Pathways of Energy Entering the Atmosphere (DP IB Environmental Systems & Societies (ESS)): Revision Note

Pathways of Energy Entering the Atmosphere

• When solar radiation (insolation) enters the Earth’s atmosphere, some of the energy becomes unavailable for ecosystems due to being:

  • Absorbed by inorganic matter

  • Reflected back into the atmosphere

• This means very little of the sunlight available from the Sun is converted into biomass in ecosystems

  • About 51% of the available energy from the Sun never reaches producers

• The pathway of radiation through the atmosphere involves a loss of radiation through reflection and absorption, with the following (approximate) percentage losses:

  • Reflection from clouds ~ 19%

  • Absorption of energy by clouds ~ 3%

  • Reflection by scatter from aerosols and atmospheric particles ~ 3%

  • Absorption by molecules and dust in the atmosphere ~ 17%

  • Reflection from the surface of the Earth ~ 9%

    • The ability of clouds and reflective surfaces on Earth (such as snow and ice) to reflect solar radiation is known as albedo 

• Of the 49% of solar radiation absorbed by the ground, only a small proportion ends up in producers

  • Most incoming solar radiation fails to enter chloroplasts in leaves because it is reflected, transmitted (passes straight through the leaf), or is the wrong wavelength to be absorbed

  • Of the radiation captured by leaves, only a small percentage ends up as biomass in growth compounds because the conversion of light to chemical energy is inefficient

  • In total, only around 0.06% of all solar radiation falling on Earth is captured by plants

From the sun to producers - the pathway of solar energy entering the atmosphere