Earth\'s average temperature is determined in part by the amount of CO_2 in the

Question

Earth's average temperature is determined in part by the amount of CO_2 in the atmosphere, by way of the greenhouse effect. The atmospheric CO_2 content may in turn be affected by the photosynthetic activity of plants, which converts CO_2 into plant (organic carbon): however, the rate of photosynthesis depends on the amount of CO_2 in the atmosphere and on global air temperature. The components of this system, atmospheric CO_2 content, global temperature, and photosynthesis rate, are intimately interconnected. By increasing global photosynthesis , plants would tend to lower the atmospheric CO_2 level. In doing so, however, the plants would lend to coal Earth. This cooling, together with the CO_2 level, might lend to reduce the photosynthesis activity of plants. On the basis of the above discussion, a system diagram of the photosynthetic ratio-CO_2-temprature system can be drawn: Examine his system diagram and share your observations and thoughts with your group members, guided by following questions. How many loops are there? Are they positive or negative loops? Pick one of the following disturbance (or imagine one by yourself), discuss the response of the system to the disturbance: (i) An increase in atmospheric CO2 due to human activities such as burning fossil fuel. (ii) A decrease in temperature due lo major volcanic eruptions sending ashes high up in the atmosphere and blocking the sunlight from reaching the surface. (iii)An increase in solar luminosity (which is a continuous forcing) through time. A good comprehension of Chapter 2, especially p. 21-26, of the textbook is required to answer these question. Grading Criteria: Advanced (AD): Answering both questions 1 and 2 by applying systems thinking correctly Competent (CP): Answering either question 1 or 2 by applying systems thinking

Explanation / Answer

A feedback loop is when one component of a system produces outputs that eventually influences its own input. The fundamental rule of system modeling is that you cannot understand a system without understanding its key feedback loops as they are crucial to understanding the system behavior and controlling it. There exist two different types of feedback loops which are, (i) Positive feedback loops or Reinforcing loops and (ii) Negative feedback loops or Balancing loops or goal-seeking loops.

Coming to the First question, there are two loops in the system described above and both of them are negative or balancing loops. The first one is involving photosynthesis rate and the atmospheric CO2 concentration. As the CO2 increases, the photosynthesis rate increases and as the plants consume more and more CO2 during photosynthesis, the CO2 concentration in the atmosphere decreases. Hence it is a negative loop. The second loop is involving both photosynthesis rate and CO2 as well as the average surface temperature. As CO2 increases the temperature also increases, and as the temperature increases photosynthesis also increases and as photosynthesis rate increases, CO2 as well as temperature tend to decrease. Hence they can be termed as negative loops. It can also be called as a 'Constrained negative or balancing loop' as the photosynthesis rate increase with the temperature only up to certain extent and then starts to decrease as the plant enzymes get denatured. While the positive loops cause either exponential growth or exponential decline, the negetive loops balances the system behavous and exhibits a goal seeking behaviour.

Coming to second part of the question, the increase in CO2 because of anthropogenic activeities causes the photosynthesis to increase in begining and then stabilises as the CO2 increases further beyond a point. Therefore the balancing behaviour of the negetive loop disrupts and the system balance is compromised.

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