METR112-Climate Modeling

•Basic concepts of climate Modeling •Components and parameterization in the model•sensitivity of the model

How can you know the future climate and climate change?

Climate Model is the most important approach!

Present futurepast time

climate models are used to predict the future change

Source: Fig. 10.4 of IPCC AR4 chapter 10

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.

Definition

Model components

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” questionsfor 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?

Climate system

http://www.usgcrp.gov/usgcrp/Library/nationalassessment/overviewtools.htm

Atmosphere: composition

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

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

Atmosphere: energy budget

(Kiehl and trenberth 1997)

Atmosphere: general circulation

•Hadley cell•Trade wind•Westerlies•ITCZ•Subtropical high•Strom track region•Polar Hadley cell

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

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 In red and cold currents are shown in blue.

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.

Role of ocean surface currents

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 exchangeAlbedoTopography forced momentum change

•Human impact directly change the land surfaceRelease of CO2 and other GHGsRelease of AerosolChange the Land surface coverUHI effect

Land: aerosols Aerosol: the small particles in the atmosphere which varying in size, chemical composition, temporal and spatial distribution and life timeSource: volcano eruptions, wind lifting of dust, biomass burning, vegetationNew result and great uncertainty of the effect of aerosol on climate

Small aerosol reflect back the solar radiationLarge aerosol can block longwave radiation

Land: Land cover/Landuse changes

Land-cover changes alter• surface albedo and

emissivity• water uptake by roots• leaf area index• canopy interception

capacity• etc

Land-cover changes enhance ice-albedo feedbackBefore deforestation

After deforestation

wind,weight

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 programshttp://stommel.tamu.edu/~baum/climate_modeling.html

Model grid

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

Differences between Regional Climate Model (RCM) and Global Climate Model (GCM)

1. Coverage: for selected region, for the globe2. Model resolution: finer resolution, coarse resolution

1 km-10km 60-250km, or larger

3. Model components are different

RCM GCM

http://www.usgcrp.gov/usgcrp/images/ocp2003/ocpfy2003-fig3-4.htm

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

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

Model uncertainty

Video: How Climate Model Works?

1. http://www.met.sjsu.edu/metr112-videos/MET%20112%20Video%20Library-MP4/climate%20modeling/