In the global effort to eliminate greenhouse gases, it is really important to have a common set of measures that everyone agrees with. Countries, industries, and companies are all being held to account for their efforts to cut emissions, so the process of measuring and reporting on those emissions should get a lot of attention.

There are many ways to count emissions.  For instance, they can be reported by country, by industrial sector, by industrial process, or by gas type.   In practice, a common way to report on emissions is to categorize them by major source: those coming from the combustion of fossil fuels vs. those coming from land use, land use change, and forestry (LULUCF).

Fossil-based emissions are the more important of the two, accounting for 84% of current emissions and about 75% of global warming experienced to date.   

Measuring fossil-based emissions is not simple, but because there are systems that measure the production and sale of fossil fuels worldwide, tallies of fossil fuel emissions are relatively reliable.

Measuring the 16% of global emissions from land use is more complicated.  The LULUCF sector is unique because forests and other forms of biomass can both emit and absorb CO2.  In this way, the sector can be thought of as a warehouse of carbon that can act as either a source or a sink of emissions.

Inventory headaches

Figuring out, how much has gone in or come out of the LULUCF “warehouse” is notoriously difficult. In concept, one needs a starting inventory at the beginning of a period and then an ending inventory. Additions or removals are the difference between the two.  

Anyone who has worked in a retail business knows what a miserable task taking inventory is.   Now imagine doing that for a forest.  Then imagine doing that for all the forests, grasslands, wetlands, and agricultural lands on the entire planet.

For instance, the amount of carbon a forest stores depends on a lot of factors.  How big is the forest?  How many trees does it contain?  How big are the trees?  What species are they? A lot of this work relies on interpreting satellite imagery and using broad estimates.  The degree of accuracy is therefore highly variable.

Then there are a whole range of other issues – like defining whether an area has been deforested or not. If a fire burns down a forest, do you assume it is gone and count its emissions? Or do you assume that over the next 20 years, it will grow back, and ignore the short-term release of carbon because you expect it will be taken up as the forested returns?

What if the trees that are cut down, have been made into 2x4s and are sitting in a Home Depot somewhere? Is that an emission?  Because the wood is not being burnt or decomposing, technically, the carbon it holds has not been released into the atmosphere.

Similarly, how would you define reforestation?  If on a parcel of land, a bunch of seedling trees were planted to replace mature trees that were cut down – do the two activities cancel each other out?  What if half of the seedlings die off in the next 5 years?

Finally – there are a variety of different technical and accounting approaches to measuring emissions from land use. Depending on the methods adopted, results differ dramatically.

Scientists disagree

Reports on greenhouse gas emissions generally come from one of two sources – country reports to the UN as part of the Paris Agreement or published studies by the global scientific community.

A lot of work has gone into trying to standardize approaches for both groups on how to measure land use emissions. The UN has published volumes of guidance on how to report and measure the sector – but there remain wide discrepancies among even the most detailed assessments.

In the scientific community, there are many research groups and projects that collect and analyze data on emissions.  These tend to be segmented by gas.

The major reference for CO2 is the Global Carbon Project and its related project, the Global Carbon Budget (GCB). The GCB is a large research collaboration that provides annual updates on global carbon emissions from both the fossil fuel and land use sectors. 

For the land use component of its work, the GCB draws on 3 major academic studies: the Bookkeeping of Land Use Emissions study (BLUE), the Object-oriented Simplified Climate-carbon cycle Response model study (OSCAR), and a study published by the independent Woodwell Climate Research Center, the H&C study, named in reference to the two lead authors, Richard Houghton and Andrea Castanho.

While these three assessments of LULUCF emissions are all peer-reviewed and scientifically sound, they produce widely varying results of the amount of CO2 being emitted.  

Over the last 20 years, the range between the global highs and lows of the three studies has averaged about 3 gigatonnes per year – a significant level of uncertainty equivalent to nearly 10% of all global CO2 emissions.  

On a national basis, the top LULUCF emitters are nations where there is widespread clearing of forests to create new agricultural land.  Three countries – Brazil, Indonesia, and the Democratic Republic of Congo – collectively account for more than half of CO2 emissions from land use.

Again, there are large LULUCF variances from the scientific community on a country-by-country basis.  Brazil’s CO2 emissions from land use are estimated to be three times higher in the OSCAR model than in the H&C study.  Two studies conclude that in 2022, China’s LULUCF sector was a net sink for CO2 emissions, while the third study concludes that China had the second highest CO2 emission from land use in the world.

The way Global Carbon Budget deals with the variation in scientific studies is that they take the median value of the three studies to come up with the overall annual LULUCF to include in their reports.  Other presentations choose to average the three studies in their reporting.

The wide range of scientific estimates of LULUCF emissions is a big deal.  What it means is that any reports we get on emissions levels from the scientific community could be significantly understated.  It should increase our urgency to cut emissions even more quickly to address the risk that we are warming the planet faster than we even realize.

A lack of national accountability

The other source of information on emissions is what nations report to the UN. These national reports come with additional issues.

The first issue is that many nations don’t report their emissions regularly.   

Under the 2015 Paris Agreement on climate change, countries are categorized into two main groups: Annex I (developed countries) and Non-Annex I (developing countries).   The UN lists 43 nations, including the EU and its member states, as Annex I parties and 155 nations as Non-Annex parties.

Annex I countries are required to submit detailed, annual reports on their emissions by sector to the UN.   The emission reporting requirements for Non-Annex countries under the Paris Agreement are less stringent compared to those for Annex I countries, reflecting the principle of “common but differentiated responsibilities and respective capabilities”. 

Net – Non-Annex countries can report as they see fit.  In practice, that means these nations have little to no official accountability to the UN for their emission.    That’s problematic because, Non-Annex countries include countries like China, India, and Brazil – some of the world’s top emitters. The last time these major emitters reported to the UN was in the mid-2010s.

The good news is that national accountability to the Paris Agreement is set to improve.  Beginning in 2024 under an Enhanced Transparency Framework, all nations, including Non-Annex countries, are being asked to submit more regular and more complete emissions reports.

Most nations lowball land use emission estimates

The second issue is that when countries do report their emissions, their LULUCF emissions are almost always lower than the estimates the scientific community produces.  

The reasons national estimates differ can be due to differences in the assumptions, technical approaches, and accounting methods used.  

National governments also differ from the scientific community in the scope of their estimates.  The Paris Agreement focuses nations on limiting anthropogenic or human-caused emissions, so national governments tend to take a narrow interpretation of what emissions are “human-caused”. This allows nations to significantly limit their responsibilities in the LULUCF sector.

For instance, in keeping with the “human-caused” principle, a government might only measure emissions in the subsection of “managed” forests in a territory.  When scientists estimate the effects of emissions from land use, they usually include all national territory. 

National governments may also interpret emissions from forest fires as part of a natural process, not human-caused, and therefore those emissions would be left out of national totals.

For example, Canada experienced unprecedented wildfires in 2023 that massively increased CO2 emissions. The fires are estimated to have released 2,400 megatonnes of CO2 – three times the amount of CO2 that Canada as a whole emitted in 2021. These emissions will not be included in Canada’s emission reports for 2023 or count against its emission reduction targets.

The net effect is that in pretty much all cases, the CO2 emissions being reported to the UN for land use emissions, which count against a country’s commitments, are consistently lower than what the scientific community concludes.  So much so, that in a lot of cases, nations report that their land use emissions are negative, removing CO2 from the atmosphere, whereas scientific studies conclude the opposite.

Nations want credit

It is no coincidence that national emission estimates are lower than scientific ones.  Governments are politically and economically motivated to reduce their obligations to cut fossil fuel emissions.  If their land use emissions calculations can be managed to result in more favorable estimates or even removals, that means they don’t have to go as far in cutting fossil fuel emissions.

Nations may go even further to increase the removals that they can report – even if the scientific community considers their land use sector a source of emissions.

Canada’s pledge to plant 2 billion trees is a case in point.  As a government-managed initiative, Canada will closely monitor and take full credit for the carbon removals for every tree planted, while ignoring the net positive emissions from unmanaged lands.

While tree planting may be a good thing, selective accounting contributes to the illusion that Canada’s LULUCF sector is removing carbon from the atmosphere, when its clearing is adding to it. Worse, net removals from the LULUCF sector, falsely offset Canada’s emissions from fossil fuel use, reducing Canada’s need to take action to cut those emissions to achieve committed targets.

Seeing the forest for the trees

In measuring emissions from the LULUCF sector, the details get very complicated – but an awareness of the challenges leads to some key conclusions:

• Despite measurement issues – stopping deforestation is undoubtedly a good thing – not just from an emissions standpoint, but also a critical element in preserving biodiversity. This is particularly important in nations beset by deforestation like Brazil, Indonesia, and the Democratic Republic of Congo.

• Re-forestation is also generally a good thing particularly when done with multiple tree species to preserve the diversity of ecosystems.  Re-forestation can’t however be promoted or perceived as an alternative to fossil emission reductions. In short – we will never tree-plant our way to net zero.

• The uncertainty associated with estimating land use emissions should compel nations to cut fossil emissions further and faster.  

• For greater transparency, national governments should set separate emissions targets to distinguish between fossil emission reductions and land use-based reductions.  That way questionable land use removals can’t relieve the need to cut fossil fuel emissions.

• Finally, national governments should align their methods for measuring land-use-based emissions with those of the scientific community. 

We all need to be working with a commonly agreed set of facts.