Transcript Lecture 11: Climate Modeling

METR112-Climate Modeling
•Basic concepts of climate Modeling
•Components and parameterization in the model
•sensitivity of the model
past
Present
future
How can you know the future
climate and climate change?
Climate Model is the most important approach!
time
climate models are used to predict the future change
Source: Fig. 10.4 of IPCC AR4 chapter 10
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.
Model components
Models can range from relatively simple to quite comprehensive.
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?
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 I
n red and cold currents are shown in blue.
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.
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
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
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 feedback
Before deforestation
wind,
weight
After deforestation
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_modelin
g.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)
RCM
1. Coverage:
2. Model resolution:
for selected region,
finer resolution,
1 km-10km
3. Model components are different
GCM
for the globe
coarse resolution
60-250km, or larger
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
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
Video: How Climate Model Works?
1. http://www.met.sjsu.edu/metr112videos/MET%20112%20Video%20LibraryMP4/climate%20modeling/