METR112-Climate Modeling

1. METR112-Climate Modeling • Basic concepts of climate Modeling • Components and parameterization in the model • sensitivity of the model

2. time past future Present How can you know the future climate and climate change? Climate Model is the most important approach!

3. climate models are used to predict the future change Source: Fig. 10.4 of IPCC AR4 chapter 10

4. Definition Climate Model (per NASA Earth Observatory Glossary http://earthobservatory.nasa.gov/Library/glossary.php3?mode=alpha&seg=b&segend=d ) A quantitative way of representing the interactions of the atmosphere, oceans, land surface, and ice. Models can range from relatively simple to quite comprehensive. Model components

5. Climate Model: • Equations believed to represent the physical, chemical, and biological • processes governing the climate system for the scale of interest It can answer “What If” questions for example, what would the climate be if CO2 is doubled? what would the climate be if Greenland ice is all melt? what………………………..if Amazon forest is gone? what…………………………if SF bay area population is doubled?

6. Climate system http://www.usgcrp.gov/usgcrp/Library/nationalassessment/overviewtools.htm

7. Atmosphere: composition Even though with small percentage, trace gases such as CO2 and water vapor act as very important gas composition in the atmosphere

8. Atmosphere: vertical structure Troposphere: where most weather processes take place Note: the height of tropopause is not the same everywhere. The tropopause is lower in high latitude than in tropics

9. Atmosphere: energy budget (Kiehl and trenberth 1997)

10. Atmosphere: general circulation • Hadley cell • Trade wind • Westerlies • ITCZ • Subtropical high • Strom track region • Polar Hadley cell

11. Ocean: critical roles in climate system Physical properties and role in climate: • The biggest water resource on earth • Low albedo  excellent absorber of solar radiation • One of the primary heat sources for atmosphere • High heat capacity  reduces the magnitude of seasonal cycle of atmosphere • Important polarward energy transport • Large reservoir for chemical elements for atmosphere

12. Ocean: surface currents – the gyres http://www.windows.ucar.edu/tour/link=/earth/Water/images/Surface_currents_jpg_image.html • Wind derived • Coriolis force and location of land affect current pattern • Clockwise in NH, anticlockwise in SH The water of the ocean surface moves in a regular pattern called surface ocean currents. The currents are named. In this map, warm currents are shown I n red and cold currents are shown in blue.

13. Role of ocean surface currents Surface ocean currents carry heat from place to place in the Earth system. This affects regional climates. The Sun warms water at the equator more than it does at the high latitude polar regions. The heat travels in surface currents to higher latitudes. A current that brings warmth into a high latitude region will make that region’s climate less chilly.

14. Land: where most human impact are applied • Lower boundary of 30% of earth surface lower heat capacity than ocean • Higher variability in interaction with atmosphere than ocean surface • Moisture exchange • Albedo • Topography forced momentum change • Human impact directly change the land surface • Release of CO2 and other GHGs • Release of Aerosol • Change the Land surface cover • UHI effect

15. Land: aerosols Aerosol: the small particles in the atmosphere which varying in size, chemical composition, temporal and spatial distribution and life time Source: volcano eruptions, wind lifting of dust, biomass burning, vegetation New result and great uncertainty of the effect of aerosol on climate Small aerosol reflect back the solar radiation Large aerosol can block longwave radiation

16. Land: Land cover/Landuse changes • Land-cover changes alter • surface albedo and emissivity • water uptake by roots • leaf area index • canopy interception capacity • etc

17. Land-cover changes enhance ice-albedofeedback Before deforestation wind, weight After deforestation

18. General climate model • Atmospheric GCM is first used in 1950s to predict short-time future weather • GCM develops and performs continuously improving since then with helps from updating computational resources and better understanding of atmospheric dynamics • A list of GCM and climate modeling programs • http://stommel.tamu.edu/~baum/climate_modeling.html Model grid

19. Regional climate model • The first generation of regional climate model is developed by Dickinson et.al (1989) and Giorgi et. al (1990) due to the coarse resolution of GCM not able to resolve local process • Second generation of RCM (RegCM2) is developed in NCAR (Giorgi et al. 1993) based on MM5 and improved boundary layer parameterizations • Third generation of RCM (RegCM3) (Pal et al. 2007) is developed with various improvements in dynamics and physical parameterizations

20. Differences between Regional Climate Model (RCM) and Global Climate Model (GCM) RCM GCM • Coverage: for selected region, for the globe • Model resolution: finer resolution, coarse resolution • 1 km-10km 60-250km, or larger • 3. Model components are different

21. The past, present and future of climate models During the last 25 years, different components are added to the climate model to better represent our climate system http://www.usgcrp.gov/usgcrp/images/ocp2003/ocpfy2003-fig3-4.htm

22. Model uncertainty Model has uncertainty because model (equations) are based on our current understanding of the climate system. But our understanding needs to improve Verify the predictions and statistics of predictions Compatibility with observations Various simulations to assure the agreement with basic theoretical understanding

23. Video: How Climate Model Works? 1. http://www.met.sjsu.edu/metr112-videos/MET%20112%20Video%20Library-MP4/climate%20modeling/