john harries, john harries, space and atmospheric physics group, blackett laboratory, imperial...

PG Lectures 1

John Harries, Space and Atmospheric Physics group,

Blackett Laboratory, Imperial College,

London,UK

30 November 2009

Climate Change:The Earth’s energy balance, IR spectral properties, and

climate feedbacks

PG Lectures 2

Acknowledgements:

Many discussions with, and results provided by:

Dr Helen Brindley, Dr Jacqui Russell, Dr Joanna Futyan, Dr Jenny Griggs, Dr Richard Bantges, Dr Claudio Belotti, Dr Claudine Chen…

Dr Adrian Tuck, Professor Tony Slingo, Professor Brian Soden, Dr Bruce Wielicki, Professor James Anderson, Professor Richard Goody, Professor Tony del Genio….and many others.

30 November 2009

PG Lectures 330 November 2009

Books:

“Atmospheric Radiation”, Goody (1964) and revised by Goody and Yung (1989), OUP.

“The Physics of Atmospheres”, Houghton (2002), CUP.

“An Introduction to Atmospheric Physics”, Andrews (2000), CUP.

“Atmospheric Science: An Introductory Survey”, 2nd Ed., Wallace and Hobbs (2006), Elsevier/Academic Press.

PG Lectures 4

ContentsPart A: Basic Radiative Transfer1. Introduction to Radiative Transfer (RT), Earth

Radiation Budget (ERB) 2. Forcing and feedback processes, and variabilityPart B: The broad band signal3. Pinatubo: a natural experiment;4. Evidence for variability of broadband LW, SW, FN;Part C: The spectrally resolved signal5. Evidence for variability of resolved spectrum LW.6. The water vapour feedback.Part D: Measurements of ERB and Spectrum7. GERB8. IRIS, IMG, AIRS, TES, and IASI

30 November 2009

PG Lectures 5

Part A: Basic Radiative Transfer

1. Introduction to Radiative Transfer (RT), Earth Radiation Budget (ERB)

2. Forcing and feedback processes, and variability

30 November 2009


Global average terrestrial energy budget

Albedo 1/3

FN = Pin – Pout = p (stored or lost energy)


Spectral complexitySpectral complexity


Some assumed relations

Planck’s radiation law (gives the spectral radiance, or energy/sec ond/area/solid angle/frequency interval

Rayleigh-Jeans approximation (long-wave limit, ):

Wien displacement law (differentiate : ) m K

Stefan-Boltzmann law (integral of over all :

1exp

22

3

Tkhc

hTB

B

4

2

Tck

TB B

2897Tm

B

4TF

TB


d

s

n

sI dsddAdsIE

dA

Radiant spectral intensity, (spectral radiance) = energy/unit area/solid angle/spectral frequency.

dd

(if I isotropic)

Flux

Some radiative transfer theory

sI

sI

n

s

I

IdIdI

ddIdIdsnIF

0

1

2

0

20

1

2

0

2

0

2

0

2

0

2

cos2)(coscos2sincos2

sincoscos.


dA

sI

d

s

n

sI dsddAdsIE

dssIsrskdI

Radiant intensity absorbed by ds at s:

Radiant intensity emitted by ds at s:

dssJsrskdI

dA

Radiant spectral intensity (spectral radiance) = energy/unit area/solid angle/spectral frequency.

s

s+ds


dssrkd

where

sJsId

sdI

sJsIsrkds

sdI

Here, k is the spectral extinction coefficient and is the optical path (depth or thickness), both functions of frequency.

It can be shown that, for a black body, J = B(T), the Planck function for a black-body radiator at temperature,T.

Schwarzchild’s equation of radiative

transfer


Integrating Schwarzchild’s equation, using an integrating factor, exp(), provides the solution which is the basis of all radiative transfer and remote sensing techniques.

sssLsL exp)0()( '''exp'exp000

dssrkssrksTBdssrkIsIs

Surface radiance, transmitted through whole atmosphere

Radiance from layer ds transmitted through atmosphere above, integrated over all layers


Studies of the Physics of the Earth’s Climate Balance, and the new

Geostationary Earth Radiation Budget experiment (GERB)

Professor John Harries

Head, Space and Atmospheric Physics

Real spectral radiances (Schwarzchild)

Surface term (atmos. window)

Integral emission (atmos. layers)

3

2

1

T2

T1

T3

Ts

Surfaceterm

Integral emission

Weighting function

dzzzzTBII ss

0

,, ),0(






Real spectral radiances (Schwarzchild)

Surface term (atmos. window)

Integral emission (atmos. layers)

3

2

1

T2

T1

T3

Ts

Surfaceterm

Integral emission

dzzzzTBII ss

0

,, ),0(


dz

d

r(z)

zWeighting function


A simple interpretation of the effect of clouds on radiance and OLR

Surface term

Integral emission

3

2

1

T2

T1

T3

Ts

Surfaceterm

Integral emission

dzzz

zTBIfclearI sssc

0

,,, ),0(1

dzzz

zTBzIfcloudyIcz

ccccc

,,, ),(


Fluxes: in quasi steady state at TOA, with time dependence: (Note: S = ITS/4)

)()(

)],,(1[)(

2

0

2

0

2

1

2

1

tOLRddtItF

ddtAtStF

LW

SW

where the radiance has a time dependence as follows (from Schwarzchild equation of radiative transfer):

Absorbed short-wave flux

Emitted long-wave flux

Surface term Integral emissionI

dzztztzTBttItI ss

0

,,,,);,0(


Heating (cooling) rates

Another important concept is the heating rate, the energy per second being absorbed (heating) or emitted (cooling) in a layer z to z + dz . Within such a layer, we may write for the rate of change of energy:

zFzFzF

wheredz

zdF

dt

zdTcz

dt

dQ

N

NpE

)(

Note: (a) is total density, not just of the absorber; (b) convention for FN can be reversed, in which case minus sign before the dF/dz term; (c) flux units are energy/m2/s, so that dF/dz is energy/m3/s.

PG Lectures 2030 November 2009Manabe and Stricker, JAS, 21, p373, 1964


The significance of transmittance and heating rates

PG Lectures 22

Part A: Basic Radiative Transfer

1. Introduction to Radiative Transfer (RT), Earth Radiation Budget (ERB)

2. Forcing and feedback processes, and variability

30 November 2009


2. ‘Forcing’ and ‘feedback’ processes. Forcing processes (External processes which impose a change of climate balance):

• greenhouse gas changes; • solar variations;• volcanic eruptions.

Feedback processes (Internal processes which respond to a forced change):

• water vapour feedback;• cloud feedback;• land surface feedback;• ice feedback;• ocean feedback.


Global Terrestrial Energy Budget (per unit surface area)

Input SW Power Pin = ITS (1 – A) / 4 = S (1 – A)

Output LW Power Pout = TE4 = (1 – g)TS

4

Power deposited = p

G = greenhouse radiative forcing (in Wm-2) = (TS4- TE4)g = normalised greenhouse effect, g = G / (TS4 ) G / 390 0.40

A = planetary albedo 0.31 = Stefan-Boltzmann constant = 5.6696 10-8 Wm-2K-4

TE = effective temperature of Earth / atmosphere 254K

TS = mean surface temperature of Earth 288K

Pin = Pout + p 1 Wm-2

(Hansen et al., Science, 2005)

235 Wm-2 (ITS 1366 Wm-2)


Terrestrial Energy Budget: feedbacks and forcings

S (1 – A) = (1 – g) TS4 + p1 + p2 + …

Feedback loops, eg: hydrological cycle, circulation patterns,

cloud, vegetation, etc.

greenhouseforcing

delayedresponses

Delay due to slow feedback processes: eg. deep ocean warming

SW LW

Measures of the SW, LW and FN (= ) fluxes at TOA give information on greenhouse forcing, cloud and water vapour feedback…..i.e. on climate processes and climate change

Forcings,eg:Direct increase in A (and smaller increase in g) due to volcano

i

ip

PG Lectures 2630 November 2009 Hansen 2005

PG Lectures 2730 November 2009 Hansen, 2005


22

outout2outout

in2in

COdCO

P+dT

dT

dC

C

P

dT

OdH

OH

P+dT

T

P=

dTdT

dC

C

P

dT

OdH

OH

P

222

2

loglog

Feedback processes.

Let us assume that CO2 is changing, and the other parameters can give rise to feedbacks on this basic forcing process. We can express dependence of Pout and Pin on cloud (C), ice (I), water vapour (H2O), temperature (T) and carbon dioxide (CO2) as follows (ignoring p):

222 ),(,,,),( COTOHTTCPTOHITCP outin

and write the dependences explicitly as follows (ignoring ice, which should be added later);

Held & Soden, 2002


where:

TP

COP

Δ outout

220 log

is the temperature response to a CO2 change with no feedbacks, and:

TP

dTdx

xP

xP outoutin

x

is a non-dimensional ratio giving the strength of the water vapour or cloud feedback process ( = 0 is no feedback; = 1.0 is complete damping)

from which re-arranging gives:

i

iCH2O2

Δ

β

Δ=

COd

dT

11log00

2


The change in surface temperature Ts for doubled CO2 as a function of the watervapour feedback parameter H2O. Results are shown for two different scenarios of other temperature dependent feedbacks that encompass the current range of predictions in Ts 1.5– 4.5K when H2O 0:4.

Held and Soden, 2002


This simple model takes account of feedback processes that affect both the SW (Pin) and LW (Pout), and can produce both positive ( 0) and negative ( 0) feedbacks.


The End

PG Lectures 33

Part B: The broad band signal

3. Pinatubo: a natural experiment;

4. Evidence for variability of broadband LW, SW, FN;

30 November 2009

PG Lectures 35

First, some questions:

How does the radiative energy budget of the Earth vary in response to a perturbation, such as increasing CO2 or a volcanic eruption?

How close to steady state is the Earth at any instant and place, and also in the average?

Is the TOA net flux always zero: how quickly does it restore to zero after a perturbation: how large are any excursions from zero?

Are broadband measurements a useful technique to monitor global climate change from space (as opposed to specific processes), or do we need spectrally resolved observations?

30 November 2009

PG Lectures 36

Next a few comments:

Earth is not in thermodynamic equilibrium, since energy flows into and out of the boundaries of the system: it is not isolated.

The Earth is a non-equilibrium (quasi) steady state system, and therefore is described by non-equilibrium thermodynamics and statistical mechanics.

As a steady-state, non-equilibrium system with many degrees of freedom (ie many routes for energy to cascade between the incoming solar beam and the outgoing thermal radiation), the Earth presumably follows the principle of maximised entropy production (MEP), [eg Paltridge (1975, 1978, 1979, 1981, 2001); see excellent review book Edited by Kleidon and Lorenz, 2003].

30 November 2009

PG Lectures 37

The total response of the climate system including the feedback processes, in response to a perturbation, such as increasing CO2, is the summation of all the individual feedback processes, each having an individual magnitude of response and time constant for the response [Soden, 2002; Hallegate et al, 2005].

It can be shown (eg Harries and Futyan, 2006) that a volcanic eruption proves to be a useful natural experiment in separating faster and slower processes (eg those which involve radiative signals of rapid processes, or other, slower dynamical processes, eg involving large scale motions of water vapour fields).

30 November 2009

PG Lectures 38

How large and long-lived a signal in the net radiationat the TOA, FN, is expected following a perturbation?

The evidence from ERB measurements (Wielicki et al.) and models (Hansen et al.), including extremely careful analyses and error studies, indicates that FN may change by up to 10 Wm-2, but quickly (TBD) returns to zero, showing very small, essentially not significant departures form zero.

Altogether, the few studies to date support the view that the Earth maintains a zero FN at TOA.

Except in the case of a volcanic eruption, such as that of Mt Pinatubo in 1991.

30 November 2009


3. Pinatubo: a natural experiment

Pinatubo (Phillipines, June 1991) was powerful (20 Mt), and directed vertically: so, a large mass of injecta quickly reached the stratosphere.

Tropospheric material was quickly washed out.

Stratospheric zonal circulation is strong, and particles quickly circulated equatorial zone, spreading N and S more slowly. Decay from stratosphere slow.


Recent work in USA has attempted to make measurements of stability of TOA radiation balance, and of evidence for “stored energy”, p, by measuring net flux anomaly at TOA.

p = FN

Question: what value should FN be, and how much can it vary ( FN(t))?

20N -20S: Wielicki et al, (2001): revision Wong et al (2005).

Mt. Pinatubo,

June 1991


• Following work on Pinatubo by Soden et al. [2002], we have used the perturbation caused by Pinatubo to study some of the process time constants in the system;

• We have analysed the time series of the following parameters, and measured the (assumed exponential) rise and decay of the perturbation in each parameter: Longwave and shortwave TOA fluxes for latitudes 60N–

60S and for 1991–1996 (note: latitude range is maximum extent of observations from ERBS); Soden et al. [2002]

confirmed no significant differences from 90N–90S). The TOA net flux anomaly, formed from the difference

between absorbed SW and emitted LW fluxes. Observed total column water vapour, and lower

tropospheric temperature, for 90N–90S (NVAP project; Randel et al., [1996]).

Observed 6.7 mm brightness temperature for 90N–90S (TOVS Radiances Pathfinder project [Bates et al., 1996].


Time series of the anomalies of the following parameters:(top to bottom)

• observed longwave and shortwave TOA

fluxes for latitudes 60N–60S and for 1991–1996;

• Observed net flux formed from the difference between absorbed SW and emitted LW fluxes;

• Observed total column water vapour and lower tropospheric temperature for 90N–90S;

• Observed 6.7 mm brightness temperature for 90N–90S

SW and LW flux anomalies

Net flux anomalies(“stored or lost energy”)

T6.7

Water vapour column and T

Harries & Futyan, 2006


Concluding remarks on Pinatubo study:• Pinatubo offers a natural perturbation to the climate

system;

• Radiative processes which can respond immediately to the “instantaneous” insertion of aerosol from the volcano show very short time constants (few months), driven by the time taken for aerosols to become distributed;

• Radiative processes which involve slower dynamical response, eg moving water vapour around, take much longer (1-2 years);

• Rise and decay process time constants differ;

• Models ought to reproduce these relaxation times as validation.


Part B: The broad band signal

3. Pinatubo: a natural experiment;

4. Evidence for variability of broadband LW, SW, FN;


4. Evidence for variability of Broadband SW, LW, FN.

…..a preliminary look


SW Wong et al, (2005), 20 N/S


(Top) Annual mean anomalies of: • 1984–2000 ES albedo

reconstruction (broken, black);

• 1999–2004 measured ES albedo anomalies (solid,

black); • SBSRN (green); • OBTGOME (red); • CERES (magenta)• ERBE (broken, red)

shortwave flux anomalies;• Smod (blue).

All anomalies are relative to the 1999–2001 period. (Bottom) Expansion for 2000–2005 period. Some of theFigure 1 (top) data sets are plotted here as monthly meanswhen available. Anomalies are normalized to 2000.. For the ES observations, ±1sd error bars are also plotted.

SW

Palle et al., 2004, 2005


Apparent agreement. Monthly mean annual cycle and standard deviation (vertical bars) of albedo from six models. These and other models are used by IPCC for pre-industrial control simulations.

SWCharlson et al, 2005


For the tropical oceans. In addition to ERA40, NCEP and SRB products there are observational and empirical data (OBS) comprising (a) HadISST ocean surface temperature; (b) columnintegrated water vapor from SMMR and SSM/I; (c) the Prata formula estimate of clear sky surface net LW radiation (SNLc) using SMMR and SSM/I data; (d) radiation budget satellite data from ERBS (1985–1990), ScaRaB (1994/1995), CERESon TRMM (1998) and CERES on TERRA (2000–2004); and (e) combined ERBS/ScaRaB/CERES and Prata-SSM/I estimates of SNLc.

Allan (2006) LW: global: annual cycle removed


LW

Wong et al,2005


Wong et al, (2005)

FN


Wong, et al, J Clim. 2005

FN


Part C: The spectrally resolved signal

5. Evidence for variability of resolved spectrum LW.

6. The Water Vapour feedback


HH2O pure rotation band

CO2 2 band

O3

HH2O 2 band

CFCl3

CH4

H2O continuum


Hanel et al, Applied Optics, 1971

Thermal emission spectra recorded by IRIS-D on Nimbus 4.

The apodized spectra have a spectral resolution between 2.8 and 3 cm-1. A hot desert case, an intermediate caseover water, and an extremely cold spectrum recorded over theAntarctic are shown. Radiances of blackbodies at several temperaturesare superimposed.


TOAs FTBG

Feedback parameter,G = B (Ts) - FTOA


The IRIS experiment measured the Earth’s spectrum in 1970: The ADEOS experiment measured the Earth’s spectrum in 1997.

How does the IR spectrum of the Earth change as the climate changes?

Can we detect spectral signatures of climate change?

Are there measurements of the Earth’s spectrum to the required accuracy?

Does the variability of the Earth’s spectrum (in time and space) mask any changes due to climate?

PG Lectures 61

Available Satellite Instruments

Instrument IRIS IMG AIRS TES IASI

Satellite Nimbus 4 ADEOS AQUA AURA METOP-A

Spectro-meter type

FTS FTS grating spectrometer

FTS FTS

Data available

Apr 1970 – Jan 1971

Oct 1996 – Jun 1997

2002 - present

2004 - present

2007 - present

Spectral coverage (cm-1)

400 – 1600 cm-1

continuous

715 – 3030 cm-1

3 bands

650 – 2700 cm-1

2378 bands

650 – 1350 cm-1

3 bands

645 – 2760 cm-1

3 bands

Spectral resolution

2.8 cm-1 0.1 cm-1 0.4–1.0 cm-1 0.1 cm-1 0.5 cm-1

Footprint (nadir)

95 km diameter

8km x 8km 13 km diameter

5x9 km 12 km diameter30 November 2009


New data from high resolution FT Spectrometers in US and Europe.


Do we have evidence of “climate forcing” by increasing greenhouse gases?

Harries et al., Nature, March 15 2001

Yes!


OK! But what about feedback signatures?


6. The Water Vapour feedback


HH2O pure rotation band

CO2 2 band

O3

HH2O 2 band

CFCl3

CH4

H2O continuum


One problem with using observed spectra is thatthe pure rotation band is not accessed(experimental difficulties).

So, while that work continues, we have also usedre-analysis data to simulate the IR spectrum atdifferent places and times.

Now we look at difference in re-analysis based simulations for different regions and times:

There is a great deal of inter-annual fluctuation, and the change in water vapour feedback is soometimes +ve, sometimes –ve.


Now we try to overcome the natural variability by taking big averages, 1970-1985 and 1986-2000, both global and tropical zone.

We find that between the first and the second 15-year periods, both the tropical and global, and both NCEP and ERA-40 show that the water vapour feedback grew weaker.

The re-analyses are known to have larger uncertainties associated with upper troposphere water vapour, so we are now testing the result by using other data.

At least, we have learned that the water vapour feedback needs to be very carefully modelled in climate change runs if the change in climate is to be accurate.


Conclusion on variability of resolved spectrum:

- Today’s new resolved spectral measurements, by AIRS, TES, IASI, etc can be used for spectral signature of climate detection; It appears from this work that monitoring the climate from the TOA is better done using the resolved spectrum than integrated measurements CLARREO

- The magnitude of spectral signatures of climate change are significantly larger than noise levels;

- IASI will fly on operational series (MetOp) for at least a decade, so that more progress should be made in detecting long term climate change signals.

- The water vapour feedback changes both positively and negatively with time, not just monotonically increasing.


The end


Concluding remarks:How close to steady state is the Earth at any instant and place, and also in the average?

Evidence from observations + models indicates that the Earth (steady-state, non-equilibrium system, maximising entropy production rate) maintains zero net TOA radiative anomaly to few Wm-2.

How does the radiative energy budget of the Earth vary in response to a perturbation, such as increasing CO2, or a volcano?

Perturbations show rise (and/or) decay controlled by the forcing process. Long term (decadal) net flux departures from zero indicate slow processes delaying temperature response to forcing.

Pinatubo rise and decay times indicate radiative time constants respond to speed of underlying dynamical processes. Time constants from weeks to years: should be added constraint on models.


Is the net flux always zero: how quickly does it restore to zero after a perturbation: how large are excursions from zero?

Variability of broadband net flux, FN , lies within 2 W m-2; FN up to – 5 Wm-2 for Pinatubo.

Evidence is that net flux returns to zero between months and years, determined by processes.

Non-zero net flux anomaly associated with delayed response processes and “stored energy”. Magnitude in latest model by Hansen is 0.75 Wm-2; analysis of earlier work, experimental and model, however, gives more like +2 Wm-2.

Evidence in observations is inadequate to draw any conclusions about evidence for stored energy in broadband signal

Can only say that net flux anomaly is maintained within 0 2 Wm-2.


Are broadband measurements a useful technique to monitor climate change from space, or do we need spectrally resolved observations?

Climate change processes cause a variety of changes at different wavelengths, which may tend to compensate in broadband. Moreover, we have seen a limit of 2 Wm-2 in practice in background variability: if Hansen is right, signal is 1 Wm-2.

The resolved IR emission spectrum can now be measured to relative accuracy of 0.1% or so, and spectral signatures may change by as much as 1% or more in modern spectra (eg IASI, TES).

So, climate trends should be monitored using resolved spectrum (broad band, however, is powerful for regional and process studies).

Less complex spectrometers can be designed, since very high spectral resolution not needed (1 cm-1 adequate).


End


CERES (polar orbiter) monthly averages :

What observational evidence do we have?

LW SW


GERB (geostationary) 15 minute averages:

LW SW

Visible (SW) Total LW = Total - SW

GERB-2 measurements


Iacono and Clough, JGR, 1996


Placeholder for variability of spectrum

PG Lectures 10430 November 2009 Hansen JGR 2005


Source Years analysed Annual, global-mean data

OLR(Wm ²־ )

Albedo, A , ( %)

Net flux, FN

(Wm ²־ )

Observations

Early measurements[Vonder Haar and Suomi (1971)]

1962 –1966 237 30 +5

Pre-1972 experiments¹[Ellis and Vonder Haar (1976)]

1959–1971 236 30.4 +2#

Pre-1972 experiments plus Nimbus 6 ERBE¹ [Campbell and Vonder Haar 1980]

1959–1978 232 30 +7#

Nimbus 6 ERB wide field of view¹[Jacobowitz et al. (1979)]

1975 –1978 234 31 +2#

(-0.1)

Nimbus 6 ERB narrow field of view¹[Campbell and Vonder Haar 1980]

1975 –1976 230 31 +6#

Nimbus 7 ERB wide field of view¹[Jacobowitz et al. (1984)]

1978 –1979 228.8 30.6 +10.9

Nimbus 7 ERB narrow field of view [Jacobowitz et al. (1984)]

1978 –1979 232.7 33.1 -3.4

NOAA scanning radiometers (AVHRR)*ª [Lucas et al. (2001)]

1979 -1999 231 - -

Table 1: Globally and annually averaged OLR flux, albedo and net flux from a number of sources

What about historical satellite measurements of FN?


ScaRaB²[Kandel et al. (1998)]

03/1994 - 02/1995

237.3 29.9 +2.4

ERBE scanner²[Barkstrom et al. (1989)]

03/1985 –02/1989

235.3 29.6 +5.0

CERES (ES9 Terra Edition 2)[Wielicki et al. (1996)]

01/2001 – 12/2002

238.7 28.7 +2.0? (+5.8)

Best estimate from all instruments(Mean and standard deviation)

1963 - 2002

234 ± 3.6

30.5 ± 1.1

+4 ± 3.6

Best estimate from later instruments (this page)

03/1985 – 12/2002

237.1 ± 2.9

29.4 ± 0.62

+3.1 ± 1.7


Model results

HadAM2ª [Pope et al. (2000)] 1979-1989

240 29.0 +2.2

HadAM3ª [Pope et al. (2000)] 1979-1989

239 28.6 +3.5

GISS SI2000 [Hansen et al (2002)]

1951-2000

+0.75


Summary (Decadal scale anomalies, Wm-2)

SW: LW: Net:

1985-1990 +1/+7 -1/+2 -1/+2

1990-1995 +1/+5 -1/+1 -1/+2.5

1995-2000 -1/+2 -1.5/+2 +0.5/+1.5

2000-2005 -1/+4 -1.5/+2 --------

Model +/-2.5 +0.75/+3.5Very preliminary!

Scatter +/- 1 to +/- 2.5 Wm-2: inconsistent reports of albedo and net flux uncertainties


Looking for accuracies < 0.3 Wm-2 or better to detect “stored energy”.

Unlikely that at present, given sampling problems, we can detect these changes in broad band: GERB may help.


Spectrally resolved measurements in 1970, 1997, 2001-now


1960 1970 1980 19901990

2000

0

6

-3


Some of the evidence for climate change,

and the uncertainties


The temperature signal at the surface and the coincident changes in CO2 , CH4 , sulphates, etc…


There are, of course, uncertainties in many forcing processes…..

IPCC

PG Lectures 115

• MEP in a complex non-equilibrium system allows for a multiplicity of MEP states for the same, or very similar energy configuration.

• Could this be a principle underlying the existence of transitions between ‘metastable’ states, that are very close together in energy….popular expression “tipping points”?

30 November 2009


But the major uncertainties are in feedbacks, not the forcings: Should we believe that we understand “climate change” well enough to predict our future?

No!

The feedback processes, especially clouds, water vapour, oceans, cause large uncertainty

Climate change runs by different models for same conditions


Variability and complexity in climate






• Climate is highly variable:+ Many processes are non-linear;

+ Some processes are chaotic;+ Natural variability in climate components;+ Feedback processes cause variability.

• Climate is very complex:+ Many greenhouse absorbers (CO2, CH4, H2O,

FCC, O3, clouds..);+ Many SW scatterers (clouds, aerosols, dust);+ Both Forcing and Feedback processes;+ Wide range of time and space scales are significant;

• Variability is in spectral, spatial and temporal space.

john harries, john harries, space and atmospheric physics group, blackett laboratory, imperial...

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