Limits & Feedbacks

This discussion will show that if all the earth’s accessible fossil fuel is consumed, the limit of surface temperature increase will only be in the range of 1 to 1.6 C, depending on how fast fossil fuels are consumed.  The LIMIT of the effect of CO2 on the earth’s environment is adressed.   The limitation is explained by feedbacks.  A “feedback” as discussed herein is defined as “The process by which a system (the environment)  is modulated, controlled, or changed by the product, output, or response it produces (in this case the earth’s surface temperature).”  A positive feedback causes the rate of change of temperature to increase as the substance is added.   For example, an electronic sound amplifier (music, microphone) gives strong positive feedback.  Conversely, a negative feedback will diminish the rate of change, as is the case of diminishing returns.

Acknowledgment: Much of the material in this page is taken from my friend Bryce Johnson, PhD, P.E.  See his Limit and Feedback  papers.

Present Conditions

  • Accessible fossil fuel in earth, including shale ≈ 10,000 GigaTonnes Carbon
  • Current fossil fuel consumption ≈ 10 GigaTonnes Carbon per year
  • The atmosphere presently contains 820 Gigatonnes Carbon
  • Oceans occupy ≈70% of the earth’s surface
  • The global annual average surface temperature is 15C, or 288K.

Major parameters

  • Water vapor in the atmosphere increases with earth surface temperature, and is the strongest contributor to the greenhouse effect (by itself, positive feedback), and increases cloud formation as it increases.
  • Clouds slightly decrease surface temperature.  As cloudiness increases (cloud formation increases as water vapor in atmosphere increases). This is negative feedback.
  • CO2 uptake (removal) is mainly by oceans, and rate of uptake increases with the amount of CO2 in the atmosphere (negative feedback), according to Henry’s Law).  About 1/2 of the CO2 added to the atmosphere is removed by nature.   Vegetation consumes (uptakes) CO2 from atmosphere, and increases with amount of CO2 in the air (negative feedback).  It also emits CO2 to the atmosphere as it decays (positive feedback).
  • Beer’s Law governs the absorption of infrared (greenhouse effect)  by atmospheric gases, which demonstrates that the rate of increase of the greenhouse effect decreases with the increase of gases in the atmosphere (negative feedback).

Graphics

  • Figure 1:  Projection of CO2 levels and earths surface temperature at present rate of addition of carbon to the atmosphere (10 gigatonnes/yr)
  • Figure 2: Projection of CO2 levels and earth’s surface temperature at ten times the present rate of carbon to the atmosphere (100 megatonnes/yr)
  • Figures 3a and 3b: Effect of Clouds on Temperature, from analysis of 28 years data by East Anglia University (3a = all clouds, 3b = low clouds).
  • Figures 4a and 4b: Addition and Removal of CO2 into and out of the atmosphere. (4a=net addition, 4b = strengths of various sinks)
  • Figure 5: Ocean following Henry’s Law
  • Figure 6: Beer’s Law effect on the  greenhouse effect (as watts/m^2) by CO2
Figure 1

Figure 1

Bryce 100 Gt yr curve

Figure 2

Figure 3a - All Clouds

Figure 3a – All Clouds

 

Figure 3b Low Clouds

Figure 3b Low Clouds

Figure 4a

Figure 4a

Figure 4b

Figure 4b

Figure 5

Figure 5

Figure 6

Figure 6

 

 

 

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