Soils, land use change and forestry

A growing world population means increasing demand for food and resources. Even if population growth halted overnight, the fact that a significant part of the global population has insufficient or poor quality food would necessitate substantial growth in food production. This necessarily comes primarily from agriculture and agriculture offers two ways of accommodating growth – through expansion (cultivating more land) or intensification (producing more from the same land). Of course, expansion can take place without using more land – for example, in vertical farming, urban agriculture, rooftop farming, etc. While such systems can contribute significantly to the production of crops such as vegetables and legumes, most systems (including greenhouses, etc. in peri-urban areas) still require land.^[80] Emissions from land use are complex and go both ways – release and sequestration. Land use change also leads to changes in albedo (a measure of energy reflectance), evapotranspiration and release of various volatile compounds.^[81]

Agriculture offers two ways of accommodating growth – through expansion (cultivating more land) or intensification (producing more from the same land)

From ancient times right up to today, new land is continually being brought under the plough. Very often this is forest land. Around 10,000 years ago, some 57 percent of the Earth’s landmass was covered in forest (the rest was wild shrub and grassland). Today, forest covers only 38 percent of Earth’s landmass.^[82] Forests represent a significant carbon reservoir and help to build up soil carbon as well as providing several other environmental services. However, forests are vulnerable to destruction and can therefore be considered as temporary storage, as the accumulated carbon is likely to be released when the trees die and decompose, unless they are replaced by new vegetation. This process of regeneration would be the normal course of events in a stable forest ecosystem, which therefore would effectively constitute long-term carbon storage.

China, India and Türkiye are currently the countries with the highest reforestation rates

The global rate at which forest is being converted to other land use, such as agriculture or infrastructure development, etc. (that is, deforestation), is currently around 5 million hectares per year, with 95 percent taking place in the tropics, estimated to contribute 6.6 percent of annual global CO₂ emissions.^[83] The major drivers of deforestation are agriculture, wood extraction and infrastructure development.^[84] In terms of agriculture, beef, soybean and palm oil are the major culprits. Beef is by far the largest driver of deforestation, especially in the Amazon rainforest.^[85]

Around half of global deforestation is countered by forest regrowth.^[86] Much of Europe’s forest was cleared centuries ago to provide land for agriculture, wood for fuel and timber for ship and house building. Temperate regions have, since 1990, generated more forest than they destroy. Since the peak deforestation rate in the 1980s, rates have slowly declined, although they still indicate net deforestation. China, India and Türkiye are currently the countries with the highest reforestation rates but it should be noted that the reforestation undertaken is often monoculture and sometimes uses invasive species – neither factor benefiting biodiversity.

Forest loss also results from degradation of forest land without necessarily changing the land use completely and where regrowth would be able to occur. Forest and carbon storage loss therefore is a result of both deforestation and forest degradation. Around a quarter of global annual forest loss is from deforestation while the rest is from degradation, more or less equally distributed between wildfires, logging and shifting cultivation (temporary fields in forest areas).^[87]

Other land cover types, such as wetlands, peatlands, steppe and grasslands, are also converted to agricultural land. Peatlands are of particular concern as they store vast amounts of carbon, accumulated over centuries, which is released through drainage, drying out and burning. Carbon emissions from land use, land-use change and forestry (LULUCF) make up as much as 21 percent of global anthropogenic GHG emissions but due to the complexity of the processes involving both emissions and sinks, the estimates are rather uncertain. Deforestation is estimated to account for around 45 percent of these emissions.^[88] The Amazon rainforest covers 6.7 million km₂ (twice the area of India), but already between 18 and 20 percent has been deforested and another 38 percent degraded, with the risk of reaching a 25 percent tipping point, after which the Amazon ecosystem is at risk of breakdown.^[89]

As mentioned in the introduction, agriculture and land use have the second largest mitigation potential after energy supply. Within this group, the biggest mitigation potential lies in “reduced conversion of natural ecosystems” (4.1 GtCO₂eq/yr) and another 2.8 GtCO₂eq/yr from “ecosystem restoration, afforestation, reforestation”. It is estimated that 30–50 percent of the Earth’s land, freshwater and ocean areas must be conserved in order to maintain the resilience of biodiversity and ecosystem services.^[90]

There is therefore a strong imperative for reversing the carbon emissions from LULUCF, and innovation and technology can provide some of the solutions.

Read less

Limiting conversion of natural ecosystems

In relation to reducing land conversion – which offers the greatest mitigation potential – policy and economics play crucial roles. However, technology can help policymakers and businesses understand the current state of forests and other high-carbon areas, visualize losses from land conversion and pave the way for efficient monitoring, which may trigger carbon financing. With the increasing availability of accurate and frequently updated data, it will be harder for decision-makers to act against climate pledges and other commitments. Satellites, drones, in-situ sensors and advanced software platforms make all this data available at low cost and often even free of charge. Furthermore, data can cross national borders, enabling a complete ecosystem or watershed approach rather than focusing only on national resources.

The demand side can also be supported with innovation and technology. All the technologies that allow farmers to be more productive by intensifying their production and by producing more with less land, can reduce the need to convert forests into new agricultural fields. However, for this to be effective, strong policy measures are also required to limit expansion of agriculture into new areas and to limit negative impacts of a more intensified agricultural system. Agricultural intensification has already had an enormous impact, clearly illustrated by the 7 percent increase in agricultural land since 1961, while global population has expanded by 147 percent.^[91]

This result was brought about not least by the green revolution and associated technological advancements, and innovation and technology continue to support this trend. This chapter has already touched on several relevant technologies and the list of options and possibilities is long indeed. The more advanced technologies associated with precision farming support this objective, as do new plant varieties, better agricultural inputs and more efficient irrigation. But simpler tools and technologies, which can provide that extra yield and security for the farmer, also make a contribution.

Ecosystem restoration, afforestation and reforestation

The protection of existing forests and ecosystems, and restoration of those that have been disturbed or destroyed, is crucial for achieving the Paris Agreement goals. In order to act as carbon sinks, forests must be monitored and protected against destructive events such as forest fires, which are already exacerbated by climate change. Here, technologies such as new tree varieties that are more resistant to fire and better adapted to variable growing conditions are important, as is forest health monitoring. Due to the vast and often relatively inaccessible areas covered by forests, drones and satellite multispectral images are particularly useful. Multispectral images can reveal detailed information on the condition of the forest, identify pest attacks and monitor several other growth parameters. This information can be treated in GIS and other advanced software systems for improved management and planning and is also a prerequisite for issuance and verification of carbon credits. Some of these technologies are described in Chapter 3 of the Green Technology Book: Solutions for Climate Change Adaptation.

What is on the land not only determines the actual storage of carbon in vegetation, etc. but also has a direct influence on the carbon that is stored underground. As such, land use change will often directly influence the carbon content of soils.

Soil carbon restoration

Soils contain large reservoirs of carbon. Globally, soils hold three times more carbon than the atmosphere contains.^[92][93] This vast amount of carbon is stored in soil organic matter, typically in the form of humus (dark organic part of soil), in the top 30–40 cm, and can be released through land use change and soil degradation. Alternatively, it can be increased through land restoration and appropriate cultivation practices.

Globally, soils hold three times more carbon than the atmosphere

GHG emissions from soils are mostly in the form of CO₂ and are complex to estimate, not least because of the many different forms of land use. For example, in the EU in 2019, member states reported net emissions of 108 million tons of CO₂ (MtCO₂) from organic soil and net removals of 44 MtCO₂ from mineral soil.^[94] The symbiosis between plants and mycorrhizal fungi in the soil also affects the mechanism of soil carbon accumulation and loss.^[95] Although soil carbon can remain stable for millennia, global warming is expected to increase the atmospheric release of soil carbon through increased microbial decomposition, potentially creating a feedback loop that will exacerbate the effects of climate change.^[96][97] Soils also contain and release nitrogen oxides (NO_x) and here also emissions take place through microbial activity that is sensitive to temperature, precipitation and other factors. However, the net emission of NOx from soils in various climate change scenarios is uncertain and is only partly understood.^[98] The soil carbon budget has been negative for decades, meaning that more soil carbon is released than is being sequestered, but this can be reversed.

The mitigation potential of soil carbon is debated, but there is general agreement that the potential is highly significant.^[99] At the 2015 United Nations Climate Change Conference (COP 21) in Paris, the “4 per 1,000 – Soils for Food Security and Climate” initiative was launched, based on the idea that increasing soil carbon by 0.4 percent per year (4 per 1,000) in the top 30–40 cm of soils, is enough to stop the increase of CO₂ in the atmosphere.^[100] However, realizing this goal will require significant permanent changes to the ways millions of farmers cultivate their lands, which effectively reduces the realistic mitigation potential significantly.

Restoring soil carbon and soil organic content not only acts as a CO₂ sink but has important co-benefits. These include improved soil fertility, and hence crop yields, increased climate change resilience and reduced soil erosion and water runoff. If soil regeneration is done through restoration of ecosystems and avoided conversion to agriculture or built-up areas, etc. it has associated benefits such as natural habitat and biodiversity gains. Restoring soil carbon therefore has intrinsic climate change adaptation benefits, and biodiversity gains may open up new income streams for farmers, such as from tourism and hunting.

One of the major challenges facing soil carbon restoration is that it requires large areas to be monitored and verified consistently over a long period. Restoration works take place over a period of 20–30 years and must be maintained permanently through proper land management to avoid reversion. However, if well maintained, soil carbon is generally less vulnerable to sudden disturbances such as fires, wind and pests than are aboveground biomass such as shrubs and trees.

Soils, with the exception of some wetlands, have a saturation point beyond which they can no longer absorb soil organic matter. However, this generally occurs only after decades of restoration, depending on the state of soil carbon depletion, and therefore does not diminish the potential of soil carbon to play an important role in the urgently needed removal of atmospheric carbon.^[101]

Biological and mineral products that help to build up soil carbon and improve soil health can be added to the soil. These can be in the form of microbes, which help to fixate carbon in the soil, pulverized minerals that speed up carbon sequestration and specific microbes that can help increase the transport of carbon from plant roots into the soil, such as rhizobacteria and mycorrhizal fungi.^[102] Carbon, in the form of biochar (see box 3.1), can be incorporated directly into the soil and is likely to remain there for millennia, thus effectively taking that carbon out of circulation.

Biochar is a charcoal-like stable form of carbon made from pyrolysis (burning without oxygen) of organic material such as farm waste and by-products (for example, rice husks, peanut- and coconut shells). As it is highly porous, lightweight, fine-grained and has a large surface area, biochar adds desirable physical properties to soil and increases soil fertility. Depending on its origin, it consists of around 70 percent carbon. Biochar production has several advantages, such as recycling organic waste, renewable energy production, removing carbon from circulation and increasing soil carbon.^[103] Biochar’s efficiency in generating these benefits depends on climate, context, methods, etc. and the mitigation potential therefore also varies considerably.

Despite all these advantages, there are still relatively few soil carbon projects compared to forest projects, for example, that can be supported by verified Emission Reduction Credits (ERCs). This is partly due to the limited experience with such projects as they were excluded from the Kyoto Protocol’s Clean Development Mechanism. However, this situation is changing rapidly and new services for registering, marketing and monitoring ERCs from regenerative agriculture are gaining popularity. By injecting carbon funding into regenerative farming and other soil carbon-positive activities, farmers may obtain the financial encouragement that makes the difference and reduces risks when deciding whether to change their practices. Incentives that make transitions economically viable for farmers are crucial for widespread adoption of new practices and include carbon-removal marketplaces, transition finance, ecosystem service payments, transition loans, crop insurance, etc. and here too innovation and technology have contributions to make.
Read less

Many ways to restore soil carbon

Several approaches and agriculture practices exist for restoring soil carbon using both simple and more advanced technologies.

Regenerative agriculture is one of the terms that often surfaces in relation to restoration of soil carbon. The term is broad and covers many technologies, techniques and practices that may have a positive impact on land and agricultural systems, and thereby soil carbon. Most often it comprises alternative land preparation practices, such as no-tillage, planting and ploughing down cover plants to protect soils from erosion and accumulate organic matter within the soil, use of nitrogen-fixating trees, legumes and cover plants, combined agriculture, forestry and also livestock in carefully managed systems, legumes in pastures, perennial crops with deep roots, peatland restoration, avoidance of pesticides, insecticides and synthetic fertilizers, and use of bio-based fertilizers, manure, compost and soil improvement additives, such as biochar. It also comprises technologies in relation to soil sampling, analyses, monitoring and validation.

Zero- and low-tillage technologies

Zero-till, no-tillage or conservation agriculture is an approach in which the soil is disturbed as little as possible and bare soil exposure is avoided. It entails leaving crop residue from the previous harvest intact and avoiding soil preparation, such as plowing and harrowing, combined with the use of cover crops. Promoted since the 1960s, the practice originally mostly targets avoiding soil erosion and is widespread, especially in the United States and Latin America, where, in Brazil and Argentina, for example, more than half of all food is grown under the no-tillage system. Other benefits are reduced use of fuel, avoidance of soil compaction, increased water infiltration, reduced pollution of waterways from runoff and improved air quality due to reduced wind erosion of bare soil.^[104] How great an effect no-tillage can have on soil carbon sequestration is debated and will depend on various factors such as the soil characteristics, crops, practices, climate, etc.^[105] Sowing and other processes require specialized equipment, typically a disc seeder which opens a slit in the soil and deposes the seed and chemical fertilizer simultaneously underground. Many adaptations to such seed drills already exist and recent advances in GPS-controlled precision agriculture machines are enabling soil disturbance and compaction to be minimized.^[106]

In practice, adoption of the no-tillage approach often goes through three steps when transforming agricultural practices into full conservation agriculture systems, namely: no-burning, no ploughing and growing a cover crop. Experience shows that reaching the last stage can be difficult for many farmers and the process can take several years.^[107] The costs related to the acquisition of new equipment are also a common barrier to adoption.^[108]

More sustainable weeding technologies

One of the major environmental drawbacks of the no-tillage approach is widespread reliance on herbicides for weeding, such as glyphosate or similar compounds under trademarks such as Roundup, Touchdown and Buster. Development of herbicide resistance in weeds is a related serious concern. Alternatives to herbicides are being developed and several bio-based products certified for biological agriculture are available, which could provide an option with fewer health risks for both soils and consumers. Especially in South America, the use of crop rotation and cover crops, some with allelopathic benefits (producing biochemicals that hamper growth of others), and mechanical weeding have been able to reduce dependency on herbicides and synthetic fertilizers.^[109] Integrated weed management and careful use of crop rotation and cover crops may reduce the amount of herbicide used, but whether herbicides can be fully eliminated is still a focus of agronomic research.^[110]

Many forms of mechanical weeding exist but most have in common the fact that they must be pulled by a tractor or similar heavy machinery, in direct opposition to the principle of no-till. But here also innovation and technology may offer alternatives. Weeding robots, being smaller and lighter, may provide a feasible option for mechanical weeding in no-till systems. Swarms of lightweight weeding robots could potentially eliminate the need for herbicides. Other solutions opt for single units with solar panels and/or swappable batteries that allow for extended periods of operation, which makes up for their sometimes-slow operating speed. Some solutions use optical sensors to identify weeds and accurately apply small doses of herbicide thus greatly reducing the use of chemicals. If spraying is done by drones guided by images of the field that identify areas where spraying is needed, the amount of herbicide used can be reduced with fewer wheels on the ground. Business models based on robot rental are helping to make them more economically attractive to farmers.

More ways to recover soil carbon

Other forms of regenerative agriculture, such as organic farming, agroecology, silvopasture (integration of trees and grazing), climate-smart agriculture, agroforestry and permaculture are all complex and not mutually exclusive agricultural systems that can have substantial positive impacts on soil carbon in specific geographies. It is often a matter of rethinking existing practices – for example, planting livestock fodder such as nitrogen-fixating alfalfa as a cover crop between rows of other crops where livestock can graze and deposit manure. Land taken out of cultivation and used for solar panels may also accumulate soil carbon. If the land with solar panels is cultivated, it has the potential to both increase soil carbon and replace fossil fuel. New agrivoltaic arrays allow more sunlight to reach the plants beneath, while some crops, such as cauliflower and cabbage, are shade tolerant. Tomatoes, berries, grapes and fruit trees have also been shown to perform well in agrivoltaic scenarios. For some crops, the protection against extreme heat makes up for the reduced direct sunlight exposure.^[111] Implementing agrivoltaics on rooftops in urban areas is also gaining attention.^[112]

In summary, increasing soil carbon can be achieved based on readily available measures that do not require large investments or more land, have a small water footprint and trigger important co-benefits.
Read less