climate models: everything you ever wanted to know, ask, and teach
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Climate Models: Everything You Ever Wanted to Know, Ask, and Teach. Randy Russell and Lisa Gardiner Spark – science education at NCAR All materials from this workshop (including movies) are available online at: spark.ucar.edu/workshops. NSTA National - Boston, April 2014. - PowerPoint PPT PresentationTRANSCRIPT
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
ageiceage
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
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Poll: Rising Emissions
B
A
C
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B
A
C
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Poll: Emissions rise then steady
B
A
C
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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