Can General Circulation Models be Trusted to Predict Global Warming

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Can General Circulation Models be Trusted to
Predict Global Warming?

• Yuk Ling Yung
• Presentation at the RCEC Academia Sinica Nov 28
  2007

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Future climate is like Dark Matter?
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Todays Outline

• What is Greenhouse Effect? (Review)
• GCM Prediction of Future (IPCC)
• NCAR Simulations (Deser, NCAR)
• Solar Cycle (Yau, CUHK)
• Cloud Feedback (Li, CIT)
• Long Period Oscillations (Heavens, CIT)
• Conclusions (Poetry)

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What is Greenhouse Effect?
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Absorption in Earths Atmosphere
H2O
O3
H2O
CO2
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Todays Outline

• What is Greenhouse Effect?
• GCM Prediction of Future
• NCAR 50 years
• Solar Cycle
• Cloud Feedback
• Long Period Oscillations

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Todays Outline

• What is Greenhouse Effect?
• GCM Prediction of Future
• NCAR 50 years
• Solar Cycle
• Cloud Feedback
• Long Period Oscillations

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• Atmospheric Radiative Forcing
• CO2 Increase and Ozone Depletion

Simulated Temperature Change 1890-1999
cooling
Altitude (km)
Altitude (hPa)
Cooling due to ozone depletion
C
warming
90N 60N 30N 0 30S 60S 90S
C/century
From IPCC 2007 Report Chapter 9
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Sea Level Pressure Trend 1950-2000
OBSERVATIONS
MODEL
0.73
- - - Linear trend significantly different from
zero (0.05 P)
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Sea Level Pressure Trend 1950-2000
OBSERVATIONS
MODEL
0.73
500 hPa Geopotential Height Trend
0.76
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Oceanic vs. Atmospheric Radiative Forcing
Sea Level Pressure Trend
500 hPa Height Trend
BOTH
OCEAN
ATMOS
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Oceanic vs. Atmospheric Radiative Forcing
Sea Level Pressure Trend
500 hPa Height Trend
BOTH
OCEAN
ATMOS
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Todays Outline

• What is Greenhouse Effect?
• GCM Prediction of Future
• NCAR 50 years
• Solar Cycle
• Cloud Feedback
• Long Period Oscillations

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VL Volcanic aerosols.
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Todays Outline

• What is Greenhouse Effect?
• GCM Prediction of Future
• NCAR 50 years
• Solar Cycle
• Cloud Feedback
• Long Period Oscillations

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Spectral Empirical Orthogonal Functions

• F(x,t,?) Si fi(x,t)gi(?)
• ltfi(x,t)gt Time average of fi(x,t)

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Todays Outline

• What is Greenhouse Effect?
• GCM Prediction of Future
• NCAR 50 years
• Solar Cycle
• Cloud Feedback
• Long Period Oscillations

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Tropics Aleutian Low Additional Evidence for
Natural Variability
Winter Aleutian Low SLP Index
Tropical Indo-Pacific Climate Index
Deser et al., 2004
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Todays Outline

• What is Greenhouse Effect? (Review)
• GCM Prediction of Future (IPCC)
• NCAR Simulations (Deser, NCAR)
• Solar Cycle (Yau, CUHK)
• Cloud Feedback (Li, CIT)
• Long Period Oscillations (Heavens, CIT)
• Conclusions (Poetry)

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????,???????????? ?????????
??? (1019-1086 )
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It happens then as it does to physicians in the
treatment of consumption, which in the
commencement is easy to cure and difficult to
understand but when it has neither been
discovered in due time nor treated upon a proper
principle, it becomes easy to understand and
difficult to cure. The same happens in state
affairs by foreseeing them at a distance the
evils which might arise from them are soon cured
but when, from want of foresight, they are
suffered to increase to such a height that they
are perceptible to everyone, there is no longer
any remedy. The Prince
Niccolo Machiavelli (1469-1527)
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Conclusions

• Short term prediction reasonably good
• (not covered)
• Stratosphere cooling
• Volcanic eruptions
• Low frequency variability (associated with
  oceans) poor
• Non--linear effects may be underestimated

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Thanks

• Yungs Group at Caltech
• Clara Deser (NCAR)
• David Camp (CalPoly SLOB)
• K. K. Tung (UW)
• Duane Waliser (JPL)