Order Code RS22964
October 6, 2008
Measuring and Monitoring Carbon in
the Agricultural and Forestry Sectors
Ross W. Gorte and Renée Johnson
Specialist in Natural Resources Policy and Specialist in Agriculture Policy
Resources, Science, and Industry Division
Summary
Proposals to reduce emissions of carbon dioxide and other greenhouse gases often
include the use of forestry and agricultural practices and lands for carbon sequestration.
However, uncertainty about the accuracy of measuring carbon from these activities has
led some to question this potential. Basic approaches for measuring forest and
agricultural carbon include on-site measurement; indirect measurement from off-site
tools; and estimation using models or inferences. Because of challenges associated with
balancing the cost and accuracy of these measurement tools, any practicable system for
measuring forest and agricultural carbon might require a mix of these approaches.
Concerns about global climate change and its impacts on the environment and the
economy are encouraging policy-makers and stakeholders to explore a range of options
to reduce emissions of carbon dioxide (CO ) and other greenhouse gases (GHGs).1
2
Congress is considering legislation that would, among other things, provide incentives for
parties to reduce or mitigate GHG emissions or to sequester (store) additional CO .2 The
2
possible use of forestry and agricultural practices and lands to mitigate or sequester CO2
is part of the debate. However, substantial uncertainty exists about current ability to
accurately quantify, monitor, and verify the amount of carbon sequestered by various
agricultural and forestry practices. By comparison, measuring the carbon from a discrete
point source, such as a power plant, is relatively easy and precise. Incorporating the
agriculture and forestry sectors in an emissions reduction program will likely require a
firm basis for measuring carbon inventories and change for forestry and agricultural
practices and lands.
1 Under the United Nations Framework Convention on Climate Change (UNFCC), GHGs include
CO , methane (CH ), nitrous oxide (N O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs),
2
4
2
and sulfur hexafluoride (SF ). Because various GHGs have different climatic consequences, they
6
are typically converted to a standard measure, usually metric tons of CO -equivalents (CO -Eq.).
2
2
2 CRS Report RL33846, Greenhouse Gas Reduction: Cap-and-Trade Bills in the 110th Congress.

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Purpose of Measuring Forest and Agricultural Carbon
Farm and forest activities can be both a source and a sink of GHGs, releasing GHGs
through plant and animal respiration and decomposition and removing CO through
2
photosynthesis, storing it in vegetation and soils (a process known as sequestration). A
range of land management, agricultural conservation, and other farmland practices can
reduce or abate emissions and/or sequester carbon. These include tree planting, soil
conservation, manure and grazing management, and land retirement, conversion, and
restoration.3 Many of these activities, however, may be impracticable for an emission
trading program because they might not meet credible standards for quantifying,
monitoring, and verifying emission reduction or carbon storage.
Reliable tools and techniques are needed for carbon inventories and carbon change
on forests and agricultural lands. The ability to measure carbon levels allows countries
that have committed to reducing GHG emissions to measure their current annual emissions
and carbon storage (and changes in carbon stocks).4 Current estimates show that forests
account for a significant share of estimated existing carbon stocks globally; agricultural
lands account for a small share of stored carbon. Also, the ability to measure carbon levels
provides the means to estimate the mitigation potential of forest or agriculture activities
that sequester additional carbon in soils or vegetation (i.e., result in a net reduction
compared to estimated baseline conditions or current sequestration). This may allow a
farm or forestry activity to be recognized as a way to mitigate or offset5 emissions —
through voluntary action, an emissions trading market, or a regulatory program.
For an emissions trading program to be credible, a participating entity is usually
required to meet a series of established protocols that specify what, when, where, and how
to measure changes in carbon. Protocols provide technical guidelines or standardized rules
for quantifying, monitoring, and verifying the mitigation of an activity. They specify
requirements on project eligibility, scale and baseline measurements, measurement
frequency, and verification. The difficulty is developing credible protocols that are
quantitatively defensible and readily applicable across areas with differing land uses,
weather, and other site-specific conditions. Protocols also address, to varying degrees,
concerns about the validity of activities, such as additionality, leakage, and permanence.6
Protocols may be either voluntary or set by regulation. In one voluntary market, the
Chicago Climate Exchange (CCX) has protocols for a range of soil and land management
3 See CRS Report RL33898, Climate Change: The Role of the U.S. Agriculture Sector.
4 The official U.S. estimates of current national GHG emissions and carbon uptake, including
agriculture and forestry estimates, are those published by the U.S. Environmental Protection
Agency (EPA) in its annual Inventory of U.S. Greenhouse Gas Emissions and Sinks.
5 In this report, offset refers to any action that reduces or mitigates GHG emissions, usually from
an unrelated source (e.g., increased carbon storage on forest or farmlands to offset emissions
from automobiles). The term offsets may also be used to refer to approved carbon reduction or
sequestration projects under specific regulatory or voluntary GHG reduction programs. See CRS
Report RL34560, Forest Carbon Markets: Potential and Drawbacks.
6 See CRS Report RL34436, The Role of Offsets in a Greenhouse Gas Emissions Cap-and-Trade
Program: Potential Benefits and Concerns; and Timothy Pearson et al., Sourcebook for Land
Use, Land-Use Change, and Forestry Projects, Winrock International, 2005.

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projects, including agricultural methane, soil carbon, rangeland soil carbon management,
and tree planting projects.7 The Regional Greenhouse Gas Initiative (RGGI) — the first
regional mandatory, market-based effort to reduce GHG emissions — is developing
technical standards for a narrower set of offset projects from the agricultural and forestry
sectors, providing for afforestation and methane reduction from livestock operations.8
Individual requirements of current protocols and standards can vary widely by program.
Decisions Needed in Setting Measurement Requirements
Numerous methods exist to measure forest and agricultural carbon. The appropriate
measure to use in specific circumstances depends on several variables, including the
purpose for measuring the carbon, the scale and basis to be measured, the frequency of the
measurement, and how the measurement is to be verified.
Scale and Baseline. Two geographic scales are commonly used for measuring
GHG emissions — the national/regional level to report GHG emissions and participate in
broad efforts to reduce emissions; and the local/site-specific level for projects to offset
emissions. Regardless of scale, the emission reduction or carbon sequestration is
compared to a baseline — the historic GHG emissions or carbon stocks at a specified
point in time. The scale and baseline timing are typically specified in the protocol of the
reporting, marketing, or regulating organization. Sometimes, for projects with multiple
land uses, the land is stratified into the various land uses (e.g., cropland, pasture, sapling
forest, mature forest), with a different baseline established for each use.9
Periodicity. Protocols typically identify when GHG emissions must be measured.
An initial measurement is needed to establish the baseline. This must be done prior to the
onset of a project, to allow for measuring the change that results from the action.
Occasionally, a historic baseline is specified; for example, the Kyoto Protocol identified
1990 emissions as the baseline for measuring emission reductions. Other options include
a current level, or other level whereby a project is compared to “business as usual.” The
protocols also identify the frequency and timing of measurements. For example, CCX
contracts for agricultural projects require annual measurements to assure that the emission
reduction or carbon sequestration is actually occurring.
Frequency of measurement also depends on the rate of change in carbon storage.
Some carbon pools, such as forest soils, change relatively slowly (unless the forest is
disturbed), and measurement once a decade may be sufficient. For other carbon pools,
such as pastures or managed lands, differences within and across years can be substantial,
and may require more frequent measurement. Timing can be critical, and alternative
measurements may vary widely. The amount of carbon stored in vegetation, in particular,
varies over the course of a year, with carbon being sequestered during the spring, carbon
stored in foliage at its maximum in late summer, and carbon being released during the
7 CCX, “CCX Offsets Program,” at [http://www.chicagoclimatex.com/content.jsf?id=23].
8 RGGI, Regional Greenhouse Gas Initiative Model Rule, 1/5/07 Final, at [http://rggi.org/docs/
model_rule_corrected_1_5_07.pdf].
9 See Suzie Greenhalgh et al., The Greenhouse Gas Protocol: The Land Use, Land-Use Change,
and Forestry Guidance for GHG Project Accounting, World Resources Institute, Oct. 2006.

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winter as the deciduous leaves decompose. Thus, consistent timing for annual measures
is an important element for agricultural and forestry carbon projects.
Verification. Verifying the emission reduction or carbon sequestration is critical
in efforts to mitigate climate change. It is particularly important for agriculture and
forestry projects, as these activities are harder to measure reliably than other types of GHG
offsets. One question is who will be responsible for verifying changes in carbon, which
raises questions about the role of a regulatory agency for accrediting claimed changes in
carbon levels from an activity.
Existing programs typically recommend or require that the carbon offset be verified
by an independent entity. Independent verification may be an auditing function, to assure
the reality and accuracy of the carbon offset for markets (buyers and sellers), regulations
(emitters and regulators), and reports (emitters and reporting organizations).10 One source
has prescribed several qualities for independent verification: an “independent, qualified,
third-party verifier” using “approved methodologies and regulations” and “whose
compensation is not in any way dependent on the outcomes of their decisions” and who
follows set procedures to avoid conflicts of interest.11
As voluntary and regulated markets for GHG emissions offsets develop, qualified,
independent organizations to verify carbon offsets will be needed. Entities qualified to
verify agriculture and forest carbon offsets must be proven to be knowledgeable about
carbon measurement. One source notes: “To provide good quality and trustworthy
oversight, a sufficiently rigorous accreditation process will be necessary to ensure that the
verifiers have the needed expertise.”12 This process could parallel the development of
independent auditors for certifying sustainable forestry programs.13
Measurement Techniques. Basic approaches for measuring agricultural and
forest carbon inventories and change include on-site measurement, indirect measurement
from off-site tools, and estimation using process models or inferences. A hybrid approach
involving a combination of approaches (e.g., combining modeling with on-site sampling
and independent verification) might improve the accuracy enough to be useful while still
containing costs. Because of the inherent challenges associated with balancing the cost of
measuring carbon and the accuracy of these measurements, any practicable system for
measuring forest and agricultural carbon might require a mix of these different methods
and approaches, rather than a single approach.
10 Zach Willey and Bill Chameides, eds., Harnessing Farms and Forests in the Low-Carbon
Economy: How to Create, Measure, and Verify Greenhouse Gas Offsets, Nicholas Institute for
Environmental Policy Solutions, 2007.
11 Offset Quality Initiative, Ensuring Offset Quality (July 2008), at [http://www.pewclimate.org/].
12 Lydia Olander et al., Designing Offsets Policy for the U.S.: Principles, Challenges, and
Options for Encouraging Domestic and International Emissions Reductions and Sequestration
from Uncapped Entities as Part of a Federal Cap-and-Trade for Greenhouse Gases, Nicholas
Institute for Environmental Policy Solutions, May 2008.
13 For more information on forest certification, see [http://www.pinchot.org/project/59].

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On-Site Measurement. Direct measurement of the carbon content of agricultural
and forestry soils and vegetation through field sampling and site-specific laboratory
estimates is perhaps the most accurate way to measure carbon levels and changes.
However, this is time-consuming, costly, and often requires continuous sampling and
replication via a census of soil and vegetation carbon for all agriculture and forestry
projects, and may be infeasible. Also, it cannot cover large areas. Samples can be taken
and the results extrapolated, based on soil survey, land cover, climate, and other spatial
data. Sampling patterns (e.g., a grid, random, or stratified random), intensity (e.g., the area
to be sampled), and frequency are likely to be specified in the protocols, and many sources
discuss sampling methods for agriculture and forestry projects.14 The more intensive and
frequent the sampling, the greater the cost, but the higher the likely accuracy of the data.
Most experts suggest some sampling to ensure the accuracy of models or off-site
measures, especially performed consistently over time.
As with verification, the entity that measures the on-site carbon can affect perceptions
of the accuracy of the measurement. Landowners or other offset sellers can perform the
measurement — both at the outset of the project (for the baseline) and periodically during
the life of the project. This could reduce costs, because they are commonly on the site, but
raises questions of credibility, since they have an interest in the reported carbon levels.
Ensuring that verification is conducted by independent verifiers might be sufficient to
assuage market concerns over credibility, but could involve high project verification costs.
Indirect Measurement with Off-Site Tools. Tools exist to calculate carbon
content without actually being on the site. Remote sensing — using photographic and
other images from aircraft or satellites — can be used to measure carbon-related factors.
For example, infrared imagery can detect live biomass, with variations in the image
reflecting variations in the type and level of biomass. Remote sensing has long been used
in forestry for calculating commercial timber volumes of forest stands.
The principal advantage of remote sensing is coverage, given its ability to assess a
wide area relatively quickly. Another advantage is that the remote sensing and the analysis
of the results are generally performed by experts, improving the credibility of the results
and probably lowering the cost of verification. It can provide highly accurate information
for some types of carbon-related measures, such as activities with readily visible results
(e.g., deforestation and afforestation) or measurable carbon pools (e.g., live above-ground
biomass). One disadvantage is the high fixed cost of providing remote coverage; satellites
are very expensive to launch and maintain. Aircraft may be less expensive but may cover
less area. Once the satellites are in place, extending satellite coverage to additional areas
is relatively inexpensive. For some carbon-related measures, such as activities with less
visible impacts (e.g., sustainable forestry) or less readily measurable carbon pools (e.g.,
soil carbon), remote sensing is problematic. Also, in some areas, cloud cover can interrupt
regular measurements. Methods for consistently and reliably interpreting remote imagery
are still under development, and are usually recommended to be used in conjunction with
other techniques.
14 For examples of the latter, see Harnessing Forest and Farm Carbon; GHG Project Accounting;
and Sourcebook for LULUCF Projects.

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Estimation Using Process Models or Inferences. Another indirect approach
is to estimate agricultural and forestry carbon with models or other analytical tools.
Models are available to estimate a variety of ecosystem processes, and are used to depict
site-specific conditions. Models, especially computer models, are typically built from
extensive research and data sets, and provide average or archetypical estimates of physical
area, temperature, precipitation, forest or soil type, slope, plant diversity, and microbial
activity. The accuracy of the results depends in large part on the validity and measurement
of the input variables for the model. Data may be presented in tabular form, called “look-
up tables” because estimates can be looked up in the table based on a few key variables,
such as forest type and tree age or soil type.15 A related simpler approach might use
inferences or generalized input data scaled up to the size of the farm or forested area to
approximate the sequestration for an activity.16 Such an approach may reduce costs, but
provide a relatively low level of precision, and possibly high verification costs.
The advantage of a modeling approach is that it is relatively simple and low-cost, and
often provides consistent estimates. However, it may not reflect actual differences within
and across sites and activities, since it relies on archetypical or average carbon estimates
and not site-specific carbon measurements. Model proponents often suggest using
occasional site-specific sampling to assure the validity of the model chosen for the project
and site, and some suggest adjusting the estimates based on the samples. This introduces
the potential for bias in reporting carbon, and significantly increases the difficulty of
verification. In addition, for most situations and project types, numerous models exist.
These competing models may yield quite different estimates for the same site, because of
the different data sets and assumptions used in constructing the models. One model may
yield the most accurate estimates in certain circumstances, while another model may yield
more accurate estimates in other circumstances.
Considerations for Congress
Congress has already taken steps to address some of the challenges associated with
measuring carbon changes from forested and agricultural lands and practices. The 2008
farm bill (P.L. 110-246, the Food, Conservation, and Energy Act of 2008) includes a
provision (Sec. 2709) directing USDA to “establish technical guidelines that outline
science-based methods to measure the environmental services benefits,” including carbon
storage, from forests and agricultural activities. This includes developing measurement
procedures and a reporting protocol and registry. The Energy Independence and Security
Act of 2007 (P.L. 110-140, Sec. 712) directs the Secretary of the Interior to develop a
methodology to assess carbon sequestration and emissions from ecosystems. This
methodology is to cover measuring, monitoring, and quantifying GHG emissions and
reductions, and provide estimates of sequestration capacity and the mitigation potential
of different ecosystem management practices.
Congress continues to face the question of whether its current authorized activities
provide adequate and sufficient guidelines for accurately measuring carbon levels from
forest and agricultural activities.
15 James E. Smith et al., Methods for Calculating Forest Ecosystem and Harvested Carbon with
Standard Estimates for Forest Types of the United States, Gen. Tech. Rept. NE-343, April 2006.
16 See, e.g., U.S. Dept. of Energy, Technical Guidelines Voluntary Reporting of Greenhouse
Gases (1605(b)) Program, March 2006, Parts H and I.

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