greenhouse effect| Causes, effect, Control, case study| example|

Greenhouse Effect 

It is a naturally occurring phenomenon that is responsible for heating of earth's surface and atmosphere due to the presence of certain gases in the atmosphere. 

1. In the absence of greenhouse effect, the average temperature of earth would have been chilly -l8°C rather than the present average of l5°C.
2. Clouds and gases reflect about one-fourth of the incoming solar radiation and absorb some of it. But, almost half of incoming solar radiation falls on earth's surface heating it, while a small proportion is reflected back.
3. Earth's surface re-emits heat in the form of infrared radiation, but part of this does not escape into space and atmospheric gases (e.g., carbon dioxide, methane, etc.) absorb a major fraction of it.
4. These gases radiate heat energy and a major part of which again comes to earth's surface, thus heating it up once again. This cycle is repeated again and again. 
5. The above-mentioned gases-carbon dioxide and thane are commonly known as greenhouse gases because they are responsible for the greenhouse effect. 

Global Warming 

It is the gradual and continuous increase in average temperature of surface of the earth a result of increase in concentration of greenhouse gases. 

Cause of Global Warming 

High levels of greenhouse gases (CO 2, CFCs, CH4, etc.) in the atmosphere. All these gases allow the heat waves to reach earth but prevent their escape and the earth become warm. 

Effects of Global Warming 

These are as follows: -

• Earth's temperature has increased by 0.6°C in last three decades. This ca uses change in precipitation patterns.
• The rise in temperature leads to harmful effects in environment leading to odd climatic changes, e.g., El Nino effect.
• The high temperature will result in melting of polar ice caps, which will lead to rise in sea level and many coastal areas will be submerged.
• The high level of temperature leads to increased weed growth, eruption of diseases and pests. Thus, the crop productivity will decrease. 

  

  Fig: - Relative contribution of various greenhouse gases to total global warming

  
  

Control of Global Warming: -

It can be done by: - 

1. Cutting down the use of fossil fuels. 
2. Improving efficiency of energy usage. 
3. Reducing deforestation. 
4. Planting trees, slowing down the growth of human population. 
5. Taking international initiatives to reduce the emission of greenhouse gases into the atmosphere. 

Ozone Depletion in the Stratosphere: -

• Ozone can be: - Bad ozone It is formed in troposphere and is harmful to plants and animals. 
• Good ozone It is present in stratosphere and acts as a shield, absorbing harmful UV radiation from the sun.
• The thickness of the ozone is measured in Dobson Units (DU). 
• Ozone gas is continuously formed by the action of UV-rays on molecular oxygen. 

• There should be a balance between production and degradation of ozone in the stratosphere. 
• This balance gets disrupted due to enhancement of ozone degradation by Chlorofluorocarbons (CFCs). CFCs are used as refrigerants.
• Ozone degradation When CFCs are discharged into lower part of the atmosphere, they move upward and reach the stratosphere. 
• In stratosphere, UV-rays act on them releasing chlorine (Cl) atoms.
• Cl degrades ozone releasing molecular oxygen with these atoms acting merely as catalysts.
• Cl atoms are not consumed in the reaction. 
• Hence, whatever CFCs are added to the stratosphere, they have permanent and continuous effect on ozone levels. 
• The ozone depletion is particularly marked over the Antarctic region. This led to the formation of a large area of thinned ozone layer, called as ozone hole. 

 Ozone Depletion by CFCs 

Harmful Effects of Ozone Depletion 

These are as follows: -

• UV-B damages DNA, causing mutation. 
• Ageing of skin, damage to skin cells and various types of skin cancer. 
• High dose of UV-B causes inflammation of cornea. This is called snow-blindness, cataract, etc. Such exposure may permanently damage the cornea. 

Control of Ozone Depletion 

Some measures for controlling ozone layer depletion are as follows: - 

• An international treaty, known as the Montreal Protocol, was signed at Montreal (Canada) in 1987 (effective in 1989) to control the emission of ozone depleting substances. 
• More protocols have been laid down for controlling emission of CFCs and other ozone depleting chemicals, separately for developed and developing countries. 

Degradation by Improper Resource Utilization and Maintenance 

It includes: -

1. The degradation of natural resources can occur not just by the action of pollutants, but also by improper resource utilization practices.
2. Results of improper resource utilization are: -

(a)Soil Erosion and Desertification 

• The formation of fertile topsoil takes centuries. 
• Due to human activities like overcultivation, unrestricted grazing, deforestation and poor irrigation practices, fertile topsoil is removed, resulting into arid patches of land.
• These barren patches when left for long time, form deserts. 
• Desertification is a major problem now a days due to increased urbanization.

(b)Water Logging and Soil Salinity

•  Irrigation without proper drainage of water leads to water logging in the soil.
• This leads to more salt deposition on the land surface or collection at the roots of the plants. 
• This salt content inhibits the growth of crops and damages agriculture. 
• Green revolution. has increased water logging and soil salinity. 

 Deforestation: -

It is the conversion of forested areas to non-forested areas: - 

1. Almost 40% forests have been lost in the tropics, compared to only I% in the temperate region. 
2. In India, in the beginning of the 20th century, forests covered about 30% of the land, whereas by the end of the century, it is reduced to 19.4%.
3. The National Forest Policy (1988) has recommended 33% forest cover for the plains and 67% for the hills. 

Reasons of Deforestation 

These include: - 

(i)Urbanization 

(ii) Cattle ranching 

(iii) Forest fires 

(iv) Demand of wood and other forest products

(v) Slash and burn agricultural or Jhum cultivation: -In this, Farmers cut down the trees and burn the plant remains. They ash is used as used for farming or cattle grazing. After cultivation, the area is left for several years to allow its recovery. In earlier time, enough times gap was given so that the land recovered from the effect of cultivation, this recovery phase is not available leading to deforestation.

Effects of Deforestation 

Various effect of deforestation are as follows: -

1. Increased levels of CO2concentration in the atmosphere.
2. Loss of biodiversity due to habitat destruction.
3. Disturbs hydrologic cycle.
4. Leads to soil erosion.
5. Desertification also occurs in extreme cases.

Conservation of Forests

Reforestation is the process of restoring a forest that once existed but was removed at some point of time in the past. Reforestation may occur naturally in a deforested area, or it can be speed up by planting trees.

Case Study: -People's Participation in Conservation of Forests

Case studies related to conservation of forests are as follows: -

• In 1731, a Bishnoi woman Amrita Devi (Jodhpur) showed, exemplary courage by hugging a tree and prevented it from cutting. Her three daughters and hundreds of other Bishnoi's followed her and lost their lives while saving the trees.
• The Government of India has recently instituted the Amrita Devi Bishnoi Protection Award for individuals or communities from rural areas that have shown extraordinary courage and dedication in protecting wildlife. 
• Chipko movement in Garhwal Himalayas started in 1974. Local women showed enormous courage in protecting trees from. the axe of contractors by hugging them. 
• The Government of India in 1980s has introduced the concept of Joint Forest Management (JFM), after realizing the value of participation of local communities in forest conservation. In return for their services to the forest, the communities get benefit of various forest products, thus sustainable development of forest can occur.