Download What is a climate model?

The evolution of climate
modeling
Kevin Hennessy
on behalf of
CSIRO & the Bureau of Meteorology
Tuesday 30th September 2003
Canberra Short course
& Climate Science Workshop
10 September 2003
Outline
• Need for climate models
• What is a climate model?
• Model evolution
• Model hierarchy
• The future
Need for climate models
• The complexity of climate system means we can’t
simply extrapolate observed trends to predict the
future
• Climate models are the best tools we have for
forecasting daily weather, seasonal climate (over the
next 3-12 months) and climate change over the
coming decades
• Models provide insight to causes of past climate
change and exploration of future scenarios, such as
different greenhouse gas or aerosol emissions
Global warming scenarios
Range of uncertainty is due to the range of future
greenhouse gas and aerosol emissions and the range of
global warming responses from 7 different climate models
Need for climate models
• Climate model output is used for regional impact
assessments, e.g. climate change impact studies for
industry, government and the IPCC
• The credibility of forecasts depends critically on the
quality of output from climate models, so
demonstrating and improving the reliability of climate
models is important
• Australia has the only substantial modeling program
in the Southern Hemisphere. We place more scrutiny
on processes and ecosystems that are unique to our
region, compared with other modeling groups that
have northern hemisphere priorities
What is a climate model?
A simplified mathematical representation of the Earth’s climate system
Four main components: the atmosphere, the land surface and biosphere, the
oceans and polar ice
Ability to simulate the climate system depends on our understanding of
physical, chemical and biological processes, e.g. clouds, currents, radiation
This understanding has improved over time, along with computer power and
our ability to represent the processes in computer models
Model evolution
1956: Phillips’ model
• 2-dimensional grid of points in a 2-level slice of the atmosphere
• uniform land surface, no ocean or sea-ice
1965: Smagorinsky’s model
• 3-dimensional atmospheric model with moisture and clouds for the
northern hemisphere
• 9 levels in the vertical direction
• 500 km between points in the horizontal direction
• uniform land surface, no ocean or sea-ice
• a 300-day simulation
1969: Manabe and Bryan’s model
• 3-dimensional global model with moisture and clouds
• 9 levels in the atmosphere
• uniform land surface with 5 levels in the ocean but no sea-ice
• 500 km between grid-points and simplified geography
• a one-year simulation took 50 days of computer time
Land surface
Ocean
Ocean
New components
developed and tested
separately, then
coupled in the model
and tested again
IPCC 2001
Model evolution
2003: CSIRO Mark 3 model
• 3-dimensional global model
• 18 levels in atmosphere
• 31 levels in ocean including sea-ice
• 6 soil levels, 9 soil types, 13 vegetation types
• 3 snow levels
• 180 km between grid-points (100 km in tropics to better
simulate El Nino)
• Data for 100 climate variables computed in 30-minute timesteps for a series of months, years decades or centuries
• Models adequately simulate observed daily weather and
average climate patterns
• A one-year simulation takes 1 day of computer time
CSIRO Mark 3 climate model
Temperature (oC)
CSIRO climate model grids
Facilitated by improved computing power and optimised programming
Mark 2 grid
Mark 3 grid
Improved simulation of El Nino
Southern Oscillation
Observed sea
surface temperature
anomaly
CSIRO Mark 2
model
CSIRO Mark 3
model
Model hierarchy
Complex
Simple
Global climate model
PC software, e.g.
MAGICC, OzClim
(grid: 180 km by 180 km)
Regional climate model
(grid: e.g. 70 km by 70 km)
Regional climate model Statistical downscaling
(grid: e.g. 14 km by 14 km)
(local sites: e.g. Perth)
CSIRO’s stretched grid model
(CCAM)
Effective resolution of 70 km over Australia
Rainfall over Australia
Summer
Observed DJF rainfall
Autumn
Observed MAM rainfall
Lots of room for
improvement!
Observed
Mark 3 DJF rainfall
Mark 3 MAM rainfall
CSIRO Mark 3
climate model
CCAM/Mark 3 DJF rainfall
CCAM/Mark 3 MAM rainfall
~ 180 km grid
CSIRO CCAM
~ 70 km grid
The future
• Need enhanced super-computer resources to facilitate
ongoing model development and evaluation
• Further improvement of model components:
–
–
–
–
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interactive terrestrial biosphere
oceanic biogeochemical & carbon cycle
sea level rise
surface hydrology, aerosols and clouds
variability, predictability, extreme events, e.g. El Nino and
tropical cyclones
• Perform a range of policy-relevant climate change
simulations, e.g. effect of stabilizing CO2
concentrations in 100 years
The future
• 20th century climate simulations with different forcing
factors (e.g. solar variations, volcanic eruptions, ozone
depletion, greenhouse gases, aerosols) required for
detection & attribution of observed climate change
• Further development of CSIRO’s stretched grid model,
including a coupled ocean, for improved regional input
to downscaling techniques
• Further development of fine resolution models for
better simulating extreme events like cyclones and hail
• Complementary development of statistical
downscaling techniques for site-specific data
• Further development of OzClim PC software
OzClim PC software
Database includes:
Observed and simulated
monthly-average data on
25 km grid
10 climate models
6 IPCC emission
scenarios
3 climate sensitivities
9 climate variables
Functions:
Plot maps and global
warming curves
Save regional average
data
Run simple impact models