Increase in the level of green house gases has led to heating of earth leading to global warming! melting of glaciers; rise in sea level that can flood the coastal areas. Greenhouse gases other than CO₂ Methane (CH₄), CFCs chlorofluorocarbon, N₂O.

A taxon is endangered when its populations have decreased or habitats have been reduced to the levels that pose immediate danger of extinction. They are not likely to survive if the factors threatening their extinction continue. 54 animals and 113 plants are endangered in India.

A species once lost is gone for ever, no species should disappear in our times, our children will inherit what we leave for them.

Slash and burn agriculture can become environment friendly if rows of trees and shrubs are left intact while clearing the area for cultivation. This will prevent soil erosion and invasion of weeds. There will the quicker recovery of forest after the area is abandoned.

1. The CFCs discharged in the lower part of atmosphere move upward and reach the stratosphere.
2. In the stratosphere, UV rays act on them releasing Cl atoms.
3. Cl acts as a catalyst and degrades ozone releasing molecular oxigen
4. Since Cl atoms are not consumed in the reaction, whatever CFCs are added to the stratosphere, continue to damage the ozone and cause ozone depletion.
5. So, the emission of CFCs must be reduced.

Conservation of wildlife has three specific objectives :
(i) To main essential ecological processes and life-supporting system (air, water and soil).
(ii) To preserve the diversity of species or the range of genetic material of world's organisms.
(iii) To ensure a continuous use of species, in fact ecosystems, that support rural communities and urban industries.

(i) 1. All the buses of Delhi were converted to run on CNG by the end of 2002. CNG is better fuel than diesel and it burns most efficiently and very little is left behind.
2. Phasing out of old vehicles and use of unleaded petrol.
(ii) Euro II norms stipulates that Sulphur be controlled at 350 ppm in diesel and 150 ppm in petrol. Aromatic hydrocarbons are to be contained at 42 per cent of the concerned fuel.

Eutrophication
Eutrophication is defined as the process of nutrient enrichment of water and consequent loss of species diversity in water bodies.
1. Increased nutrient content of the water body causes algal bloom, i.e. excess growth of algae, especially cyanobacteria.
2. It covers the water surface, secretes toxins and reduces the dissolved oxygen content of water.
3. These toxins inhibit the growth of other algae and plants and cause death of aquatic animals.
4. Oxygen deficiency may be a cause for death of animals.

Greenhouse Effect
1. Greenhouse effect is a naturally occurring phenomenon, in which the shortwave radiations are absorbed and the longwave radiations are reflected by the earth and is responsible for heating of earth's surface and atmosphere.
2. Increase in the level of greenhouse gases is mainly responsible for global warming, as the CFCs disrupt the balance between the formation and degradation of ozone layer in the stratosphere which shields and absorbs the UV radiation from the sun.

1. The natural ageing of a lake is called eutrophication. It is the biological enrichment of its water.
2. In a young lake, there is very little life and the water is cold.
3.  As time advances, the streams draining into it start adding nutrients like phosphates and nitrates.
4. They stimulate the growth of algae, phytoplanktons and some small plants.
5. So, the quantity of organic matter increases and the water becomes warmer and shallower; hence the decomposers start flourishing.
6. The decomposers flourish and make use of a large quantity of oxygen for decomposition.
7. This leads to depletion of dissolved oxygen of the water and mortality of fish and other aquatic organisms.
8. The eutrophied water bodies can lead to algal blooms, which further add organic matter and lead to oxygen depletion.

(ii) Biodiversity can be conserved in the following two ways:
In situ conservation Sacred groves, biosphere reserves (terrestrial and marine), national parks and wildlife sanctuaries, etc.
Ex situ conservation Scared plants, home gardens, seed banks, gene bank, cryopreservation, botanical garden, zoological garden and aquariums.
(iii) For conserving biodiversity, the Earth Summits was held in 1992 and World Summits was held in 2002.
(iv) Respect for nature, scientific attitude with a vision of the future.

Electrostatic precipitator can remove over 99% particulate matter present in the exhaust from a thermal power plant by the following mechanism
1. It has electrode wires that are maintained at several thousand volts, which produce a corona that releases electrons.
2. These electrons attach to dust particles giving them a net negative charge.
3. The collecting plates are grounded and attract the charged dust particles.
4. The velocity of air between the plates is kept low enough to allow the dust to fall.

Causes of global warming:
(i) Deforestation
(ii) Burning of fossil fuels
(iii) Excess use of nitrogenous fertilisers
(iv) Increased amounts of greenhouse gases \(\left( { CO }_{ 2 },{ CH }_{ 4 },CFCs,NP \right) .\)
It is a warning to humans because
(i) it leads to deleterious changes in the environment resulting in odd climatic changes.
(ii) it can lead to melting of polar ice caps and ice caps on mountain tops and result in a rise in sea level which can submerge many coastal areas.
Control measures:
(i) Reducing emission of greenhouse gases by limiting the use of fossil fuels and using alternate sources of energy.
(ii) Increasing the vegetation cover.
(iii) Reducing deforestation.
(iv) Minimising the growth of human population
(v) Developing substitutes for CFCs