feedback loops (ELSS)

Question 1

dynamic equilibrium

Answer 1

the state in which a system adapts to changes eg in the inputs, stores or flows, but that through a feedback a balance or equilibrium is achieved

Question 2

feedback

Answer 2

the automatic response of a system when a change to a flow of energy or materials through it occurs

Question 3

positive feedback

Answer 3

occurs when a change (to an input or store) causes further changes in the system which can make the system unstable

Question 4

negative feedback

Answer 4

occurs when a change causes the system to alter so that equilibrium (balance) is recovered and the system does not change

Question 5

water cycle feedback loop:
positive
global scale

Answer 5

-increasing temps increase rates of evaporation
-as water vapour is a greenhouse gas more long wave radiation is absorbed
-this means that the atmosphere then warms so the global temperature increases further
-this means that the rate of evaporation will increase further

Question 6

water cycle feedback loop:
positive
local scale

Answer 6

-within a drainage basin higher levels of precipitation lead to increased rates of evaporation
-there is higher rates of evaporation from surface storage and river discharge increases
-more water makes its way into the groundwater storage if the rocks are permeable
-this feedback mechanism will therefore increase the water availability for evaporation, so precipitation will also increase (unless groundwater storage is large)

Question 7

water cycle feedback loop:
negative
local scale

Answer 7

-increased atmospheric water vapour can cause cloud cover to increase due to higher rates of condensation
-increased cloud cover means that more incoming solar radiation is reflected back out into space
-less incoming radiation means that temps will fall
-the decrease in temps will cause the amount of water vapour in the atmosphere to decrease due to less evaporation

Question 8

water cycle feedback loop:
negative
local scale

Answer 8

-in drought years an individual tree becomes more stressed due to the lack of water for roots to take up
-this causes the tree to shed leaves in summer to reduce water loss from transpiration
-the fewer the leaves the lower the rate of transpiration and so this negative feedback mechanism will maintain survival

Question 9

carbon cycle feedback:
positive
global scale

Answer 9

-rising global temps increases the rate of decomposition of organic material
-this means that more carbon dioxide is released into the atmosphere from more decomposition
-higher CO2 concentrations trap more outgoing radiation which causes global warming
-global warming causes the rate of decomposition to increase further

Question 10

carbon cycle feedback:
positive
regional scale

Answer 10

-in the arctic tundra and arctic ocean increased melting of snow and ice leads to more sunlight being absorbed as less energy is reflected back to space
-the sun warms the top layer as it is now exposed and so the permafrost thaws
-the warmer soil then experienced higher rates of decomposition of the organic material within it. This increases atmospheric CO2 concentrations
-this increased CO2 concentration leads to more warming and therefore more melting of ice

Question 11

carbon cycle feedback:
negative
global

Answer 11

-higher levels of atmospheric CO2 encourage photosynthesis and growth of plants, algae and phytoplankton in a process called carbon fertilisation
-more carbon is therefore stored in these organisms which reduces atmospheric CO2 levels
-this negative feedback therefore reduces global CO2 concentrations and lowers rate of photosynthesis
-increased primary production apps relies on other factors needed for photosynthesis such as sunlight, nutrients, nitrogen and water being readily available