Soils store enormous amounts of carbon. Due to climate change and intensive agriculture, however, they risk transforming from a carbon sink into a source of emissions. “Carbon farming” aims to prevent this and EU regulations establish the legal framework. Yet, many challenges persist.

Paradox of the soil: from carbon sink to carbon emitter

For a long time, the significance of healthy soils remained largely absent from political discourse. Only in recent years has increased attention been directed toward them, particularly as a mechanism for achieving climate targets. This shift is well-founded: healthy soils sequester two to four times as much carbon as the atmosphere and vegetation combined, thus offering a critical contribution to limiting global warming to below two degrees Celsius.

However, the implications extend beyond carbon storage, as Alfred Hartemink, Professor of Soil Science at the University of Wisconsin-Madison, explains: “The soil is at the intersection of all important environmental challenges like climate, biodiversity, food, and water security.” Generally, a high proportion of soil organic carbon (SOC) correlates with enhanced soil quality and greater resilience against external stressors.

Conversely, intensive agricultural practices and climate change exert significant pressure on soils, depleting their stored carbon content. Simultaneously, alterations in soil carbon levels influence the climate, resulting in a feedback loop. Carsten Müller, Professor of Soil Science at the TU Berlin, illustrates this dynamic: “Since humans transitioned from hunter-gatherers to sedentary agriculture and livestock farming, we have been losing carbon from our soils. Through our agricultural practices – our 'way of life,' so to speak – and our cultivation systems, we initially lost carbon, and this remains the case in part, simply due to land use. [...] What further complicates matters now is anthropogenic climate change. This means many systems are losing their resilience, particularly due to catastrophic events such as large-scale wildfires, which are occurring more frequently because of climate change. These events simultaneously reset the storage function and lead to an increased release of carbon.”

Rising temperatures, shifting precipitation patterns and prolonged droughts affect soil moisture, vegetation and microbial activity. Consequently, organic substances in the soil may decompose more rapidly, diminishing its carbon sequestration capacity. In the worst-case scenario, the soil transforms from a carbon sink into a net carbon source – with direct consequences for atmospheric CO2 concentrations.

The complexity of measuring soil organic carbon

While measuring atmospheric CO2 concentrations is scientifically straightforward, determining the carbon sequestration capacity of soils proves significantly more challenging. Soils exhibit spatial heterogeneity; even minor plots can show vast differences in vegetation, reflecting diverse structures and nutrient levels. Consequently, individual soil samples are rarely representative. Furthermore, agricultural management continuously alters soil architecture. Practices such as ploughing, sowing, and fertilizing cause constant fluctuations in carbon content, as Müller explains: “Management itself introduces uncertainties, primarily because it generates varying soil densities. Freshly tilled soil is relatively loose, but subsequent operations throughout the year – along with natural settling – lead to fluctuating soil volumes. This is a critical factor: when the same mass of soil occupies a different volume, you must establish a relationship between the two, which makes the process incredibly difficult.”

Data accuracy depends not only on location and method but also on timing: “Looking at the annual cycle, carbon levels fluctuate within certain amplitudes between harvesting, sowing and fertilizing. These variables further complicate the assessment”, says Müller.

While established measurement methods are judged to be reliable, they remain too labour-intensive and costly for large-scale application. Scientists are therefore increasingly integrating field measurements with models to estimate carbon dynamics across expansive areas, as Hartemink explains: “We need soil sampling to reduce the uncertainty of soil carbon assessments, and we need models to make predictions across very large areas. We can't sample everywhere all the time.”

Supporting policies through research

This integrative approach is employed by the EU-funded project MRV4SOC, which seeks to establish a robust and transparent monitoring, reporting and verification (MRV) system for soil organic carbon and greenhouse gas balance. Project coordinator Marta Giménez Gómez describes its methodology:

“The project aims at designing a robust, transparent, and cost-effective Tier 3 approach to capture the dynamics of soil organic carbon storage. This means we are using process-based models. Process-based models allow us to simulate the response of adopting carbon farming practices under different conditions and scenarios; therefore, assessments can be upscaled to larger areas without having all the datasets measured at all locations, assuming proper model calibration. Depending on the processes to be represented in the model, conditions and area of analysis, a scaleable model-based Tier 3 approach combining in-situ and remote sensing data may be a more cost-effective approach than a 'measure-remeasure' approach.”

The project operates across 15 diverse sites, ranging from agricultural and forestry lands to peatlands. Given the site-specific variability, the framework incorporates multiple parameters, including ecosystem health, soil condition, climate data and historical land-use patterns.

These scientific advancements are highly relevant to current policy developments. With the Carbon Removal and Carbon Farming (CRCF) Regulation, enacted in late 2024, the EU established a voluntary legal structure to certify permanent carbon removals, carbon farming and carbon storage in products. However, specific methodologies for soil carbon certification are to be determined, with the European Commission having launched a public consultation in January 2026.

The core purpose of carbon farming is to incentivise sustainable land management by rewarding farmers with tradable carbon credits for verified sequestration. The viability of such a market depends entirely on reliable measurement – a gap the MRV4SOC project intends to bridge, says Giménez Gómez: "We are contributing to high-level policy discussions related to the certification methodologies as we are studying how to measure the effects of carbon farming practices in terms of robustness, transparency and cost-effectiveness."

From sequestration to certification: what are the limits of the "soil solution"?

Significant hurdles remain when it comes to the permanence of these sinks. Extreme weather events and land-use changes can cause a release of stored carbon – back into the atmosphere. Project coordinator Giménez Gómez agrees: “Weather extremes and long-term climate shifts must be also considered because they may cause a reversal of the positive effects achieved through the adoption of carbon farming practices.”

Furthermore, soil carbon sink capacity is finite, and trade-offs with other greenhouse gases – such as nitrous oxide (N2O), which has a significantly higher global warming potential than CO2 – must be considered. While carbon farming promises additional income for farmers, it is in stark contrast to economic realities. Carbon certificate prices are subject to high volatility, and participants may face substantial monitoring and bureaucratic costs. Moreover, a system rewarding additional sequestration risks penalising those who have already adopted sustainable practices.

The implementation of carbon farming also hinges on social factors. Ensuring farmer buy-in is critical, yet hurdles such as market uncertainty, resistance to change and the technical complexity of carbon farming techniques persist. Many EU-level specifics regarding methodologies, thresholds and monitoring periods remain politically undefined.

Crucially, the system’s credibility must be protected against greenwashing. Without reliable data, corporations might use credits to offset emissions rather than actually reducing them. “You need to make soil carbon models and predictions verifiable, transparent, and comparable. If people are making claims about offsetting carbon, they actually have to show that - extraordinary claims require extraordinary evidence,” says Hartemink.

While soils offer relevant sequestration potential, the focus on carbon content is too narrow, points out Müller: “Much more decisive than the pure quantity is the function of soil carbon for fertility, water retention and the climate. It is a central element of the soil – yet it is often forgotten that carbon is only one part of the total organic matter. The positive aspect is that by increasing humus content, we simultaneously promote many other functions, such as biodiversity. Nevertheless, this holistic benefit is still frequently overlooked in the current debate.”

A sustainable approach must therefore integrate economic incentives and certifications with soil health, establishing it as the fundamental pillar of climate-resilient land use.

Article by Cornelia Trefflich