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CH4-CO2 replacement method has the advantages of sequestering carbon dioxide and sediment stability compared to other methods such as depressurization and thermal stimulation. However, the production efficiency using CH4-CO2 replacement method is lower than any other method. In this study, effects of soaking process on CH4-CO2 replacement efficiency were determined. The soaking process was the time to close all valves for the enhancement of CH4-CO2 reaction which resulted in the long reaction time between the injected CO2 and methane hydrate and consisted of the 1st and the 2nd production with soaking time after dynamic replacement. Results showed that total replacement efficiency increased with increasing number of soaking processes and more soaking time. The increasing rate of replacement efficiency in the first soaking process was higher than that in the second process. However, the soaking process showed the disadvantage that the total production time increased with increasing soaking time and process, which could result in the production cost increase. Therefore, appropriate soaking time and number of soaking processes are required to improve the replacement efficiency considering production cost. 2020 The Authors This research was made possible by an NPRP grant # NPRP8-594-2-244 from the Qatar National Research Fund (a member of Qatar Foundation ). And this work was supported by the National Research Foundation of Korea( NRF ) grant funded by the Korea government ( MSIT ) ( 2020R1A2C101235211 ). Also, this research was partially supported by the Ministry of Trade, Industry, and Energy ( MOTIE ) through the Project "Gas Hydrate Exploration and Production Study ( 20-1143 )" under the management of the Gas Hydrate Research and Development Organization (GHDO) of Korea and the Korea Institute of Geoscience and Mineral Resources (KIGAM). Also, this research was supported by a grant ( 2018-MOIS31-009 ) from Fundamental Technology Development Program for Extreme Disaster Response funded by Korean Ministry of Interior and Safety (MOIS). Scopus

The main focus of efforts to mitigate climate change is on the avoidance of fossil fuel emissions. However, the Kyoto Protocol rules permit the use of forestry activities that create carbon offset credits. These could obviate the need for lifestyle-changing reductions in fossil fuel use. Therefore, it is necessary for policy purpose to determine the cost effectiveness of creating forest sink carbon credits. In this study, meta-regression analyses with 1047 observations from 68 studies are used to determine factors that affect carbon sequestration costs. Results indicate that forest plantations and use of harvested biomass for energy make forestry activities more attractive. It also turns out that forestry activities are competitive with emissions reduction in tropical regions and, perhaps, boreal regions but certainly not in Europe. Finally, the regression estimates are used to project the potential costs of carbon uptake for various forest management scenarios— costs range from 0 to over 200US$/t CO2. Le principal objectif des efforts visant à atténuer les changements climatiques consiste à éviter les émissions de combustibles fossiles. Cependant, les règles de le protocole de Kyoto permettent d'utiliser les activités forestières qui génèrent des crédits pour compenser les émissions de carbone, ce qui pourrait éviter de devoir réduire l'utilisation de combustibles fossiles qui entraînerait un changement de style de vie. Par conséquent, pour établir des politiques il est nécessaire de déterminer le rapport coût-efficacité de la création de crédits en utilisant la forêt comme puits de carbone. Dans cette étude, des analyses de méta-régression avec 1047 observations provenant de 68 études sont utilisées pour déterminer les facteurs qui influencent les coûts de séquestration du carbone. Les résultats indiquent que les plantations forestières et l'utilisation de la biomasse qui est récoltée pour produire de l'énergie rendent les activités forestières plus attrayantes. De plus, les activités forestières sont compétitives avec la réduction des émissions dans les régions tropicales et possiblement dans les régions boréales, mais certainement pas en Europe. Finalement, les estimations des régressions sont utilisées pour prédire le coût potentiel de la séquestration du carbone associé à différents scénarios d'aménagement forestier; les coûts varient de 0 à 200 $US par tonne de CO2.

Closed forests cover about 3 billion hectares, or 20% of the world's total land area (excluding Antarctica). Forest plantations comprise less than 1% of this area. Natural forests range from the intensively managed ones of Central Europe and Scandinavia to the wild boreal forests of Russia and Canada and the deep jungles and dry forests of the tropics. Numerous techniques—largely drawn from the ordinary repertoire of forest management—are available to enhance our ability of these forests to sequester and store C. Although the costs of sequestering additional C in these forests may be quite low (even in comparison with intensive plantation options), increased use of natural forests for this purpose raises a host of concerns about competing forest uses, biological risk, and the capacity to actually measure the incremental C sequestered. The problems of poverty, expanding populations, weak institutions, incomplete scientific knowledge, and climatic change itself will challenge the world's capacity t...

Soil organic carbon (SOC) plays a vital role in ecosystem function, determining soil fertility, water holding capacity and susceptibility to land degradation. In addition, SOC is related to atmospheric CO, levels with soils having the potential for C release or sequestration, depending on land use, land management and climate. The United Nations Convention on Climate Change and its Kyoto Protocol, and other United Nations Conventions to Combat Desertification and on Biodiversity all recognize the importance of SOC and point to the need for quantification of SOC stocks and changes. An understanding of SOC stocks and changes at the national and regional scale is necessary to further our understanding of the global C cycle, to assess the responses of terrestrial ecosystems to climate change and to aid policy makers in making land use/management decisions. Several studies have considered SOC stocks at the plot scale, but these are site specific and of limited value in making inferences about larger areas. Some studies have used empirical methods to estimate SOC stocks and changes at the regional scale, but such studies are limited in their ability to project future changes, and most have been carried out using temperate data sets. The computational method outlined by the Intergovernmental Panel on Climate Change (IPCC) has been used to estimate SOC stock changes at the regional scale in several studies, including a recent study considering five contrasting eco regions. This 'one step' approach fails to account for the dynamic manner in which SOC changes are likely to occur following changes in land use and land management. A dynamic modelling approach allows estimates to be made in a manner that accounts for the underlying processes leading to SOC change. Ecosystem models, designed for site scale applications can be linked to spatial databases, giving spatially explicit results that allow geographic areas of change in SOC stocks to be identified. Some studies have used variations on this approach to estimate SOC stock changes at the sub-national and national scale for areas of the USA and Europe and at the watershed scale for areas of Mexico and Cuba. However, a need remained for a national and regional scale, spatially explicit system that is generically applicable and can be applied to as wide a range of soil types, climates and land uses as possible. The Global Environment Facility Soil Organic Carbon (GEFSOC) Modelling System was developed in response to this need. The GEFSOC system allows estimates of SOC stocks and changes to be made for diverse conditions, providing essential information for countries wishing to take part in an emerging C market, and bringing us closer to an understanding of the future role of soils in the global C cycle. (C) 2007 Elsevier B.V. All rights reserved.

Carbon terrestrial sinks are seen as a low-cost alternative to fuel switching and reduced fossil fuel use for lowering atmospheric CO2. As a result of agreements reached at Bonn and Marrakech, carbon offsets have taken on much greater importance in meeting Kyoto targets for the first commitment period. In this study, meta-regression analysis is used to examine 981 estimates from 55 studies of the costs of creating carbon offsets using forestry. Baseline estimates of costs of sequestering carbon through forest conservation are US$ 46.62–US$ 260.29/t C ($12.71–$70.99/t CO2). Tree planting and agroforestry activities increase costs by more than 200%. When post-harvest storage of carbon in wood products, or substitution of biomas for fossil fuels in energy production, are taken into account, costs are lowest – some $12.53–$68.44/t C ($3.42–$18.67/t CO2). Average costs are greater, between $116.76 and $1406.60/t C ($31.84–$383.62/t CO2), when appropriate account is taken of the opportunity costs of land. Peer review of the studies increases costs by a factor or 10 or more, depending on the model. The use of marginal cost estimates instead of average cost results in much higher costs for carbon sequestration, in the range of thousands of dollars per t C, although few studies used this method of cost assessment.