Lesson 7: Positive and Negative Feedback

Question 1

Define negative feedback

Answer 1

Acts to minimise the effect of new inputs in order to regain stability and equilibrium

Question 2

Example of negative feedback

Answer 2

There is more snowfall, the glacier would advance, meaning more ice would enter the ablation zone so more snowmelt would occur.
This would mean that a balance would be gained whereby the input of snowfall would equal the output of snowmelt

Question 3

Define positive feedback

Answer 3

Amplifies the effects of an input which would cause a shift in the system

Question 4

Example of positive feedback

Answer 4

Glacier has a positive mass balance and the glacier surface area is increasing, there will be an increase in ice albedo. This will cause a further reduction in air temperature, thus increasing accumulation and initiating a positive feedback cycle in which the glacier will continue to advance

Question 5

Area of Greenland ice sheet

Answer 5

1.7 million km2

Question 6

How much stored ice on Greenland ice sheet?

Answer 6

2.5 million km3

Question 7

How thick is the ice in the centre? How much does it depress the crust by?

Answer 7

Ice is 3km thick which depresses the earth’s crust by 1km in depth

Question 8

Overall mass balance of Greenland ice sheet?

Answer 8

-30 km