Solar Radiation and Greenhouse Effect

Incoming Solar Radiation

• Not all solar radiation reaches Earth's surface.
• Reflection and Absorption:
• 26% reflected back by clouds and atmosphere
• 19% absorbed by atmosphere/clouds and radiated out to space and Earth
• Remaining radiation reaches Earth's surface, where absorption/reflection depends on surface's albedo.
• Darker surfaces (low albedo) absorb sunlight and emit infrared radiation (heat).
• Lighter surfaces (high albedo) reflect sunlight back, preventing absorption.

Greenhouse Effect

• Greenhouse gases in the atmosphere trap heat from the sun; essential for life on Earth.
• Process:
• Solar radiation (UV & visible light) heats the Earth.
• Earth's surface emits infrared radiation.
• Greenhouse gases absorb this and radiate heat back to Earth and out into space.

Major Greenhouse Gases:

• CO₂: From fossil fuel combustion, decomposition, and deforestation.
• Methane (CH₄): From natural gas extraction, agriculture, and anaerobic decomposition.
• Nitrous Oxide (N₂O): Emitted from agricultural soils via denitrification.
• CFCs/HFCs: Used in refrigeration and aerosol products.
• Water Vapor (H₂O): Acts as a greenhouse gas but its levels are temperature-dependent.

Global Warming Potential (GWP):

• Measures how much a gas contributes to warming over 100 years relative to CO₂.
• Factors:

1. Residence time in atmosphere.
2. Infrared absorption efficiency.

• GWP of gases compared to CO₂, which has a GWP of 1:
• Methane: GWP > 1, around 12 years residence time.
• Nitrous Oxide (N₂O): GWP > 1, 115 years residence time.
• CFCs: GWP much higher, 50-500 years residence time.