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by S. Antony Norbert, Senior Lecturer in Geography, University of Colombo

It is estimated that by 2020, the world's population will reach 7.5 billion. Much of this growth will occur in the developing world. To meet this increasing global demand for cereals, for example, the world's farmers will have to produce 40 per cent more grain in 2020.

The average per capita cereal production for the period of 1986-1998 actually fell in Africa and the Middle east.

These disturbing trends have many negative implications for food security and poverty alleviation especially in some parts of the world. This was viewed in conjunction with the increasing frequency of extreme weather events.

Human disaster

Over the 1996-2000 period, there was an alarming increase in the number of countries affected by natural disasters which rose from 28 to 46, mostly in the developing world, where disasters have exacerbated the problems of food security, poverty and land degradation. Severe droughts during 1999-2001 affected much of Western Asia, Central Asia and the middle East, which resulted in large crop losses. It is important to recognize that food security involves climate, not only as a natural hazard but also as a natural resource. Climate is a renewable resource, but is variable in time and space.

Drought is a natural hazard originating from a deficiency of precipitation that results in a water shortage for some activities. It is the consequence of a reduction in the amount of precipitation over an extended period of time, often associated with other climatic factors - such as high temperatures, high winds and lower relative humidity - that can aggravate the severity of the event.

In 2001, much of Western Asia, Central Asia and the Middle East suffered the third year of a continuing drought that severely reduced crop yields in many countries.

Scientists around the world have concluded that flooded cities, diminished food production, and increased storm damage all seem to be the result of global warming and could affect the lives of millions of people. The world's leading scientists agree that global warming is real and already occurring.

The questions now are how fast will it occur and how bad will it be. Population growth is one of the factors contributing to global warming. Consequently, global warming could be disastrous for much of the earth's population. Emissions from our vehicles, factories and power plants are rapidly increasing concentrations of "greenhouse" gases in the Earth's atmosphere, warming the planet and distrupting our climate.

What is global warming?

The phrase 'Global Warming' has become familiar recently as environmental issues have hit the headlines. Within the past decade, there has been a considerable rise in public awareness and interest on global climate. Such interest is particularly acute amongst environmental scientists, but is also prevalent amongst politicians, economists and some industrialists and has resulted in continuing attention in the media.

The focus of attention has been upon the present and continuing effects upon climate of both domestic and industrial fuel use and of other process both agro-environmental and industrial that lead to the release into the atmosphere of so-called 'greenhouse' gases. A recorded rise in temperature this century is mainly attributable to human activities and this rise will both accelerate and continue until well after greenhouse gas emissions are stabilized.

Records show an increase in the global temperatures: consolidated data from selected terrestrial stations and marine sea-surface temperature (SST) records round the world reveal that the seven warmest years this century have occurred since 1980.

The recorded rise in temperatures has been linked to an estimated 30 per cent rise of carbon dioxide concentrations in the lower atmosphere over the last 200 years. As the carbon dioxide concentrations in atmosphere continue to rise, there might be major temperature rises and perhaps even catastrophic climate change in the next century.

Recent changes in world temperature

The climate has changed significantly in historic times.

The little ice age that lasted from about 1550 to 1850 was a period when the global climate was cooler and winters were particularly cold. Since the 19th century there have been temperature data available from weather stations throughout the world. But it is difficult to compile an accurate picture of changes in world temperature over the last century due to various problems and errors.

Overall estimate is that there has been a worldwide warming of about 0.5 degree C since the end of the 19th century.

During this time there have been two periods of rapid temperature increase, one between 1910 and 1930 and the other between 1970 and the present.

The 1990 was the warmest decade and 1998 the warmest year. On average, between 1950 and 1993, night-time daily minimum air temperature overland increased by about 0.2 degree C per decade.

Warmest episodes of the El Nino Southern Oscillation (ENSO) phenomena have been more frequent, persistent and intense since the mid 1970s, compiled with the previous 100 years.

The elements of global warming

(i) Fossil Fuels

Since the industrial revolution there has been an increase in the concentration of carbon dioxide in the atmosphere with a particularly rapid rise since the 1940s.

It has been inferred that it is human distruption of the natural biological and chemical interchange of carbon that is responsible for the increase. Since prehistoric times people have burnt wood and other plant remains to produce heat and light.

As wood became scarce in Europe in the 18th century, the use of coal became increasingly important. The demand for energy increased sharply during the industrial revolution to fuel the new industries and to provide for the domestic needs of a rapidly expanding urban population. This demand was largely met by the increased use of fossil fuels, primarily coal.

Industrial revolution gathered pace in the early part of the 19th century was restricted geographically. But it has grown at an unprecedented rate after the second world war. As a consequence coal consumption has increased rapidly.

Worldwide industrial development is one factor driving increased carbon dioxide production, but at the same time the world's population has increased from 3 billion in 1960 to over 5 billion in 1990, producing an ever-increasing demand for energy. Many countries have a great capacity to increase carbon dioxide emissions in the future as their economies develop and their per capita usage of energy increases.

Carbon dioxide is a greenhouse gas. The amount of it in the atmosphere has risen by about 30 per cent due to human activities since the beginning of the Industrial revolution.

The present concentration of 360 parts per million (ppm) means that 360 of every million molecules of gas in the atmosphere are carbon dioxide. Why is carbon dioxide increasing? Increased industrialization of the planet-wide economy is the predominant cause.

Burning fossil fuels (oil, gas, coal etc.) is one way that carbon dioxide is released into atmosphere, while another source is the burning of timber and vegetation. Trees and plants remove carbon dioxide from the atmosphere in the course of the photosynthesis process.

(ii) Landuse changes

The burning of fossil fuels is not the only way in which carbon dioxide can be released into atmosphere. Large amounts are also produced as a consequence of land use changes. Infact, it is only since about 1960 that emissions from fossil fuel combustion have become more important. Up untill then the rise in the atmosphere concentration of carbon dioxide can be largely ascribed to deforestation and agricultural changes. Landuse changes can release carbon dioxide into atmosphere by causing the oxidation of carbon compounds in the vegetation or the soil.

The burning of forests for the purpose of land clearance releases carbon dioxide rapidly into the atmosphere by combustion, whereas decomposition of felled trees releases Emissions of carbon dioxide due to landuse changes are greatest for developing tropical countries with large forest reserves. However, the estimated emission of carbon dioxide due to land use changes is only about 20 per cent of the total.

(iii) Deforestation

Most of the deforestation underway at present takes place in the tropical forests of South America, Southeast Asia and Africa. The latest published figures from satellite surveillence indicates that 150,000 square km of tropical rainforest in the Amazon Basin fell to deforestation in the decade 1978-1988.

This deforestation takes place as a result of a complex mix of economics, politics and historical forces within the developing countries of the tropics.

There is another aspect of human activity that may be affecting the fixing of carbon in the biomass. Life depends on the availability of the inorganic nutrients nitrogen and phosphorous. We have altered the natural abundance of these nutrients with intensive applications of fertilizers.

(iv) Methane

Methane is produced as a by-product of a number of anaerobic (oxygen-deficient) chemical reactions in the land portion of the biosphere. The main sources of methane are emissions from natural wetlands, rice paddies, and animal digestive processes. Additional sources include methane emissions released as a result of drilling for natural gas and oil, burning of vegetation, the prolific eating habits of termites and the anaerobic decay of organic material in landfills.

A methane molecule is much more effective in absorbing infrared radiation than a carbon dioxide molecule. Thus methane is an important greenhouse gas, even though its amount in the atmosphere is small. The atmospheric concentration of methane has increased by 1060 ppb (151%) since 1750.

(v) CFCs and Nitrous oxide

CFCs (Chlorofluorocarbons) were developed for industrial purposes such as refrigerants, spray-can propellants and solvents. CFCs do not react readily with other chemicals. The nonreactive characteristics of CFCs is their chief liability once they enter the atmosphere. They are destroyed by ultraviolet solar radiation in the stratosphere at a very slow rate, which gives them a long lifetime. Nitrous oxide is produced naturally from a variety of chemical reactions in land biota and in the oceans. Human activities such as combustion and the use of fertilizers have increased the amount of this substance in the atmosphere.

Measurements of carbon dioxide concentrations in the atmosphere have been taken since the late 1950s and the estimated rise, since the late eighteenth century (275 to 360 ppmv) has been confirmed by measuring carbon dioxide concentrations in air bubbles trapped in ice cores and by modern observations. In 1990, the annual average of carbon dioxide was about 350 parts per million and present estimates are that this value may double sometime in the next century. The increase of greenhouse gases in the atmosphere changes the radiative balance of the earth-atmosphere system. In present times, an argument has put forward that the energy produced from the sun has caused the increase in global warming.

Sun's magnetic field

In the sun, 91% of the energy is produced by the proto-proton chain and the rest by the carbon cycle. Solar flares consisting of electrically neutral, Ionized hydrogen (protons and electrons), enhance the solar wind.

Accompanying any solar flare is a pulse of electromagnetic radiation that takes eight minutes to reach the Earth. The enhanced solar wind arrives one or two days after this magnetic pulse and disturbs the Earth's geomagnetic field. very large solar flares are called proton events. A proton event can destroy 20 per cent of the Earth's ozone in a matter of a few days.

The sun's magnetic field varies with sunspot activity and act actually reverses every 11 years. Because it takes 22 years to return to its original state, the sun's magnetic cycle is 22 years, rather than 11. More recently scientists have found a relationship between the 11-year sunspot cycle and weather patterns across the Northern Hemisphere. Fluctuations in solar output may account for climatic changes over time scales of decades and centuries.

To date, many theories have been proposed linking solar variations to climate change, but none have been proven. However, instruments aboard satellite and solar telescopes on the earth are monitoring the sun to observe how its energy output may vary.

Sun's magnetic field is generated by a dynamo located at the bottom of the convection zone, which lies roughly 30% of the distance from the solar surface to the solar core. The strength and structure of the resulting magnetic field is determined by the solar surface. The differential rotation produces a toroidal field near the base of the convection zone. The convection zone has a very high thermal conductivity and heat capacity.

Sunspots variations

The leading hypothesis in climate science is that most of the warming during the 20th century was due to man-made gases, enhancing the natural greenhouse effect that reduces heat loss into space. There is also renewed attention to natural changes in climate due to the Sun.

There is a link between sunspots and climate that has been a popular idea for 200 years, but recently measurements by spacecraft cast doubt on it. They showed that the Sun is brighter when there are many sunspots, at the climax of each sunspot cycle of roughly 11 years, but the variations seemed too small to have a major effect on climate. During the cycle, the number of sunspots and flares on the Sun's surface varies because of underlying changes in magnetic activity.

During the past ten years astronomers and solar-terrestrial physicists have reappraised the role of the sun. Some American Scientists have argued that previous changes in sun's brightness were greater than those seen during the short period of satellite measurements. In Europe, there has been more emphasis on other ways in which the sun may affect the climate, either by invisible X-rays and ultrviolet radiation which peak where there are many sunspots, or by the solar wind, which blows non-stop from the sun and became more vigorous during the 20th century.

Mike Lockwood studied the results from the ESA-NASA solar spacecraft Ulysses and deduced that the magnetic field carried by the solar wind has doubled in strength since 1990.

An the climate record from weather satellites, showing changes in the earth's cloud cover, suggest that cloud formation is affected by cosmic rays arriving from the Galaxy. When the Sun is most active, there are fewer cosmic rays and fewer clouds. There are corelations between sunspot cycles and climatic effects. It is known that thunderstorms and lightining activity increase worldwide during peak periods of sunspot activity.

STONE 'N' STRING

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