Contents
Environmental biology is one of the critical Biology Topics that involves understanding how humans impact the environment and how to address environmental issues.
Causes and Effects of Climate Change – Environmental Pollution and the Global Burden of Disease
A. Green House Effect
A greenhouse is a small glass house used for growing plants, especially in winter. The glass panels of the greenhouse let the light in and reflect it back but entrap the heat inside. As a result, the inside of the house warms up.
Carbon dioxide is a natural constituent of the atmosphere under normal conditions (with normal concentration). It regulates the temperature balance of the atmosphere acting like the greenhouse. The spectral properties of CO2 in the atmosphere are such that it tends to prevent the long wave radiations (i.e., infrared heat radiation) escaping from Earth into outer space from reflecting back to Earth, as a result, an optimum temperature in which life is sustained, prevails on the earth’s surface. When CO2 increases in the atmosphere beyond normal concentration, such a thick layer of CO2 covering retains more infrared heat radiations, as a result, the earth’s surface becomes overheated. This process of heating the earth’s surface by infrared heat radiation waves due to the presence of atmospheric CO2 layer is termed by Turk (1974), Lee (1974), and Smith (1977) as the Green House Effect.
The greenhouse effect is solely responsible for maintaining the Earth’s optimum temperature. It is surprising to note that if there would be no such effect, the normal average temperature of Earth, which is 15°C, would have fallen upto -18°C. It would render our earth lifeless. Apart from CO2, other gases also contribute to this phenomenon, like CH4, N2O, and CFC together they are called Greenhouse gases. But, during the past century, these gases have increased in concentrations in the atmosphere, due to some anthropogenic activities. Such increased levels have led to increased entrapment of heat inside the Earth’s atmosphere causing a rise in temperature. In the last three decades, about 0.6°C increase in the average temperature of the Earth has been recorded. Such an increase in global temperature is termed as Global Warming. This rise in temperature interrupts worldwide weather patterns, which may be a serious threat to global food production. Recently, certain ecologists have tried to correlate air pollution with serious and prolonged droughts, heavier rains, and floods, and responsible for more serious hurricanes and tornadoes (Southwick, 1976).
Sources of Green House Gases:
| Gases | Sources |
| 1. CO2 | Coal, combustion of fossil fuels like Petroleum, Cement industry, Combustion of organic or inorganic substances. |
| 2. NO | Wood, Coal, Petrol Combustion |
| 3. CO | Combustion of Petroleum, Organic Substances |
| 4. N2O | Combustion of Petroleum, N2-fertilizer, Emission of smoke from car |
| 5. CH4 | Wetland, decomposition of organic matter, organic waste |
| 6. CFCs | Air conditioner factories, aerosol spray, plastic and foam-making factories |
B. Global Warming
The greenhouse effect is a natural phenomenon and the basis of sustenance of life on Earth as it maintains a uniform temperature throughout, but due to recent advancements of human civilization, like industrialization, population explosions, modernization, deforestation, and pollution, the levels of the greenhouse gases have increased alarmingly. IPCC (Intergovernmental Panel on Climate Change) has done an assessment and recorded the following gases and their effects responsible for global warming.
Causes of Global Warming
1. Carbon dioxide (CO2):
It contributes about 60% to global warming. Its concentration was recorded at 280 ppm in 1750 and 368 ppm in 2000. The main reasons behind such rise in levels are deforestation, combustion of fossil fuels and change in use of land. 33% of Indian land was covered by forest at the beginning of the 20th century but has reduced to only 19.4% till recently. Deforestation causes less incorporation of CO2 by plants, while on the other hand, the use of fossil fuels excessively increases its levels in the atmosphere.
2. Methane (CH4):
It has a 20% contribution to global warming in the world. Its concentration in the atmosphere has shockingly increased from 700 ppb before industrialization to 1750 ppb in 2000. The incomplete combustion of fossil fuels and incomplete decomposition by anaerobic methanogens contribute mainly to increasing methane levels.
3. Chlorofluorocarbons (CFC):
These are synthetic compounds made up of carbon and halogen elements (Cl, F). These are inert, inflammable, non-toxic, odorless compounds. These are used as coolants in refrigerators, and air conditioners, and also used in aerosols, solvents, fire extinguishers, jet fuels, etc. The main characteristic of CFCs is that they are highly persistent (45-260 years), so their concentration keeps on increasing in the atmosphere with their widespread use. They can react with nitrates and ozone present in the atmosphere and degrade the O3 molecules. Such an effect is causing ozone depletion (discussed later).
4. Nitrous Oxide (N2O):
It contributes about 6% to the global rise in temperature. Its concentration in the pre-industrial time was 270 ppb but now it is about 316 ppb. It is produced by the breakdown of artificial fertilizers, combustion of livestock wastes, nylon industries, etc.
Effects of Global Warming
1. Effect on Weather and Climate:
Climatic changes are the most evident. As the temperature increases, moisture moisture-carrying capacity of air also increases. As a result currents of air as well as water change directions. The frequency of precipitation changes, so threats of floods and droughts also increase. This in turn affects the life cycle of pathogens and vectors, further increasing threats to human health.
2. Changes in Sea Level:
Temperature rise causes thermal expansion of seawater, and melting of polar ice caps and glaciers, leading to a rise in sea level. According to a report by NASA, the melting of glaciers has led to a rise in sea level by 15 cm during the 20th century at a rate of 1-2 mm per year. Thus, one-third of the human population residing in coastal areas is facing danger of submersion. Estuaries, salt marshes, islands, fisheries, and wetlands are on the verge of becoming extinct.
3. Effects on Flora and Fauna:
Due to the rise in temperature, the latitudinal zonation will be altered. The temperate region will shift towards the poles by about 250-600 km. The flora sensitive to temperature will die out along with wiping out the animals depending on the same. So, arid regions will develop in many areas of Earth.
4. Effects on Agriculture:
Crop productivity is also affected. A rise in temperature will increase the transpiration rate, and growth of weeds and cause increased disease incidence, especially in the tropics. It has been estimated that for every 1°C rise in temperature, rice yield will decrease by 5% in South-East Asia. An increase in temperature will have a detrimental effect in temperate areas also.
Measures to be taken to Control Global Warming
The following measures can be taken to avoid the effects of global warming:
- Afforestation at a huge scale throughout the world.
- Replacement of CFCs with ozone-friendly substitutes.
- Reducing the use of artificial fertilizers and depending more on natural manure and organic farming.
- Encouraging the use of alternate sources of energy like solar energy, hydel power, and wind energy.
C. El Nino Effect
El Nino is a climatic cycle in the Pacific Ocean with a global impact on weather patterns. This cycle begins when warm water in the western tropical Pacific Ocean shifts eastward along the equator toward the coast of South America.
Occurence:
El Ninos occur every three to five years but may come as frequently as every two years or as rarely as every seven years.
Historical Evidence:
El Nino was originally named El Nino de Navidad by Peruvian fishermen in the 1600s. This name was used for the tendency of the phenomenon to arrive around Christmas. Climate records of El Nino go back millions of years, with evidence of the cycle found in ice cores, deep sea muds, coral, caves, and tree rings.
Effects of El Nino:
During an El Nino, the trade winds weaken in the central and western Pacific. Surface water temperatures become warm and South America warm up, because there is less upwelling of the cold water from below to cool the surface. The clouds and rainstorms associated with warm ocean waters also shift toward the east. The warm water releases so much energy into the atmosphere that weather changes all over the planet. An El Nino creates stronger wind shear and more stable, air over the Atlantic, which makes it harder for hurricanes to form. However, the warmer-than-average ocean temperatures boost eastern Pacific hurricanes, contributing to more active tropical storm seasons.
D. Acid Rain
Acid rain is the result of the scientific activities of human beings. Acid rain is due to the simultaneous causing effect of H2SO4 and HNO3 of which H2SO4 is 60-70% and HNO3 is 40-30%.
Unscientific and rapid industrialization is the increase in acid rain. Every year several million tonnes of SO2 and NO2 are being injected into the atmosphere. So acid rain has become a global problem. These oxides can travel a long distance in the atmosphere and are involved in many physical and chemical reactions to change the nature of the atmosphere. The atmospheric acids drift to a long distance from the source of origin and can cause acid rain there. In this way, oxides produced in one place can come down as acid rains in other distant places.
Chemical Processes
Combustion of fuels produces sulfur dioxide and nitric oxides. They are converted into sulfuric acid and nitric acid.
Gas Phase Chemistry
In the gas phase sulfur dioxide is oxidized by a reaction with the hydroxyl radical via an intermolecular reaction.
SO2 + OH → HOSO2
Which is followed by HOSO2 + O2 → HO2 + SO3
In the presence of water, sulfur trioxide (SO3) is converted rapidly to sulfuric acid:
SO3 (g) + H2O (l) → H3SO4 (aq)
Nitrogen dioxide reacts with OH to form nitric acid:
NO2 + OH → HNO3
Effects of Acid Rain
Soils:
Soil biology and chemistry can be seriously damaged by acid rain. Some microbes are unable to tolerate changes to low pH and are killed. The enzymes of these microbes are denatured by the acid.
2H+ (q) + Mg2+ (clay) → 2H+ (clay) + Mg2+ (aq)
Soil chemistry can be dramatically changed when base cations, such as calcium and magnesium, are leached by acid rain thereby affecting sensitive species, such as sugar maple (Acer saccharum).
Forests and Other Vegetation:
Adverse effects may be indirectly related to acid rain. High concentration of gaseous precursors to acid rain. High altitude forests are especially vulnerable as they are often surrounded by clouds and fog which are more acidic than rain. Other plants can also be damaged by acid rain, but the effect on food crops is minimized by the application of lime and fertilizers to replace lost nutrients. In cultivated areas, limestone may also be added to increase the ability of the soil to keep the pH stable, but this tactic is largely unusable in the case of wilderness lands.
Human Health Effects:
Acid rain does not directly affect human health. The acid in the rainwater is too dilute to have direct adverse effects. However, the particulates responsible for acid rain (sulfur dioxide and nitrogen oxides) do have an adverse effect. Increased amounts of fine particulate matter in the air do contribute to heart and lung problems including asthma and bronchitis.
Other Adverse Effects:
Acid rain can damage, historic monuments and statues, especially those made of rocks, such as limestone and marble, that contain large amounts of calcium carbonate. Acids in the rain react with the calcium compounds in the stones to create gypsum, which then flakes off.
CaCO3 (s) + H2SO4 (aq) → CaSO4 (s) + CO2 (g) + H2O
The effects of these are commonly seen on old graveyones, where acid rain can cause the inscriptions to become completely illegible. Acid rain also increases the corrosion rate of metals, particularly in iron, steel, copper, and bronze.
E. Photochemical Smog
Nowadays PCS (Photochemical smog) is a burning problem all over the world. A mixture of fog and smoke is aggregately called smog. This smog is filled up with air pollutants like O3, PAN, NO2, H2O2, etc. These are formed due to chemical reactions between NO2, hydrocarbons, and O2. This reaction is called photochemical reaction. At night and in cloudy days the smog is formed densely. In our country Delhi, Mumbai, Kolkata, Chennai, Ahmedabad, and Kanpur are the cities where the smog formation is increasing at an alarming rate. Automobile exhaust, industries, and various plants are the sources of this smog. In 1987, Mumbai was covered by such smog continuously for ten days.
