AnnouncementsAll recent lab quizzes up front

Makeup for all labs is next week (April 22 and 24) –

Please e-mail me and remind me if you need to make up a lab; bring

documentation

The “quiz” for this week’s lab = take home assignment

Intergovernmental Panel on Climate Change (IPCC)

• All countries that are members of UN can have scientists participate

• Scientists from many areas of expertise:– Read scientific literature (papers) – Compile and analyze the data– Make future predictions of climate change

IPCC Reports

1990 First Assessment Report (FAR)

1996 Second Assessment Report (SAR)

2001 Third Assessment Report (TAR)

2007 Fourth Assessment Report (AR4)

Today we will look at results from 2007 (average change) and 2001 (Sphere models)

Predicted Average Global Temperature Change

• From 2007 IPCC report

• Red, green, blue are three different model results

• This is averaged over the entire Earth!

Global Circulation Models (GCMs)

• How are GCMs made?

• Should you believe everything that comes out of a computer?

• Results– Average global temperature increase– Regional temperature changes

Global Circulation Models (GCMs)

• Are physical climate models• Based on our understanding of physics,

chemistry, biology of different parts of climate

• 3 different models today – made by 3 different groups of scientists for IPCC– GFDL – CCSM – UKMET

Running a GCM model

IPCC Models: Step 1 Input

• Forcings: things that are going to change climate

Human activity

IPCC models: Step 1 Input

• Greenhouse gases, including human input– Increase to 720 ppm CO2 by 2080

– Pre-industrial: 280 ppm CO2

– Today: 380 ppm CO2

• Sulfate aerosol concentrations and volcanic aerosols

• Changes in sunlight reaching Earth

• Changes in ozone

Running a GCM model

IPCC Models: Step 2 Climate Simulation

• Internal interactions

Human activity

Structure of a General Circulation Model

• Each subsystem modeled separately

• Link subsystems together with a “coupler” program– Example: interaction

between atmosphere and oceans

http://www.ccsm.ucar.edu/models/ccsm3.0/

veg

Running a GCM model

IPCC Models: Step 3 Results

• Internal responses

Human activity Temperature

Model Resolution

• See more detail with higher resolution!

• But higher resolution takes more computer power

Higher resolution

(Smaller block size)

Lower resolution

(Larger block size)

GCM resolution

Vertical Layers

• Split oceans, land, atmosphere into blocks

• Grid: size of blocks• Grids are different

sizes in different models

• Grids are not always uniform (different block sizes)

Example of a grid at the surface of the ocean

1 degree longitude isn’t same distance everywhere

http://academic.brooklyn.cuny.edu/geology/leveson/core/linksa/lat_long.html

Numerical problems with poles!

• The distance between longitude grid spacing goes to zero at poles

• Computers can’t handle this

• Models deal with this for oceans by shifting the entire grid (North Pole on a continent) or by inventing a new land mass!

http://academic.brooklyn.cuny.edu/geology/leveson/core/linksa/lat_long.html

Change the grid

http://climate.lanl.gov/Models/POP/images/tripolegrid.jpg

To the sphere!

Is the computer model right?

1. Different models by different groups should give similar results

2. Higher resolution should give better results

3. The results of the model should not be influenced by the way the model is constructed

Is the computer model right?

• Must make assumptions

• Don’t understand everything about physics and chemistry of climate

• Difference between reality and possibility

• Should we follow the model’s predictions even if they might not come true?