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Climate models and open source software

Climate models and open source software. Andy Pitman and Steven Phipps Climate Change Research Centre University of New South Wales. Background. The Earth’s climate is changing. Background. 385 ppmv – increased from 280 in ~100 years. 260-280 ppmv over 10,000 years. Temperature.

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Climate models and open source software

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  1. Climate models and open source software Andy Pitman and Steven Phipps Climate Change Research Centre University of New South Wales

  2. Background • The Earth’s climate is changing

  3. Background 385 ppmv – increased from 280 in ~100 years 260-280 ppmv over 10,000 years

  4. Temperature • Continued greenhouse gas emissions at or above current rates would cause further warming - very likely larger than those observed during the 20th century. 2008 2007 2006 2005

  5. How do we know ? • Observations • radiation changes • temperature changes • pressure, humidity, acidity etc • Basic theory • Backs of envelopes … and • Climate models

  6. Climate models • Mathematical representations of • Atmosphere • Ocean • Terrestrial surface • Cryosphere • Fluxes of energy, mass and carbon between these systems

  7. Climate Modelling Governing equations Forcing conditions Initial conditions Model output

  8. Three-Dimensional Climate Models (GCM)

  9. Climate models • ~300 x 300 km grid • ~20 vertical levels in atmosphere, 30 in ocean • 300,000 grid points • Solves basic dynamics equations, parameterizes physics • Solve all equations with a ~15 minute timestep for 200 year integrations • Something like 2 x 1018 calculations per run

  10. Climate models work Rainfall [annual] Which is observed and which is modelled ?

  11. Climate models

  12. Climate models • Written in Fortran • Mainly f95 or f90, some f77 • best language [efficiency and safety] • python, c, other wraps • Mostly written by scientists not software engineers • Cannot [usefully] re-write in other languages • Run on NCI, or similarly large systems – main rationale for a Pflop system in Australia • Generate ~5 Tb per run. Data sets now > 1 Pbyte

  13. Why ? • Not resourced or requested to provide this code in suitable standard • Costs of supporting open source • hardware compatibility • complier variability, • user support problems • Code maintenance • Dispute resolution/managing expectation • It’s a myth that climate modeling groups are well resourced … • Many climate models are variants of forecasting systems – commercial value

  14. Why ? • Groups sometimes associated with defense departments • Culture • Fear of inappropriate use • IP concerns • Unwillingness to be exposed to independent evaluation • Strategic issues with best models • Why would you provide open source ?

  15. So why open source? • Bugs per 1000 lines of code: • Commercial software: • ~1-7 [Jones, 2000] • ~20-30 [CyLab, 2004] • Open source software: • 0.17 [Linux kernel, Coverity, 2004] • 0.434 [open source projects, Coverity, 2006] • So open source more reliable; better

  16. So why open source? • A state of the art climate model has: • ~1 million lines of code • a software development lifecycle that lacks: • external testing, • comprehensive internal testing • error checking. • Analagous to commercial software? • contains ~1000-30,000 bugs?

  17. So why open source? • National Institute of Standards & Technology, USA, 2002 • software errors cost US economy US$59.5 billion/yr • Despite industry practice of spending 80% of development costs on identifying and correcting faults • Most modeling groups would not have one person dedicated to identifying and correcting faults • An open source climate model has a community dedicated to identifying and correcting faults

  18. The climate model challenge • More components • Longer simulations • Finer spatial and temporal resolution • Serious computational challenges • 6 months to port to new computer system • Super computer time valuable

  19. What I want … • model test plans with pre-defined performance • Software developers know how … • Code developed in a F95 via subversion • You are welcome to try • Simple and elegant scripting • Suggestions welcomed • Tools to slice and dice netCDF • Talk to the modelers – embed in R • Enhancements to openDAP … • Implementation of agreed coding standards

  20. Summary • Climate models have been developed over 20 years – with IT systems engineers in some cases • Few are open source – those that are were commonly developed with IT engineers • Hard to contribute – cannot ad hoc – little low hanging fruit • But a commitment in this area can be an invaluable contribution over time. Needs to be based on a dialog with the modelers

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