By Dr. S.M. ALAM
Jan 12 - 18, 2003



Climate change is not a new phenomenon. Change has been a consistent feature of the earth's climate. Periods of relatively cool temperatures caused the ice ages. For the past 10,000 years, however, the earth has experienced the longest period of consistently warm temperatures, since the beginning of life. That warm period almost exactly matches the period over which modern agriculture has evolved.

For the first time in the history, climate appears to be changing as a direct result of human activity. People have released chlorofluorocarbons (CFCs) into the atmosphere, thereby degrading stratospheric ozone and increasing biologically harmful ultraviolet (UV) radiation that reaches the earth's surface. Through mining and combustion of fossil fuels, deforestation, maintenance of livestock nerds, and even through crop cultivation, people have released enormous quantities of carbon dioxide (CO2), methane (CH4), and other "greenhouse" gases into the atmosphere. Samples from ice cores show that in past the fluctuations in global temperatures were strongly correlated with concentrations of atmospheric CO2. Simulation models of global atmospheric circulation predict that greenhouse gases will cause a 2-8C global temperature rise before the end of the 21st century.

International research organizations all over the world and the United States Environmental Protection Agency (USEPA) are cooperating to determine the effects of a likely global climate change on crop production. Under such studies are: i) direct and indirect effects of ultraviolet-B (UV-B) radiation on crop, and ii) the direct and indirect effects of increased CO2 and temperature on different crop plants.

Ultraviolet-B (UV-B) radiation damages leaf tissues in crop seedlings. Leaves become stunted, stomata collapse, and photosynthesis decreases. Some crop varieties appear to be better able than others to withstand the adverse effects of UV radiation. Leaves of tolerant varieties contain phenolic compounds, which are natural chemicals that filter out harmful UV-B radiation before it can damage sensitive tissues. Research is now in progress to predict possible regional losses in crop productivity if UV-B radiation continues to increase, and whether plant breeders can prevent those yield losses by developing new varieties that tolerate UV radiation.

In addition to its adverse direct effects on crop plants, UV-B may change the susceptibility and/or tolerance to disease. Although, there is no evidence as of yet that susceptibility to blast is affected by UV-B, it appears that the tolerance for blast decreases. In other words, disease frequency is not increased by UV-B, but the effects of disease on plant growth is enhanced by UV-B radiation.

GLOBAL WARMING: Although, increasing atmospheric CO2 stimulates plant growth, the beneficial effects on crop growth have been observed for levels only up to 500 ppm. Some plant species respond positively to CO2 levels up to 1,000 ppm. Experts predict that atmospheric CO2 will surpass 650 ppm before the end of the 21st century. Furthermore, the benefits of increased CO2 would be lost if temperatures also rise. That is because increased temperatures shortens the period over which crop grows. Research is being conducted to identify means by which crop plants may better benefit from increases in atmospheric CO2 while minimizing the adverse effects of warmer temperatures.



Plant growth and development and primarily governed by environmental conditions of the soil and climate of a country. The success and failure of agricultural crop productivity is generally related to the prevailing weather conditions. Weather plays an important role from germination of seeds to the maturity of the crops. Interestingly, the most important fact about climate is that it changes on every scale of time and space, every year, decade, century and in every region of the world.

The green revolution has made a tremendous conditions to food production by prevailing weather condition but does not move forward as per expectation. The changes in weather fluctuation have been largely responsible for slowly down the production momentum of the green revolution of early 1960. The earlier high yielding varieties of cereal crops have become sensitive to weather vagaries and thus the yield of such varieties have gone down substantially. The atmosphere is becoming warmer day by day due to increase in pollutants such as CO2, CH4, CO, SO2, SO4, nitrous oxides and particulate matters in the atmosphere. The most important atmospheric pollutant is carbon dioxide (CO2) and its content is increasing rapidly all over the world due to burning of fossil fuels, coal, fire wood, etc.

The USA is the maximum producer of carbon dioxide. It produces about 160 billion tons of CO2 annually, which is about 25 % of the total CO2 produced in the world. Other main producers of CO2 are China, India, Australia, Canada, Ukraine, Mexico, U.K., Brazil, France, Spain, Germany, etc. The presence of CO2 in the atmosphere causes the colossol warming of climate, and thus the change is rainfall pattern, a process on which crops are highly dependent. Hill storms, flood, severe winds blow and frosts are also expected under such conditions, which ultimately affects the productivity of the crops 1n a country.

If the climate of any country becomes even more warm and dry, the food production can be a tremendous problem. According to the agricultural weather experts, the last 45 years were exceptionally stable climatically, which have contributed towards the greatest food expansion all over the world. Now the situations have been changed and this is unlikely to continue in the future due to rapid environmental degradation. However, agrometeorological informations can increase agricultural yield in the country.