1 / 18

Climate Modeling Basics

Climate Modeling Basics. Michael Winton 19 September 2007 NOAA/GFDL. Six Basic Questions. What is a global climate model? How do we use them? Why do we believe them? What do they agree on? Why do they disagree? How do we improve them?. What is a global climate model?.

moton
Download Presentation

Climate Modeling Basics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Climate Modeling Basics Michael Winton 19 September 2007 NOAA/GFDL

  2. Six Basic Questions • What is a global climate model? • How do we use them? • Why do we believe them? • What do they agree on? • Why do they disagree? • How do we improve them?

  3. What is a global climate model? A GCM is a mathematical representation of the major climate system components and their interactions. The GCM equations operate on a global grid and are solved on a computer. Atmosphere Land Ocean Ice Physical CM Concentrations of radiatively active species Emissions of radiatively active species ESM* *Earth System Model

  4. GCM evolution

  5. GCM components: Atmosphere • Radiation • Winds • Water cycle (vapor, clouds, precipitation) • Chemistry Atmosphere Land Ocean Ice

  6. GCM components: Land • Surface characteristics • Snow cover • Soil water, rivers • Carbon components Atmosphere Land Ocean Ice

  7. GCM Components: Ocean • Currents and mixing • Biogeochemistry • Main climate system heat and carbon store Atmosphere Land Ocean Ice

  8. GCM components: Ice • Sea Ice – surface reflectivity, ocean freshwater forcing • Ice sheets and shelves – sea level, ocean freshwater forcing (currently offline) Atmosphere Land Ocean Ice

  9. Components cast on global grids

  10. Simulated vs. Parameterized • Simulated processes: larger than grid-scale, based on bedrock scientific principles (conservation of energy, mass and momentum). Example: storms. • Parameterized processes: smaller than grid scale, formulations guided by physical principles but also make use of observational data. Example: clouds.

  11. How do we use GCMs? • Diagnostic: current climate, last glacial maximum • Detection and Attribution: role of anthropogenic forcing in 20th century climate change • Prognostic: • 21st century scenarios • decadal prediction • seasonal/interannual

  12. How do we use GCMs?Role in the policy process Emissions Scenarios Impacts/Adaptations Analysis Climate Simulations Cost-Benefit Analysis Mitigation • Climate modeling is essential for optimal decision-making • Climate model disagreement is responsible for part of the uncertainty • Climate modeling informs but does not prescribe policy

  13. Why do we believe GCMs? • Based on well-founded physical principles. • Extensively checked by a large community of modelers and analysts • Accurate simulations of current and past large-scale climates • Accurate hindcast of 20th century climate change including ocean heat content

  14. What do the GCMs agree on? • Temperatures will rise • Precipitation will change • Sea level will rise • Arctic sea ice will decrease

  15. Why do GCMs disagree? • Forcings are different: e.g. aerosols • Feedbacks are different: e.g. clouds • Natural variability: but we can reduce this with ensemble of simulations Radiative Forcings (CO2, aerosols, …) Natural Varaibility Climate Feedbacks (water vapor, clouds, …)

  16. How do we improve GCMs? • Improve completeness: addition of new processes, more comprehensive forcing • Improve correctness: compare to observations, better theory, reformulate • Improve resolution: climate simulation advances as increased computing power allows better resolution of previously resolved processes and resolution of previously parameterized processes.

  17. GFDL’s Climate Modeling Effort • Past: first and foremost (Manabe era) • Present: one of a handful of leading centers worldwide, one of the best climate simulations • Diverse and deep pool of climate modeling expertise built up over many years • State-of-the art climate modeling at GFDL depends upon the availability of state-of-the art computational resources

  18. Where is world-class GCM work done?

More Related