Climate regime shifts
Kyle Swanson
University of WisconsinMilwaukee
The interesting past century…
Volcanic? Solar?
Solar?
GHG?
SO2? GHG? ???
Randomness and Climate Change
And so, ultimately, the question of questions
boils down to the placement of the boundary
between predictability under invariant law and
the multifarious possibilities of historical
contingency…
From a discussion of determinism in evolution,
Wonderful Life by Stephen J. Gould.
What are regimes?
Low order dynamical analogues
Example: Coupled Lorenz Systems
(Molteni and Corti 1998)
System #1:
Lorenz X-variable
System #2
Lorenz X-variable
Models exhibit regime-like behavior
GFDL CM2.1: Dynamically evolving sensitivity
4-member ensemble
10-year least squares fit for sensitivity
Annual mean data
Internal anomalies can be negative or positive:
GFDL CM2.1 AR4 SRESA1B simulation
Key question: What happens when the
lull ends?
T
t
2000
Fast signal rise
2000
Slow signal rise
ENSO activity: What’s anomalous?
-K ò (SOI ) dt
What changed?
Regime shift possibilities:
TOA radiative balance or heat storage
S0
Fout
Atmosphere
Q = surface/atmosphere flux
h
Surface (ocean)
S0 – Fout + Q = 0
wCp d(hT)/dt = S0 - Fout
Are these changes real?
ERBE Scanner
CERES-EBAF
45˚S - 45˚N
Question: Why does a radiative flux F change?
P = Distribution of T
R = Transfer function
F=
¥
ò R(T )P(T )dT
0
dF @
¥
¥
0
0
ò R(T )dP(T )dT + ò dR(T )P(T )dT
R(T) for CERES/ERBE
Structure of R suggests bias!
Observed behavior
lies far outside the
model spectrum!
Adjusting for bias:
ERBE Scanner
CERES-EBAF
45˚S - 45˚N
Dynamics: Temperature
and Vertical Velocity
F=
dF »
òò R(T, w)P(T,w)dTdw
òò R(T,w)dP(T,w)dTdw + òò dR(T,w)P(T,w)dTdw
30˚N-30˚S Distribution:
The tropics in T-w space
Log(Area)
CERES/ERBE period differences:
Clear-sky OLR R
CERES-ERBE
CERES/ERBE R:
All-sky OLR
CERES/ERBE R:
Cloud OLR+SW outgoing
Is the radiative response
stationary?
Assumption: Spatially local radiative
flux behavior has global implications
Divide annual mean tropical radiative fields into CERES
and ERBE groups; remove spatial means within groups.
1)Calculate pattern correlations (OLR,SW) vs. total
outgoing for interannual variability within groups.
2)Find the fields that optimally distinguish between
CERES and ERBE periods.
3)Compare the pattern correlations (OLR,SW) vs. total
outgoing for those fields with the results of 1).
These correlations should be the same if the climate
is stationary…
Pointwise anomalies
for field that optimally
distinguishes CERES
and ERBE periods.
X = Observed
Green = Models
Climate regime shifts?
• Current lull represents an
unprecedented opportunity to
understand the climate system.
• Can climate warm outside of an El Niño
dominated regime?
• Is climate stationary? Shortwave
dominance on interdecadal scales, not
reproduced by models! No effective
longwave damping?