Question

1. What is a climate feedback? Why are they not a cause of climate change? List 3 climate feedbacks, and whether they are positive or negative feedbacks.

Answer 1

Feedback mechanism is a dynamic sequence in which a previous process either reinforces or reduces the effect of a latter process. In climate study the varied phenomena existing in nature having a direct or an indirect effect on the climate are usually taken in sequence such that any previous step can affect a latter step in either positive way (reinforces) or a negative way (reduces), hence the name Positive Feedback or Negative Feedback.

Climate feedback mechanisms are the directions in which climatic processes are driven and are never a cause of the initiation of those processes.

The 3 examples of feedbacks are given below:

1) Cloud Feedback: Higher temperature as well as higher solar insolation is supposed to increase the rate of evaporation on earth. The higher rate of evaporation leads to the formation of more clouds both in troposphere as well as stratosphere which in turn decrease the solar insolation incident on the surface as clouds have a higher rate of reflectivity (higher albedo). In this way the same energy that is meant to increase the total surfacial temperature of earth leads to the fall in temperature on earth's surface. This is an example of a Negative feedback mechanism wherein the previous process tends to decrease the effect of a latter process.

2) Ice-Cover Feedback: As most of the troposphere is heated not by direct absorption of light from the sun but from the heat released by the earth after first itself getting heated due to absorption of incident light (Terrestrial Radiation). Higher ice cover over poles and over mountains leads to higher albedo (ice has one of the highest albedos) which in turn leads to lower heat absorption by the earth's surface and which leads to the cooling of earth and subsequent increase in the size of ice cover.While the decrease in the size of polar glaciers and ice caps leads to the decrease of albedo which in turn leads to more absorption of heat and increase in overall surfacial temperatures which inturn lead to the melting of more and more glaciers. This is a classic example of a Positive feedback mechanism.

3) Carbon-Limestone Feedback: The Chemical formula for limestones (calciated) is CaC0₃ and for dolomites (magnesiated) is MgC0₃ . In both cases huge amounts of carbon is sequestered in them. Lime/dolo-stones are depostied in the oceans upto a certain level and whose deposition is extremely sensitive to the Ph of the ambient ocean. With the increase in temperature the carbon dissolution in water increases which increases the amount of Carbonic acid present in the water and which inturn decreases the Ph of oceans. This increase in the Ph leads to abrupt dissolution of limestones in oceans which in turn lead to the emission of ample quantites of carbon gas in the atmosphere. Increased carbon in air leads to further warming of the oceans which then drives this cycle more towards desequestration (release) of carbon from the sinks. This is an example of a Positive feedback mechanism.