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Climate Models

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Climate Models

  1. 1. SMILE Workshop, Aug. 2, 2021 Climate Models Andreas Schmittner Oregon State University
  2. 2. Textbook
  3. 3. Hierarchy of Climate Models • 0D Energy Balance Model (EBM) • 1D EBM • 1D Radiative-Convective Models • Intermediate Complexity Models (e.g. 2D EBMs) • 3D General Circulation Models (GCMs) Increasing Complexity
  4. 4. Climate Models Equations based on conservation of • mass • momentum • energy • water • carbon • ... Equations are solved in each of the grid boxes of the model. Typically global climate models have about 20-30 layers in the atmosphere and about the same amount in the ocean. The horizontal grid box size varies from about 5 degrees (500 km) to about 1 degree (100 km) or less. Models with smaller grid box sizes r e s o l v e m o r e d e t a i l s ( h i g h e r resolution), but they are also more computationally expensive to run.
  5. 5. Interactive Components Included • Atmosphere • Ocean • Sea Ice • Land Surface (sometimes with interactive vegetation) • Ocean Biology and Chemistry (e.g. Carbon, Nutrient, and Oxygen Cycles) • (Ice Sheets, usually prescribed) Models that include biogeochemistry are also often called Earth System Models
  6. 6. Parameterizations • Processes that cannot be resolved (smaller than grid box size need to be expressed in terms of resolved quantities; often empirical formulas) • Examples are clouds, convection (atmosphere), and mixing (ocean)
  7. 7. Forcings • Models are driven by boundary conditions, e.g. incident solar radiation at the top-of-the-atmosphere, surface properties (albedo), changes in atmospheric CO2 • Interior is solved without the use of observations
  8. 8. Model Evaluation Models are tested by comparing results to observations.
  9. 9. What are climate models used for? • Paleoclimate Studies How did climate change in the past and why? • Detection and Attribution Is climate changing signi fi cantly and if so why? • Projections How may climate change in the future?
  10. 10. High-Resolution Climate Model 1024x512 grid points (30 km) Water vapor
  11. 11. Global Climate Model Grid Box Size ~ 1 degree NS x 1 degree EW
  12. 12. Sheehan et al. 2015 Vegetation Type 4 km grid vegetation & fi re model Fire Frequency West of the Cascades fi re frequency increases from ~80 yr recurrence times in 20th century to ~27 yr in 21st century Coast Range forests shift from conifer to more fi re resistant mixed forests. No fi re suppression
  13. 13. Thank You!