Mitigating climate change requires clean energy and removing atmospheric carbon. Building soil carbon is an appealing way to increase carbon sinks and reduce emissions due to the associated benefits to agriculture. However, practical implementation of soil carbon climate strategies lag behind the potential, partly because we lack clarity around the magnitude of opportunity and how to capitalize on it. Here we quantify the role of soil carbon in natural (landbased) climate solutions (NCS), and review some of the project design mechanisms available to tap into the potential. We show that soil carbon represents 25% of the 23.8 GtCO2eyr-1 NCS potential of which 40% is protection of existing soil carbon and 60% is rebuilding depleted stocks. Soil carbon comprises 9% of the mitigation potential of forests, 72% for wetlands, and 47% for agriculture and grasslands. Soil carbon is important to land-based efforts to prevent carbon emissions, remove atmospheric carbon dioxide and deliver ecosystem services in addition to climate mitigation. Protecting and restoring soil organic matter delivers many benefits to people and nature 1,2. Globally, soils hold three times more carbon than the atmosphere 3 , and the role of soil organic matter as a regulator of climate has been recognized by scientists for decades 4. Recent work has highlighted the historical loss of carbon from this pool 3 , and the threat of future accelerated loss under warming scenarios 4,5. Soil organic carbon as a natural climate solution (NCS) thus has a role both through restoring a carbon sink and protecting against further CO 2 emissions in response to predicted land use change and climate change. This dual role for soil in the global carbon budget suggests climate benefits can be achieved through strategies that both conserve existing soil organic carbon stocks (avoid loss), and restore stocks in carbon-depleted soils 6. There are important additional benefits. Protecting and increasing soil carbon storage can (i) protect or increase soil fertility, (ii) maintain or increase resilience to climate change, (iii) reduce soil erosion, and where implemented through conservation of natural ecosystems iv) reduce habitat conversion, all in line with the United Nations Sustainable Development Goals (SDG's) 7 , the goals of the United Nationals Framework Convention on Climate Change (UNFCCC) and the United Nations Convention on Combating Desertification (UNCCD). As such, soil carbon is promoted as a common denominator amongst a variety of global and national initiatives 7. Although recent academic comment and perspective pieces point the way towards accelerated action on soils 8,9 , there remains much uncertainty around actionable pathways for achieving the global opportunity. Here we examine the scientific and policy context surrounding soil carbon projects, to aid prioritization and decision making.

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a b s t r a c tTo meet the challenge of proactive ecosystem-based climate mitigation and adaptation, new sources of funding are needed. Peatlands provide the most efficient global store of terrestrial carbon. Degraded peatlands, however, contribute disproportionally to global greenhouse gas (GHG) emissions, with approximately 25% of all CO 2 emissions from the land use sector, while restoration can be cost-effective. Peatland restoration therefore provides a newopportunity for investing in ecosystem-based mitigation through the development of carbon markets. Set in the international policy and carbon market context, this paper demonstrates the necessary scientific evidence and policy frameworks needed to develop ecosystem service markets for peatland restoration. Using the UK and NE Germany as case studies, we outline the climate change mitigation potential of peatlands and how changes in GHG emissions after restoration may be measured. We report on market demand research in carbon market investments that provide sponsors with quantification and officially certified recognition of the climate and other co-benefits. Building on this, we develop the necessary requirements for developing regional carbon markets to fund peatland restoration.

Temporal and vertical changes in the humus form profile during a primary succession of Pinus sylvestris. Emmer, I.M.; Sevink, J. Published in:Plant and Soil Link to publication Citation for published version (APA):Emmer, I. M., & Sevink, J. (1994). Temporal and vertical changes in the humus form profile during a primary succession of Pinus sylvestris. Plant and Soil. General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. The development of the humus form profile during a primary succession of Pinus sylvestris has been studied along chronosequences on dunes and in blow-outs. Attention was given to vertical variation within the humus form and how this changes during profile development. The mot-type ectorganic profile features marked vertical gradients of several soil attributes, while its constituting horizons show no or only small changes of chemical properties during succession. These changes in particular involve increasing calcium and nitrogen concentrations in the organic matter. After an initial high rate of organic matter accumulation in the successive organic horizons, these rates are strongly reduced, suggesting the attainment of a dynamic equilibrium within the time span of the chronosequences on dunes and blow-outs. Blow-outs differ from dunes in the sense that they have a lower amount of organic matter and a higher F/H ratio. This different ratio likely relates to microclimatic conditions less conducive to decomposition.An attempt is made to explain the vertical trends in terms of processes affecting the characteristics of the organic horizons. Main conclusions are that the development of the ectorganic profile results from a combined effect of decay dynamics, rhizosphere processes and atmospheric deposition, which cannot be unentangled quantitatively with the data available. Furthermore, the distinction between F and H horizons has morphological rather than chemical or ecological relevance, as major vertical changes occur within the F horizon.

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