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One of the more predictable consequences of global warming is sea level rise

Dr. S.M. Alam and R.Ansari
June 11 - 17, 2001

Global environmental change is nothing new. Abundant evidence exists of past climates radically different from today. However, as we approach the 21st century, there is a new agent of global environmental change and that agent is: Mankind. The exploitation of the world's natural resources notably coal, oil and gas to provide energy and food for a growing, and increasingly affluent, global population has been changing the composition of the atmosphere. The by-products, if industrialization and resource use include the so-called greenhouse gases-carbon dioxide (CO2), methane (CH4), the chloroflurocarbons (CFCs), nitrous oxide (N2O) and tropospheric ozone (O3). These gases are emitted as a result of fossil combustion and deforestation with a proportion remaining in the atmosphere. For instance, over the last 200 years, atmospheric CO2 has increased in concentration by 25 %. The CO2 concentration is presently growing at a rate of nearly 0.5 % per annum as we spew about 7 billion tons of carbon into the atmosphere annually. Methane has more than doubled over the same time period, chloroflurocarbons (CFCs) concentrations, virtually negligible 50 years ago, but at present are responsible for about 20 % of recent changes in global warming.

One hears about carbon dioxide referred as a polluting gas, but it is also a life giver, because the removal of carbon dioxide from our atmosphere would lead quickly to the extermination of all plant and animal life. The energy cycle that nature has provided is miraculous and beautifully well balanced. Plants turn water and carbon dioxide into food, fuel and oxygen, while man and other animals eat the food and burn the fuel in carbon dioxide, so reversing the process. Large changes in global climate from increasing concentrations of carbon dioxide and other greenhouse gases are distinct possibilities for the 21st century. It is assumed that by 2030, the world could be 1-2C warmer and sea level 14-25 cm higher than to-day.

Important agricultural regions in coastal low lands are threatened by flooding, erosion and salt extrusion. Although, the small, low-lying island states are particularly at risk and vulnerable to sea level rise. But, if the rise is significantly larger, the result could be disastrous. With seas rising as much as 1 m, enormous areas of densely populated. Bangladesh would become uninhabitable. In Bangladesh, the deeper inundation in the interior floodplain may lead to a reduction in the areas suitable for cultivating the dominant strain of paddy rice and necessitate a shift to a lower yielding variety. It is to be noted that most of land area of the 1,190 small islands constituting the Republic of the Maldives in less than two meters above sea level. These locations of small islands are at the total risk of tidal waves, because, if the phenomenon of tidal waves or current occur, they will inundate these small Islands and thus uprooting their population. Hundreds of millions of people would have to migrate out of unlivable regions. Public health could be suffered. Rising seas would contaminate water supplies with salt. Saltwater intrusion may also become, a problem. This maybe further intensified by groundwater pumping and any related subsidence, which may occur. As sea level rises, salt water will penetrate further into estuaries and intrude inland into fresh water and aquifers. This is already a problem in some small island states. Salt-water intrusion will also have serious effects on agriculture, reducing the viability and yields of some crops. Many Pacific islands are dependent on root crops form a principal part of their diet and crops such as pulaka and taro are grown in shallow pits, which risk salt contamination. Salt-water intrusion is not a threat only to small islands.

In the Netherlands for example, it is already a problem in polder areas, which are below sea level flashing and rinsing of'the polders and canals with fresh water is necessary, but in dry summers, crop damage is unavoidable due to insufficient supplies of fresh water. Salt-water intrusion means that some crops may have to be abandoned or alternative varieties may be-cultivated. Drainage may also be impeded as sea level rises resulting in loss of yield or ultimately a change in land-use of agricultural area. Greenhouse gases affect the leaf balance of the earth by absorbing long wave radiation, which would otherwise escape to space. The worry is that additions to the atmosphere will cause a rapid global warming and sea level rise, with adverse consequences. One of the more predictable consequences of global warming is sea level rise. There are several ways in which global warming could be expected to affect sea level, i.e. the thermal expansion of sea water, increased melting of mountain glaciers and changes in mass of the huge icecaps of ice land green land and Antarctica. Changes in the volume of seawater without the addition of mass (water) result in steric changes in sea level. steric sea level is affected by ocean density, which in turn, affected by water temperature, as the oceans warm they expand. The hundreds of mountain and glaciers present in the world in different countries represent less than 1 per cent of the world's total land ice, the equivalent of 30-60 cm of sea level, if completely melted.

If greenhouse gas emission continue to increase at their present rates, the level estimates indicate a global warming of approximately 0.5C by 1995-2005; 1.5C by 2015-2050 and 3C by 2050-2100 with greater increases evident at higher latitudes, such increases appear to be small yet the earth's temperature has not varied by more than 1-2oC in the past 10,000 years. In the present century, the level of carbon dioxide is increasing day by day and the concentration of CO2 is by far the most important, which affects the greenhouse. The increase in surface temperature is known as "greenhouse heating" or the "greenhouse effect". The gases responsible have become known as "greenhouse gases", and the concentrations of greenhouse gases at present are increasing and in pre-industrial period (1860), the concentrations (in ppm) of CO2, methane, N2O and CFCs were 275, 1.2, 0.2, zero (0), respectively, while the concentrations (in ppm) of these gases estimated for the year 2035 were 475, 2.8, 0.38 and 0.0016, respectively.

What can be done to ameliorate the effect of sea level rise? For most small, developing countries the construction of sea walls, dykes and storm surge barriers, such as the Delta works in the Netherlands and Thames Barrier in the UK, are not feasible options. Existence of mangroves and other natural features will help this to intrusion of sea water. Higher levels of urban ozone, the result of stronger sunlight and warmer temperatures, could worsen respiratory illnesses. More frequent hot spells could lead to a rise in heat related deaths. Warmer temperatures could widen the range of disease, carrying rodents and bugs, such as mosquitoes and ticks, increasing the incidence of dengue fever, malaria, encephalitis, Lyme disease and other afflictions. Humans will have a hard enough time adjusting, especially in poorer countries but for wildlife, the changes could be devastating. In near future, nearly 6 billion to 35 billion tons of carbon dioxide will enter the atmosphere.

A decade ago, the idea that the planet, was warming up as a result of human activity was largely theoretical. We knew that since the Industrial Revolution began in the 18th century, factories and power plants and automobiles and farms have been loading the atmosphere with heat-trapping gases, including carbon dioxide and methane. Worldwide temperatures have climbed more than 5C over the past century and the 1990's were the hottest decade on record. Similarly, steady warming has led an impact on no fewer than 420 physical processes and animal and plant species on all continents. Faced with these hard facts, scientists no longer doubt that global warming is happening, and almost nobody questions the fact that humans are at least partly responsible. Already, humans have increased the concentration of carbon dioxide the most abundant heat trapping gas in the atmosphere, to 30 per cent above pre-industrial levels and each year the rate of increase gets faster. Thus, it is obvious conclusion that temperatures will keep going up. These changes will be problematic enough, with storms/hurricanes getting more frequent and intense, droughts or flood more pronounced, coastal areas or floodprone even more severely eroded by rising seas, rainfall scarcer and the agricultural land and ecosystems thrown out of balance, where crops are already at the limit of their temperature range, the decrease would start right away. In temperate zones, warmth and increased CO2 would make some crops flourish at first.

There is increasing evidence that rising emissions of carbon dioxide, methane nitrous oxide and other relatively active gases will lead to an increase in the average surface temperatures at the earth. In addition to changes in global temperature, there will be changes in precipitation. The rate and magnitude of these climatic changes is much that they could have a significant impact on agricultural potential in many parts of the world. The nature and extent of such changes will vary regionally and are dependent upon on the level of climatic changes in each region, the agriculture and management practices used at present and the ability of agricultural systems to adapt to change. The profound effect that weather can have on agricultural crops can be seen in the common year to year fluctuations in yields. Frosts, excess rain, high temperatures during ear growth or grain growth, cool temperature and during grain filling and wet weather at harvest will all affect yield adversely. Thus, any change in climate, which alters the frequency intensity, or timing of such events could have a substantial effect on agriculture.

Ozone (O3) is also an important gas which is always present in the earth atmosphere in trace quantities in the stratosphere (altitude range 15-50 kms.). The role of high concentration of ozone in the stratosphere is vital as much as it acts as a very effective filter for absorbing ultra violet rays, which are an integral component of sunlight. In stratosphere, it acts as a shielding layer to protect us from the effects of ultra violet rays. Without adequate population of ozone, there would be an increase in the intensity of ultra violet rays falling on the surface of the earth resulting in very serious health hazard to humans in the form of skin cancer. At levels as low as 15 ppm, it causes headaches, eye irritations coughing chest discomfort.

High concentration of ozone in the trososphere has been reported to have caused reduction in crop yields by 20-45 % depending on the relative humidity, concentration of ozone and duration of exposure of the crops to the ozone gas. According to an estimate, exposure of plants to ozone levelswof 0.05 to 0.07 ppm in the trososphere for 7 hours per day during one season, has caused crop loss amounting to 5.0 billion dollars in US alone. On an International Scale, the grain yield losses on account of elevated levels of ozone layer may run into several billion dollars each year. Destruction of ozone layer will increase the temperature of the earth. Rise in temperature will cause damage to the crop production, because the growing of food grain crops mainly depend on temperature. Thus, increase in temperature of the planet, has the potential of changing the overall pattern of food production globally.

The most important consequences for agriculture would stem from a reduction in soil moisture due to higher rates of transpiration from plants and of evaporation from soil surfaces exposed to higher temperature. Increases in CO2 in the atmosphere can enhance plant growth in a number of ways: It,can increase the rate of photosynthesis, leading to greater leaf expansion and a larger,canopy and it can also reduce water losses from plants. Research suggests that for many species a doubling of CO2 will lead to a 10-15% increase in dry matter produ'ction,>providing all other factors remain constant. For wheat and barley, yield increases of as much as 40% have been suggested. Majority of plants fall into C3 and C4 groups, according to their method of assimilating C atoms. C3 plants (such as wheat, barley, rice and potatoes) responded vigorously to CO2 enhancement. Similarly, C4 plants (including maize, sorghum, millet and sugarcane) do not.

Water is continuously lost from plants through the process of transpiration. Water loss due to transpiration, is unavoidable, so that at some point most plants will suffer from water stress when evaporative demands are greater than water supply. Under such conditions plants began to wilt, causing the stomata to close. This restricts water loss but also limits CO2 assimilation and thereby plant growth and yield. Higher levels of atmospheric CO2 will lead to increased efficiency of water use by reading transpiration rates. It was concluded from the above discussion that global warming is affecting the environment and particularly its effects on agricultural productivity on the decreasing sides. Although, the global warming is a man made problem, but still there are many ways to decrease the warming phenomenon of the earth and the environment. In this connection, it is pointed out that CO2 as the main gas, which increase environment pollution to much extent. However, one can reduce its concentration through adaptation of modern technology. It is not an individual problem, primarily collective behaviour of the citizens are responsible for creating this pollution, we should remember the saying of Our Prophet Hazrat Muhammad (peace be upon him), that cleaning is half faith. But in fact, we citizens have totaliy forgotten the saying of Our Holy Prophet Muhammad (PBUH), and this is one reason of downfall. We should always fear Almighty Allah, who is Omnipotent, Omnipresent and Omniscient and we must obey His order. In this way, our many worldly problems maybe solved by the order of Allah.