The evolution of climate modeling

Kevin Hennessy

on behalf of CSIRO & the Bureau of Meteorology

Tuesday 30th September 2003 Canberra Short course

& Climate Science Workshop10 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

New components developed and tested separately, then coupled in the model

and tested again

Land surface

Ocean Ocean

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 time-

steps 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

Mark 3 grid

Mark 2 grid

Facilitated by improved computing power and optimised programming

Improved simulation of El Nino Southern Oscillation

Observed sea surface temperature anomaly

CSIRO Mark 2 model

CSIRO Mark 3 model

Model hierarchy

Global climate model(grid: 180 km by 180 km)

Regional climate model(grid: e.g. 70 km by 70 km)

Regional climate model(grid: e.g. 14 km by 14 km)

Statistical downscaling(local sites: e.g. Perth)

PC software, e.g. MAGICC, OzClim

Complex Simple

CSIRO’s stretched grid model (CCAM)

Effective resolution of 70 km over Australia

Observed

Rainfall over Australia

CSIRO Mark 3 climate model ~ 180 km grid

CSIRO CCAM ~ 70 km grid

Summer Autumn Lots of room for improvement!

The future • Need enhanced super-computer resources to facilitate

ongoing model development and evaluation• Further improvement of model components:

– 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 softwareDatabase 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