森林が二酸化炭素の排出を削減する潜在力はどのくらいか

投稿日投稿者しとらす

赤道直下の熱帯雨林から亜寒帯の森林に至るまで、森林が炭素（二酸化炭素やメタンガスなどの温室効果ガス）をどれほど固定するのか、その評価をどのように行ったらいいのか・・・みたいなお話。

過小評価してアフリカや南米、東南アジアで乱開発の末に熱帯林が削られていくのを見過ごすわけにはいかないけど、かといって理念だけ説いて止まるはずもなく、先進国から森林の維持費をキッチリ支払うくらいのことはせなあかん、さてその額やら何やらをどうやって計算するか？

AI（と高性能スパコン）が進化した今なら数値化できそうだから、気候変動対策で経済を回すためにも森林の維持を経済的に評価することを確立していくべき・・・ということで日本の大学も頑張ろう。文科省と財務省も国立大にちゃんとお金配れや。

あと、日本の森林に関してはこんな話も↓

 

◆Global forests store vast carbon wealth but credit systems undervalue their true potential, study finds【PHYS.ORG：Sumanta Das　2025年8月27日】


〔(a) Global distribution of forest loss and gain (%). The colors on the map represent changes in the extent and density of tree cover over a 20-year period. Green areas denote regions where tree cover has remained stable, red areas highlight regions where tree cover has been lost, and blue areas indicate areas where tree cover has increased. Magenta shades signify regions of high turnover, where both significant losses and gains in tree cover occurred within the same period, reflecting dynamic changes in vegetation; (b) Worldwide loss of the area of tree cover within primary forest extent; (c) Worldwide yearly loss of tree cover across different countries; (d) Global annual tree cover loss by dominant driver; (e) Factors contributing to net global tree cover change. Credit: Journal of Environmental Management (2025). DOI: 10.1016/j.jenvman.2025.126987〕

When we walk into a forest, we often think less about the shade or the silence and more about the invisible work trees do—pulling carbon dioxide out of the air and storing it in their trunks, roots and soils. Forests are our oldest, most reliable carbon banks. Yet, when we dove into the data, we realized something unsettling: The financial systems designed to reward forests for this service often undervalue them.

That realization drove me and my team to conduct a two-decade global assessment of forest carbon sequestration, sustainable forest management (SFM), and carbon credit valuation. Our results, published recently in the Journal of Environmental Management, show a sobering disparity between what forests give and what they get in return.

Forests cover roughly 31% of the world’s land area, and they quietly absorb about 7.6 gigatons of CO2 each year. To put this in perspective, that’s nearly 20% of global fossil fuel emissions. This capacity makes them one of the strongest natural solutions to climate change.

But global markets don’t treat this service with the seriousness it deserves. Carbon credits, meant to put a price on emission reductions or carbon capture, consistently undervalue forest carbon sequestration compared to industrial technologies.

“Forests are far more than just timber,” I often remind myself. “They are living infrastructures of climate stability.”


〔Global distribution of forest biomass (a) and carbon density (b). Credit: Journal of Environmental Management (2025). DOI: 10.1016/j.jenvman.2025.126987〕

We analyzed global forest carbon dynamics from 2004 to 2024. Our dataset captured both natural and managed forests, from the Amazon to boreal ecosystems. Our findings revealed that forests stored 662 gigatons of carbon in 2024, an increase of 32 gigatons compared to 2004. Annual sequestration rates varied regionally, with tropical forests absorbing the most carbon despite facing deforestation and degradation pressures.

At the same time, the global carbon credit system recognized only a fraction of this value. The average carbon credit price for forestry projects ranged from $3 to $15 per ton of CO₂, while the social cost of carbon—what society truly pays in damages from emissions—was estimated at $51 to $150 per ton. This gap shows how undervalued forests remain in financial markets.

The contradiction was stark. Forests offered society an enormous mitigation service, yet credit mechanisms failed to reflect their true worth. As we note, “Forests sequester vast amounts of carbon, but current credit prices fall far short of the social cost of carbon.”

This disparity means communities protecting forests receive inadequate compensation, weakening incentives for conservation. It also skews global climate finance toward engineered carbon capture, even though forests remain the most effective, immediate, and scalable option.


〔Interactions in forest carbon management: ecological, economic, and policy dimensions. Credit: Journal of Environmental Management (2025). DOI: 10.1016/j.jenvman.2025.126987〕

We also examined how sustainable forest management contributes to both carbon storage and livelihoods. Properly managed forests can balance timber harvest with biodiversity protection and long-term sequestration.

For instance, in parts of Southeast Asia and Africa, community-led forest management increased local incomes while maintaining high carbon stocks. Yet, these success stories remain underrepresented in carbon markets.

We found it inspiring that forests can be both climate allies and economic engines if we design systems that value them properly.

One of the interesting findings was the uneven distribution of carbon sequestration potential.

  • Tropical forests (Amazon, Congo, Southeast Asia) absorbed nearly half of the global forest carbon but are most vulnerable to deforestation and fires.
  • Boreal forests stored carbon largely in soils and peat, making them critical long-term reservoirs, though threatened by warming and permafrost thaw.
  • Temperate forests in Europe and North America showed steady sequestration thanks to sustainable management policies, offering a model for others.

Yet, when we compared regional sequestration rates with carbon credit revenues, the imbalance widened. Regions contributing the most to global carbon storage often earned the least in financial returns.

Why markets undervalue forests

Several reasons emerged for this undervaluation. The first is uncertainty and permanence concerns—Critics argue forest carbon may be reversible through fires or logging. The second is the complexity in measurement—Unlike industrial projects with fixed baselines, forests require satellite and ground monitoring to track. And the third is policy asymmetry—Industrial carbon capture benefits from subsidies and innovation funds, while forest credits face bureaucratic hurdles.

But these challenges are solvable. Advances in remote sensing and AI-driven monitoring already allow us to track forest carbon with remarkable accuracy.

To unlock forests’ true potential, our study recommends three key actions:

  • Raise forest credit prices to align with the social cost of carbon.
  • Strengthen community-based management to ensure local benefits.
  • Integrate forests into national climate strategies, not as offsets but as core mitigation pillars.

“Forests should not be seen as optional extras,” the study says. “They are central to achieving net-zero targets.”

Writing and leading this study reminded me of my own childhood in rural Bengal, where forests were not just landscapes but living teachers. I learned to see trees as more than resources—they were relatives in the climate family. Today, science confirms what I intuitively felt: without forests, our climate struggle is lost.

And yet, the financial mechanisms we built undervalue them, sometimes treating them as second-class solutions. That must change.

Conclusion

Overall, our research concludes that forests store immense carbon wealth, but current global carbon credit systems undervalue their role in climate mitigation. Bridging this gap is not just a matter of fairness, it is a climate imperative.

I believe that the next decade must be one where forests are finally given their rightful place at the center of global climate finance. Anything less would be a betrayal of both nature and humanity.

◆Harnessing green wealth: A two-decade global assessment of forest carbon sequestration and credits and the economic implications of sustainable forest management practices【ScienceDirect　2025年8月18日】

Abstract

As climate change accelerates, forests play a pivotal role in global carbon dynamics by providing both carbon sequestration and ecosystem resilience. This review synthesizes two decades (2004–2024) of research on the interrelationships between forest carbon sequestration, carbon credit mechanisms, and the economic dimensions of sustainable forest management (SFM). Despite substantial progress, notable gaps persist in the economic valuation of forest carbon credits and their integration into SFM strategies. Drawing on systematic analysis of Web of Science data, it examines four core interconnected research themes: (i) global trends and international collaboration in forest carbon research, (ii) economic valuation of forest ecosystem services to mitigate deforestation and enhance sequestration, (iii) the influence of forest management practices, species diversity, and climate zones on soil organic carbon and its economic value, and (iv) the interplay between economic, ecological, and policy drivers shaping carbon credit markets. Findings reveal a 12.16 % annual growth rate in publications, strong global collaboration (39.11 % co-authorship), and priority research themes such as aboveground biomass, climate change, carbon storage, and carbon credits. Recent emphasis has shifted toward advanced tools (e.g., LiDAR), sustainable management approaches, and interdisciplinary strategies, reflecting a broader focus on climate resilience and policy integration. SFM practices, such as agroforestry, selective logging, and afforestation, emerge as effective for enhancing carbon stocks while generating economic returns. Persistent challenges include policy inconsistencies, insufficient community participation, and a lack of standardized methods for carbon measurement and valuation. Regional disparities in carbon values complicate international trading and climate agreements. Overall, the review offers practical insights for policymakers, researchers, and practitioners by connecting forest management, carbon sequestration, and economic incentives. Moreover, it underscores the need for long-term, socio-economically integrated studies, strengthened policy frameworks, and enhanced cooperation to align SFM with global sustainability objectives.