Among the five layers of the earth's surface ozone is present in the stratosphere which absorbs UV radiation before it reaches the ground. The main cause of ozone depletion is manufactured chemicals especially CFCs, these compounds reach the stratosphere by winds, where they release halogen atoms through photodissociation and cause the breakdown of ozone into oxygen. The ozone hole formed due to this increase the exposure of direct UV rays on earth carrying the potential risk of skin cancer and other negative effects. Direct exposure of harmful UV rays that penetrates skin can damage the genetic material I.e., DNA in skin cells and if the body is unable to recover the damage the cells stars to divide and grow uncontrollably which eventually leads to a tumour.

Hence, the correct answer is 'More ultraviolet rays come to earth'.

Desertification
Defining desertification can be complex – with over 100 different definitions existing within scientific literature.

Many people believe the phase was first coined by French scientist Andre Aubrville in 1949. He used the term to describe the human-induced degradation that transformed the African savannah into desert.

Restricted overgrazing

By pounding the soil with their hooves, livestock compact the substrate, increase the proportion of fine material, and reduce the percolation rate of the soil, thus encouraging erosion by wind and water. Grazing and the collection of firewood reduce or eliminate plants that help to bind the soil.

In 1987, twenty seven industrialized countries signed the Montreal Protocol for reduction in production and release of ozone layer depleting CFCs(Chloro fluoro carbons) into the atmosphere. It was followed by increasingly stringent amendments in London in 1990 and in Copenhagen in 1992.

A greenhouse gas is a gas that absorbs and emits radiant energy within the thermal infrared range.Greenhouse gases cause the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide and ozone.

Reforestation is the process of restoring a forest that once existed but was removed at some point of time in the past. 

Its chlorofluorocarbon(CFC), it is one of the green house gases which are responsible for ozone depletion. When UV rays from sun come into earth's atmosphere it strikes with many gases there in which cfc is one of them. When uv strikes CFC the C-Cl bond breaks and produces Cl atom which then treated with O₃(ozone) and break its bond.

The excess amount of CO₂ forms a thick blanket in the atmosphere which is transparent to sunlight but absorbs infrared radiation trapping heat near the earths surface. In this way, due to CO₂ blanket, the earths atmosphere works very much like agreen-house which causes warming up of the interior. So, carbon dioxide is called green house gas.

Reflection of light and heat takes place from plant community and soil. The reflected heat absorb by co₂ and produces heating in atmosphere. It is known as greenhouse effect.

Chipko Movement, started in 1970's, was a non violent movement aimed at protection and conservation of trees and forests from being destroyed. The name of the Chipko moment originated from the word 'embrace' as the villagers used to hug the trees and protect them from wood cutters from cutting them.

Ethane is not a greenhouse gas.
Greenhouse gases present in the atmosphere trap the radiations and do not allow heat to leave. Examples of greenhouse gases include carbon dioxide, methane, sulphur dioxide.