The document discusses the concept of an international reference network for greenhouse gases. It provides context on existing reference networks for essential climate variables and greenhouse gases. NOAA's Global Greenhouse Gas Reference Network is overviewed as an example, noting both its successes and challenges. Key considerations for developing an international greenhouse gas reference network are outlined, including benefits like improved data quality and preservation of knowledge, as well as potential pitfalls like increased overhead. The network could help distinguish highest quality records and support satellite measurements.

1. Towards an International
Reference Network for
Greenhouse Gases
Arlyn Andrews1, Andrew Crotwell1,2, Ed Dlugokencky1, Kirk Thoning1, Colm
Sweeney1, John B. Miller1, Kathryn McKain1,2, Gabrielle Pétron1,2, Bradley Hall1,
Steve Montzka1, James W. Elkins1, Dale Hurst1,2, Pieter Tans1
1NOAA Global Monitoring Laboratory, Boulder, Colorado
2Cooperative Institute for Research in Environmental Sciences, University of
Colorado
ICOS Science Conference
15-17 September 2020

2. Outline
• What is a reference network and why is this a timely concept for the
international greenhouse gas research community?
• Overview of NOAA’s Global Greenhouse Gas Reference Network
• Considerations for an international GHG Reference Network

3. International Context
GCOS Essential Climate Variables &
Established Reference Networks

4. The ten basic principles (in paraphrased form) were adopted by the Conference of the Parties (COP)
to the United Nations Framework Convention on Climate Change (UNFCCC) through decision 5/CP.5
at COP-5 in November 1999. This complete set of principles was adopted by the Congress of the
World Meteorological Organization (WMO) through Resolution 9 (Cg-XIV) in May 2003; agreed by the
Committee on Earth Observation Satellites (CEOS) at its 17th Plenary in November 2003; and adopted
by COP through decision 11/CP.9 at COP-9 in December 2003.
• Note there are 10 basic principles and 10 additional principles specific to satellite systems
https://gcos.wmo.int/en/essential-climate-variables/about/gcos-monitoring-principles

5. 1. The impact of new systems or changes to existing systems should be assessed prior to implementation.
2. A suitable period of overlap for new and old observing systems is required.
3. The details and history of local conditions, instruments, operating procedures, data processing algorithms
and other factors pertinent to interpreting data (i.e., metadata) should be documented and treated with the
same care as the data themselves.
4. The quality and homogeneity of data should be regularly assessed as a part of routine operations.
5. Consideration of the needs for environmental and climate-monitoring products and assessments, such as
IPCC assessments, should be integrated into national, regional and global observing priorities.
6. Operation of historically-uninterrupted stations and observing systems should be maintained.
7. High priority for additional observations should be focused on data-poor regions, poorly observed
parameters, regions sensitive to change, and key measurements with inadequate temporal resolution.
8. Long-term requirements, including appropriate sampling frequencies, should be specified to network
designers, operators and instrument engineers at the outset of system design and implementation.
9. The conversion of research observing systems to long-term operations in a carefully-planned manner should
be promoted.
10.Data management systems that facilitate access, use and interpretation of data and products should be
included as essential elements of climate monitoring systems.

6. GCOS Essential Climate Variables
https://gcos.wmo.int/en/essential-climate-variables

7. GCOS Essential Climate Variables
https://gcos.wmo.int/en/essential-climate-variables

8. https://gcos.wmo.int/en/ecv-review-2020

9. https://gcos.wmo.int/en/ecv-review-2020

10. Existing Reference Networks
The Global Climate Observing System (GCOS) Reference
Upper-Air Network (GRUAN) is an international reference
observing network, designed to fill an important gap in the
current global observing system. GRUAN measurements will
provide long-term, high-quality climate data records from the
surface, through the troposphere, and into the stratosphere.
These will be used to determine trends, constrain and
calibrate data from more spatially‐comprehensive observing
systems (including satellites and current radiosonde
networks), and provide appropriate data for studying
atmospheric processes.
Sites must be “certified” and data is centrally processed.
"reference quality" means that a data product:
• is traceable to an accepted standard (generally to the SI unit)
• provides a comprehensive uncertainty analysis.
• is properly documented (e.g. in peer-reviewed publications)
and validated (e.g. through inter-comparisons).https://www.gruan.org/

11. Existing Reference Networks
The vision of the USCRN program is to provide
a continuous series of climate observations for
monitoring trends in the nation's climate and
supporting climate-impact research.
• Triple sensor redundancy for air temperature,
precipitation, and soil moisture and
temperature to produce the highest quality
climate data possible.
• The USCRN adheres to the Global Climate
Observing System’s Climate Monitoring
Principles as recommended by the National
Research Council (NRC 1999).
• Operated by National Centers for
Environmental Information in partnership with
NOAA Air Resources Laboratory.
https://www.ncdc.noaa.gov/crn/
U.S. Climate Reference Network

12. Why is the concept of an International GHG Reference Network timely?
• Increasing urgency and recognition of the climate problem.
• Proliferation of satellite and remote sensing retrievals with significant and
insufficiently characterized systematic biases.
• A well-designed reference network is needed to anchor satellite products
and enable reliable bias-correction.
• Emerging urban sensor networks.
• Use of low-cost sensors with large uncertainties and systematic biases.
• Challenges with representativity even when high-quality sensors are used.
• Impending major WMO CO2 scale revision will require reprocessing/scale
conversion of existing records.
• Comprehensive documentation of traceability will be needed to optimally
correct historical data.

13. Overview of NOAA’s Global Greenhouse
Gas Reference Network

14. e
NOAA’s Global Greenhouse Gas Reference Network
• The term reference network is intended to emphasize data quality and traceability
compared to satellite retrievals and to lesser quality in situ measurements.
• We are not claiming to be the Global Greenhouse Gas Reference Network, we acknowledge
that improvements to our program are needed, and we are eager to partner with ICOS and
other institutions to build an International GGGRN.
• Cross-laboratory among the WMO Global Greenhouse Gas Measurement Techniques
community are critical for tracking data compatibility, and cross-method comparisons are
needed to diagnose systematic errors.
Aircraft
Surface Continuous
Tower
Observatory
Surface Discrete
e

15. 2005 2015
• Growth of surface network has exceeded expectations: > 90 sites in 2015/2016
• Several US and state agencies have supported short-term sampling or regional
monitoring, but not all records are linked to WMO calibration scales and not all
have long-term funding
surface continuous
tall tower (>100m)
Continuous CO2 monitoring in North America

16. 2018:
140 sites
Data Providers
In Situ:
• NOAA
• Environment and Climate Change Canada
• Penn State University
• NCAR
• Oregon State University
• Lawrence Berkeley National Lab
• Earth Networks
• California Air Resources Board
• Harvard University
• University of Minnesota
• Scripps
• NASA JPL
• NEON
Remote Sensing:
• TCCON
• GOSAT
• OCO-2
Establishing comparability among datasets is
crucial for flux estimation and trend detection.
Which of these sites provide reference quality
data?
US National Ecological
Observatory Network (NEON)
-short towers with eddy
covariance data and
calibrated CO2

17. • Need to clarify which datasets are part of GGGRN (sites, time periods, species)
• Some sites start in a research and development mode and protocols evolve over time before
stabilizing (e.g. tall tower systems, early CRDS implementation, CO2 in N2 standards)
• Data sometimes extend beyond the calibrated range (e.g., nighttime data at low intake heights prior
to expansion of WMO-scale, fires or anomalous events)
• Artifacts in flask datasets
• Humidity dependent bias affecting substantial fraction of tower and aircraft flask samples
• New bias correction for CO2 and N2O at sites with long storage times (Antarctic sites)
• Significant revision of the WMO CO2 Scale coming soon (X2007 -> X2019). Successful transition will
require improved documentation of traceability to WMO primaries. Impacts NOAA GGGRN and all
partners/customers using WMO CO2 standards.
• Recent progress toward fully automated in situ CO2/CH4/CO/H2O measurements on regional
commercial aircraft. Contract in place to begin routine flights over Africa. No in-flight calibrations.
We will rely on pre-deployment and post-deployment analyzer response curves and water-
sensitivity characterization.
Examples of NOAA GGGRN challenges and successes:

18. Considerations for an International
GHG Reference Network

19. • The need for international reference networks has been recognized for water vapor and
meteorological parameters but not for GHGs.
• Satellite measurements of CO2 and CH4 alone cannot provide useful estimates of surface emissions
and removals. Small systematic errors confound flux estimation.
• Many of the GCOS principles are already accepted and used by ICOS, NOAA and throughout the
GAW GGMT community.
• Shortfalls are primarily due to resource limitations and logistical challenges.
• The reference network concept provides a framework to promote national and international
commitment to long-term high quality records crucial for climate research and decision
support.
• Not all existing GHG records are of equal quality.
• There is a clear need to distinguish true reference records from non-reference quality records.
• NOAA and ICOS could collaborate to develop protocols for consistent uncertainty reporting and
compatible data archiving to comprehensively and publicly document traceability to enable
future data reprocessing (e.g. when the WMO scale is updated or when uncertainty or bias-
correction algorithms are improved).
Some observations:

20. • Creation of a comprehensively-documented record of anthropogenic greenhouse gases
• Well-defined certification criteria and accountability will improve measurement quality
• Preservation of institutional knowledge
• Users will be able to easily identify highest quality records
• Opportunity to promote research-quality monitoring
Some benefits of an international reference network:
• Continued innovation will be needed. Measurement methods should not be frozen.
• Scientists must continue to directly oversee measurement quality and participate in
analysis/application of the data.
• Increased overhead and potential for bureaucratic creep.
• Certification and accountability requirement could be daunting. Community support
will be needed for new and under-resourced contributors.
Potential pitfalls:

21. GOSAT
2009 …
OCO-2
2014 …
Sentinel 5p
2018 …
GOSAT-2
2018… 2019
OCO-3/ISS
FUTURE
GEOCarb
MERLIN
202?
Towards an International Integrated Greenhouse Gas Observing System – lots of
potential for reference quality measurements
NOAA-20
CrIS
Note: Not a comprehensive depiction of all current measurement programs
2002 …
AIRS IASI
2006…
Future Regional
In Situ Aircraft
NOAA GGGRN

22. Backup Slides

24. https://gcos.wmo.int/en/ecv-review-2020
From 2018 US Report “Thriving on Our Changing Planet:
A Decadal Strategy for
Earth Observation from Space”:
Random error: XCO2: goal = 1 ppm,
threshold = 3ppm; Systematic error:
XCO2: goal = 0.2 ppm, threshold = 0.5
ppm; Mission duration: 3-5 years
provides a snapshot of current
conditions; Trends and interannual
variability will require systematic
measurements >10 yrs

25. Estimates of Signals Created in the Atmosphere from Emissions*
Source or Sink Emission Rate
(MT C / year)
Plume width
(km)
Total Column
(ppm)
Boundary Layer 1km
(ppm)
US fossil fuel
emissions
1600 3134 0.76 6.8
20% emissions
reduction
320 3134 0.15 1.4
Biological Uptake
during July
5800 3134 2.9 26.5
Terrestrial sink
annual anomalies
200 3134 0.1 0.9
Chicago 21.6 53 0.6 5.4
1GW Coal Fired
Power Plant
1000 1.7 2.3 20.6
Barnett Shale
Thermogenic CH4
0.3 100 - 225 0.002 - 0.01 0.02 – 0.01
Aliso Canyon CH4 0.35 1.7 0.1 – 0.3 0.9 – 2.7
*After Verifying Greenhouse Gas Emissions: Methods to Support Climate Agreements (NRC 2010)
• point source signatures depend on assumed horizontal resolution of sensor, here assumed to be
1.7 km comparable to OCO-2 and proposed CarbonSat
• nominal wind speed of 5 m/s assumed for all cases