Forcings and Feedbacks

Question 1

What does Q’ denote?

Answer 1

The radiative forcing.

Question 2

What is radiative forcing?

Answer 2

Net downward radiative flux change from external drivers.

Question 3

Give examples of radiative forcings.

Answer 3

Changes in insolation, CO2 concentration, H20 concentration.

Question 4

What are the units of radiative forcing?

Answer 4

Wm^-2

Question 5

What does lambda denote?

Answer 5

The radiative feedback.

Question 6

What is radiative feedback?

Answer 6

The net downward radiative flux change per kelvin. (The atmospheric mechanisms that rebalance the Earth after a forcing)

Question 7

How do Q’ and lambda relate?

Answer 7

Q’ = -lambda . T’_S

Question 8

What is the equation for lambda?

Answer 8

lambda = dN_TOA/dTs

Question 9

For what range of Kelvin is the equation relating forcing and feedback valid for?

Answer 9

Approximately 10K

Question 10

How do we lock in the relationship between surface and atmospheric temperature?

Answer 10

T^4_A = T^4_S/2

Question 11

What is the effect of volcanic sulfate aerosol particles as a forcing?

Answer 11

These are a negative forcing as they work to scatter incoming radiation so less can be absorbed by the surface, hence decreasing the temperature.

Question 12

What is the physical meaning of the Planck feedback?

Answer 12

The understanding that an increased temperature results in an increased level of emission, hence cooling down quicker (a negative feedback)

Question 13

What is the physical meaning of the H20 vapour feedback?

Answer 13

Increased atmospheric H20 traps outgoing radiation from the surface (positive feedback as it warms)

Question 14

What is the physical meaning of the Lapse-Rate feedback?

Answer 14

Changes in the upper tropospheric temperatures differ to the surface temperatures. The tropospher warms more than the surface, cooling the Earth. - reduces convection as the upper level is warmer, cooling the surface.

Question 15

What is the physical meaning of the surface-albedo feedback?

Answer 15

Increased melting of snow/ice allows for more radiation to be absorbed, hence heating the earth, causing more snow/ice to melt (positive feedback)

Question 16

Which feedback can be illustrated in the simple one-layer model?

Answer 16

The Planck feedback, as inner convection for the atmosphere cannot be modelled when assuming it is a uniform slab.

Question 17

In actuality, which feedback dominates models?

Answer 17

The cloud feedback due to such high levels of uncertainty.