What is the main cause of greenhouse effect?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Increasing CO2 concentration
The greenhouse effect is the warming of the Earth because gases in the atmosphere let sunlight in but hold in the heat radiated back from the ground. Its main driver today is the rising concentration of carbon dioxide, released by burning coal, oil and gas and by cutting down forests.
Why the other options are incorrect
Option (1) Fertilizer use — Incorrect. Nitrogen fertilisers release some nitrous oxide, a greenhouse gas, but they are a smaller contributor than CO2.
Option (2) Water logging — Incorrect. It is a soil problem in which the land stays saturated with water, often from over-irrigation.
Option (4) Rain water run off — Incorrect. Runoff is rainwater flowing over the land; it causes soil erosion, not warming.