The correct option is 2 and 3 only.
Explanation
Water vapour is a variable gas in the atmosphere that plays a critical role in the hydrological cycle and the Earth's heat budget. Its concentration varies significantly with latitude and altitude.
- Statement 1 is Incorrect: Water vapour is a variable gas that decreases with altitude, not increases. The concentration is highest near the Earth's surface, with nearly 90 % of the total water vapour found within a height of 5 km from the surface.
- Statement 2 is Correct: The concentration of water vapour decreases from the equator towards the poles. In warm and wet tropics, it may account for up to four % of the air by volume, whereas in the dry and cold polar regions, it constitutes less than one % of the air.
- Statement 3 is Correct: Water vapour acts as a greenhouse gas. It absorbs a portion of the incoming solar radiation (insolation) and traps the Earth's radiated heat (terrestrial radiation). This "blanket" effect prevents the Earth from becoming too cold or too hot.
Key Takeaway: Water vapour concentration decreases with an increase in altitude and latitude. It is a primary greenhouse gas that regulates the Earth's temperature by absorbing both insolation and terrestrial radiation.