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Accuracy Requirements
for Climate Change
GSICS Meeting
William and Mary Universithy
Williamsburg, VA, March 4, 2013
Bruce Wielicki
NASA Langley Research Center
Hampton, Va
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The Three Laws of Climate Change
Accuracy
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The Three Laws of Climate Change
Accuracy, Accuracy
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The Three Laws of Climate Change
Accuracy, Accuracy, Accuracy
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Decadal Survey defines CLARREO
NOAA CLARREO
• CERES (Clouds and Earth’s Radiative
Energy System)
• TSIS (Total Solar Irradiance Sensor)
NASA CLARREO
• New accuracy for climate change
• Solar reflected spectra: SI traceable
relative uncertainty of 0.3% (k=2)
• Infrared emitted spectra: SI traceable
uncertainty of 0.1K (k=3)
• Global Navigational Satellite System
Radio Occultation: SI traceable
uncertainty of 0.1K (k=3).
• Three 90 degree orbits for diurnal cycle
sampling
CLARREO is a Cornerstone of the Climate Observing System
Mission Concept Review 17Nov10
NASA Internal Use Only
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Decadal Change Climate Science
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Examples of Key Climate Change Observations
Blue = CLARREO Solar Reflected Spectra Science
Red = CLARREO IR spectra & GNSS-RO Science
Earth's
Climate
- Greenhouse Gases
- Surface Albedo
- Temperature
- Water Vapor
- Clouds
- Radiation
- Snow/Ice Cover
Cloud Feedback
Water Vapor/Lapse Rate Feedback
Snow/Ice Albedo Feedback
Roe and Baker, 2007
50% of CLARREO Science Value is in Reflected Solar Spectra
50% of CLARREO Science Value is in Infrared Spectra & GNSS-RO
100% of CLARREO Science Value is in the Accuracy of the Data
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Feedbacks Space/Time Sampling Requirements
Temperature Feedback
Water Vapor Feedback
Global Mean = -4.2 W/m2/K
Global Mean = 1.9 W/m2/K
Albedo Feedback
Cloud Feedback
Land and ocean zonal
annual means
required for
temperature lapse
rate and water
vapor feedbacks,
surface albedo
feedbacks
1000 km regional
scale required for
cloud feedbacks
Global Mean = 0.30 W/m2/K
Global Mean = 0.79 W/m2/K
Multi-model ensemble-mean maps of the temperature, water
vapor, albedo, and cloud feedback, computed using climate
response patterns from the IPCC AR4 models and the GFDL
radiative kernels
Soden et al. 2008
Seasonal cycle
required for
reflected solar:
cloud feedback,
snow/ice albedo
feedback
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Determining the Accuracy of Decadal Change Trends
and Time to Detect Trends
• A perfect climate observing system is limited in trend accuracy only by
climate system natural variability (e.g. ENSO) (Leroy et al, 2008).
• Degradation of accuracy of an actual climate observing system relative to a
perfect one (fractional error Fa in accuracy) is given by:
Fa = (1 + f 2i)1/2 - 1 , where f 2i =  2i i /  2var var
for linear trends where s is standard deviation,  is autocorrelation time, var
is natural variability, and i is one of the CLARREO error sources.
• Degradation of the time to detect climate trends relative to a perfect observing
system (fractional error in detection time Ft) is similarly given by:
Ft = (1 + f 2i)1/3 – 1
Degradation in time to detect trends is only ⅔ of degradation in accuracy.
Provides an integrated error budget across all decadal change error sources
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Decadal Change Trends
• The absolute accuracy of climate change observations is required only at
large time and space scales such as zonal annual, not at instantaneous field
of view. Therefore all errors in climate change observation error budgets are
determined over many 1000s of observations: never 1, or even a few.
• Climate change requirements can be very different than a typical NASA Earth
Science process mission interested in retrievals at instantaneous fields of
view at high space/time resolution, where instrument noise issues may
dominate instantaneous retrievals
• So what accuracy relative to a perfect observing system is needed?
Requirements focus on long term climate change
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Infrared Accuracy and Climate Trends
IPCC next few decades
temperature trends:
0.16C to 0.34C varying
with climate sensitivity
An uncertainty of half the
magnitude of the trend
is ~ 0.1C. Achieved
15 years earlier with
CLARREO accuracy.
Length of Observed Trend
High accuracy is critical to more rapid understanding of climate change
LaRC/GSFC Meeting Nov 16, 2012
NASA internal Use Only
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Accuracy and Climate Trends
Climate Sensitivity Uncertainty
is a factor of 3 (IPCC) which =
a factor of 9 uncertainty in climate
change economic impacts
Climate Sensitivity Uncertainty =
Cloud Feedback Uncertainty =
Low Cloud Feedback =
Changes in SW CRF/decade
(y-axis of figure)
Higher Accuracy Observations =
CLARREO reference intercal of
CERES = narrowed uncertainty
15 to 20 years earlier
High accuracy is critical to more rapid understanding of climate change
LaRC/GSFC Meeting Nov 16, 2012
NASA internal Use Only
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Decadal Change Reference Intercalibration Benchmarks:
Tracing Mission Requirements
Climate Model
Predicted
Decadal Change
Natural Variability
Natural Variability
Observed
Decadal Change
VIIRS/CrIS/CERES
L3 Time Series
Stable
Orbit Sampling
VIIRS/CrIS/CERES
L3 Time Series
Sampling
Uncertainty
Sampling
Uncertainty
VIIRS/CrIS/CERES
L2 Variable Data
Stable Retreival
Algorithms & Orbit
VIIRS/CrIS/CERES
L2 Variable Data
Retrieval
Uncertainty
Retrieval
Uncertainty
VIIRS/CrIS/CERES
L1B Data
Stable Operational
Instrument Design
VIIRS/CrIS/CERES
L1B Data
GSICS
InterCalibration
Uncertainty
GSICS
InterCalibration
Uncertainty
CLARREO
L1B Data
Stable CLARREO
Instrument Design
CLARREO
L1B Data
Pre & Post Launch
Calibration
Uncertainty
Pre & Post Launch
Calibration
Uncertainty
SI
Standard
DECADE 1
Stable
SI Standard
SI
Standard
DECADE 2
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Science Instruments
Infrared (IR) Instrument
•
•
•
•
Fourier Transform Spectrometer
Systematic error less than 0.1K (k=3)
200 – 2000 cm-1 contiguous spectral
coverage
0.5 cm-1 unapodized spectral resolution
17 km nadir FOV
• Mass: 74.8 Kg
• Power: 124 W
Reflected Solar (RS) Instrument
•
•
•
•
Two Grating Spectrometers
Gimbal-mounted (2-axis)
Systematic error less than 0.3% (k=2) of earth
mean reflectance
320 – 2300 nm contiguous spectral coverage
4 nm sampling, 8 nm res
0.5 km nadir FOV, ~ 100 km swath
• Total Mass: 53.2 Kg
• Total Power: 96 W
Small Instruments, Higher Accuracy, On-board Calibration Traceability
CLARREO ISS Mission Concept
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Calibration Reference Spectrometers (IR/RS)
for Global Climate, Weather, Land, Ocean satellite instruments
Provide spectral, angle,
space, and time
matched orbit crossing
observations for all leo
and geo orbits critical
to support reference
intercalibration
Endorsed by WMO &
GSICS (letter to
Freilich)
Calibrate Leo and Geo
instruments: e.g.
- JPSS: VIIRS, CrIS,
CERES
- METOP: IASI, AVHRR
- Landsat, etc land imagers
- Ocean color sensors
- GOES imagers/sounders
CLARREO Provides "NIST in Orbit": Transfer Spectrometers to SI Standards
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Summary
• A perfect climate observing system is limited in trend accuracy only by
climate system natural variability: actual observations further degrade climate
model tests and observations of anthropogenic climate change.
• Absolute SI traceable accuracy on orbit is critical to move beyond stability
assumptions and to eliminate the large effect of data gaps
• 0.3% (k=2) requirement for the solar spectrum
• 0.07K (k=2) requirement for the infrared spectrum
• These achieve climate change accuracy within 20% of perfect observations
• These achieve climate change detection within 14% of perfect observations
• GSICS plus CLARREO can achieve these levels of accuracy for the complete
range of reflected solar and infrared earth observations from LEO & GEO
• For further details, see the CLARREO overview paper accepted for
publication in BAMS: Wielicki et al., 2013, and included references.
The Three Laws of Climate Change: Accuracy, Accuracy, Accuracy
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CLARREO Presentations
• Reflected Solar (RS) Spectrometer Accuracy
Thome et al.
• CLARREO Reference RS Intercal: Polarization
Lukashin/Sun
• CLARREO Reference RS Intercal: Sampling
Lukashin et al.
• CLARREO Infrared (IR) Spectrometer Accuracy
Mlynczak et al.
• CLARREO Reference IR Intercalibation
Tobin et al.
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Backup Slides
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Economic Value of Climate Science
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Accuracy and Climate Trends
Climate Sensitivity Uncertainty
is a factor of 3 (IPCC) which =
a factor of 9 uncertainty in climate
change economic impacts
Climate Sensitivity Uncertainty =
Cloud Feedback Uncertainty =
Low Cloud Feedback =
Changes in SW CRF/decade
(y-axis of figure)
Higher Accuracy Observations =
CLARREO reference intercal of
CERES = narrowed uncertainty
15 to 20 years earlier
High accuracy is critical to more rapid understanding of climate change
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Value of Information (VOI)
Calculation
Worked with Roger Cooke, RFF
IPCC lead author, chapter on
economic impacts
• Current IPCC factor of 3 uncertainty in climate sensitivity =
factor of 32 = factor of 9 uncertainty in economic impacts
VOI Calculation
Assumptions
• Discount rate = 3%
• Climate Sensitivity = IPCC (2007) uncertainty distribution
2205
• SCC = $209 T
2015
• BAU emissions
Baseline
VOI Calculation
Assumptions
• Discount rate = 3%
• Climate Sensitivity = IPCC (2007) uncertainty distribution
• Decision Trigger in 2055
2205
2055
• SCC = $209 T
Switch to Reduced
Emissions
2015
2205
• BAU emissions
SCC = $65 T
Current Observing System
VOI Calculation
Assumptions
• Discount rate = 3%
• Climate Sensitivity = IPCC (2007) uncertainty distribution
• Decision Trigger in 2035
2035
Switch to Reduced
Emissions
2205
• SCC = $209 T
2015
• BAU emissions
2205
SCC = $53 T
Improved Accuracy Observing System (2020 launch)
Improved accuracy yields savings of $11.7 T in net present value
Value of Information Parameters
Decision Context
Trigger Variable
T/decade
CRF/decade
Trigger Value
0.2C or 0.3C/decade
3C for 2X CO2
Confidence Level
80%, 95%
80%, 95%
Launch Date
2020, 2025, 2030
2020, 2025, 2030
Trigger Policy Change
DICE Optimal, Aggressive
DICE Optimal, Aggressive
Discount Rate
2.5%, 3%, 5%
2.5%, 3%, 5%
Aerosol Forcing Obs
Start Date = CLARREO
Start Date = CLARREO
Run 1000s of Monte Carlo cases with:
- Full pdf of climate sensitivity uncertainty in IPCC fit to Roe and Baker (2007)
- Gaussian climate natural variability as specified in the CLARREO BAMS article
for global mean temperature and SW cloud radiative forcing.
Results are the ensemble mean of the 1000s of Monte Carlo Simulations
How Sensitive are Results to Assumptions?
Parameter Change
CLARREO/Improved
Climate Observations
VOI (Trillion US 2015
dollars, NPV)
3% discount rate
Baseline (blue values)
$11.7 T
BAU => AER
$9.8 T
0.3C/decade trigger
$14.4 T
2030 launch
$9.1 T
• Delaying launch by 10 years reduces benefit by $2.6 T
• Each year of delay we lose $260B of benefits
Value of Information Summary
Discount Rate
VOI for
CLARREO/Impro
ved Climate
Observations
Cost of 30 yrs of
improved
full climate
observing
system (4X
current effort)
Payback Ratio
VOI / Obs
Improvement
Cost
2.5%
$17.6 T
$260B
65
3%
$11.7 T
$245B
45
5%
$3.1 T
$200B
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• All economic values in Net Present Value (NPV) in 2015 U.S. dollars
• Even with the most pessimistic discount rate, the return on
investment is large: factors of 15 to 65.
Science Value Matrix Concept
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Why a Science Value Matrix?
• Science is a cost/value proposition with uncertainty in both costs and value
– Cost can be determined with ~ 30% uncertainty and is always addressed
– Science value or priority for mission elements of design are rarely addressed, but
could be and often should be
• CLARREO has developed a new science value matrix concept to assist in:
– Understanding cost/value
– Understanding robustness of mission options
– Understanding how one aspect of the mission (e.g. instrument accuracy) relates
to others (science goals, climate record length, orbit sampling, instrument noise)
– Understanding the impact of baseline vs threshold mission
– Optimizing the mission design for cost/schedule/risk
– Eliminating mission requirements "creep"
– Communicating the mission design trades to NASA HQ
– Moving the CLARREO science team discussions from "I feel" or "I think" or "I'm
sure" to more quantitative basis on mission requirements
– Improving and quantifying communication between scientists and engineers
A Science Value Matrix is a valuable tool to optimize mission design
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Science Value Metrics
• Science Value of a Science Objective =
Science Impact * Trend Accuracy * (Record Length)0.5 * Verification * Risk
• Science Impact
– Uniqueness of CLARREO contribution
– Importance of science objective to reducing climate change uncertainties
• Accuracy
– Accuracy in decadal change trends for a given record length
• Climate Record Length
– Sqrt(record length) reduction in noise from natural variability
• Verification
– SI traceable calibration verification
– Independent instruments, analysis, observations (CCSP chapter 12, metrology)
• Risk
– Technological, budget, schedule, flexibility of mission options
Instrument Absolute Accuracy set for < 20% Trend Accuracy Degradation
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Original Decadal Survey Mission:
IR/IR/RO, IR/IR/RO, 2 year gap, IR/IR/RS/RS/RO
Original Decadal Survey Mission defined as 100% science value
LaRC/GSFC Meeting Nov 16, 2012
NASA internal Use Only
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CLARREO Mission Options
Mission
% of CLARREO
MCR Baseline
Mission Science
Mission Cost
Estimate
($RYM)
Decadal Survey Concept (2007)
(11 instruments, 4 spacecraft, 4
launches)
112%
~ $1.6B
Launches 2017, 2019
MCR Baseline Mission Concept
(6 instruments, 4 smaller
spacecraft or 2 larger)
100%
$800 - $1000
+ Launch Vehicle(s)
Launches 2018, 2020
MCR Minimum Mission Concept
(3 instruments, 1 spacecraft,
e.g. DAC-4 free flyer)
62%
$675 - $750
+ Launch Vehicle
Launch 2021
ISS Mission Concept
(2 instruments on ISS, RO is
obtained from COSMIC-2)
73%
$340 - $390
cost includes launch
EV-2 ISS full cost guidelines
Cost estimates are full mission cost in real year dollars.
For MCR baseline and minimum mission, launch vehicle not included
ISS is highest science value/cost
LaRC/GSFC Meeting Nov 16, 2012
NASA internal Use Only
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