A dramatic increase in the global food grain production since the 1960s occurred with the initiation of the green revolution, which was primarily based on the high technology package involving large scale use of chemical fertilisers, pesticides, high response better seeds and extensive irrigation. The increase in India’s annual food grain production from just about 55 million tons in 1947 to about 180 million tons in the 1990s is clearly a result of the emphasis given to large scale irrigation which has risen from less than 20 per cent to over 35 per cent of total arable land of 160 million ha. during this period. Ironically however, the negative repercussions of the very practice of irrigation due to water logging, inadequate drainage and indiscriminate use of chemical fertilisers have resulted in making the soil in the irrigated areas highly saline and unproductive. It is estimated that over one third of the approximately 200 million ha. of irrigated cultivable land in the world is already salt affected (Swaminathan 1980). Almost 40 per cent of the highly fertile Indo-gangetic plain in India, which was once the cradle of civilisation, suffers from intense salinity making it unfavourable for crop growth. Almost 25 per cent of the arable land area in every continent has be­come problem land with another 25 per cent having very low productivity.

The extreme pressure of population and industrialisation particularly in the developing countries has resulted in the annual rate of deforestation of 17 million ha including almost 4 million ha. in Asia (Fig. 5). An imperative consequence of deforestation is increased run off of rain water and severe soil erosion resulting in the deterioration of the top soil, degradation of land and sedimentation of water bases. The high rate of soil erosion in deforested areas in India, China and elsewhere ranges from 10 t/ha. in the plains to almost 30 t/ha. in the north-eastern hilly regions, as against just 1 t/ha in the forested area. World wide soil erosion has reached the limit of 100 million tons per year as against 45 million tons in 1860 and less than 16 million tons three hundred years ago. Extensive deforestation has resulted in increased carbon dioxide in the atmosphere, increased rain precipitation run off from 20 per cent to almost 50 per cent, frequent flooding and a gradual extinction of biodiversity (Khoshoo 1990; Brown 1992). Overgrazing, deforestation, encroachment by agricultural crops and general mismanagement of land and water resources have resulted in increasing desertification in Asia, Africa and Latin America. About 3000 million ha, a quarter earth’s land surface has now turned out as desert or damaged by factors that contribute to desertification. On a global scale the desertification is increasing almost by 1 million ha. per year. The changes in climatic and rain patterns gradually setting in because of deforestation are yet to be fully understood due to our inadequate understanding of the phenomena, particularly the energy exchange between the surface aerodynamic roughness over the forest and the atmosphere above it.

Management of water resources particularly in the developing countries, has been even more pathetic. Optimal management of water becomes crucial in the dry land tracts of tropical countries where most of the precipitation occurs in less than 100 days as compared to mid and high latitude countries where snow and rain precipitation continue to keep the soil moisture in tact for almost 8 months in a year. With the added problems of higher temperature regimes and higher evapo-transpiration rates, need for optimal harvesting of run off and recharging of underground aquifers in tropical countries assumes paramount importance. Although major irrigation projects and big dams have contributed to improved agricultural production in the last few decades, the problem of water-logging, salinization and loss of valuable bio-resources have led to gradual degradation of land in many areas in the developing world. Intensive use of chemical fertilizers and pesticides combined with poor management of water-sheds and highly fragmented land holdings have resulted in severe water stress, pesticide contamination not only in the water but also in the agricultural crops, resulting in the severe degradation of over 1.2 billion ha. across the world, in the last 45 years alone (Fig. 6). The material delivery from rivers to the oceans which was just 9.3 billion tons 50 years ago has now increased to 25 billion tons a year, with the largest discharge of over 15 billion tons per year coming from Asia alone.

Superimposed on these seemingly insurmountable difficulties is the real prospect of the widely accepted global warming scenario due to the unprecedented anthropogenic intervention causing a rapid increase in the green house gases, upsetting the delicate greenhouse equilibrium which could lead to irreversible climatic changes (Ramanathan 1985). Particularly since the beginning of the industrial revolution, CO₂ concentration in the atmosphere has steadily increased from 280 ppmv to 350 ppmv and at the present rate of increase is expected to reach 450 ppmv by 2050. Concentration of methane in the atmosphere has also been increasing steadily at the rate of about 0.9 per cent per year and has now already reached 1.7 ppmv. Detailed rigorous analysis of surface temperature over the last century indicates an average increase in global temperature of about 0.5^o K. While the primary cause of the global temperature increase in the past has been the increasing atmospheric concentration of CO₂ due to industrialisation, fossil fuel burning and extensive deforestation, the rapid increase of CFCs in the last decade which has large residence time of over 100 years in the atmosphere has further added to the global environmental problem. In spite of the universal adoption of the Montreal Protocol the spectre of global warming, which can cause depletion of ozone, rise in sea level, inundation of highly populated coastal areas and severe modification of climatic and rain pattern, continues to pose a real threat unless all countries, both developed and developing, make appropriate structural adjustments in their life style and consumption pattern.