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:
- Residence time in atmosphere.
- 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.