Mitigation of atmospheric CO2 concentrations by increased carbon sequestration in the soil

 The International Panel on Climate Change distinguished three main options for the mitigation of atmospheric CO₂ concentrations by the agricultural sector: (1) reduction of agriculture-related emissions, (2) creation and strengthening of C sinks in the soil, and (3) production of biofuels to replace fossil fuels. Options for sustained sequestration of C in the soil through adapted management of land resources are reviewed in the context of the ongoing discussion on the need to reduce greenhouse gas concentrations in the atmosphere. Enhanced sequestration of atmospheric CO₂ in the soil, ultimately as stable humus, may well prove a more lasting solution than (temporarily) sequestering CO₂ in the standing biomass through reforestation and afforestation. Such actions will also help to reverse processes of land degradation, thus contributing to sustained food productivity and security for the people in the regions concerned. Received: 1 December 1997     

Should we store carbon in trees?

In order to explore for the most effective strategy for using forests to mitigate global climate change, we have constructed a simple model of C uptake during forest growth and the fate of this C when forests are harvested and used as fuel to replace fossil fuels. We suggest that trees are equally effective in preventing the accumulation of CO₂ in the atmosphere if they remove a unit of C from the atmosphere or if they supply a sustainable source of energy that substitutes for a unit of C discharged by burning fossil fuels. The model shows that the most effective strategy for using forest land to minimize increases in atmospheric CO₂ will depend on the current status of the land, the productivity that can be expected, the efficiency with which the forest harvest is used to substitute for fossil fuels, and the time perspective of the analysis. For forests with large standing biomass and low productivity the most effective strategy is to protect the existing forest. For land with little standing biomass and low productivity, the most effective strategy is to reforest or otherwise manage the land for forest growth and C storage. Where high productivity can be expected, the most effective strategy is to manage the forest for a harvestable crop and to use the harvest with maximum efficiency either for long-lived products or to substitute for fossil fuels. The longer the time perspective, the more likely that harvesting and replanting will result in net C benefits.     

Offsetting global CO2 emissions by restoration of degraded soils and intensification of world agriculture and forestry

Increase in atmospheric concentration of CO₂ from 285 parts per million by volume (ppmv) in 1850 to 370 ppm in 2000 is attributed to emissions of 270 ± 30 Pg carbon (C) from fossil fuel combustion and 136 ± 55 Pg C by land‐use change. Present levels of anthropogenic emissions involve 6·3 Pg C by fossil fuel emissions and 1·8 Pg C by land‐use change. Out of the historic loss of terrestrial C pool of 136 ± 55 Pg, 78 ± 12 Pg is due to depletion of soil organic carbon (SOC) pool comprising 26 ± 9 Pg due to accelerated soil erosion. A large proportion of the historic SOC lost can be resequestered by enhancing the SOC pool through converting to an appropriate land use and adopting recommended management practices (RMPs). The strategy is to return biomass to the soil in excess of the mineralization capacity through restoration of degraded/desertified soils and intensification of agricultural and forestry lands. Technological options for agricultural intensification include conservation tillage and residue mulching, integrated nutrient management, crop rotations involving cover crops, practices which enhance the efficiency of water, plant nutrients and energy use, improved pasture and tree species, controlled grazing, and judicious use of inptus. The potential of SOC sequestration is estimated at 1–2 Pg C yr⁻¹ for the world, 0·3–0·6 Pg C yr⁻¹ for Asia, 0·2–0·5 Pg C yr⁻¹ for Africa and 0·1–0·3 Pg C yr⁻¹ for North and Central America and South America, 0·1–0·3 Pg C yr⁻¹ for Europe and 0·1–0·2 Pg C yr⁻¹ for Oceania. Soil C sequestration is a win–win strategy; it enhances productivity, improves environment moderation capacity, and mitigates global warming. Copyright © 2003 John Wiley & Sons, Ltd.     

Inventory of Emissions of Greenhouse Gases in Israel

As a Party to the United Nations Framework Convention on Climate Change, Israel is committed to develop a national inventory of anthropogenic emissions and removals of greenhouse gases. This paper presents the national inventory, which was developed according to the guidelines of the Intergovernmental Panel on Climate Change (IPCC). The inventory includes the following sectors: energy, industrial processes, agriculture, forestry and waste. In this paper, only the inventory of the direct greenhouse gases (CO₂, CH₄ and N₂O) is presented. Emissions of these gases were converted to CO₂ equivalent emissions by means of their Global Warming Potentials (a measure of the radiative effects of the different gases relatively to CO₂). CO₂ emissions from burning fossil fuels to produce energy are by far the largest source (50 million tons in 1996). The contribution of methane emissions from decomposition of landfilled municipal solid waste is second in importance (8 million tons of CO₂ equivalent). Industrial processes emit about 2 million tons CO₂ equivalent, the most important process being cement production. Agricultural emissions amount to about 2 million tons CO₂ equivalent and are due to soil emissions of nitrous oxide, methane emissions from enteric fermentation in domestic livestock and N₂O and CH₄ emissions from animal waste management. Although most forests in Israel are in a growing stage and atmospheric CO₂ is therefore removed to form biomass, this removal amounts to 0.4 million tons only and is very small as compared to emissions from other sectors. On a per capita basis, Israel's emissions of CO₂ from fuel combustion are not far behind those of some of the most developed countries.     

Biofuels, biodiversity, and people: Understanding the conflicts and finding opportunities

The finitude of fossil fuels, concerns for energy security and the need to respond to climate change have led to growing worldwide interests in biofuels. Biofuels are viewed by many policy makers as a key to reducing reliance on foreign oil, lowering emissions of greenhouse gases and meeting rural development goals. However, political and public support for biofuels has recently been undermined due to environmental and food security concerns, and by reports questioning the rationale that biofuels substantially reduce carbon emissions. We discuss the promise of biofuels as a renewable energy source; critically evaluate the environmental and societal costs of biofuel use; and highlight on-going developments in biofuel feedstock selection and production technologies. We highlight net positive greenhouse gases emissions, threats to forests and biodiversity, food price increases, and competition for water resources as the key negative impacts of biofuel use. We also show that some of these environmental and societal costs may be ameliorated or reversed with the development and use of next generation biofuel feedstocks (e.g., waste biomass) and production technologies (e.g., pyrolysis). We conclude that certain types of biofuels do represent potential sources of alternative energy, but their use needs to be tempered with a comprehensive assessment of their environmental impacts. Together with increased energy conservation, efficiencies and technologies such as solar-power and wind turbines, biofuels should be included in a diverse portfolio of renewable energy sources to reduce our dependence on the planet’s finite supply of fossil fuels and to insure a sustainable future.     

Biomass management and energy

The impact of managing biomass specifically for the conservation or production of energy can become a significant factor in the global management of atmopsheric CO₂ over the next century. This paper evaluates the global potential for: (1) conserving energy by using trees and wood for shading, shelterbelts, windbreaks, and construction material; and (2) increasing the use of biomass and improving its conversion efficiency for producing heat, electricity, and liquid biofuels. The potential reduction in CO₂ emissions possible by the anticipated time of atmospheric CO₂ doubling was estimated to be up to 50×10⁶t C yr^?1 for energy conservation and as high as 4×10⁹ t C yr^?1 for energy production. Of the many opportunities, two stand out. Through afforestation of degraded and deforested lands, biomass energy production offers the potential of 0.36 to 1.9×10⁹t C yr^?1 emission reduction. Dedicated energy crops, which include short-rotation woody crops, herbaceous energy crops, halophytes, some annual crops, and oilseeds, offer the potential of 0.2 to 1.0×10⁹t C yr^?1 emission reduction. Also addressed in the paper, but not quantified, were establishment of new forests, increasing the productivity of existing forests, or protecting forests to sequester C as an offset against CO₂ emissions from burning fossil fuels or forest destruction. Also addressed are uncertainties, gaps in scientific knowledge about ecosystems and their management, and policy considerations at the international and national levels.     

Greenhouse Gas Emissions from a Hydroelectric Reservoir (Brazil’s Tucuruí Dam) and the Energy Policy Implications

Greenhouse gas emissions from hydroelectric dams are oftenportrayed as nonexistent by the hydropower industry, and havebeen largely ignored in global calculations of emissions fromland-use change. Brazil’s Tucuruí Dam provides an example with important lessons for policy debates on Amazonian development and on how to assess the global warming impact ofdifferent energy options. Tucuruí is better from the pointof view of power density, and hence greenhouse gas emissions per unit of electricity, than both the average for existing dams in Amazonia and the planned dams that, if all built, wouldflood 3% of Brazil’s Amazon forest. Tucuruí’s emission of greenhouse gases in 1990 is equivalent to 7.0–10.1 × 10⁶ tons of CO₂-equivalent carbon, an amount substantially greater than the fossil fuel emission of Brazil’s biggest city, São Paulo. Emissions need to beproperly weighed in decisions on dam construction. Althoughmany proposed dams in Amazonia are expected to have positivebalances as compared to fossil fuels, substantial emissionsindicated by the present study reduce the benefits often attributed to the planned dams.     

农业生物质能温室气体减排潜力

中国拥有丰富的农作物秸秆和畜禽粪污等农业废弃物资源。农业生物质能技术是促进农业废弃物资源有效利用的重要途径，既能够解决农业废弃物的环境污染问题、减少因焚烧或无序堆放排放温室气体，又能够替代化石能源减排CO2、提升土壤固碳能力，未来在"双碳"背景下发展潜力很大。该研究基于LCA全生命周期评价方法，研究8种不同生物质能技术的温室气体排放因子，核算农业生物质能转化与利用过程消耗能源的排放、抵扣化石能源减排、副产物土壤碳汇3个方面，并基于秸秆和畜禽粪污两大类农业废弃物资源禀赋及能源化利用潜力，预测3种不同情景下，农业生物质能替代化石能源的潜力，以及减排温室气体的贡献。结果表明，从减排因子看，热解炭气联产和规模化沼气/生物天然气技术的温室气体减排贡献最大。其次为成型燃料、捆烧供暖、生物质发电、炭化和燃料乙醇等技术，而户用沼气的减排贡献相对较小，8种不同生物质能技术的温室气体排放因子分别为-3.47、-3.20、-2.57、-2.63、-2.58、-2.48、-2.42 t/t（单位为标准CO2当量/标准煤当量）；基于现有政策及规划情景、技术水平提升情景、能源需求结构变化情景等3种不同情景下，评价农业生物质能对温室气体减排贡献潜力。结果显示，2030年农业生物质能替代化石能源潜力为6 490×104～7 664×104 t，温室气体减排贡献为1.97×108～2.34×108 t；2060年替代化石能源潜力为9 073×104～10 763×104 t，温室气体减排贡献为2.79×108～3.36×108 t。该研究为实现农业农村领域碳达峰碳中和目标提供数据支撑。     

Historical pyrogenic sources of black carbon during the last 150 years in the Great Hinggan Mountains,Northeast China

Purpose

Black carbon (BC) refers to solid charred residues produced by the incomplete combustion of fossil fuels and biomass. The Great Hinggan Mountains are located on the margin of the East Asian monsoon region, and BC from fossil fuel sources could be deposited in this region through transport by westerlies and the monsoon. The overall objective of this study was to evaluate the sources and intensity of BC deposited during the last 150 years in the Great Hinggan Mountains, Northeast China.

Materials and methods

BC concentrations, stable carbon isotope values of BC (δ¹³C-BC), and charcoal counts in the Motianling (MP2) peatland were measured in this study. BC values measured via the chemical method were regarded as total BC concentrations, and the BC values measured via the microscope method (i.e., charcoal) represent BC from biomass burning.

Results and discussion

The results showed that BC in MP2 peatland was mainly produced from local fire events before the 1930s. After the 1930s, with the increase in European fossil fuel BC emissions, the BC produced by fossil fuels became the major BC sources in the MP2 peatland, and the total BC fluxes in the MP2 peatland were much higher than those before the 1930s. With the decrease in European BC emissions and increase in Chinese BC emissions after the 1970s, the BC emitted by China became the major fossil fuel BC source in the MP2 peatland. However, the implementation of environmentally friendly policies decreased the BC emissions from fire events, leading to the gradual decrease in BC depositional fluxes in recent years.

Conclusions

In recent years, fossil fuels remain the major sources of BC, but the implementation of environmentally friendly policies has decreased fossil fuel BC emissions, leading to the gradual decrease in BC depositional fluxes in the Great Hinggan Mountains.

     

生物柴油对能源和环境影响分析

生物柴油是从植物或动物脂肪酸通过酯化反应而得到,由于生物柴油无毒,可生物降解和可以再生,因此受到越来越多人的关注。生物柴油的性质和普通柴油非常相似,它能直接被用到发动机上而不需要改动发动机的结构。该文基于美国能源部对生物柴油的统计数据,利用生命循环分析法,对生物柴油从生产到消耗的生命循环中的能量消耗和产出、循环中的排放以及生物柴油汽车尾气排放等方面进行了分析。生命循环开始于普通柴油或生物柴油生产的原料提取,结束于成品油在发动机上的使用。只有分析生命循环中的所有过程,才能确定它对自然环境总量的影响。例如研究温室效应就要对整个生命循环中CO₂的排放进行分析。该文利用生命循环分析法分析了在生产生物柴油或柴油生命循环过程中的能量平衡、温室气体排放及对气体和固体污染物排放,提供了生物柴油生产过程和在发动机上使用的详细数据。分析结果表明∶生物柴油循环的石化能效比大大提高,大约是柴油的4倍;生物柴油循环中CO₂排放大大降低,大约降低了78.4%;发动机排气管有害物质的排放中,除NO_x排放增加8.89%外,CO、HC、PM等有害物质的排放大大降低（分别降低了46%、37%和68%）。     

Forest sector carbon offset projects: Near-term opportunities to mitigate greenhouse gas emissions

The Framework Convention on Climate Change separately recognizes sources and sinks of greenhouse gases and provides incentives to establish C offset projects to help meet the goal of stabilizing emissions. Forest systems provide multiple opportunities to offset or stabilize greenhouse emissions through a reduction in deforestation (C sources), expansion of existing forests (CO₂ sinks) or production of biofuels (offset fossil fuel combustion). Attributes and dimensions of eight forest-sector C offset projects, established over the past three years, were examined. The projects, mostly established or sponsored by US or European electric utilities, propose to conserve/sequester over 30 × 10⁶ Mg C in forest systems at an initial cost of $1 to 30 Mg C. Given the relative novelty and complexity of forest sector C offset projects, a number of biogeochemical, institutional, socio-economic, monitoring, and regulatory issues merit analysis before the long-term potential and cost effectiveness of this greenhouse gas stabilization approach can be determined.     

Conserve or convert? Pan-tropical modeling of REDD–bioenergy competition

The land competition between tropical bioenergy plantations and payments for forest carbon conservation (e.g., through an international scheme for Reduced emissions from deforestation and forest degradation, REDD+) is modeled using spatially explicit data on biofuel feedstock (oil palm and sugar cane) suitability and forest biomass carbon stocks. The results show that a price on the (avoided) carbon emissions from deforestation at the same level as those from fossil fuel use makes clearing for high yielding bioenergy crops unprofitable on about 60% of the tropical evergreen forest area. For the remaining 40% deforestation remains the most profitable option. Continued profitability of forest clearing is most pronounced for oil palm bioenergy systems in Latin America and Africa, with REDD+ making deforestation for sugar cane plantations unprofitable on 97% of evergreen forest land. Results are shown to be relatively robust to assumptions regarding potential yields and to the addition of a ‘biodiversity premium’ on land use change emissions. While REDD+ may play an important role in stemming biodiversity loss and reducing carbon emissions from tropical deforestation in the near future, in the longer run reliance on a system that values forests solely for their carbon retention capacities poses a serious risk. It is imperative that the institutions and policies currently being established as part of REDD+ readiness activities are resilient to future changes in the incentive structures facing tropical forest countries due to, e.g., climate policy induced demand for biofuels.     

After the Kyoto Protocol: Can soil scientists make a useful contribution?*

Abstract. Over 170 countries have ratified the UN Framework Convention on Climate Change (UNFCCC) which aims at ‘the stabilisation of greenhouse gases in the atmosphere at a level that will prevent dangerous anthropogenic interference with the climate system’. The Kyoto Protocol, signed in 1997, commits the developed (‘Annex 1′) countries to a reduction in gaseous emissions. The global increase in atmospheric CO₂, the main greenhouse gas, comes mainly from fossil fuels (6.5 Gt C yr^?1), together with about 1.6 Gt C yr^?1 from deforestation. The atmospheric increase is only 3.4 Gt C yr^?1, however, due to a net sink in terrestrial ecosystems of about 2 Gt C yr^?1, and another in the oceans. Increasing net carbon sequestration by afforestation of previously non-forested land is one way of reducing net national emissions of CO₂ that is permitted under the Kyoto Protocol. Future modifications may also allow the inclusion of carbon sequestration brought about by other forestry and agricultural land management practices. However, associated changes in net fluxes of two other greenhouse gases identified in the Protocol — nitrous oxide (N₂O) and methane (CH₄) — will have to be taken into account. Growth of biomass crops can increase N₂O emissions, and drainage of wetlands for forestry or agriculture also increases them, as well as emissions of CO₂, while decreasing those of CH₄. The problems of how to quantify these soil sources and sinks, to maximize soil C sequestration, and to minimize soil emissions of CH₄ and N₂O, will present a major scientific challenge over the next few years — one in which the soil science community will have a significant part to play.     

高原缺氧环境下生物质燃料对柴油机性能和排放的影响

为了研究不同类别的含氧生物质燃料在高原缺氧环境下对发动机性能和排放的影响,在一台卧式双缸柴油机上分别燃用柴油、乙醇柴油E10(含10%体积分数的乙醇和90%体积分数的柴油)及生物柴油-乙醇-柴油B10E10(含10%体积分数的生物柴油,10%体积分数的乙醇和80%体积分数的柴油)3种燃料进行了对比试验。试验结果表明,在不对柴油机做任何调整的情况下,分别燃用E10和B10E10 2种含氧生物质混合燃料后,柴油机动力性下降,外特性转矩平均下降幅度分别达到4.24%和5.49%;当量燃油消耗率基本低于柴油,经济性有所改善。燃用含氧生物质燃料后,柴油机的经济性变化情况除了与燃料本身的属性相关,还与转速和负荷相关。燃用E10混合燃料后,柴油机的一氧化碳(CO)排放在低负荷时高于柴油,高负荷时低于柴油;碳氢化合物(HC)排放高于柴油水平,升高幅度范围达4.9%~27.4%;氮氧化物(NOX)排放在低负荷时低于柴油,高负荷时趋于柴油水平。燃用B10E10混合燃料后,一氧化碳(CO)和碳氢化合物(HC)排放在低负荷时都趋于柴油水平,高负荷时都低于柴油水平;氮氧化物(NOX)排放在低负荷时低于柴油,高负荷时高于柴油水平。柴油机在燃用E10和B10E10 2种混合燃料后,碳烟排放均低于柴油水平。柴油机燃用B10E10混合燃料后的碳氢化合物(HC)排放,碳烟排放以及低负荷时的一氧化碳(CO)排放均低于E10,氮氧化物(NOX)排放基本高于E10。与E10燃料相比,B10E10混合燃料在柴油机的一氧化碳(CO)和碳氢化合物(HC)以及碳烟排放方面具有更好的改善效果;但是动力性下降幅度较大,氮氧化物(NOX)排放增加。该研究可为含氧生物质燃料在高原缺氧地区的应用提供参考。     

Carbon cycling and sequestration opportunities in South America: the case of Brazil

Abstract. A carbon emission inventory of the Brazilian agricultural sector was used to compare greenhouse gas emissions with estimated carbon offsets promoted by two main changes in agricultural management: the replacement of conventional tillage by no-tillage and the cessation of annual burning in sugar cane production. Using the IPCC revised 1996 guidelines for national greenhouse gas inventories, we estimate that 12.65 Mt C are emitted annually from agricultural land in Brazil. Ongoing conversion of conventionally tilled land to no-tillage currently accumulates 9 Mt C yr⁻¹. Industrial by-products like alcohol and bagasse from sugar cane processing substitute fossil fuel for transportation and power generation offsetting 10 and 8 Mt C yr⁻¹, respectively. An additional opportunity for 0.53 Mt C yr⁻¹ sequestration is presented by avoiding burning before harvesting of sugar cane. These data show that there could be almost full compensation between sources and sinks/offsets in the agricultural carbon cycle. There is a great opportunity to achieve this mitigation benefit because the adoption of new technologies is increasing rapidly.     

Functional dependencies of soil CO2 emissions on soil biological properties in northern German agricultural soils derived from a glacial till

Agricultural soil CO₂ emissions and their controlling factors have recently received increased attention because of the high potential of carbon sequestration and their importance in soil fertility. Several parameters of soil structure, chemistry, and microbiology were monitored along with soil CO₂ emissions in research conducted in soils derived from a glacial till. The investigation was carried out during the 2012 growing season in Northern Germany. Higher potentials of soil CO₂ emissions were found in grassland (20.40 µg g^?1 dry weight h^?1) compared to arable land (5.59 µg g^?1 dry weight h^?1) within the incubating temperature from 5°C to 40°C and incubating moisture from 30% to 70% water holding capacity (WHC) of soils taken during the growing season. For agricultural soils regardless of pasture and arable management, we suggested nine key factors that influence changes in soil CO₂ emissions including soil temperature, metabolic quotient, bulk density, WHC, percentage of silt, bacterial biomass, pH, soil organic carbon, and hot water soluble carbon (glucose equivalent) based on principal component analysis and hierarchical cluster analysis. Slightly different key factors were proposed concerning individual land use types, however, the most important factors for soil CO₂ emissions of agricultural soils in Northern Germany were proved to be metabolic quotient and soil temperature. Our results are valuable in providing key influencing factors for soil CO₂ emission changes in grassland and arable land with respect to soil respiration, physical status, nutrition supply, and microbe-related parameters.     

Greenhouse gas mitigation potential of agricultural land in Great Britain

The aim of this paper is to assess the greenhouse gas (GHG) mitigation potential of croplands and grasslands in Great Britain under different management practices. We consider the feasible land management options for grass and cropland using county level land‐use data with estimates of per‐area mitigation potential for individual and total GHGs, to identify the land management options with the greatest cost‐effective mitigation potential. We show that for grasslands, uncertainties still remain on the mitigation potential because of their climatic sensitivity and also their less intensive management. For croplands in Great Britain, the technical mean GHG mitigation potentials for all cropland management practices range from 17 Mt CO₂‐eq. per 20 yr to 39 Mt CO₂‐eq. per 20 yr. There are significant regional variation in all cases, with the greatest potentials in England, negligible potential in Wales and intermediate potential in Scotland, with country differences largely driven by the areas of cropland and grassland in each country. Practices such as agronomic improvement and nutrient management are the most promising options because of their impact on N₂O emissions and also their larger potential at low cost. In terms of annual emissions from agriculture, calculated mitigation potentials are small, where the technical mitigation potential of agronomy and nutrient management strategies are ca. 4.5 and 3.8%, respectively (agricultural emissions account for ca. 9% or 47.7 Mt CO₂‐eq., of total Great Britain GHG emissions, Department of Energy and Climate Change, UK). However when compared with the land use, land‐use change and forestry sector (LULUCF) emissions, nutrient management would reduce further emission reductions by approximately half of the 2005 LULUCF sink (i.e. ?1.6 Mt CO₂‐eq. per year).     

基于清单算法的湖北省土地利用碳排放效应和趋势分析

土地利用/覆被变化是仅次于化石燃料燃烧的大气CO₂浓度急剧增加的最主要的人为原因,也是影响陆地生态系统碳循环的主要因素。结合国内外低碳经济和低碳土地利用的研究背景和实践,以湖北省为研究区域,采用样地清单法计算2003—2010年间湖北省的土地利用碳排放量,分析不同土地利用方式的碳排放效应和趋势。得出的主要结论如下:（1）湖北省土地利用总碳排放量从2003年的4 921.997万t增加到2010年的9 124.897万t,呈显著上升趋势;（2）耕地和建设用地是主要的碳源。其中耕地的碳排放量成递减趋势,从2003年的265.176万t减少到2010年的262.189万t,建设用地的碳排放量呈快速上升趋势,从2003年的5 194.871万t增加到2010年的9 414.589万t;（3）林地是主要的碳汇,从2003年的536.645万t增加为550.607万t,林地的碳汇功能逐年加强。通过对不同土地利用方式的碳排放效应和趋势研究,为湖北省低碳土地利用结构优化提供了依据。     

Consequences of feasible future agricultural land‐use change on soil organic carbon stocks and greenhouse gas emissions in Great Britain

The aim of this study was to assess the consequences of feasible land‐use change in Great Britain on GHG emissions mainly through the gain or loss of soil organic carbon. We use estimates of per‐area changes in soil organic carbon (SOC) stocks and in greenhouse gas (GHG) emissions, coupled with Great Britain (GB) county‐level scenarios of land‐use change based on historical land‐use patterns or feasible futures to estimate the impact of potential land‐use change between agricultural land‐uses. We consider transitions between cropland, temporary grassland (<5 yr under grass), permanent grass (>5 yr under grass) and forest. We show that reversion to historical land‐use patterns as present in 1930 could result in GHG emission reductions of up to ca. 11 Mt CO₂‐eq./yr (relative to a 2004 baseline), because of an increased permanent grassland area. By contrast, cultivation of 20% of the current (2004) permanent grassland area for crop production could result in GHG emission increases of up to ca. 14 Mt CO₂‐eq./yr. We conclude that whilst change between agricultural land‐uses (transitions between permanent and temporary grassland and cropland) in GB is likely to be a limited option for GHG mitigation, external factors such as agricultural product commodity markets could influence future land‐use. Such agricultural land‐use change in GB could have significant impacts on Land‐use, Land‐Use Change and Forestry (LULUCF) emissions, with relatively small changes in land‐use (e.g. 5% plough out of grassland to cropland, or reversion of cropland to the grassland cover in Nitrate Vulnerable Zones of 1998) having an impact on GHG emissions of a similar order of magnitude as the current United Kingdom LULUCF sink. In terms of total UK GHG emissions, however, even the most extreme feasible land‐use change scenarios account for ca. 2% of current national GHG emissions.     

A framework for integrating the terrestrial carbon stock of estates in institutional carbon management plans

Many institutions have substantial landholdings, but few consider soil carbon preservation and augmentation in their carbon management plans. A methodical framework was developed to analyse terrestrial carbon stocks (soil and tree biomass) for credible carbon offsetting strategies in institutional land. This approach was demonstrated at two farms (805 hectares) managed by Newcastle University. Soil carbon for three depths (0–30 cm, 30–60 cm and 60–90 cm) and above-ground tree biomass were quantified. These data provided a terrestrial carbon baseline to evaluate future land management options and effects. Historical land-use records enabled the following comparisons: (1) agricultural land vs. woodland; (2) arable land vs. permanent grassland; (3) organic vs. conventional farming; (4) coniferous vs. broadleaved woodland; and (5) recent vs. long-established woodland. Carbon storage (kg/m²) varied with land usage and woodland type and age, but only agricultural land vs. woodland, and for agriculture, arable land vs. permanent grassland, significantly affected the 0–90 cm soil carbon. At the university-managed farms, current terrestrial carbon stocks were 103,620 tonnes in total (98,050 tonnes from the 0–90 cm soil and 5,569 tonnes from tree biomass). These terrestrial carbon stocks were equivalent to sixteen years of the current carbon emissions of Newcastle University (6,406 tonnes CO₂ equivalents-C per year). Using strategies for alternative land management, Newcastle University could over 40 years offset up to 3,221 tonnes of carbon per year, or 50% of its carbon emissions at the current rate. The methodological framework developed in this study will enable institutions having large landholdings to rationally consider their estates in future soil carbon management schemes.