Balancing biomethane growth and emissions in the Netherlands

Following the outbreak of the Russian-Ukrainian war, and its impact on Europe’s natural gas supply, the potential contribution of biomethane to energy security has gained significant prominence. The EU’s Action Plan for Biomethane 2024-2040 , established as part of the REPowerEU package in 2022, aims to achieve a production of 35bn cubic meters (bcm) of biomethane by 2030. In this context, the Dutch government approved (in Dutch) a target to produce 2bcm of “green gas” by 2030. It also added a target to achieve at least 1.6bcm through a biomethane blending obligation for retail gas suppliers (those providing heating gas to households and small businesses). This target was recently revised downward to 1.1bcm by 2030. Given that Dutch biogas production stood at just 0.23bcm in 2022, both the reduced production target and the blending obligation still send a clear signal to the market that biogas remains a policy priority. According to the approved Dutch targets for biomethane production and blending, meeting the production target will result in a GHG reduction of 2.4 megatons of carbon dioxide equivalents (MT CO2e), the standard metric for GHG emissions (see box 1).

In this article, we dive into the assumptions behind the Dutch biomethane policy, assessing whether the climate contribution of the proposed biogas target is properly substantiated within both the current European and the relevant scientific framework.

Biomethane – the more technical term for green gas (in Dutch) – is purified biogas. Biogas can be produced through the anaerobic digestion of different biomass inputs. After undergoing an upgrading process known as methanization, biogas can, in principle, substitute for natural gas. Because biomass production affects multiple ecosystems, assessing the sustainability of biomethane requires a comprehensive evaluation of all its environmental impacts. These include those associated with upstream raw material production, which may include effects on soil, water or air quality.

The most common biomethane production methods involve the fermentation or gasification of different feedstocks. In the fermentation process, microorganisms convert raw materials into biogas – a mixture of mainly methane and CO2. In the gasification process, biomass is heated in the absence of oxygen, producing a combustible gas.

There are various raw materials that can be used as feedstock to produce biomethane. These include manure, organic waste, sewage sludge, pruning waste, and certain crops. To assess whether a feedstock can be considered sustainable, the EU has developed specific sustainability criteria. If a selected production method for a raw material meets these criteria, it may count toward achieving EU sustainability policy objectives and qualify for applicable subsidies. These criteria specify, among other things, that the use of whole trees, edible crops, and animal feed crops should be minimized. Also, the production of biomass must be sustainable, implementing practices that demonstrably prevent soil degradation and ensuring that it’s not sourced from high-biodiversity forests.

Policies supporting the use of biomethane are based on the assumption that it contributes positively to the reduction of CO2 emissions versus natural gas. For this reason, this article focuses on assessing the validity of that claim. This is particularly relevant because each biomethane feedstock has its own supply chain and associated climate impact.

To determine if biogas production has a lower climate impact than natural gas, we must evaluate the entire life cycle of both. The environmental impacts of producing biogas and natural gas span all stages of their life cycles. For natural gas, all production steps – such as drilling, treatment, transportation, and leakage – contribute to its total climate impact, not just the emissions from combustion.

Assessing the climate impact of biomethane versus natural gas

To assess the potential GHG emissions savings from replacing natural gas with biomethane, we must first identify the climate impacts across the entire life cycle of natural gas and choose an appropriate benchmark for this purpose.

In the Netherlands, the Ministry of Climate Policy and Green Growth bases its targets on the framework set by the European Renewable Energy Directive (RED). The latest version of this directive, RED III, considers an emission factor of 80 grams of CO2e per megajoule (g CO2e/MJ) of useful heat as the benchmark for natural gas. Actual real-world emissions, however, depend on multiple (and evolving) factors, such as the combustion efficiency of the appliance used, or the leaks that may occur during transport.

To better understand whether this RED III benchmark is suitable to assess the role of biomethane in the Dutch context, we can take a closer look at its rationale. Across EU member states, the quality and composition of natural gas are standardized, as a result downstream emissions from combustion are expected to be quite similar. However, upstream emissions – those resulting from different natural gas sourcing routes – can vary. Research (in Dutch) conducted by the consultancy Haskoning provides more insights into this issue.

Haskoning assesses total emissions from natural gas combustion based on its supply route, with values ranging from under 60g CO2e/MJ to just over 80g CO2e/MJ. When comparing the RED III benchmark with Haskoning’s assessment, it is important to note that Haskoning reports emissions per unit of supplied energy, whereas RED III expresses them per unit of useful heat. By nature, total emissions per megajoule of useful heat are slightly higher due to conversion losses produced between supplied energy and useful heat. Therefore, it is logical that the RED III benchmark falls within the upper range of Haskoning’s results.

Haskoning’s research also illustrates that natural gas extracted in the Netherlands has much lower upstream emissions compared to imports from Russia or to LNG shipped from the US. The import mix in EU grids varies across member states and over time, influenced by trade and geopolitical dynamics. Therefore, it is impossible to precisely and consistently determine emissions for any given country at any specific point in time.

In this context, the RED III value can be considered a reasonable benchmark, since there is no single, evidence-based absolute or fixed value that perfectly serves policy needs. Moreover, key factors – such as additional emissions from methane leakage during gas extraction – are often underestimated or inaccurately reported. These challenges in accurately assessing emissions from heating fuels are common across all fuel value chains.

Recognizing that emissions reduction policies require a benchmark to assess potential improvement, the 80g CO2e/MJ value – based on the evidence discussed – can be considered a logical and balanced reference point.

Is green gas greener?

A letter to the Dutch House of Representatives of February 9, 2024 (in Dutch) states that 0.4bcm of biomethane produced from manure digestion results in a reduction of 2.4MT CO2e versus the use of natural gas. This implies a reduction of 168g CO2eq/MJ for each MJ of biomethane. How does this key assumption align with the EU framework discussed earlier?

As with natural gas, a comparative analysis of biomethane emissions requires selecting a benchmark production method. In this article, we examine the case of mono-digestion of cattle manure, in line with the focus of Dutch policy. As discussed earlier, the values for avoided emissions along the manure (or any other) production chain are, by nature, averaged and aggregated estimates, derived through a calculation process similar to that used for natural gas. Any final figure is necessarily an approximation, assuming animal manure is a homogeneous source – regardless of whether it originates from pigs, cattle, or other livestock. Additionally, the variations that may arise from different gas upgrading techniques are also condensed in the benchmark.

The biomethane life cycle begins with manure production, which emits GHGs, primarily methane (CH4) and nitrous oxide (N2O). In addition to manure-related emissions, cattle also release GHGs through enteric fermentation – methane produced during digestion by microbes in the rumen. These enteric emissions constitute the largest portion of total methane emissions from ruminants. However, they are excluded from the RED III chain emission benchmark, as they are unaffected by the downstream processes involving stored manure. Once manure is stored, RED III distinguishes between open and closed manure storage systems for biomethane production. Closed systems may include flue gas combustion, which combusts or flares residual methane in the exhaust, effectively eliminating methane emissions from the final output.

Based on stakeholder consultations during its drafting and scientific research conducted by the European Commission, RED III assigns a value of -88g CO2e/MJ to biomethane produced using gas-tight manure storage, without flue gas combustion.

Compared to untreated manure, biogas production reduces emissions in two ways: first, by avoiding GHG emissions from untreated manure (88g CO2e/MJ); and second, by replacing natural gas in the energy system, which would otherwise emit 80g CO2e/MJ. Combined, these avoided emissions total 168g CO2e/MJ – forming the basis of current Dutch policy.

From barn to biogas: Emission insights from Dutch manure digestion

While the previous section outlines the rationale behind EU and Dutch policy at the national level, understanding its implications at the facility level requires a more granular view of operational details. In this regard, Wageningen University & Research (WUR) conducted a seminal study (in Dutch) on expected emissions from different types of farms.

WUR developed 26 models representing typical Dutch farms, based on key operational parameters such as the ratio of young to adult cattle, the number of days per year cattle spend in the meadow, and the type of barn systems used to collect and store manure.

Using statistical data and scientific literature, WUR compared the national emissions derived from individual models with the national inventory estimates, as assessed using the National Emission Model for Agriculture (NEMA). The consistency between both approaches shows that individual models are representative.

With this calibrated representation of individual farm types, the research helps identify which factors drive the variation of emissions at each step of the manure chain. A literature review (in Dutch) of emission factors enabled WUR to compare emissions from conventional farms without biogas systems to those from farms using mono-digestion.

In the latter case, WUR assumed a barn system with a solid floor and manure scraper, daily manure removal, covered storage, and central fermentation of the (wet) slurry. The resulting average for the 26 types of farms included[1] in the study is shown in figure 2, contrasted with the average from current practices.

[1] To enable comparison with the values considered in RED III, we have converted the units of WUR’s analysis to grams of CO2e per megajoule. We have adopted WUR’s proposed factor of 547 megajoule of biomethane output per metric ton of manure input to calculate the emissions per megajoule.

When installing a digester at a farm, the greatest potential for reducing GHG emissions lies in how manure is handled in the barn. Mono-digestion requires daily emptying of stables and gas-tight manure storage. These changes significantly reduce methane emissions during the initial storage phase, as methane no longer accumulates in open or poorly sealed conditions. Although the subsequent controlled digestion still produces methane, it becomes part of the intended biogas output. In light of this assessment, mono-digestion can lead to GHG emissions reductions of up to 80% (see figure 2).

WUR’s research shows that while mono-digestion introduces new steps – primarily from energy use, transportation of manure, and upgrading to biomethane – which result in additional emissions, these are more than offset by the reductions achieved in barn emissions. Moreover, emissions related to energy demand for processing can potentially be reduced. Since mono-digestion requires low-temperature heat (around 40 degrees Celsius), it is well-suited for heat pumps or renewable energy sources. Emissions from transport can also be further reduced by electrifying transport equipment.

Since emissions reduction is crucial to determining whether biomethane aligns with a long-term climate-neutral energy system, it is important to closely examine the additional emissions introduced during the digestion phase. Upgrading biogas to biomethane results in separated streams of (bio)methane and CO2. Nevertheless, this additional CO2 is part of what is known as the short carbon chain of biogas. This means that equivalent amounts of CO2 were previously captured upstream during the growth of the grass consumed by cattle – typically within less than a year. As a result, these additional CO2 emissions are considered neutral and are not reflected in life cycle emission figures.

For the facilities analyzed by WUR, manure digestion results in total emissions of 82g CO2e/MJ. In comparison, the case without digestion adds up to 295g CO2e/MJ of emissions, leading WUR to conclude that biomethane production achieves a 213g CO2e/MJ emission reduction during the production phase. At the end of the life cycle, biomethane can replace natural gas. Since biomethane produced in this way is part of a short carbon cycle, CO2 emissions from combustion are not taken into account.

Figure 3 shows a comparison between WUR’s assessment and the European policy framework. The WUR study uses a natural gas emissions factor of approximately 66g CO2e/MJ.

As expected, there are differences between the emission values in the WUR case study and the benchmarks adopted in RED III, both in terms of the replaced natural gas and the manure value chain. This is inevitable, since the values in RED III are aggregated approximations. Conversely, as WUR’s research illustrates, figures derived from a specific group of farms cannot necessarily be extrapolated to all farms. These unavoidable methodological differences illustrate that using aggregated values is the only plausible way to develop a harmonized policy across larger geographical areas with many individual farms.

While the exact emissions reduction potential ultimately depends on the specific details of each process, WUR’s analysis helps further understanding the structure and scale of the values adopted in the EU’s regulatory framework.

In short, compared with WUR’s findings for specific types of Dutch facilities, the expected climate contribution of the biogas policies enshrined in the EU RED III framework represents a conservative estimate of the potential emissions reductions achievable.

As discussed, evaluating the avoided emissions of climate policies requires comparison with a reference scenario. RED III uses the current state of the farming sector as its baseline – characterized by substantial direct emissions from both enteric fermentation in cattle and manure management. In this context, the so-called “reduced emissions” from biogas or biomethane production do not represent absolute negative emissions, but rather a substantial improvement over the baseline. As illustrated by the reviewed research and framework, while the value chain emits less than the current scenario, it still results in significant absolute emissions.

This necessary relative perspective, while logical, can lead to ambiguous or even controversial interpretations of the sustainability of manure fermentation. Critics argue that more manure will always lead to more absolute emissions, even if this manure is mono-digested. The opposite also holds true: In the absence of mono-digested, significantly higher total emissions may be released for the same number of cattle on a farm.

As previously discussed, introducing digestion reduces emissions in the cattle sector compared to the baseline. With the same herd size, fewer emissions are produced per cow. However, if biogas support policies lead to an increase in herd size, the resulting rise in total emissions could offset the per-animal reductions.

Both manure digestion and sectoral downsizing can contribute to emissions reduction, and they are not mutually exclusive in the short term. From a climate perspective, maximizing the use of currently available manure for biogas and biomethane production is beneficial – regardless of whether the sector grows or shrinks.

In the view of the framework and research discussed in the former section, biomethane from manure digestion is justifiably considered a valuable transition fuel, as long as it’s based on the current size of the farming sector. However, the analysis remains incomplete without also considering the drivers behind total absolute emissions. To determine whether the RED III benchmark can lead to both relative and absolute emissions reductions, short-, medium-, and long-term perspectives must be integrated.

Keeping absolute emissions in check

It’s important to note that enteric methane emissions are four times greater (in Dutch) than methane emissions released later from manure. In other words, the larger share of emissions comes simply from livestock digesting food. The relevance of both types of emissions is illustrated in figure 4.

To stay below the 2 (or preferably 1.5) degrees Celsius global temperature increase target as set by the Paris Agreement, absolute emissions need to be reduced. In the livestock sector, this means starting with the biggest sources of emissions – particularly enteric fermentation and its associated methane. Addressing these hotspots can significantly reduce absolute emissions, even if herd size remains constant.

The potential of these priority measures can be enhanced by also using manure digestion to produce biogas, which helps to reduce emissions from all sources. However, in the long term, achieving further absolute reductions will likely require shrinking the livestock population, to also cut emissions from enteric fermentation.

The total amount of biomethane that can be produced through digestion is directly tied to the amount of manure available. However, if promoting biomethane encourages herd expansion, the resulting increase in enteric fermentation emissions could even offset the benefits of mono-digestion. In the worst-case scenario, a larger herd could lead to significantly higher total emissions that surpass the reductions achieved through manure digestion.

So the subsequent question is: how much emission from livestock production would be compatible with a climate-neutral system?

Unlike fossil fuels, emissions from cattle are part of a short carbon cycle. This cycle begins with grass absorbing atmospheric carbon during growth. Cattle consume the grass and digest its cellulose to support their metabolism – releasing methane through enteric fermentation – and produce manure, which emits additional GHGs. While this cycle does not introduce new carbon to the atmosphere, it does release methane, a potent GHG. As a result, cattle herds are not climate-neutral.

Over time, methane breaks down into CO2 and water. If methane emissions remain constant, an equilibrium may eventually be reached in which the cycle – methane emissions, breakdown into CO2, uptake by grass, and restart – becomes balanced. Scientists have been studying what concentrations of methane and other GHGs are considered safe, but there is no clear answer. The IPCC Sixth Assessment Report provides the most up-to-date insights on the matter.

A key principle is that biogenic methane and CO2 emissions do not need to be zero by definition in a climate-neutral food and energy system. This perspective is adopted by RaboResearch in our analysis of net-zero implications for the agricultural sector.

Manure-based biogas can contribute to climate goals, as long as total biogenic methane emissions from agriculture decline at a pace aligned with global net-zero targets. Therefore, manure-based biogas can only serve as a partial solution for reducing total agricultural emissions. Its effectiveness depends on ensuring that deploying digestion does not result in a growing herd size, which could compromise future methane budgets.

Manure digestion presents a short-term opportunity for significant relative reductions in GHG emissions. Biomethane production can help lower livestock-related emissions – provided it is not accompanied by herd expansion – while also reducing demand for natural gas. Realizing this potential and developing a viable biomethane market model would be a meaningful contribution to climate goals.

However, policies promoting biomethane must be carefully designed to avoid incentivizing further investment in livestock, which could lead to increased methane emissions. In the Netherlands, the livestock population is already expected to decline in the coming years, RaboResearch's Vision for agri-food 2040 outlines four scenarios for 2040, all of which are based on a shrinking herd size. This trend is driven primarily by pressure on local ecosystems and political incentives. In several regions of the Netherlands, the use of natural space exceeds ecological boundaries and must be reduced to remain within sustainable limits.

While this research has focused on assessing the relative GHG emissions of treated versus untreated manure life cycles, other potential impacts – such as methane leaks – should not be overlooked. Even though existing research shows significantly lower methane leakage for biomethane than for fossil gas supply, a solid framework for methane leak detection and repair will also be essential in effectively realizing GHG emissions reduction.

Finally, safeguarding the climate in the long term will require a shift in the policy framework – from focusing on relative avoided emissions benchmarks under RED III to emphasizing absolute emissions reduction targets.

In summary, biomethane from manure digestion can contribute to a more sustainable society in the long term – provided that supportive policies do not incentivize herd expansion. The policies implemented by both the European Commission and the Dutch government show strong alignment with current knowledge regarding the sustainability potential of biogas production.