Mitigation of climate change - Land Based Carbon Management

Carbon Sinks and Land-Use Strategies Introduction Forests, soils, and wetlands can absorb and store carbon dioxide, acting as carbon sinks—natural reservoirs that remove carbon from the atmosphere. Understanding how to protect and manage these carbon sinks is essential for climate change mitigation. This unit covers the major land-based strategies for carbon sequestration, including forest conservation, reforestation, soil management, and protection of peatlands and wetlands. Forest Conservation and the Power of Existing Forests Forests are Earth's most important terrestrial carbon sinks. They store approximately 60% more carbon than secondary regrowth forests (younger forests that have regrown after disturbance). This means that existing, mature forests are exceptionally valuable for climate mitigation. Proforestation is the strategy of allowing existing forests to reach their full ecological potential—essentially protecting them from degradation and allowing them to continue accumulating carbon. This is particularly effective: intact forests in the United States sequester twice as much carbon annually as they emit, making protection of existing forests one of the highest-impact climate strategies available. Preventing deforestation in tropical regions is especially critical. The mitigation potential is enormous: stopping tropical deforestation could prevent 4.2 to 7.4 gigatonnes of carbon dioxide equivalent emissions per year. This matters because once forests are cleared, both the standing trees and the soil carbon are lost, and recovering that carbon storage takes decades. The key insight here: protecting existing forests is generally more effective than planting new ones, because mature forests have already accumulated their carbon stocks and continue to grow and sequester more. Afforestation and Reforestation: Creating New Forests While protecting existing forests is most effective, establishing new forests also plays an important role. Understanding the difference between these two approaches is crucial: Afforestation means planting trees on land that had no recent tree cover—such as grasslands or abandoned agricultural land. Large-scale afforestation could potentially store over 2,300 gigatonnes of carbon dioxide by 2100. However, afforestation competes with other land uses, particularly food production and natural grassland ecosystems, so it requires careful planning to avoid negative trade-offs. Reforestation means replanting trees on land that was recently forested but has become degraded or deforested. Reforestation can capture at least 1 gigatonne of carbon dioxide per year at a cost of US$5–15 per tonne—making it cost-effective. Importantly, reforestation generally provides higher carbon storage than afforestation because existing root systems and soil carbon in the degraded forest land are retained, giving the new forest a "head start." The effectiveness of tree planting varies significantly by region, tree species, and land availability. Large-scale campaigns can offset a decade of global CO₂ emissions, but this potential is location-dependent and must be weighed against other priorities like food security and biodiversity conservation. Soil Carbon Management and Conservation Farming Soils contain vast amounts of carbon—in fact, soil stores more carbon than the atmosphere and all living plants combined. Yet conventional farming practices often deplete this soil carbon, degrading soils over time and releasing stored carbon. Conservation farming protects and rebuilds soil carbon. Key practices include: Reduced tillage or no-till farming: Minimizing or eliminating the turning of soil, which prevents the oxidation of soil organic matter Cover cropping: Growing non-commercial plants (like legumes or grasses) during off-seasons to add organic material to soil Organic amendments: Adding compost or other organic material to rebuild soil health These practices can increase soil organic carbon stocks by 0.1–0.4 tonnes of carbon per hectare per year. This may seem modest, but globally, if implemented broadly, restoring healthy soils could remove approximately 7.6 billion tonnes of carbon dioxide from the atmosphere each year—exceeding the total annual carbon emissions of the United States. Measuring and accounting for soil carbon changes is complex because carbon storage varies widely depending on soil type, climate, and management practices. This complexity makes it challenging to quantify exactly how much carbon is being sequestered in a given area. Biochar: Ancient Wisdom Meets Modern Carbon Science Biochar is a specially produced form of charcoal created by heating biomass (plant material) in the absence of oxygen, a process called pyrolysis. About half of the biomass carbon is released as energy during production; the other half remains locked in stable biochar that can persist in soil for thousands of years. When biochar is added to soil, it provides multiple benefits: Carbon storage: Up to 1 tonne of carbon per tonne of biochar produced can be sequestered, making it a credible negative-emissions pathway Improved soil fertility: Biochar increases water retention and nutrient availability, particularly benefiting acidic soils Agricultural productivity: These soil improvements can boost crop yields Additionally, the heat released during biochar production can be captured for bioenergy, making the process potentially carbon-negative while also providing useful energy. Above-Ground and Below-Ground Carbon: Understanding Tree Carbon To fully understand how forests contribute to carbon sequestration, it's important to recognize the distinction between carbon stored above and below ground. Trees capture atmospheric carbon dioxide while growing above ground, storing it in their wood. Simultaneously, trees exude carbon (through their root systems) that becomes part of the soil carbon sponge—the organic matter in soil that holds carbon and water. However, there's a critical difference in what happens to this carbon: Carbon in standing wood: When wood is burned for fuel or energy, this carbon is released immediately as carbon dioxide Carbon in dead wood and soil: If dead wood remains untouched and decomposes naturally, only a portion of its carbon returns to the atmosphere as decomposition occurs; some continues to accumulate in soil organic matter This distinction matters for climate strategy: planting trees for eventual harvest and burning does not provide the same climate benefit as allowing forests to grow and letting their carbon accumulate in living wood and soil over time. Peatlands and Wetlands: High-Value but Vulnerable Carbon Stores Certain ecosystems are exceptionally valuable for carbon storage because they accumulate carbon at rates far exceeding normal forests. Peatlands are among the most carbon-rich terrestrial ecosystems. They store roughly one-third of all global soil carbon, despite covering only about 3% of Earth's land surface. This concentrated carbon storage occurs because peatlands are waterlogged, which slows decomposition and allows carbon to accumulate over thousands of years. However, peatlands are extremely vulnerable. When peatlands are drained for agriculture or development, the water table drops and previously waterlogged peat is exposed to oxygen. This triggers rapid decomposition, releasing massive quantities of both carbon dioxide and methane—a particularly potent greenhouse gas. Protecting intact peatlands is essential to avoid these large, abrupt carbon emissions that could significantly accelerate climate warming. Coastal wetlands, particularly mangroves, can sequester carbon at a relatively low cost of approximately US$1,800 per tonne of carbon, making them among the most cost-effective nature-based climate solutions. In contrast, inland wetlands have higher restoration costs (US$4,200–49,200 per tonne of carbon) and are generally better preserved than restored for climate purposes. AFOLU: Land-Based Mitigation Strategies The term AFOLU stands for Agriculture, Forestry, and Other Land Use. This encompasses all the land-based mitigation strategies discussed in this unit. AFOLU mitigation options include: Preventing deforestation and forest degradation Restoring degraded ecosystems Improving agricultural practices to increase carbon uptake in soils Protecting peatlands and wetlands Implementing conservation farming practices Land-based mitigation strategies are particularly valuable because they often provide co-benefits beyond carbon sequestration, such as improved soil health, enhanced biodiversity, and increased agricultural resilience. <extrainfo> Additional Considerations Ocean Acidification and Marine Impacts: While focusing on land-based carbon sinks, it's worth noting that increased atmospheric CO₂ has consequences for oceans. Higher CO₂ levels lower ocean pH, making water more acidic. This threatens marine organisms that build calcium carbonate shells—including corals, shellfish, and some plankton. Ocean acidification reduces these organisms' ability to build and maintain their shells, potentially disrupting marine food webs. Enhanced Weathering: Another emerging strategy involves spreading silicate minerals on land. These minerals naturally absorb carbon dioxide, but spreading them accelerates this carbon capture process while also potentially improving soil health. Best Management Practices for Specific Regions: For European soils specifically, effective practices include converting arable land to grassland, incorporating straw into soil, reducing tillage intensity, and using ley cropping systems (alternating between crops and pasture). </extrainfo>