the atmosphere part 8 climate change sensitivity and feedbacks n.
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The Atmosphere: Part 8: Climate Change: Sensitivity and Feedbacks. Composition / Structure Radiative transfer Vertical and latitudinal heat transport Atmospheric circulation Climate modeling. Suggested further reading: Hartmann, Global Physical Climatology (Academic Press, 1994).

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the atmosphere part 8 climate change sensitivity and feedbacks
The Atmosphere:Part 8: Climate Change: Sensitivity and Feedbacks
  • Composition / Structure
  • Radiative transfer
  • Vertical and latitudinalheat transport
  • Atmospheric circulation
  • Climate modeling

Suggested further reading:

Hartmann, Global Physical Climatology (Academic Press, 1994)

a simple 2 box model
A simple 2-box model
  • Two equal mass boxes, temperatures T1 and T2
  • Radiatively relaxed to temperatures Te1 and Te2 with time constant τr
  • Temperatures mixed with time constant τd
a simple 2 box model1
A simple 2-box model
  • Two equal mass boxes, temperatures T1 and T2
  • Radiatively relaxed to temperatures Te1 and Te2 with time constant τr
  • Temperatures mixed with time constant τd

radiation

a simple 2 box model2
A simple 2-box model
  • Two equal mass boxes, temperatures T1 and T2
  • Radiatively relaxed to temperatures Te1 and Te2 with time constant τr
  • Temperatures mixed with time constant τd

dynamics

a simple 2 box model3
A simple 2-box model
  • Two equal mass boxes, temperatures T1 and T2
  • Radiatively relaxed to temperatures Te1 and Te2 with time constant τr
  • Temperatures mixed with time constant τd

steady state solutions

{

where .

slide6

Equilibria of 2-box model

Fix Te, vary γ

with polar ice

Assumes ice in high latitude box (T2 < 263K)

slide7

Equilibria of 2-box model

with polar ice

Assumes ice in high latitude box (T2 < 263K)

equilibria of 2 box model
Equilibria of 2-box model

ice-free

with polar ice

Assumes ice in high latitude box (T2 < 263K)

Assumes high latitude box is ice-free (T2 > 263K)

equilibria of 2 box model1
Equilibria of 2-box model

Ice-albedo feedback➙ multiple equilibrium states

ice-free

with polar ice

Assumes ice in high latitude box (T2 < 263K)

Assumes high latitude box is ice-free (T2 > 263K)

multiple equilibria

slide10

Equilibria of 2-box model

Fix γ, vary Te

T1

ice-free

with polar ice

T2

climate forcings and sensitivity
Climate forcings and sensitivity

in equilibrium, net incoming flux is

Function of temperature, water vapor, clouds, CO2 and other greenhouse gases …

Function of solar constant, albedo (ice cover, cloudiness, vegetation, …)

}

Climate forcing due to ith process (all else held fixed) = δQ

(e.g., [CO2] doubling to 600ppm ➙

δQ = 4 Wm-2)

climate forcings and sensitivity1
Climate forcings and sensitivity

in equilibrium, net incoming flux is

Function of temperature, water vapor, clouds, CO2 and other greenhouse gases …

Function of solar constant, albedo (ice cover, cloudiness, vegetation, …)

}

➙ climate sensitivity

Climate forcing due to ith process (all else held fixed) = δQ

(e.g., [CO2] doubling to 600ppm ➙

δQ = 4 Wm-2)

feedbacks

radiative response only no feedbacks
Radiative response only(no feedbacks)

Suppose Te = Ts - constant

(Te = 255 K)

➙ (Need doubling of CO2 or 1.6% increase of solar constant to produce 1K warming)

water vapor feedback
Water vapor feedback

-4 Wm-2K-1 +2Wm-2K-1

w.v. feedback

ice albedo feedback
Ice albedo feedback

(overestimate — have neglected clouds)

-4 Wm-2K-1

+2 Wm-2K-1

cloud feedback
Cloud feedback

Current climate: cloud amount ~ 50%

10% increase in Ac

➙ would offset CO2 doubling