Models in Environmental Research, Specifically: Climate Models

Models in Environmental Research, Specifically: Climate Models
Institut für Küstenforschung I f K Models in Environmental Research, Specifically: Climate Models Hans von Storch Geesthacht, 21. Mai 2001

A model of sediment erosion
Institut für Küstenforschung I f K A model of sediment erosion

Institut für Küstenforschung
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I f K ( 20. Auflage Leipzig, Mannheim 1998) Modell ... .... Naturwissenschaften: ein Abbild der Natur unter Hervorhebung für wesentlich erachteter Eigenschaften und unter Außerachtlassen als nebensächlich angesehener Aspekte. Das Modell ... ist umso realistischer oder wirklichkeitsnäher, je konsistenter es den von ihm umfassten Erfahrungsbereich zu deuten gestattet und je genauer seine Vorhersagen zutreffen; es ist umso tragender, je größer der von ihm beschriebene Erfahrungsbereich ist. Modelle entstehen aus der Wechselwirkung zwischen Hypothesenbildung und Beobachtung: Die Hypothese lenkt die Beobachtung, und deren Resultate geben ihrerseits Anlass zur Verifizierung der Hypothese. Damit sind Modelle grundsätzlich nicht endgültig: sie müssen immer wieder der Erfahrung angepasst und, sofern das in einer konsistenten Weise nicht möglich ist. verworfen und durch neue Modelle ersetzt werden.

I f K Hydraulisches Modell Sündermann und Vollmers (1972)

I f K Surface currents Sündermann und Vollmers (1972)

I f K Sündermann und Vollmers (1972)

TIDAL CURRENTS & SEA LEVEL
Institut für Küstenforschung I f K TIDAL CURRENTS & SEA LEVEL State variables • vertically averaged components of current (u, v) • sea level (relative to undisturbed level h) (z)

I f K Sündermann und Vollmers (1972)

Institut für Küstenforschung APPLICATION
I f K APPLICATION replicate hydraulical model derive numerical values in high spatial and temporal resolution no problem to “measure” state variables examine sensitivity to boundary conditions relevance of processes Example: Coriolis force

I f K Surface currents Sündermann und Vollmers (1972)

Result with CORIOLIS Force
Institut für Küstenforschung I f K Result with CORIOLIS Force Sündermann und Vollmers (1972) Surface current

Institut für Küstenforschung Hesse’s concept of models
I f K Hesse’s 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. 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. Hesse, M.B., 1970: Models and analogies in science. University of Notre Dame Press, Notre Dame 184 pp.

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Models as surrogate reality
Institut für Küstenforschung I f K Models as surrogate reality • experimentation tool (test of hypotheses) • design of scenario • dynamically consistent interpretation and extrapolation of observations • forecast of detailed development (e.g. weather forecast) characteristics: complexity quasi-realistic mathematical/mechanistic engineering approach

Models are Institut für Küstenforschung
I f K Models are • • • smaller than reality (finite number of processes) • • • 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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I f K Dynamical processes in the atmosphere

I f K Dynamical processes in a global atmospheric model

Models can not be verified because reality is open.
Institut für Küstenforschung I f K Models can not be verified because reality is open. Coincidence of modelled and observed state may happen because of model´s skill or because of fortuitous (unknown) external influences. (see debate on global warming vs. solar influence)

Models can be shown to be consistent with observations.
Institut für Küstenforschung I f K Models can be shown to be consistent with observations. However the technically possible representation of the (yet) unknown the (e.g. 2xCO2) is in principle questionable (but perhaps plausible)

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I f K 1880–2049 ECHAM3/LSG 1973–1993 ERA ECMWF

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I f K How well are these processes represented in climate models? atmosphere ocean Bray and von Storch, 1999 Results of a survey among climate modellers

detailed parameterization Institut für Küstenforschung I f K Roeckner & Lohmann, 1993 Latitude-height distribution of temperature (deg C) Effect of black cirrus Difference “black cirrus” - detailed parameterization No cirrus Difference “no cirrus” - detailed parameterization

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A new set of IPCC Emissions Scenarios (SRES Scenarios )
Institut für Küstenforschung I f K A world of rapid economic growth and rapid introduction of new and more efficient technology. A very heterogeneous world with an emphasis on family values and local traditions. A world of “dematerialization” and introduction of clean technologies. A world with an emphasis on local solutions to Economic and environmental sustainability. “ business as usual ” scenario (1992). A1 A2 B1 B2 IS92a

I f K Scenario A2 Annual temperature changes [°C] (2071–2100) –(1961–1990) Scenario B2 Danmarks Meteorologiske Institut

I f K Consistency of regional change in precipitation in different climate model scenarios. (consistency: 7 out of 9 scenarios agree)

forecast 1 day in advance Institut für Küstenforschung I f K Prediction of air pressure field over North America observed state after 1 day

forecast 3 days in advance Institut für Küstenforschung I f K observed state after 3 days

forecast 10 days in advance Institut für Küstenforschung I f K observed state after 10 days

Models for reduction of complex systems
Institut für Küstenforschung I f K Models for reduction of complex systems identification of significant, small subsystems and key processes often derived semi–empirically constitutes “understanding”, i.e. theory construction of hypotheses characteristics: simplicity idealisation conceptualisation fundamental science approach

I f K Energy balance at the surface of Earth (W/m²)

I f K Idealized energy balance

Kurzwellige Langwellige Ausstrahlung Erdoberfläche
Institut für Küstenforschung I f K Kurzwellige Einstrahlung Langwellige Ausstrahlung E b E a A Substanzen (1–b) E A (1–a) A Erdoberfläche Ausstrahlung A = ksT 4 Balance erfordert (1–b) E = a A daher, bei reduzierter „Durchlässigkeit“ a a   A   T 

Conclusions „Models“ can be very different species
Institut für Küstenforschung I f K Conclusions „Models“ can be very different species The different species have different functional properties, namely understanding and detailed simulation. Quasi-realistic models are the only option for making “experiments” with the environment (incl. climate) and forecasts of unprecedented changes. Such models can hardly be verified. Their credit comes from their consistency with physical theory. For further reading, refer to: von Storch, H., S. Güss und M. Heimann, 1999: Das Klimasystem und seine Modellierung. Eine Einführung. Springer Verlag ISBN , 255 pp and: Stehr, N., und H. von Storch, 1999: Wetter, Klima, Mensch. Beck Verlag München, ISBN , 128 pp.

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