What is the net effect of greenhouse gases on global temperatures?

• A. They trap heat and influence global temperatures
• B. They block all sunlight
• C. They originate only from volcanic activity
• D. They exclusively warm the stratosphere

Answer: (A)

Greenhouse gases trap heat radiating from Earth's surface, creating a warming effect. They let in sunlight but absorb infrared radiation, so more heat stays near the surface and in the lower atmosphere. The net result is higher global temperatures. They do not block all sunlight; visible light still reaches the surface. They come from many sources, not just volcanic activity, with human activities adding large amounts of CO2. They don’t exclusively warm the stratosphere; the warming is most evident in the surface and lower atmosphere, though radiative changes in higher layers occur too.