the globe has led to increased demand of energy. Coal accounts for 62% of India's energy supply. A sustainable development in the use of coal as a source of power needs detailed research in the Carbon Capture and Storage says Malti. Quoting a STERN report she says that Economics of Climate Change has come out with the recommendation that cost of stabilization of greenhouse gas emission is within our reach and would not exceed 1% of GDP. But again this raises the need for more research to make the project viable.

It is but natural that CO₂ will mix with water in the subsurface and at any given time it could be a major source of pollution. The earlier cited case study of the thermal power plant in USA says that in addition to CO₂, the Plant's chimneys belch 10,000 tons of Sulphur dioxide, 10,200 tons of Nitrogen oxide, 500 tons of particles smaller than 10 microns, 220 tons of Hydrocarbons, 720 tons of Carbon monoxide, 225 pounds of arsenic, 114 pounds of lead, 4 pounds of cadmium and many other toxic metals like mercury. 

Imagine if all this reaches the subsurface, pollutes groundwater and the same water is ignorantly used for water supply, what would be the fate of the people! Therefore first and foremost the technique being proposed has to ensure that pollutants do not reach the subsurface and if at all they reach then they are confined in the labyrinths of the abandoned coal mine only.

The German Federal Ministry of Education and Research has worked out laboratory models which involves the injection of liquefied CO₂ in rock formations that contain Calcium Sulphate. This converts CO₂ to Calcium Carbonate, which is environmentally safe.

Next is the issue of cost. First is the cost of catching the CO₂ and then comes the cost of transporting it for sequestration. Apart from coal mines, other places for safe dumping carbon dioxide have also to be located. For example from the Power plants in the coal mine areas of Central and Eastern India it may be economically beneficial and possible to transport the obnoxious gas back to the mines, but the cost of transporting CO₂ from a plant located in Northern India (Delhi), is anybody's guess!

Technology has advanced through new concepts and ideas only. Time is not far when it will be feasible to divert the anthropogenic obnoxious emissions to the subsurface to remain ensconced there till eternity!