Report on Global Carbon Sequestration Changes Induced by Land Cover Conversions (1981-2019) and Implications for Sustainable Development Goals

1.0 Introduction: Land Use and the Urgency of Climate Action (SDG 13)

Achieving the United Nations Sustainable Development Goals (SDGs), particularly SDG 13 (Climate Action) and SDG 15 (Life on Land), requires a comprehensive understanding of the global carbon cycle. Terrestrial ecosystems are critical carbon sinks, yet their capacity is significantly altered by Land Cover Conversions (LCC) driven by human activities such as deforestation, agriculture, and urbanization. This report analyzes the net impact of LCC on global carbon sequestration, measured by Net Ecosystem Productivity (NEP), from 1981 to 2019. The findings are based on an analysis using the remote sensing-driven Biosphere-atmosphere Exchange Process Simulator (BEPS) model and the high-resolution HILDA+ land cover dataset. This analysis provides crucial insights for developing evidence-based land-use policies to advance global carbon neutrality and sustainable development.

2.0 Key Findings: Global and Regional Carbon Dynamics

2.1 Global Land Cover Conversion Trends (1981-2019)

Analysis of the HILDA+ dataset reveals significant global land cover transformations over the 39-year period, with direct implications for SDG 15 (Life on Land) and SDG 2 (Zero Hunger).

• Forests: A net decline of 790,000 km², resulting from a gross loss of 3.43 million km² (primarily in the tropics) and a gross gain of 2.64 million km² (primarily in the Northern Hemisphere). This net loss poses a direct challenge to SDG 15.2, which calls for an end to deforestation.
• Cropland: A net expansion of 710,000 km², reflecting increasing pressure on land resources to meet global food demands (related to SDG 2).
• Urban Areas: A net expansion of 390,000 km², often at the expense of productive agricultural land or natural ecosystems, impacting SDG 11 (Sustainable Cities and Communities).
• Pastureland: A net decrease of 360,000 km².

2.2 Net Impact of LCC on Global Carbon Sequestration (SDG 13)

Despite the net loss of global forest area, LCC resulted in a surprising net global carbon gain, highlighting a complex interplay of factors crucial for climate action strategies.

1. Overall Carbon Budget: LCC led to a net terrestrial carbon sequestration gain of 229 Tg C between 1981 and 2019.
2. Forest-Related Conversions: Forest dynamics were the primary driver of carbon flux changes.
   • Gains from Afforestation/Reforestation: The establishment of new forests contributed a massive carbon gain of 1559 Tg C. This demonstrates the powerful potential of restoration activities in achieving SDG 13 and SDG 15.
   • Losses from Deforestation: The conversion of forests to other land uses resulted in a nearly equivalent carbon loss of -1544 Tg C.
3. The Offsetting Effect: The carbon sequestration from newly established forests in the Northern Hemisphere almost completely counterbalanced the emissions from tropical deforestation. This underscores a critical geographic imbalance in progress toward global climate goals.

2.3 Regional Disparities in Carbon Flux and SDG Progress

The impact of LCC on carbon sequestration is not uniform, revealing significant regional disparities in land management practices and their alignment with sustainable development.

• Regions of Carbon Gain (Advancing SDG 13):
  • Europe: +310 Tg C
  • United States: +220 Tg C
  • China: +215 Tg C
  • Russia: +143 Tg C

  These gains were primarily driven by afforestation and reforestation programs, where pasture, cropland, and shrubland were converted to forests. These actions directly support SDG 15.1 and 15.2.

• Regions of Carbon Loss (Hindering SDG 13 & SDG 15):
  • Indonesia: -278 Tg C
  • Brazil: -157 Tg C
  • Democratic Republic of Congo: -120 Tg C

  These losses were predominantly caused by deforestation for agricultural expansion (cropland and pasture), directly undermining efforts to halt biodiversity loss and deforestation as mandated by SDG 15.

2.4 The Critical Role of Forest Age in Carbon Sequestration Efficiency

A key finding is that the age of a forest is a determining factor in its carbon sequestration efficiency. This has profound implications for sustainable forest management (SDG 15.2).

• Higher Efficiency of Young Forests: Newly established forests, primarily located in temperate regions (average age: 73 years), demonstrated a superior carbon sequestration capacity. Forest gain resulted in an accumulative NEP increase of 281 g C/m².
• Lower Efficiency of Old Forests: Older, degraded forests, mainly in tropical deforestation hotspots (average age: 160 years), were less efficient sinks. The loss of these forests resulted in an NEP reduction of 192 g C/m².
• Conclusion: The high sequestration efficiency of younger forests, despite their smaller total area, was sufficient to offset the carbon losses from the larger area of cleared, older forests. This highlights that strategic reforestation can yield disproportionately large climate benefits.

3.0 Implications for Policy and Achieving the Sustainable Development Goals

The findings provide a clear mandate for spatially informed and age-conscious land-use strategies to accelerate progress towards carbon neutrality and the SDGs.

1. Prioritize Halting Tropical Deforestation (SDG 15): The significant carbon losses in Southeast Asia, the Amazon, and Central Africa are a major impediment to global climate goals. International cooperation and support (SDG 17) are essential to help these nations implement policies that protect primary forests, such as establishing protected areas and incentivizing sustainable agriculture.
2. Promote and Sustain Afforestation Efforts (SDG 13 & 15): The success of afforestation in the Northern Hemisphere should be scaled and supported. Policies must ensure the long-term management of these young, growing forests to maximize their carbon sink potential as they mature.
3. Integrate Agricultural and Forest Policy (SDG 2 & 15): Cropland expansion remains a primary driver of deforestation. Achieving Zero Hunger (SDG 2) must not come at the expense of Life on Land (SDG 15). Policies should focus on agricultural intensification on existing farmland—using techniques like crop rotation, reduced tillage, and organic fertilization—to increase yields without expanding land use.
4. Leverage Forest Age Dynamics in Management: Forest management strategies should be tailored to forest age. While protecting old-growth forests for their immense carbon stock and biodiversity value is crucial, strategic harvesting post-maturity in managed plantations, coupled with vigorous reforestation, can optimize the overall carbon sequestration cycle.

Analysis of Sustainable Development Goals in the Article

1. Which SDGs are addressed or connected to the issues highlighted in the article?

The article on land cover conversions (LCC) and their impact on carbon sequestration is directly and indirectly connected to several Sustainable Development Goals (SDGs). The primary focus on carbon dynamics, forest management, and land use change links the research to the following SDGs:

• SDG 13: Climate Action: This is the most central SDG to the article. The entire study revolves around quantifying terrestrial carbon sinks, understanding the impact of land use on Net Ecosystem Productivity (NEP), and informing “evidence-based climate mitigation strategies” and “carbon neutrality goals.” The article’s focus on carbon sequestration as a mechanism to mitigate climate change directly addresses the core of SDG 13.
• SDG 15: Life on Land: The article is fundamentally about the management of terrestrial ecosystems. It provides detailed analysis of “deforestation,” “afforestation and reforestation,” and the conversion of land between forests, cropland, and pasture. It explicitly discusses the need to “halt deforestation, restore degraded forests and substantially increase afforestation and reforestation globally,” which is a key component of SDG 15.
• SDG 2: Zero Hunger: The article links land use change to agriculture, noting that “cropland expanded by 7.1 × 10⁵ km²” and that this expansion is a major driver of deforestation. It also proposes “intensified agricultural management” and “enhancing productivity within existing croplands” as a strategy to reduce ecological damage, which connects to the goal of achieving sustainable food production systems.
• SDG 11: Sustainable Cities and Communities: The article identifies urbanization as a factor in land cover change. It states that “urban areas expanded by 3.9 × 10⁵ km²” and quantifies the negative impact, such as in Indonesia where “urban sprawl further reducing NEP by 67 Tg C.” This relates to the need for sustainable urban planning that minimizes environmental impact.

2. What specific targets under those SDGs can be identified based on the article’s content?

Based on the article’s detailed analysis, several specific SDG targets can be identified:

1. Under SDG 13 (Climate Action):
   • Target 13.2: “Integrate climate change measures into national policies, strategies and planning.” The article’s conclusion explicitly aims to inform “carbon-neutral policies through optimized land management practices” and highlights the importance of “spatially informed land-use strategies in strengthening carbon sinks.”
2. Under SDG 15 (Life on Land):
   • Target 15.1: “By 2020, ensure the conservation, restoration and sustainable use of terrestrial and inland freshwater ecosystems and their services, in particular forests…” The study’s quantification of carbon sequestration (an ecosystem service) gains from afforestation and losses from deforestation directly relates to the sustainable use and restoration of forest ecosystems.
   • Target 15.2: “By 2020, promote the implementation of sustainable management of all types of forests, halt deforestation, restore degraded forests and substantially increase afforestation and reforestation globally.” The article’s core finding is that “afforestation and reforestation increased NEP by 1559 Tg C, largely offsetting deforestation-driven losses (−1544 Tg C).” It directly analyzes the progress and challenges related to this target.
   • Target 15.3: “By 2030, combat desertification, restore degraded land and soil… and strive to achieve a land degradation-neutral world.” The article discusses how land conversions lead to NEP reductions in 26.8% of terrestrial regions, which can be considered a form of land degradation. The promotion of afforestation and restoration is a direct action towards this target.
3. Under SDG 2 (Zero Hunger):
   • Target 2.4: “By 2030, ensure sustainable food production systems and implement resilient agricultural practices that increase productivity and production, that help maintain ecosystems…” The article’s discussion on how “global agricultural expansion has driven substantial deforestation” and its suggestion to enhance “productivity within existing croplands” to mitigate ecological losses directly addresses the need for sustainable agricultural practices that do not compromise ecosystems.
4. Under SDG 11 (Sustainable Cities and Communities):
   • Target 11.3: “By 2030, enhance inclusive and sustainable urbanization and capacity for… sustainable human settlement planning and management…” The article’s finding that “urban expansion” contributes to a reduction in carbon sequestration underscores the environmental impact of unsustainable urban growth, thereby highlighting the importance of this target.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

Yes, the article provides quantitative data and metrics that serve as direct or proxy indicators for measuring progress towards the identified targets.

• For Targets 15.1 & 15.2 (Indicator 15.1.1: Forest area as a proportion of total land area): The article provides explicit figures on forest area change: “forest coverage exhibited a gross gain of 26.4 × 10⁵ km² and a gross loss of 34.3×10⁵ km², resulting in a net decline of 7.9 × 10⁵ km²” between 1981 and 2019. These figures directly measure changes in forest cover.
• For Target 15.3 (Indicator 15.3.1: Proportion of land that is degraded over total land area): The study’s metric of “LCC-induced changes in net ecosystem productivity (NEP)” serves as a proxy for land degradation. The finding that “26.8% of terrestrial regions exhibited NEP reductions attributable to LCC” can be interpreted as a measure of land degradation from a carbon sequestration perspective.
• For Target 11.3 (Indicator 11.3.1: Ratio of land consumption rate to population growth rate): The article provides a direct measure of the land consumption rate for urban areas, stating that “Urban areas expanded by 3.9 × 10⁵ km²” over the study period. This data is a key component of the official SDG indicator.
• For Target 2.4 & 15.2: The article quantifies the area of cropland expansion (“7.1 × 10⁵ km²”) and identifies the source of this expansion, noting that “forest and pasture reductions predominantly driven by conversion to cropland.” This serves as an indicator of the pressure agriculture places on other ecosystems.
• For Target 13.2: The core metric of the study, “Net Ecosystem Productivity (NEP),” measured in “Tg C” (teragrams of carbon), is a direct indicator of the effectiveness of land-based climate mitigation efforts. The net gain of “229 Tg C” despite forest area loss is a key finding that can inform climate policy. The analysis of carbon sequestration efficiency based on forest age (e.g., “newly established forests exhibited higher sequestration efficiency”) provides a nuanced indicator for guiding effective forest management policies.

4. Table of SDGs, Targets, and Indicators

Source: nature.com