introduction to coupled climate modelling
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Introduction to coupled climate modelling. Andy Pitman. Outline. What is it What can you do What can’t you do What opportunities exist with Mk3L ? Assuming you want papers in top journals like Climate Dynamics and J. Climate. background:. - PowerPoint PPT PresentationTRANSCRIPT
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Introduction to coupled climate modelling
Andy Pitman
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Outline
• What is it
• What can you do
• What can’t you do
• What opportunities exist with Mk3L ?
• Assuming you want papers in top journals like Climate Dynamics and J. Climate.
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background:
• Climate models are how we project the future of the Earth’s climate
• They are different from Earth System models – Mk3 is a climate system model, not an Earth System Model
• It is absolutely not an EMIC
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Climate models work …
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Climate models work …
• Most of the time.
• All models are not equally good, and no one model is best.
• No single measure of model performance presently exists [though we are working on it]
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Climate models work
• stunningly well at large spatial scales [continental to global]
• Superbly on long time scales [seasonal to multi-annual averages] [they do not all capture all modes of variability equally well]
• For prognostic and diagnostic quantities
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Climate models work
Isotherms show temperature, colours show error
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Climate models work
Rainfall [annual]
Which is observed and which is modelled ?
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Climate models work
• Adequately at regional scales [say averages over >9 grid squares]
• For prognostic and diagnostic quantities
• but be very very careful:
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Most climate models work
Or at least, some models work
40% error
30-50% error
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Most climate models work
Or at least, some models work
25% error40% error
30-50% error
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Climate models work
Climate models are not equal …
observedobserved
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Climate models work
Though perhaps don’t look too close
MAM precip over eastern Pacific
obs
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Bad, does not matter
Bad &matters Good and matters
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Climate models work
• Unreliably at local scales
• Increasingly unreliably at monthly – daily scales
• Combining these to look at fine resolution and short time scales requires – (a) great care;– (b) close contact with model developers
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• Don’t use the models blindly – work with a “real” climate modeller !
• Evaluate for your specific purpose
• climate modellers do not assert that the models are reliable below continental scales [IPCC, 2001, Chapter 8]
• they remain are our best tool …
Climate models work
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CSIRO Mk3L
• Personal view – do not use this model for this:
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Personal view – don’t use it for this
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What should we use it for?
Lat Lon levels Total
4 x 7 40 48 5 9600
3.3 x 5.6 54 64 10 3584
2.8 x 2.8 64 128 15 122880
1.25 x 1.25 144 288 30 1244160
You can run 35 of the 3.3 x 5.6 model for one run of the 2.8 x 2.8
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What should we use it for?
• For multi-realization experiments
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What should we use it for?
• For multi-realization experiments – why ?
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What should we use it for
Models do not agree … but physics or chaos ?
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… sensitivity of adding new processes [nitrogen]
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What should we use it for?
• Understanding abrupt change
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Summary
• In my view, if you want to explore regionally-specific issues, with a state of the art climate model, build links to groups that run such a model [CSIRO Mk3, CCAM or wait for ACCESS]
• This is not what the CSIRO-Mk3L is for
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Summary
• A cheap coupled climate model is not to be used as if it were an expensive high resolution model
• You must design experiments in full understanding of the strengths and weaknesses of the “L” in CSIRO Mk3L
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Summary
• Weaknesses:– Poorer regional skill– Poorer signal-noise ratio from local perturbations
• Strengths– Capacity to run “n” realizations where “n” might be 10,
20, 50 …– Use it for uncerainty analysis, estimation of probability– Use it to build and test parameterization
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Summary
• CSIRO Mk3L is a low resolution coupled climate model
• Its weaknesses can be overcome by careful experimental design
• If you are not a climate modeller seek advice on design - from a “real” climate modeller – someone who builds rather than uses them
• Then do innovative science like Manabe, Staniforth, Murphy etc and bask in the glory of Nature and Science papers