The Art and Role of Climate Modelling

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Institute of Coastal Research, GKSS Research
Centre Geesthacht, und Klimacampus, Universität
Hamburg,Hans von Storch
Klimamodelle - was können sie und was können sie
nicht?
Österreichische Akademie der Wissenschaften, Kommi
ssion für Reinhaltung der Luft. Klima Modelle,
Prognosen, Strategien - Was nützen sie
? Donnerstag, 26. Februar 2009, 1600 bis
1900Theatersaal, Sonnenfelsfasse 19, 1010 Wien
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Conceptual aspects of modelling
Hesses concept of models Reality and a model
have attributes, some of which are consistent and
others are contradicting. Other attributes are
unknown whether reality and model share them.
The consistent attributes are positive
analogs. The contradicting attributes are
negative analogs. The unknown attributes are
neutral analogs.
Hesse, M.B., 1970 Models and analogies in
science. University of Notre Dame Press, Notre
Dame 184 pp.
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Validating the model means to determine the
positive and negative analogs. Applying the model
means to assume that specific neutral analogs are
actually positive ones.
The constructive part of a model is in its
neutral analogs.
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Models are smaller than reality
(finite number of
processes, reduced size of phase space)
simpler than reality   (description of
processes is idealized) closed, whereas
reality is open   (infinite number of
external, unpredictable forcing factors
is reduced to a few specified factors)
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• Models represent only part of reality
• Subjective choice of the researcher Certain
  processes are disregarded.

• Only part of contributing spatial and temporal
  scales are selected.
• Parameter range limited

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Models can not be verified because reality is
open. Coincidence of modelled and observed
state may happen because of models skill or
because of fortuitous (unknown) external
influences, not accounted for by the
model. Trivially all models are false ( have
negative analogs)
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Purpose of models reduction of complex systems
? understanding surrogate reality ?
realism
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• Models for reduction of complex systems
• good for
• constitution of understanding, i.e. theory
• construction of hypotheses

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• Models as surrogate reality
• dynamical, process-based models,
  
  
• characteristics
• complexity quasi-realistic
  mathematical/mechanistic engineering approach

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atmosphere
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Dynamical processes in the atmosphere
Dynamical processes in a global atmospheric
general circulation model
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The model can be validated only for that part of
the phase space, which is sufficiently covered
by observations.
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Klimazonen
Modell
Beobachtet
Klassifikation nach Koeppen
Erich Roeckner, pers. Mitteilung
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Observed
Winter (DJF)
Simulated
Zyklogenese
Sturmbahn-dichten
Erich Roeckner, pers. Mitteilung
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Precipitation in IPCC AR4 models
Erich Roeckner, pers. Mitteilung
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Applying the model outside the admissible domain
means to exploit a neutral analog.
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Purposes

• process sensitivity analysis neutral analog
  embedding of process in dynamics
• experimentation tool (test of hypotheses)
  neutral analog all processes significant to the
  hypothesis are operating in the model.
• forecast of detailed development (e.g. weather
  forecast) neutral analog future development
• dynamically consistent interpretation and
  extrapolation of observations in space and time
  (data assimilation) - neutral analog
  space-time correlations
• reconstruction of global past states and
  construction of scenarios - neutral analog
  sensitivity to external forcings

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detailed parameterization
Latitude-height distribution of temperature (deg
C)
Effect of black cirrus
Difference black cirrus - detailed
parameterization
Roeckner Lohmann, 1993
No cirrus
Difference no cirrus - detailed parameterization
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Testing the MBH hockeystick method

• Simulating the process of reconstructing
  historical climate variations using the data from
  the 1000 year historical ECHO-G simulation.
• Done by constructing pseudo-proxies.
• Short-term (lt20 yrs) variations about ok, but
  long-term variations (gt100 years) severely
  underestimated.
• MBH method methodically flawed.

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Erklärung für die jüngste Klimageschichte
C
Modellrechungen ohne anthropogene
Einflüsse Beobachtungen relativ zu 1961-1990
Mittel
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Erklärung für die jüngste Klimageschichte
C
Modellrechnungen mit anthropogenen
Einflüssen Beobachtungen
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Globale Szenarien gt Abschätzung der Wirkung von
Emissionsminderungen
SRES ScenariosSRES IPCC Special Report on
Emissions Scenarios
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Zwei Szenarien (A1B und B1) der Änderung der
jährlichen Niederschlagssummen in 2061-2090
relativ zu 1961-1990. CLM modell Beate Geyer,
GKSS Regionale Spezifikation gt Anpassung
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Lokale Modellierung Potentiale für Mikroskaliges
Klimamanagement
Gill et al.,2007
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• Zusammenfassung
• Quasirealistische Modelle sind validiert für das
  gegenwärtige Klima, d.h. sie beschreiben die
  wesentlichen, großskaligen Statistiken des
  derzeitigen Klimageschehens.
• Für Klimawandeluntersuchungen dienen
  quasirealistische Modelle
• der Detektion und Attribution von gegenwärtigem
  Klimawandel,
• der Abschätzung der Sensitivität des globalen
  Klimasystems gegenüber der Intensität von
  Emissionen,
• der Spezifikation von möglichen zukünftigen
  Anpassungsbedarfen
• der Erforschung des Potentials lokalen
  Klimamanagements

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Zu diesem Thema kann man lesen von Storch, H.,
S. Güss und M. Heimann, 1999 Das Klimasystem und
seine Modellierung. Eine Einführung. Springer
Verlag ISBN 3-540-65830-0, 255 pp von Storch,
H., and G. Flöser (Eds.), 2001 Models in
Environmental Research. Proceedings of the Second
GKSS School on Environmental Research, Springer
Verlag ISBN 3-540-67862, 254 pp. Müller, P., and
H. von Storch, 2004 Computer Modelling in
Atmospheric and Oceanic Sciences - Building
Knowledge. Springer Verlag Berlin - Heidelberg -
New York, 304pp, ISN 1437-028X