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The Climate Web 10/5/2026
Top-Level Topical Headings
Top Level Extracted Materials Headings
E - Mitigation Top Level
E - Mitigation Options
E - Mitigation Policies and Measures
E - Market Mechanisms
E - Carbon Offset Knowledgebase
E - Offset Criteria
E - Offset Additionality
Parents
Carbon Offsets TOC
E - Evaluating Carbon Offsets
E - Offset Criteria
Children
“Additionality fatigue” is not new
2003 Extreme vs. Loose additionality and CDM offset supply for 2010
2003 MACC with additionality screening for 2010
2003 MACC with additionality screening for 2020
2008 Gresham's Law rephrased
2008 Scoring additionality on a 0-1000 scale - energy efficiency
2008 Scoring additionality on a 0-1000 scale - riparian reforestation
2008 Scoring the additionality of an offset portfolio on a 0-1000 scale
2008 That additionality concept - 1
2008 The challenge of widely varying sectoral additionality
2009 Slide - Custom vs. Standardized Rules
2009 Slide - Markets are Growing Rapidly
2009 Slide - Not All Offsets are Created Equal
2009 Slide - Offset Rules Will Determine Offset Outcomes
2009 Slide - Press Coverage Follows Market Activitiy
2009 Slide - Supply Depends on Offset Rigor
2009 Slide - The Criteria Offsets Need to Meet
2009 Slide - The Importance of Clear Objectives
2009 Slide - The importance of offsets
2009 Slide - The Voluntary Carbon Market
2009 Slide - Voluntary Market Standards
200X One additionality continuum example - coalmine methane
200X Scoring additionality on a 0-1000 scale - coalmine methane
200X The additionality continuum - energy efficiency
200X The additionality continuum - nuclear energy
200X The additionality continuum - riparian reforestation
2010 Business as Usual" reductions in the U.S. - our own calculations
2011 The cause and effect relationships in assessing offsets
2011 The definition of additionality is often circular
2012 Example of how emissions for a prospective baseline scenario might appear
2012 Example of how emissions from a historical baseline scenario might appear
2012 Illustration of baseline movement due to regulatory changes
2012 Process for determining the baseline and demonstrating additionality
2012 Seven main principles that relate to additionality
2014 Approach to assessing project level additionality - key components
2014 Assessing additionality (improving reference case)
2014 Farms adopting with and without payment
2014 How to calculate additionality
2015 AAU surplus converted to potential tons
2015 Additionality "investment analysis" rarely transparent
2015 Additionality claims worst for large projects
2015 Based on a random sample many additionality claims not plausible
2015 Big surpluses were built into the Kyoto Protocol's targets
2015 Environmental integrity appears to vary by the evaluating entity
2015 Environmental integrity can vary dramatically across sectors and countries
2015 Environmental integrity of six largest JI projects in sample
2015 Environmental integrity of the six largest project types
2015 JI project additionality claims got worse over time
2015 Plausibility of additionality claims of sample set of 60 JI projects
2015 Project types in JI and relative magnitudes
2015 Track 2 JI much better, but very small fraction of credits
2016 Assessment of additionality on credits during first commitment period
2016 Assessment of additionality on credits during second commitment period
2016 Average IRR impact of CER revenues by project type
2016 How additional is the CDM?
2016 Overall evaluation of CDM project types
2016 Potential CER supply
2016 Projects considered automatically additional as microscale project activities
2016 Projects considered automatically additional under small-scale project activities
2017 Offset supply and likelihood of additionality with CDM projects
2017 Potential trade-off between number of projects, quality, and effectiveness
2017 Project Additionality
2018 Gas emitters regulation reduction options 2007 - 2011
2019 Decision-making tree for additionality assessment under Art. 6.2 and 6.4
2019 Example baseline approaches for different project types
2019 Examples for mitigation project additionality by project type, baseline, type of activities, additionality risks
2019 Examples of how GHG programs approach baseline setting
2019 List of how different GHG programs address additionality
2019 There are many potential baselines when thinking about national actions and targets
A rough cost distribution of legitimate offsets
A successful offset protocol should by definition suggest an adequate screening for additionality
Additionality “testing” is a misnomer
Additionality approaches used in various offset standards and programs
Additionality can be operationalized if we recognize the context in which it has to operate
Additionality comes down to the "why" of an emissions reduction
Additionality has been the biggest challenge to carbon offsets
Additionality has gotten more confusing over time
Additionality is a means to an end, not an end
Additionality matters because there are SO many “anyway tons.”
Additionality policy design principle #3
Additionality screening has to account for human behaviors, making it more uncertain
All additionality tests are trying to answer the same question
And expressed as ERUs
Any offset protocol is (very) likely to include at least some false positives
Basing emissions trajectories on scenario analysis and modeling is challenging, and there is a risk of inflated baselines and over-crediting due to the uncertainties
Because offsets justify emissions, they have to meet certain criteria
Broekhoff_EPRI_Additionality[1]_10
Broekhoff_EPRI_Additionality[1]_11
Broekhoff_EPRI_Additionality[1]_12
Broekhoff_EPRI_Additionality[1]_13
Can greater demand solve additionality?
Carbon offset baselines vs. additionality
Carbon offset mitigation benefit vs. additionality
CDM Additionality Tool - Version 5
Conceptually, the need for of additionality is very simple
Defining additionality
Definition of additionality
Definitions proposed for additionality
Different groups may behave very different, with significant consequences for additionality screening
Different sectors perform very different when it comes to additionality thresholds
Different sectors perform very differently in terms of “offset confidence”
Discounting the number of offsets tells you nothing about their environmental credibility
Distribution of wind farms in the U.S.
E - Offset Testing
Evaluating the additionality of ag-based offset credits - nitrogen fertilization corn
Even tests for physical variables like pregnancy are not infallible
Forestry offset provide a lot of co-benefits
Gaming of offset rules will generally increase the likelihood of false positives getting into the offset pool
GHG market fundamental #1
GHG market fundamental #2
GHG market fundamental #3
GHG market fundamental #4
GHG market fundamental #5
GHG market fundamental #6
GHG market fundamental #7
Hypothesis testing can never be perfect, and it’s not for carbon offsets
If getting a market going is the key goal, be transparent about it
If you don’t think about false positives, you can’t draw any conclusions about offsets’ environmental integrity
Illustrative additionality tests
In designing most tests, you can know whether you got it right or wrong. Not so for additionality.
Is additionality really important?
It is not easy to assess the additionality of an offset pool
It is possible to put together an effective additionality testing system - but it may require a lot of work
Large markets + additionality screening is the best situation
Legitimate carbon offsets have to be traceable to the carbon offset market
Many additionality “proxies” have no obvious empirical basis.
Many of the additionality “proxies” being used have not been empirically validated.
Many physical tests are first evaluated on how they balance false positives and false negatives
Measurement and monitoring cannot substitute for additionality screening
Never has so much been said about a topic . . .
No offset pool can be perfect
Not all offset criteria should be judged equally, including for scoring purposes
Offset economics are at least a useful initial additionality screen
Offset profit margins and cost-effectiveness vs. environmental integrity
Offsets come down to a confidence assessment
One of the few papers looking at the performance of forestry offset projects
Only “additional” offsets can generate “additional” co-benefits
Potential additionality tests
Potential offset supply in a world on track for a 2oC scenario
Potential offset supply in a world without adequate public policy
Practice adoption vs. receiving payments for adoption
Project vs. standardized additionality screening
Project-level and program-level additionality have to correlate
Representative additionality stringency supply curves for 2010
Representative additionality stringency supply curves for 2020
Representative regional offset supply curves
Representiative sectoral offset supply curves
Saying offsets are limited in number says nothing about their additionality or effectiveness
Setting avoided deforestation baselines is more challenging that setting baselines for other project types
Setting sectoral performance standards for entire sectors can reduce the risk of over-crediting
Some additionality bottom lines
Someone has to decide the acceptable balance of false positives and false negatives
Statistical concept #1
Statistical concept #2
Statistical concept #3 - errors can't be fully eliminated
Statistical concept #4 - the approriate error balance is specific to the nature of the test
Summary of metrics for selected conservation practices
The additionality challenge is common to all offset systems
The additionality wars could continue forever
The Catch-22 of additionality screening
The CDM Additionality Tool
The distribution of CA's forestry offset projects
The implications of ignoring additionality
The potential supply of false positives is probably larger than you think
The problem is that false positive tons are probably dwarfing false negative tons in the offset pool
The question of “how many false positives is too many” is not a technical question
The relative proportions of "phantom reductions" and "lost opportunities" depends on multiple variables
The report uses an incorrect definition of additionality
The theoretical offset supply
The theoretically potential supply of carbon offsets
There is no difference between project, sectoral, and policy additionality
There is no universally right answer to additionality, but it is critical to the market
There is no way to “test” for additionality the way we “test” for pregnancy
There is no way to minimize for false positives and false negatives simultaneously
Use of offsets in California's climate change policies
Variations in additionality terminology in climate policy literature - 1
We all understand that some guilty individuals will be found innocent in a courtroom
We all understand that some innocent people will be found guilty in a courtroom
We inuitively understand that fewer falsely guilty outcomes is more important than more falsely innocent outcomes
We should all recognize that some “false positive” tons will make it into a carbon offset pool
We should all understand that some “true positive” tons will be excluded from offset pools
We should all understand that we’re trading off false positive and false negative tons
We should take advantage of the best possible information when it comes to additionality screening
What can we really say about additionality screening?
What perfect additionality screening would look like
What potentially overly strict additionality screening looks like
What reasonable additionality screening might look like
What weak additionality screening looks like
Where legitimate offsets fit in the scheme of avoided emissions and removals
Why market size matters to additionality screening
Wind capacity by power grid
Without adequate additionality screening, offsets can’t maintain environmental integrity
Jumps
I - OffsetAdditionality