The art of climate modeling

1. The art of climate modeling David Noone, Phil Rasch, Natalie Mahowald NCAR ASP Colloquium, June 2006

2. This talk • Motivation for the colloquium • Overview of the next two weeks • Few details on tutorials and projects Things you must do by the end of today • Project group and topic • Computer ready for today’s tutorial: • your laptop works (X-windows/ssh) • your accounts work (cryptocards)

3. Many thanks to… • Folks at NCAR Advanced Study Program (ASP)Kathleen Barney, Scott Briggs, Paula Fisher, Maura Hagen • TutorsChristine Shields, Dani Coleman, Keith Lindsay, Dave Bailey, Sam Levis • HelpersMatt Rothstein, Rich Neale, and Tutors • Lecturers for donating their time and effort to visit Boulder

4. Monday Tuesday Wednesday Thursday Friday 89° F|56° F 32° C|13° C 91° F|55° F 33° C|13° C 86° F|52° F 30° C|11° C 88° F|52° F 31° C|11° C 86° F|52° F 30° C|11° C Partly Cloudy Partly Cloudy Partly Cloudy Chance of T-storms 20% chance of precipitation Chance of T-storms 20% chance of precipitation Welcome to Boulder Boulder is at 5430 feet a.s.l. (1655 m) (NCAR Mesa Lab is 280 m higher) Sunny and dry: drink lots of water, use lots of sunscreen (especially if going on hikes) Climate 4 June: Ave High: 75 FAve Low: 50 F Record High: 94 F (1990) Record Low: 38 F (1951) May hotter than 57 year mean (76 F vs 72F, 8th hottest) May drier than 57 year mean (29 mm vs 77 mm, 5th driest) Is this climate change?

5. Observed temperature(Instrumental record) Greenhouse gases, aerosols, solar variability, volcanoes, ocean circulation patterns… Climate is not just temperature IPCC, TAR

6. Climate signals in proxy records Etheridge et al. CO2 in bubbles from Law Dome ice core Climate signals seen in even the smallest parts of the climate system Temperature based on rings Mann et al. “Hockey Stick”

7. Correlation is not causality! Not necessarily understanding. Quantify and demonstrate knowledge by modeling.

8. Expected 2100 (ppm) Not just global warming, but understanding the coupled system Today (365 ppm) Forcing &response External and internal

9. What is a model?(Key ingredients) • State variables – what quantifies “climate” • Rules that govern changes • Conservation rules(energy, momentum, mass – often define state) • Diagnostics (output) • Choices: what processes are important, which aspects can be ignored, how much complexity/detail. This choice is art. • Ideally, measure of error or uncertainty • Also, method for validation. Is there a model prediction that can be tested with observations?

10. Climate system models Atmosphere (momentum, temperature, mass, humidity) Atmospheric chemistry Terrestrial biology Sea ice Land surface Ocean biology Ocean chemistry Ocean(momentum, temperature, salinity, mass) CCSM is structured more-or-less like this.

11. "Several sciences are often necessary to form the groundwork of a single art" - Mills, 1843 • "Science is knowledge which we understand so well that we can teach it to a computer; and if we don't fully understand something it is an art to deal with it" - Knuth, 1974

12. Models vs. data Both anthropogenic and natural forcing (e.g., solar and volcanic aerosol) are required to explain historical changes Model allows hypothesis testing. But does the match mean the model is correct?

13. Projecting climate change Temperature Emissions • Uncertainty about human decisions • Uncertainty in physical feedbacks and coupled behavior • Uncoupled response may be “simple”, but coupled response may not. • Processes that couple often non-linear, and can be subtle. CO2 IPCC, TAR

14. Objectives for the colloquium • Explore coupled climate problems • Develop sense of what models can do to help • Have a working knowledge of parts of a climate model and the theoretical basis for those parts • Understand limitations of models, and how construct a research methodology that exploits model strengths • Understand limitations, and what would be needed to improve models • At end of 2 weeks, you should be able to use and modify CCSM for your own research – thesis and beyond. • No exams, no grades. Just the science and learning. The more you put in the more you get out. • Ask lots of questions

15. Notes on agenda • Lectures - 2 or 3 per dayThis week: Intro to coupled models, atmosphere, ocean, land and sea iceNext week more focused on climate system. • Tutorials – one each day this weekAimed to develop skills needed to run CCSM.Today: Building and running CCSM, navigating supercomputers. Then atmosphere, ocean, sea ice, land focus. • Projects – start today! (And will be the focus of lab time next week) Each day has combinations of the three.

16. Projects • This is the primary task for the two weeks, and should be given you fullest attention. • Projects are your (group’s) work • Open ended, unlikely to be an known “answer”(How will you know if model experiments work?) • Mentors are there to be a resource and will help guide scope of projects, but definition and refinement of project topics and tasks are yours • Presentation of project outcome next Friday. • Planning:Today, 5 minutes presentation by mentors. • By the end of lunch, you need to submit your top 3 preferences for projects. • At 4 pm we will meet in project groups to discuss details of: a) project title and aim (report back to group)b) type of experiments to runc) ideally, an outline plan for how to proceed • Note scope of projects limited to experiments that can be done with the order of 10 year model simulations. • Meet daily with mentors during office hours, plus some longer discussions in the agenda

17. Tutorials Build, run, analyze, modify the model input/output, modify the model Fortran code. Develop skills to help with project work, and for your thesis work! • Today – Intro to CCSM (3 hours, Christine Shields) • Tuesday – Atmosphere focus (2 hours, Dani Coleman) • Wednesday – Ocean focus (1 hour, Keith Lindsay) • Thursday – Sea ice focus (1 hour, Dave Bailey) • Friday – Land focus (1 hour, Sam Levis) Tutorial assignments and some NCL scripts are on the wiki.

18. Lectures • Range of topics on climate system modeling by experts gathered from around the US. • This week, aimed to introduce coupled models by focusing on each part of the CCSM, and science problems typical with each component. • Next week, broader “climate system” • Plenty of time after lectures for discussion. • Lecturers will be around for at least a few days – feel free to quiz them on any related topics. They may have useful suggestions on your project! • Typically in the morning and after lunch.

19. Community Climate System Model(CCSM) • Atmosphere (CAM) • Ocean (POP) • Land (CLM) • Sea ice (CSIM) • As users of CCSM, please be considerate of the science others have invested/are investing in code • Also, when using computers, be mindful of resource use and other users (this group, and all other users)

20. Notes on logistics • Challenging workshop • Hopefully all important resources on wiki (notes, tutorials, …) http://atoc.colorado.edu/~dcn/ACM • Any logistical problems ask David, Natalie or Phil (who will probably direct you to Scott Briggs or Kathleen Barney) • Computer problems ask tutors, tutorial/project helpers, or Scott. Mentors may also know. • Meals in NCAR cafeteria (just downstairs), and coffee breaks in Damon room. • Lots of details on ASP web site:http://www.asp.ucar.edu/colloquium/2006/climate-model/logistics.jsp

21. All work no play? • Dinner together tonight • Movie night tomorrow • B.B.Q. at Phil’s house Saturday(transportation details to come) • Weekend to explore Boulder area • Plenty great science can be done on hikes around NCAR at lunchtime!

22. Reminder 1If you using your laptop, please check that it works before the tutorial. i.e., during lunchtime or at 1 pm. • Reminder 2Be sure you can log on to the supercomputers using your cryptocard