Global warming is caused due to

Concept: Global warming is the long-term rise in Earth’s average surface temperature, driven mainly by the greenhouse effect: certain atmospheric gases — greenhouse gases such as carbon dioxide (CO2), methane, and water vapour — absorb and re-radiate outgoing infrared heat, trapping extra thermal energy in the atmosphere and oceans.

Application: Since the Industrial Revolution, burning fossil fuels, deforestation, and industrial activity have sharply raised atmospheric CO2 — from about 280 ppm in pre-industrial times to over 420 ppm today. A higher CO2 concentration strengthens the greenhouse effect, trapping more heat and raising the planet’s average temperature. This rise in carbon dioxide is the direct, scientifically established cause of global warming.

Cross-check: each remaining option moves in the wrong direction for warming:

• An increase in glaciers would mean cooling, not warming — observed warming instead shrinks glaciers, so glacier growth cannot be a cause of it.

• A decrease in carbon dioxide would weaken the greenhouse effect and counter warming, not cause it — the observed industrial-era trend is a steady rise, not a fall.

• Increased forestation removes carbon dioxide from the air through photosynthesis, acting as a carbon sink that mitigates warming rather than driving it.