Climate change is the most serious environmental challenge confronting society.

Current and future changes in the Earth’s climate depend on atmospheric concentrations of greenhouse gases (GHGs), which are increasing because of human activities such as burning fossil fuels, agriculture, and manufacturing (learn more ). The need to reduce GHG emissions is becoming more urgent as heat waves, wildfires, and other impacts of climate change become more frequent and severe.

Since the 2015 adoption of the Paris Agreement to limit global temperature rise, many nations, regions, cities, and corporations have made ambitious commitments to reduce GHG emissions. Decision makers need useful, accurate, and trusted information to determine how best to meet GHG emissions reduction targets, and to track progress in meeting them. Many approaches for measuring and tracking emissions are available, but they are at different levels of maturity and have a range of strengths and limitations.

What information do decision makers need? How are GHG emissions quantified? How should decision makers evaluate GHG emissions information?

Decision Maker Needs for GHG Information

The need for GHG emissions information began as a necessary ingredient in the international policymaking process. Today, nations report and use GHG information as part of that process and often also to inform and support national climate-related objectives and targets. In turn, this has stimulated national governments, regional governments, cities, and non-governmental and private entities to become producers and consumers of GHG information.

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Global and national scales


Subnational scales


Facility and corporate scales

Barriers to Widespread Use of Emissions Information

Decision makers require timely and accurate information to base management decisions on, and to evaluate the effectiveness of policy responses. However, information uptake and translation of GHG emissions data and information to actionable knowledge and insight can fail to occur for a variety of reasons:

Capacity Decision-makers must have the capacity to either collect and analyze their own emissions data or utilize datasets generated from other sources to inform action.

Transparency The processes and methods used in developing GHG information may not be provided in a transparency manner or clearly communicated.

Accessibility Data may not be available in formats that are easily accessible or usable for decision makers.

Relevance Data may not be relevant, or perceived to be irrelevant, for a decision maker, limiting its application and uptake.

Timeliness Emissions inventories are typically available with a few year time lag and may not be indicative for decision makers requiring real-time information on which to base policy decisions.

Trust Users need to find the GHG emissions information trustworthy. With competing political and financial interests involved, there can be a lack of trust or at least suspicion that can create missed opportunities.

Awareness Decision makers may not necessarily be aware of the data available to them on which to base policy decisions.

Long-term support Long-term funding support for GHG measurements and analyses is important to inform decision making but challenging to maintain beyond political cycles.

Quantifying GHG Emissions

Quantifying GHG emissions is challenging because there are many types of emissions sources to consider and countless individual emitters. Emissions can be estimated and presented in many ways: by individual GHG, source (e.g., fossil fuel use), geographical region (e.g., city, province, nation), economic sector (e.g., transportation, food), or individual emitting infrastructure (e.g., facilities, buildings, roads).

Global net anthropogenic emissions of well-mixed greenhouse gases from 1990 to 2019. CO<sub>2</sub> from fossil fuel use and industry contributes about 64% of emissions as of 2019, making these sources a priority for reducing emissions. Source: IPCC WG3 (2022)
FIGURE Global emissions of well-mixed greenhouse gases (excluding halocarbons, GHG precursors, and aerosols) from 1990 to 2019. CO2 from fossil fuel use and industry contributes about 64% of emissions as of 2019 (using 100-year global warming potentials), making these sources a priority for reducing emissions.
Source: Intergovernmental Panel on Climate Change Working Group 3 Summary for Policymakers (2022)
CO2FFI = CO2 from fossil fuel and industry
CO2LULUCF = CO2 from land use, land use change, and forestry
GtCO2-eq yr-1 = gigatons CO2-equivalent per year using 100-year global warming potentials

Approaches to Quantifying GHG Emissions

GHG inventories are tools for quantifying GHG emissions, often divided into economic and industrial sectors for a specific place and time. GHG inventories allow policy makers to identify key GHG-emitting sectors and make informed decisions by setting emission baselines, tracking emission changes over time, and assessing emission mitigation efforts. GHG inventories are developed using a wide range of approaches.

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Hybrid Approaches

Evaluating GHG Information

As more GHG emissions information becomes available and as more decision makers use this information, a common evaluation framework can help users determine what information products best meet their needs and understand the limitations of that information. The framework is comprised of six pillars, or criteria, that would ideally be met in order to provide the most useful and trustworthy information to decision makers.


Usability means that GHG emissions information is relevant to decision makers and that the information can be incorporated into decision making with ease. Timeliness means the GHG emissions information is available on timescales relevant to decision making. This pillar ensures that investment and efforts in GHG emissions information system development are focused on the most relevant questions, usable by decision makers, and built in such a way that changes and evolution of the policy environment and the subsequent information needs are met.

Information transparency means that the data and methods used to produce GHG emissions information are publicly available and traceable. This includes the primary and key supporting data sources and the methods or models used with definitions, version numbers, documentation, funding sources, and open access (i.e., freely available, not behind a paywall). Information transparency enables trust between information providers and users, contributing to political credibility and trust between agencies and actors.

Evaluation and validation mean that the GHG emissions information and the data and methods used to create the information have been rigorously assessed to ensure they are reliable, of sufficient accuracy and quality for the intended purpose, and the uncertainties are quantified. Evaluation and validation should be performed by the creators of the GHG emissions information as well as by independent auditors, researchers, or users.

Completeness means that the GHG emissions information for the geographic boundary covers all sources and sinks, and all GHGs. Approaches as well as information and inputs to approaches should have comprehensive spatial and temporal coverage and all emissions sources should be included. To achieve completeness, many different sources of information may be integrated.

Inclusivity means that the GHG emissions information is generated by all relevant or applicable stakeholders, including decision makers, individual entities, locally-based experts, and the public. It considers who is involved in the creation of and covered by the GHG emissions information. Greater representation and participation would increase public understanding and trust in GHG emissions information.

Communication means that the GHG emissions information is effectively communicated to the public and decision makers. Ways to effectively communicate GHG emissions information include websites that are simple to navigate, data that can be freely downloaded, data formats that are widely used, metadata including units and other details, and documentation presented in several languages. Descriptions and supporting documentation should be provided in nontechnical language that is easy to understand.

How do the Three Major Approaches Stack up?

Qualitative evaluation of the three approaches to quantifying GHG information against the six evaluation pillars shows the strengths and weaknesses of each approach. The volume and diversity of existing activity-based, atmospheric-based, and hybrid approaches to quantify GHG emissions information makes single assignments challenging as there are inevitably exceptions in most cases.

Approaches Pillars Usability and Timeliness Information Transparency Evaluation and Validation Completeness Inclusivity Communication Methods Medium High Medium Medium Low Medium Data Medium Medium Low Medium Low Medium Methods Low High Medium Medium Low Low Data Medium Medium High Medium Low Medium Methods & Data Low Low Medium Medium Low Low Activity-based Atmospheric- Based Hybrid

Guidance for Evaluating GHG Emissions Information

Decision makers, media, and other stakeholders can evaluate the credibility and usefulness of new GHG emissions information by considering the following questions.

Information should be provided transparently in formats that are widely used and traceable. It should be made available on websites that are easy to navigate, where data is free to download, with non-technical documentation, in multiple languages, and in formats that are easy to understand.

GHG emissions information collected for a limited time, a small geographic area, or for a limited number of source types may not be sufficient to draw broad conclusions about an entire emissions sector, geography, or GHG. Data providers should exercise caution when communicating with the public about the results of a single study and clearly explain the limitations of their data and methods.

Evaluation against independent data and methods is key to giving users confidence in GHG emissions information. Data should be assessed for reliability, accuracy, completeness, and quality for the user’s intended purpose. Ideally, biases and uncertainties associated with the information would be quantified and an assessment of the limitations of the approach would be provided.

Multiple independent data sources or approaches may support a central conclusion, or help identify gaps or discrepancies where further attention is needed. The strengths of the hybrid approach come from the integration of multiple approaches and data sources to support completeness, evaluation, and, in some cases, validation of GHG emissions information.

Building local capacity for measurement and monitoring contributes to sustainability and inclusivity. Meaningful engagement with affected populations also increases the inclusivity of GHG emissions information. Many avenues of engagement, through for example public comment periods, stakeholders workshops, or citizen science data collection opportunities, would enhance GHG emissions information quality and usability.

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Explore additional National Academies’ resources on reducing greenhouse gas emissions: