“You can’t manage right what you don’t measure right” – Peter Drucker.

Dear Climate Healers Family,

Is it 14%, 18%, 24%, 34%, 51%, 53%, 66%, 87%, or 118%? There are a whole lot of percentage figures associated with the climate impact of animal agriculture. In this article, we will examine why there are such wide discrepancies and where the truth actually lies.

At Climate Healers, we’ve been saying 87% and now 118%, while most others seem to be stuck on 14% at the other end. So, what is the truth behind these numbers?

Two Questions

The two main questions around which scientists have been compiling animal agriculture’s climate impact estimates are:

A) How much of the annual climate impact is caused by animal agriculture?

B) How much of the cumulative climate impact is caused by animal agriculture?

While Question A is concerned with the rate of change in warming, Question B is concerned with the totality of warming since the pre-industrial era.

The Emissions Components

In the UN IPCC’s guidelines for emissions reporting, unchanged since 1996, only three emissions components are included. All three of them are greenhouse gases responsible for heating effects:

1) Carbon dioxide (CO2);

2) Methane (CH4); and

3) Nitrous Oxide (N2O).

Since 1996, seven other emissions components have been identified, but not yet included in the IPCC’s reporting guidelines for policy makers. Three of them are also greenhouse gases responsible for heating effects:

4) Halocarbons;

5) Non Methane Volatile Organic Compounds plus Carbon Monoxide (NMVOC+CO); and

6) Black Carbon.

Four more emissions components are aerosols, causing cooling effects in the atmosphere:

7) Sulfur dioxide (SO2);

8) Ammonia (NH3);

9) Nitrogen Oxides (NOx); and

10) Organic Carbon.

11) Albedo,

is a measure of how much sunlight (solar radiation) a surface reflects without absorbing it. It is the 11th component that we need to consider as albedo changes typically lead to more land surface reflectivity, thereby cooling the earth.

A final component that needs consideration is the

12) Carbon Opportunity Cost (COC) of the land used for animal agriculture.

COC is an estimate of how much additional CO2 can be sequestered on the land used for animal agriculture with reasonable effort on our part.

COC is not a direct emission and therefore, it is not included in totals, but it is included in the animal agriculture sector component. With COC, the emissions estimate for the animal agriculture sector can even exceed 100% (yes, that’s right!), meaning that when we choose to end animal agriculture, there is more sequestration than emissions and therefore, global warming will actually decrease over time.

The Metric Used for Emissions Impact (GWP100, GWP20, or ERF)

A final source of the discrepancy between the various estimates is the metric used for comparing the impact of various emissions components.

GWP100, the Global Warming Potential over a 100 year period is the metric used in the UN IPCC’s 1996 guidelines. In this metric, the total heating or cooling caused by 1 ton of the emitted component over a 100 year period is compared with the heating caused by 1 ton of CO2 over the same 100 year period in order to relate all emissions species to a CO2 equivalent.

GWP20 is another time dependent metric where the window of consideration is narrowed to 20 years from 100 years in order to convert all emissions components to a CO2 equivalent.

ERF is the Effective Radiative Forcing metric, which directly uses the warming or cooling impact of the increase in the concentration of the emissions component from 1750 to present.

FAO 2013: The 14% Estimate (Question A, Emissions Components 1-3, GWP100)

This estimate is for Question A and it was compiled with the GWP100 metric using just 3 emissions components: CO2, CH4 and N2O. It was authored by the UN Food and Agriculture Organization (FAO) in conjunction with the International Meat Secretariat, the International Dairy Federation, the International Poultry Council and the International Egg Commission as part of the Livestock Environmental Assessment and Performance (LEAP) Partnership in 2013.

This is the animal agriculture industry’s self-calculated estimate of the emissions contribution of the industry.

It used outdated statistics from 1964, 1982, 1993, 1999, 2001 and 2002 without proper date corrections.

It used efficient, first-world processes from Minnesota as representative in order to calculate the impact of global operations, even though most of the world is not as technologically well equipped as Minnesota.

It failed to correct for known undercounting of farmed animal numbers.

Finally, it omitted emissions from the manufacturing of all secondary by-products of the animal agriculture industry such as leather and all fishing operations.

However, this is the most often quoted estimate, even by Vegan activists.

FAO 2006: The 18% Estimate (Question A, Emissions Components 1-3, GWP100)

This estimate is for Question A and it was compiled with the GWP100 metric using just 3 emissions components: CO2, CH4 and N2O. It was authored by the UN Food and Agriculture Organization (FAO) in 2006 and it contained all of the errors and omissions listed above for the 14% estimate.

IPCC 2021: The 24% Estimate (Question B, Emissions Components 1-3, GWP100)

This estimate is for Question B and it was compiled with the GWP100 metric using just 3 emissions components: CO2, CH4 and N2O. It was authored by the UN Intergovernmental Panel on Climate Change in its Sixth Assessment Report of 2021.

EDGAR: The 34% Estimate (Question A, Emissions Components 1-4, GWP100)

This estimate is for Question A and it was compiled with the GWP100 metric using 4 emissions components: CO2, CH4, N2O and Halocarbons. It was authored by scientists at the Joint Research Center of the European Commission. However, they used land use change data from the UN FAO.

This estimate also included food processing, distribution and waste emissions and therefore, it was a life-cycle estimate, whereas the ones above only considered production emissions.

G/A 2009: The 51% Estimate (Question A, Emissions Components 1-3 & 12, GWP20)

This estimate is for Question A and it is a lower bound compiled with the GWP20 metric using 3 emissions components: CO2, CH4, N2O as well as a Carbon Opportunity Cost (COC) component. It was authored by Goodland and Anhang, environmental assessment specialists at the World Bank Group. Their report identified the errors and omissions in the UN FAO’s 18% and 14% estimates as listed above.

In their original report, the authors utilized a 20-year time frame for methane released as a consequence of animal agriculture, but a 100-year time frame for methane released from other sources. This is an error in their report, which was corrected in our position paper by treating the breathing contribution of farmed animals plus the overlooked land use component as COC and therefore, not part of direct emissions.

In the table from the position paper, in the Goodland/Anhang and White Paper columns, the total emissions is 11.5/0.29 + 7.732/0.37 +1.82/0.65 = 63.36 Gt. Then, 32.56 Gt is coincidentally, still 51% of 63.36 Gt.

Using the GWP100 metric instead of GWP20, the total emissions is 11.5/0.29 + 2.685/0.37 + 1.82/0.65 = 49.72 Gt. The sector contribution of animal agriculture becomes 11.5 + 2.685 + 1.82 + 11.5 = 27.5 Gt, which is 55% of the total for the greenhouse gas emissions contribution of animal agriculture on an annual basis.

GWB 2025: The 53% Estimate (Question B, Emissions Components 1-11, ERF)

This estimate is for Question B and it was compiled with the ERF metric using 11 emissions components, with only Carbon Opportunity Cost (COC) as the missing component. It was authored by Gerard Wedderburn-Bisshop and published in the Environmental Research Letters in 2025.

This is an estimate that included all cooling effects, not just the heating effects. It also used gross land use change CO2 emissions so that it is consistent with the gross accounting for fossil fuel based CO2 emissions. In the 1996 guidelines, the UN IPCC mixed net land use change with gross fossil fuel based CO2 emissions, causing statistical confusion, which likely led to the ineffective climate mitigation policies that the world has experienced over the past three decades.

J-H 2025: The 66% Estimate (Question B, Emissions Components 1-11, ERF)

This estimate is for Question B and it was compiled with the ERF metric using 11 emissions components, with only Carbon Opportunity Cost (COC) as the missing component. It is an update of Gerard Wedderburn-Bisshop’s 53% estimate, taking into account the increased potency of SO2 as a cooling gas and the increased CO2 doubling sensitivity as reported in Hansen et al. 2025.

CH 2019: The 87% Estimate (Question A, Emissions Components 1-3 & 12, GWP20)

This estimate is for Question A and it is a lower bound compiled with the GWP20 metric using 3 emissions components: CO2, CH4, N2O as well as a Carbon Opportunity Cost component. This is an update on Goodland and Anhang’s 51% estimate, with the COC corrected to include soil and root systems as well as above ground vegetation components. It assumes that soil and root systems can store twice as much CO2 as above ground vegetation, which is the lower limit of the range supplied in the Fifth Assessment Report of the UN IPCC.

Using the GWP100 metric instead of GWP20, the sector contribution of animal agriculture would rise to 50.5 Gt, which is 102% of the total, 49.72 Gt.

CH 2021: The 118% Estimate (Question A, Emissions Components 1-3 & 12, GWP20)

This estimate is for Question A and it is a lower bound compiled with the GWP20 metric using 3 emissions components: CO2, CH4, N2O as well as a Carbon Opportunity Cost component. This is an update on the Goodland and Anhang’s 51% estimate, with the COC corrected to include soil and root systems as well as above ground vegetation components. It assumes that soil and root systems can store 3.7 times as much CO2 as above ground vegetation, which is the ratio supplied in the Sixth Assessment Report of the UN IPCC.

Using the GWP100 metric instead of GWP20, this estimate would rise to at least 140% from at least 118% for the greenhouse gas emissions contribution of animal agriculture on an annual basis.

Where the Truth Lies

In reality, the estimates for both questions should take into account all 12 emissions components, not just a subset of them.

If we use ERF as the metric of choice, we can augment the 66% estimate with a COC component to answer Question B.

In order to answer Question A, we need to compute the derivative of the answer to Question B. This analysis is being conducted at the moment and we will report on our findings shortly.

Please stay tuned.

Register for V-COP23

As systems crumble and the earth races towards ecological and societal collapse, going vegan and ending animal agriculture is just revolutionary common sense.

One small change. One powerful movement. One healing planet with all 7 planetary boundary transgressions mitigated. One Earth resuscitated.

Please register for our Vegan Convergence Of the Peoples #23 (V-COP23) which will be held in-person on Nov 1-2, 2025 in Toronto, Canada. Join us as we discuss how to Redirect, Relinquish and Restore our beautiful planet.

Please be there or forever regret missing out.

With much love,