The natural process by which the atmosphere heats up due to the trapping of re-radiated infrared radiation is known as the **greenhouse effect**. Here’s how it works:

1. Incoming Solar Radiation: Solar energy from the Sun reaches the Earth’s atmosphere and surface.

2. Absorption and Reflection: Some of the solar radiation is absorbed by the Earth’s surface, which warms it. The Earth’s surface then re-emits this energy as infrared radiation (heat).

3. Greenhouse Gases: Certain gases in the Earth’s atmosphere, such as carbon dioxide (CO2), methane (CH4), water vapor (H2O), and others, are known as greenhouse gases. These gases trap and absorb the infrared radiation emitted by the Earth’s surface.

4. Radiative Balance: The absorbed infrared radiation warms the atmosphere, contributing to the overall temperature of the Earth. This process maintains a balance between the incoming solar radiation and the outgoing infrared radiation, regulating the Earth’s temperature and making it suitable for life—a phenomenon known as the greenhouse effect.

Human activities, such as burning fossil fuels and deforestation, have increased the concentration of greenhouse gases in the atmosphere, intensifying the greenhouse effect and leading to global warming and climate change.

Project Tiger was launched in India in the year 1973. It was initiated on April 1, 1973, with the objective of ensuring the conservation and preservation of Bengal tigers in their natural habitats, as well as to protect and enhance their populations through habitat management and conservation efforts. The project has been instrumental in saving the critically endangered Bengal tiger and has served as a model for tiger conservation efforts in other countries.

UNEP stands for the United Nations Environment Programme. It is a specialized agency of the United Nations (UN) that coordinates environmental activities, assists developing countries in implementing environmentally sound policies and practices, and promotes sustainable development globally. UNEP works on a wide range of environmental issues, including climate change, biodiversity, pollution, and ecosystem management.

Ozone Day, also known as the International Day for the Preservation of the Ozone Layer, is observed annually on September 16th. This day marks the anniversary of the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer in 1987, which is an international treaty designed to phase out the production and use of ozone-depleting substances (ODS). Ozone Day serves to raise awareness about the importance of protecting the ozone layer and the achievements made under the Montreal Protocol in mitigating ozone depletion and climate change.

Lichens are indeed excellent indicator species for pollution levels, particularly air pollution. They are very sensitive to sulfur dioxide (SO2) in the air. Sulfur dioxide is a common pollutant emitted from industrial processes, burning fossil fuels (such as coal and oil), and volcanic eruptions. High concentrations of sulfur dioxide can harm lichen populations, leading to their decline or absence in polluted areas. Therefore, the presence and health of lichen populations can provide valuable information about air quality and pollution levels in a given environment.