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Februar 2003 Workshop Kopenhagen 1
Assessing the uncertainties in regional climate predictions of the 20th and 21th
century
Andreas Hense
Meteorologisches Institut
Universität Bonn
Februar 2003 Workshop Kopenhagen 2
Overview
• The problem– Climate system and climate models as random
systems• The consequences of randomness
– Estimation of randomness at various levels– Predictability of forced climate variations – Comparison of simulations with observations
• The conclusions
Februar 2003 Workshop Kopenhagen 4
The problem: the climate system as a random system
• Due to the high dimensionality ~ 10 32 degrees of freedom: statistical physics
• Due to the nonlinearities in the atmosphere, ocean and the interactions: dynamical systems theory
Februar 2003 Workshop Kopenhagen 5
The problem continued: climate models as random systems
• Due to high dimensionality ~ 10 8 degrees of freedom
• Due to nonlinearities in the model atmospheres, oceans and interactions
• Due to parametrized subgrid scale processes („clouds, rain, convection etc..“)
• Due to model errors
Februar 2003 Workshop Kopenhagen 6
The consequences: Estimation of randomness
• From the real climate system– one observation / realisation available
• randomness has to be modelled– e.g. assuming ergodicity, probabilities by
„counting“, frequentist‘s approach– bayesian approach, modelling by probability
densities• ... more at the end
Februar 2003 Workshop Kopenhagen 7
The consequences: Estimation of randomness
• In models by Monte Carlo simulations, sampling the uncertainties in initial conditions, parameters, models Initial conditions
Februar 2003 Workshop Kopenhagen 9
The consequences: predictability of forced climate variations
• Forced variations: Greenhouse gases, solar forcing, volcanoes
• overlaid by random variations– in models – in reality
• Forced variations > random variations ?– Predictability of the 2nd kind– In models Analysis-of-Variance– on specified space and time scales
Februar 2003 Workshop Kopenhagen 14
The consequences: comparison of simulations with observations, Bayesian
Classification (Attribution)
Februar 2003 Workshop Kopenhagen 15
A Bayesian attribution experiment
• ECHAM3/LSG 1880-1979 Control• ECHAM3/LSG in 2000 Scenario• NCEP Reanalysis Data 1958-1999 Observations• Northern hemisphere area averages
– near surface (2m) Temperature– 70 hPa Temperature
• joint work with Seung-Ki Min, Heiko Paeth and Won-Tae Kwon
Februar 2003 Workshop Kopenhagen 17
Conclusions
• Inherent uncertainty in the climate system – due to the chaotic nature – strong dependance on space and time scales and
type of variable– annual temperature on a regional scale ~ 70%
predictable– annual sum of precipitation on a regional scale
~ 20%– decadal sum of precipiation ~ 70%
Februar 2003 Workshop Kopenhagen 18
Conclusion
• Uncertainty introduced by model errors are large on the regional scale
• Uncertainty introduced by randomized parametrizations not yet explored
• Despite of all uncertainties climate change signals on the global / hemispheric scale can be detected
• Uncertainty has to be quantified as additional input for impact studies, „meta-information“
• scales in space, time and variable have to be selected from the discipline