Climate Models: Everything You Ever Wanted

to Know, Ask, and TeachRandy Russell andLisa Gardiner

Spark – science education at NCAR

All materials from this workshop(including movies) areavailable online at:

spark.ucar.edu/workshops

NSTA National - Boston, April 2014

National Center for Atmospheric Researchin Boulder, Colorado

Workshop Overview

• Climate model components• Resolution activity• Systems Game• The Very, Very Simple Climate

Model• Climate/Carbon Bathtub

Using Models in Education

“Essentially, all models are wrong,but some models are useful.”

- George E. P. Box (1951)

Evolution of Climate Models

Credit: Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4): Working Group 1: Chapter 1, page 99, Fig. 1.2

Climate Model Components

Credit: UCAR (Paul Grabhorn)

Resolution: What Does It Mean?

Improving Resolution of Climate Models

Credit: Warren Washington, NCAR

Grid Cell Sizes

• 1990s (T42)• 200 x 300 km• 120 x 180 miles

• 2000s (T85)• 100 x 150 km• 60 x 90 miles

Improving Resolution of Climate Models

Credit: Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4): Working Group 1: Chapter 1, page 113, Fig. 1.4

Vertical Resolution of Climate Models

Vertical Layers

• 1990s• 10 layer atmosphere• 1 layer “slab” ocean

• 2000s• 30 layer atmosphere• 30 layer ocean

Credit: UCAR

Horizontal and Vertical Grid

Horizontal and Vertical Grid

Hexagonal Grid and Sub-grids

Credit: UCAR (Lisa Gardiner)

Resolution: Spatial & Temporal (Time)• Timesteps can be a few minutes to 12 hours or

more• Durations can be hours to centuries

40 km resolution in 1-D model

20 km resolution in 1-D model

10 km resolution in 1-D model

40 km resolution in 2-D model

20 km resolution in 2-D model

10 km resolution in 2-D model

Resolution and Computing Power

Double resolution – increase number of nodes – more calculations!

One Dimension

Two Dimensions

2 times as many nodes

4 times as many nodes

Resolution and Computing PowerWhat if we increase model to three dimensions (space) plus time?

Resolution and Computing PowerWhat if we increase model to three dimensions (space) plus time?

16 times as many nodes – 16x computing power required!

This is why we need supercomputers!

Weather vs Climate Models

Why do we think we can make meaningful 100 year climate projections when we can’t forecast the day-to-day weather a month from now?

Weather Model vs Climate ModelCompare and Contrast

Differences (and similarities) betweenWeather vs. Climate Models

• Area Covered (scale)• Resolution – distance (spatial) and time (temporal)

• Timespan covered by model runs• Impacts on computing resources needed, time required to run models

Weather Model vs Climate ModelArea Covered

Weather Model – up to about continental size scale

Climate Model – global size scale

Larger area requires either more computing power/time or lower resolution (spatial and/or temporal)

Weather Model vs Climate ModelResolution and Precision

Weather Model• resolution typically about 3-10 km• timesteps of hourly to 6 hours, forecast for next 3-4 days

Climate Models• resolutions from about 25-30 km up to 100 (or a couple

hundred) km• running computer models can take days or weeks, which

would be impractical for weather models

Precision – why Wx forecast for Christmas is suspect, but temperature next July is reliable (relationship to chaos)

Weather Model vs Climate Model

Timeframe

Weather Forecast – hours to days(up to about 10 days)

Climate Projection – decades to centuries or longer(climate is usually defined as at least 30 years of observations)

Source: Meehl et al NCAR

spark.ucar.edu/sites/default/files/SystemInMotionMaster.pdf

Greenhouse Effect Review

CO2 absorbs heat in the atmosphere

When heat accumulates in the Earth system, the average global temperature rises

Increased CO2 & the Greenhouse Effect When the amount of carbon dioxide in the atmosphere

increases,

average global temperature rises. Longwave radiation emitted by CO2 is absorbed by the

surface,

so average global temperature rises

Emissions -> More CO2 in Air -> Higher Temperature

15°

18°

Climate Sensitivity - definitionWhenever the amount of carbon dioxide in the

atmosphere doubles, average global temperature rises by 3 degrees Celsius.

15°

18°

15°

18°

Learning from the Past (ice cores)

Ice ageIce ageIce ageIce age

CO2 Emissions – Where are we now?

In 2014, CO2 emissions are around 10 gigatons (GtC) per year (10,000 million tons in units used on this graph)

CO2 in Atmosphere – Where are we now?

iceage

iceage ice

age

iceage

396 ppm in 2013

For hundreds of thousands of years, CO2 varied between 180 and 280 parts per million, beating in time with ice ages

Since the Industrial Revolution, CO2 has risen very rapidly to about 400 ppm today

Math of Climate SensitivityWhen the CO2 concentration in the atmosphere doubles,temperature rises by 3°Celsius (about 5.4°F)

Examples: If CO2 rises from 200 ppmv to 400 ppmv,

temperature rises 3°C If CO2 rises from 400 ppmv to 800

ppmv,

temperature rises 3°C Note: as CO2 rises from 200 to 800

ppmv

(800 = 4 x 200),

temperature rises 6°C

( = 2 x 3 degrees, not 4 x 3 degrees)

Climate Sensitivity Calculator demo

spark.ucar.edu/climate-sensitivity-calculator

Climate Sensitivity Calculator Activity

Use the calculator (previous slide) to determine the expected temperature for the various CO2 concentrations listed in column 1 of the table above (students fill in column 2); then have them graph.

Advanced Climate Sensitivity Math

T = T0 + S log2 (C / C0)

T : new/current temperatureT0 : reference temperature (e.g. 13.7 degrees C in 1820)S : climate Sensitivity (3 degrees C)C : new/current atmospheric CO2 concentrationC0 : reference atmospheric CO2 concentration (e.g. 280 ppmv in 1820)

Example:

What is new temperature if CO2 rises to 400 ppmv (from 280 ppmv)?

T = T0 + S log2 (C / C0) = 13.7 + 3 log2 (400/280) = 13.7 + 3 log2 1.43 = 13.7 + 1.54 = 15.2 degrees C

Dry air mass of atmosphere = 5.135 x 1018 kg = 5,135,000 GigatonsCO2 currently about 599 ppm by mass (395 ppmv) = 0.0599%CO2 current mass = 0.0599% x 5,135,000 Gt = 3,076 GtCO2 current emissions = 9.5 GtC/yearAtmospheric fraction = 45%

M = M0 + [0.45 x (3.67 x m)] = 3,076 GtCO2 + [0.45 x (3.67 x 9.5 GtC/yr)] = 3,076 + 15.7 GtCO2 = 3,092 GtCO2

CO2 concentration = 3,092/5,135,000 = 602 ppm by massCO2 concentration = (602/599) x 395 ppmv = 397 ppmv

Math of CO2 Emissions andAtmospheric Concentration

(16 + 12 + 16) / 12

= 44/12 = 3.67

GtC vs GtCO2

Poll: Rising Emissions

B

A

C

?

?

?

Poll: Rising Emissions

B

A

C

?

?

?

B

A

C

?

?

?

Poll: Emissions rise then steady

B

A

C

?

?

?

Poll: Emissions rise then fall

Very Simple Climate Model demo

spark.ucar.edu/simple-climate-model

Why does temperature continue to rise as emission rate declines?

Atmosphere

CO2 in Atmosphere

CO2

Emissions

CO2 Removal byOceans & Plants

spark.ucar.edu/climate-bathtub-model-animations-flow-rate-rises-fallsspark.ucar.edu/imagecontent/carbon-cycle-diagram-doe

Please fill out session evaluations!

ALL Workshop Materialsare Available Online at:

spark.ucar.edu/workshops