土地利用が植物および土壌の炭素量を大きく減少させることを発見(Land use severely reduces global carbon in plants and soils)

2025-08-15 ミュンヘン大学(LMU)

ミュンヘン大学(LMU)の地理学者 Raphael Ganzenmüller 教授らによる研究によれば、人間の土地利用によって陸域に蓄えられていた炭素が全球で約24%(3,440億トン)も喪失していることが明らかになった。この推定は、高解像度の地球観測データと歴史的・現在の土地利用情報を機械学習で解析して導かれたもので、損失の主因は放牧地や農地の拡大、さらには森林管理に起因している。3440億トンという規模は、過去50年間の化石燃料(石炭、石油、天然ガス)由来のCO₂排出量と相当し、自然界における植生や土壌の劣化が引き起こす地球規模の炭素循環への影響を強く示唆する。LMU の地理学者 Julia Pongratz 教授は、「本研究は気候政策にとって、土地上の炭素回復の有効性を評価する重要な知見を提供する」とコメントし、炭素蓄積の回復が地球規模の気候目標達成に向けた大きな潜在力を持つと強調した。

<関連情報>

人類は地球の陸上炭素貯蔵量を四分の一減少させた Humans have depleted global terrestrial carbon stocks by a quarter

Raphael Ganzenmüller ∙ Wolfgang A. Obermeier ∙ Selma Bultan ∙ Seth A. Spawn-Lee, ∙ Florian Zabel ∙ Julia Pongratz
One Earth  Published:July 10, 2025
DOI:https://doi.org/10.1016/j.oneear.2025.101392

Graphical abstract

土地利用が植物および土壌の炭素量を大きく減少させることを発見(Land use severely reduces global carbon in plants and soils)

Science for society

Natural ecosystems play a crucial role in regulating the climate, storing more carbon than all fossil fuel reserves combined. However, land-use activities such as agricultural expansion and forest management are massively altering vegetation and soil carbon stocks, releasing vast amounts of carbon into the atmosphere, which substantially contribute to global warming. Yet, quantifying carbon loss from natural ecosystems globally at high resolution has been challenging.

Our research addresses this gap by providing a consistent estimate of this deficit: globally, carbon in vegetation and soil has been reduced through land-use activities by 24% (344 PgC), comparable to all fossil fuel emissions over the past 50 years. We also find that current global vegetation models considerably underestimate this loss. Our findings offer valuable insights for policymakers to prioritize conservation and restoration efforts, guide sustainable land-use decisions, and improve global vegetation models.

Highlights

  • Global terrestrial carbon stocks have been depleted by 24% (344 PgC)
  • Our estimates of the carbon deficit are at unprecedented resolution and consistency
  • Pasture expansion, cropland expansion, and forest management are major drivers
  • Dynamic global vegetation models underestimate the carbon deficit by 37% on average

Summary

Mitigating global climate change requires massive greenhouse gas emission reductions and carbon removal efforts. Although terrestrial ecosystems store large amounts of carbon, land-use change has substantially diminished these stocks in many regions. However, a consistent, high-resolution approach to quantify the differences between actual and potential carbon stocks in vegetation and soils—the terrestrial carbon deficit—remains elusive, limiting the evaluation of global climate models. Here, we combine semi-empirical data with machine learning to estimate the terrestrial carbon deficit to be 344 (251–393) PgC, equivalent to a 24% depletion, predominantly driven by pasture expansion (30%), cropland expansion (24%), and forest management (23%). We reveal that dynamic global vegetation models (DGVMs) underestimate the terrestrial carbon deficit by 37% on average (range: 2%–58%), highlighting critical limitations. Our findings support assessments of anthropogenic impacts on ecosystems and help constrain global climate models to better evaluate nature-based solutions and climate mitigation policies.

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