How does volcanic ash in the atmosphere affect the amount of solar radiation reaching Earth's surface?

• A. It decreases the radiation reaching the surface by reflecting it into space
• B. It increases the radiation reaching the surface by absorbing sunlight
• C. It has no effect on solar radiation reaching the surface
• D. It warms the surface by greenhouse trapping

Answer: (B)

When volcanic ash and related aerosols fill the atmosphere, they increase the sky’s reflectivity, bouncing a portion of incoming sunlight back into space. This scattering and reflection reduce the amount of solar radiation that makes it down to Earth’s surface, often leading to cooler conditions for a period after eruptions. While some particles can absorb sunlight in the atmosphere and warm the air above, the net effect on surface insolation is a decrease, not an increase. The idea that ash would warm the surface through greenhouse trapping isn’t how these aerosols behave. The correct concept is that volcanic ash lowers the solar radiation reaching the surface by reflecting and scattering sunlight.