Balancing Temperature- Heat Budget

• The Earth itself needs to get rid of the energy it absorbs to maintain equilibrium. If it did not, over time, it would become too hot to live on the planet.
• The Earth radiates energy as infrared radiation. These are longer wavelengths than the short ultraviolet radiation that the Sun radiates.
• Refraction

  1. Light hits the atmosphere

  2. Light bends or refracts
• Reflection

  Light or light's energy gets bounced off the surface of the Earth and back to space
• Scatter


  Light bounces off a rough surface in many different directions
• Gases in the atmosphere that absorb long-wave infrared radiation

  • Water vapor (H2O)
  • Carbon dioxide (CO2)
  • Ozone (O3)
  • Methane (CH4)
  • Nitrous oxide (N2O)
  • CFCs
• Oxygen (O2) and nitrogen (N2) do NOT absorb infrared radiation.
• Almost all the ultraviolet is absorbed in the upper atmosphere by ozone.
• Water vapor contains heat, and as it rises, it gives off energy to the atmosphere, which is part of what goes back into space.
• Air that was heated because of conduction also rises into the atmosphere and heads back into space.
• The Earth's surface, clouds, and the atmosphere can all reflect some of that heat energy back to space.
• God created the Earth to be in perfect equilibrium. This means that the energy entering the Earth should be equal to the energy leaving the Earth.
• If more energy leaves the Earth than comes into it

  The Earth would cool over time
• If more energy comes into the Earth's atmosphere than leaves the Earth

  The Earth would heat up over time
• The only way heat energy leaves or comes into the Earth is by radiation.
• The Earth is constantly adjusting itself. Scientists call this the Earth's energy budget, or the Earth's radiation budget, or heat budget.
• What happens to the 100% of insolation reaching the Earth

  • 16% absorbed by atmosphere
  • 6% reflected by atmosphere
  • 3% absorbed by clouds
  • 20% reflected by clouds
  • 51% absorbed by Earth's surface
  • 5% reflected by Earth's surface
• The Earth then radiates the heat that it has absorbed, back into space from the clouds, atmosphere, land, and oceans, mostly in the form of infrared radiation.
• When the Sun warms the ocean, lakes, or even puddles, the molecules on the surface increase their vibration and kinetic energy due to solar energy. This causes those molecules of water vapor to evaporate carrying 23% of the heat in the water vapor up into the clouds and atmosphere.
• The air covering the land also conducts heat and sends 7% of this heat back into the atmosphere.
• The Earth's surface re-radiates 21%.
• The final amount of heat directly radiated into space from the Earth is equal to 6% because 15% of what is radiated is reabsorbed into the atmosphere.
• The Earth absorbs 64% of the radiation coming from the Sun. Fifty-one percent is absorbed by the land and oceans, and carbon dioxide, ozone, and water vapor take the other 13%.
• In the past, when the Earth was not at equilibrium, and the Earth radiated more energy than it absorbed, we had an Ice Age.