Climate models and open source software

Andy Pitman and Steven PhippsClimate Change Research Centre

University of New South Wales

Background

• The Earth’s climate is changing

Background

260-280 ppmv over10,000 years

385 ppmv – increasedfrom 280 in ~100 years

Temperature

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

20052006

20072008

How do we know ?

• Observations– radiation changes– temperature changes– pressure, humidity, acidity etc

• Basic theory

• Backs of envelopes … and

• Climate models

Climate models

• Mathematical representations of– Atmosphere– Ocean– Terrestrial surface– Cryosphere– Fluxes of energy, mass and carbon between

these systems

Climate ModellingGoverning equations

Forcing conditions

Initial conditions Model

output

Three-DimensionalClimate Models(GCM)

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

Climate models work

Rainfall [annual]

Which is observed and which is modelled ?

Climate models

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

Model Nationality Open source ?BCC China

BCCR Norway

CCSM USA

CGCM Canada

CNRM France

CSIRO Aus

ECHAM Germany

ECHO-G Germany

FGOALS China

GFDL USA

GISS USA

INM Russia

MIROC Japan

MRI Japan

PCM USA

UKMO UK

Model Nationality Open source ?BCC China

BCCR Norway

CCSM USA

CGCM Canada

CNRM France

CSIRO Aus

ECHAM Germany

ECHO-G Germany

FGOALS China

GFDL USA

GISS USA

INM Russia

MIROC Japan

MRI Japan

PCM USA

UKMO UK

Model Nationality Open source ?BCC China

BCCR Norway

CCSM USA

CGCM Canada

CNRM France

CSIRO Aus Via license, never latest versionECHAM Germany

ECHO-G Germany

FGOALS China

GFDL USA

GISS USA

INM Russia

MIROC Japan

MRI Japan

PCM USA

UKMO UK Via license, never latest version

Model Nationality Open source ?BCC China

BCCR Norway

CCSM USA

CGCM Canada

CNRM France

CSIRO Aus Via license, never latest versionECHAM Germany

ECHO-G Germany A variant may be availableFGOALS China

GFDL USA A variant may be availableGISS USA

INM Russia

MIROC Japan

MRI Japan

PCM USA

UKMO UK Via license, never latest version

Model Nationality Open source ?BCC China

BCCR Norway

CCSM USA Yes – fully accessibleCGCM Canada

CNRM France

CSIRO Aus Via license, never latest versionECHAM Germany

ECHO-G Germany A variant may be availableFGOALS China

GFDL USA A variant may be availableGISS USA Yes – fully accessibleINM Russia

MIROC Japan

MRI Japan

PCM USA

UKMO UK Via license, never latest version

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

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 ?

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

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?

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

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

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

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