Misconceptions about climate processes, especially those involving confusion between the phenomena of ozone depletion and global warming, are commonly observed in discussions of climate and atmospheric change among students and even presented by professors to students. For instance, many believe or have been told that the Earth is warming as a result of more solar radiation entering the atmosphere through the ozone hole. This is not at all the case and the ozone "hole" has nothing to do with climate change.

Another misconception understands the greenhouse effect as the trapping of reflected solar energy by greenhouse gases or clouds. Many students thought it was the greenhouse gases themselves that were being trapped

This misunderstanding of the greenhouse effect may result in part from the direct analogy to a greenhouse maintaining heat by preventing convection and trapping warm air inside. In most instances, longwave radiative processes did not appear to play any part in students' models of the greenhouse effect. This indicates that students have difficulties viewing the Earth (let alone greenhouse gases) as radiating bodies. Many students were not aware of the natural greenhouse effect produced by atmospheric gases that maintains a habitable temperature on Earth and that the issue of global warming is related to the enhanced greenhouse effect.

A proper understanding of the "greenhouse effect/global warming" involves an understanding of how shortwave length radiation emitted by the Sun and long wavelength radiation emitted by the finite temperature of the Earth, act in concert with atmospheric gases to control and balance the average surface temperature of the Earth. This energy balance is shown in the Figure below.



Tbis figure illustrates the following:

1. Of the 100% of incoming solar energy that reaches the top of our atmosphere, almost 1/2 of it is lost before it reaches the ground. This means that our atmosphere is mostly transparent to optical radiation because it is thin.
   
   Losses occur via the following channels:
   
   Reflection based losses:
   • Reflection by clouds (usually high cirrus clouds made of ice) dominates the loss channel at 20%
   • 6% just bounces off the atmosphere back to space
   • 4% bounces off the surface of the Earth (dirt is not highly reflective and neither are the oceans - only ice is highly reflective)
   • Total reflective losses are then 30% and this is called the planetary albedo. For Earth, A=0.3
   
   
   Absorption losses:
   • 16% is of this optical radiation is absorbed by the atmosphere directly
   • Only 3% is directly absorbed by clouds (clouds are ineffective absorbers at short wavelengths)
   • Total absorption losses are therefore 19%
   
   
   So the total loss of optical radiation is 30+19 = 49% leaving 51% to be absorbed by the Earth as shown in the Figure. The earth absorbs this radiation (energy) and warms up and returns that absorbed short wavelength radiation as long wavelength infrared radiation. To keep the Earth in thermal balance (over long timescales) as much energy is emitted as absorbed.
   
   Now lets see the components that make up 100% of this emitted long wavelength radiation.
   
   
   • 30% of the energy goes into mechanical energy associated with producing rising air (7%) and via the thermodynamic process that makes planetary water vapor (basically rising and cooling of air - 23%)
   • Only 6% of this radiation is directly emitted by Earth back into space, meaning that the atmosphere intercepts much of this radiation.
   • This leaves 64% to be absorbed and re-radiated by clouds and the atmosphere. Thus any alteration of the absorption properties of the atmosphere are significant in terms of changing the overall energy balance and this is exactly what humans are accomplishing. Hooray for us ...
   
   
   We can schematically represent these interactions by considering the structure below. Basically our atmosphere can be modeled as a thin slab of material of finite temperature:
   
   
   
   A qualitative discussion of the figure above:
   
   
   
   The quantitative analysis of this figure is shown below:
   
   
   1. Incident flux from the sun on the top of our atmosphere F_o is filtered through the atmosphere by its short wavelength transmittance T_s , where 0 < t_s < 1.0

   2. The flux that reaches the ground is then F_o * T_s

   3. That flux is absorbed by the ground and the ground heats up to some temperature (T_g).

   4. The ground then re-radiates that heat as outgoing long wavelength IR radiation (F_g).

   5. Some of that flux (F_g) is absorbed by the atmosphere through its long wavelength transmittance T_t , where 0 < t_t < 1.0

   6. The combination of absorption of short (s) and absorption of long (t) wavelength radiation causes the atmosphere to heat up to a temperature (T_a) and then radiate that temperature away as flux (F_a); 1/2 of it up (into space) and 1/2 of it down (back to ground)
      
      
   7. Since as much flux goes out of the system as comes into the system we can set up the following equilibrium conditions.

      
      
      Top of the atmosphere: F_o = F_a + T_t *F_g
      
      At the ground: F_g = F_a + T_s *F_o

   8. Let F_a = F_o - T_t *F_g and substitute then; eventually get that:
      F_g = F_o *(1+T_s)/(1+T_t)
   
   
   For our atmosphere: T_s = 0.9; T_t =0.2 F_g = 1.6*F_o which leads to a 30-35K increase in the nominal surface temperature. Now virtually all of that temperature increase comes from the presence of water vapor. Water vapor is the natural greenhouse gas on the Earth. The addition of CO₂ leads to the augmented or enhanced greenhouse effect.
   
   The figure below shows the important spectral response of these two gases. The right hand curve labeled 255 K is the emission spectrum of the Earth. The arrow represents the wavelength at which most of the Earth's re-radiated energy is emitted. Notice that right of the arrow, the water vapor spectrum is almost entirely black. This means that all of those wavelengths are absorbed by water vapor and this is why water vapor is the dominant greenhouse gas in our atmosphere.

   The bottom panel shows the absorption spectrum of CO₂. It does not have large, blacked out areas meaning that it absorbs only over a small range of wavelengths. Unfortunately, that small range of wavelengths coincides exactly with the wavelengths at which the Earth re-radiates most of its absorbed solar energy. It is this unfortunate physical coincidence that makes CO₂ an effective absorber of infrared radiation and, therefore, a contributor to increased atmospheric heating, which in turn leads to increased surface heating.