March 7, 2022
Fact Sheet: Areas where differences between state greenhouse gas (GHG) inventories
and the EPA's Inventory of U.S. Greenhouse Gas Emissions and Sinks by State: 1990-
2019 estimates may occur
The EPA recognizes that there will be differences between the EPA's state-level estimates and some inventory
estimates developed independently by individual state governments. Inventories compiled by states may differ for
several reasons and differences do not necessarily mean that one set of estimates is more accurate, or "correct".
The EPA has strived to ensure that the coverage, methodological and accounting approaches are clearly described
so that users can clearly understand differences with how states may compile their inventories. The results should
be viewed as complementary and supplement existing state data.
• Organization of sectors. The EPA has organized estimates by sector and their respective source and sink
categories consistent with the national Inventory and international reporting guidelines1. Standardization
of sectors in international reporting promotes comparability across countries and supports cooperation
on climate action. States may use alternate organization of data, such as economic sectors, for presenting
emissions rather than IPCC sectors. Some states may use IPCC sectors as the basis of their inventory, but
allocate some categories differently across sectors, such as reporting some Industrial Process and Product
Use categories in the Energy sector (e.g., SF6 from electrical transmission and distribution). Comparability
also depends on similar coverage. The completeness and geographic disaggregation of the report are
consistent with the national Inventory, meaning in addition to estimates for states, the methods also
address emissions and removals occurring in the District of Columbia, U.S. territories, and tribal lands.
• Methods and data. In some cases, the EPA may be using different methodologies, activity data, and
emission factors, or may have access to the latest facility-level information through the EPA's Greenhouse
Gas Reporting Program (GHGRP). The EPA used as a basis, or starting point, the same methods or
methods based on those used to compile the national-level estimates. States may use the same methods
but use different sources of activity data.
• Accounting approaches. In other cases, states may have adopted different accounting decisions that
differ from those adopted by the IPCC and UNFCCC, (e.g., use of different category definitions and
emission scopes consistent with state laws and regulations). For example, the EPA's approach is to focus
on emissions that occur within geographic state boundaries ("Scope 1"), whereas some states include
emissions that are caused by activity within their borders but which actually occur in other states ("Scope
2 or 3") or use consumption-based accounting approaches. For example, some states include emissions
from imported electricity, or electricity production that occurs outside state boundaries. EPA's use of
geographic state boundaries to allocate emissions is consistent with IPCC guidelines.2 Differences in
accounting approaches also include differences in the approach to estimating transportation, cross-
border aviation and marine emissions, or treatment of biogenic CO2. For example, the EPA does not
include biogenic CO2 emissions in state energy sector totals because, in accordance with IPCC
1 The international reporting guidelines under the UNFCCC require reporting GHG emissions and removals across five sectors:
energy, industrial processes and product use (IPPU), agriculture, land use, land use change and forestry (LULUCF) and waste.
Note, while the UNFCCC reporting guidelines require use of methods from the 2006 IPCC Guidelines for estimating GHG
emissions and removals, they require separate, rather than combined reporting of emission and sinks from agriculture, forestry
and other land use sectors as presented in the IPCC Guidelines.
2 Per the 2006 IPCC Guidelines, national inventories include greenhouse gas emissions and removals taking place within
national territory and offshore areas over which the country has jurisdiction with some minor exceptions. For example, an
exception, "CO2 emissions from road vehicles should be attributed to the country where the fuel is sold to the end user." See
Volume 1, Chapter 8, Section 8.2.1 on Coverage available online at: https://www.ipcc-
nggip.iges.or.jp/public/2006gl/pdf/l_Volumel/Vl_8_Ch8_Reporting_Guidance.pdf.
-------
March 7, 2022
methodological guidelines, CO2 emissions and removals due to the harvesting, combustion and growth of
biomass are included in the carbon stock changes of the relevant land use category of the Agriculture and
LULUCF sectors, where the biomass originates, and inclusion of these emissions in energy sector totals
would result in double-counting.3 Users of state GHG data should take care to review and understand
differences in accounting approaches to ensure that any comparisons of estimates is equivalent or an
apples to apples comparison of estimates.
• Time Series. The EPA has developed state-level estimates for 1990-2019 consistent with the national
Inventory published in April 20214 and current UNFCCC reporting requirements. States may estimate
emissions and sinks over a different time period based on state goals, designation of different base years,
legislation and available state data. Some states may not estimate back to 1990 and include only more
recent years. Other states may have published estimates for earlier years previously, but which have not
been recalculated or otherwise updated in more recent publications despite changes in methods, activity
data, or emissions factors. Similarly, new emissions sources may be added in recent years but not
estimated for more distant years.
• Global Warming Potentials (GWPs). States may use different metrics for carbon equivalency of non-C02
gases, such as different values for global warming potentials (GWPs). Consistent with the national
Inventory, in this report the EPA is using 100-year Global Warming Potentials (GWP) from IPCC's Fourth
Assessment Report (AR4) calculate carbon dioxide equivalency of non-CC>2 emissions, as required in
reporting annual inventories to the UNFCCC. The EPA will be shifting to use of 100-year GWPs from the
IPCC's Fifth Assessment Report (AR5) in 2024 with the first reporting under the Paris Agreement starting
in 2024. Until then, consistent with UNFCCC reporting guidelines, the EPA will continue to use AR4 100-
year GWPs.
3 See Q2-10 of Frequently Asked Questions on general guidance and other inventory issues, https://www.ipcc-
nggip.iges.or.jp/faq/faq.html.
4 The national Inventory is available online at https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-and-
sinks-1990-2019.
------- |