(a) Climate Change: 

1. The climate change refers to seasonal changes over a long period with respect to the growing accumulation of greenhouse gases in the atmosphere.

2. Recent studies have shown that human activities since the beginning of the industrial revolution, have contributed to an increase in the concentration of carbon dioxide in the atmosphere by as much as 40%, from about 280 parts per million in the pre-industrial period, to 402 parts per million in 2016, which in turn has led to global warming.

3. Several parts of the world have already experienced the warming of coastal waters, high temperatures, a marked change in rainfall patterns, and an increased intensity and frequency of storms. Sea levels and temperatures are expected to be rising.

(b) Acid Rain:

1. Acid rain is one of the consequences of air pollution. 

2. It occurs when emissions from factories, cars or heating boilers contact with the water in the atmosphere. 

3. These emissions contain nitrogen oxides, sulphur dioxide and sulphur trioxide which when mixed with water becomes sulfurous acid, nitric acid and sulfuric acid. 

4. This process also occurs by nature through volcanic eruptions.

5. It can have harmful effects on plants, aquatic animals and infrastructure.