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1.
Livestock constitutes an integral component of Indian agriculture sector and also a major source of GHGs emissions. The study presents a detailed inventory of GHG emissions at district/state level from different age-groups, indigenous and exotic breed of different Indian livestock categories estimated using the recent census 2003 and country-specific emission coefficients based on IPCC guidelines. The total methane emission including enteric fermentation and manure management of livestock was estimated at 11.75 Tg/year for the year 2003. Enteric fermentation constitutes ~91 % of the total methane emissions from Indian livestock. Dairy buffalo and indigenous dairy cattle together contribute 60 % of the methane emissions. The total nitrous oxide emission from Indian livestock for the year 2003 is estimated at 1.42 Gg/year, with 86.1 % contribution from poultry. The total GHGs emission from Indian livestock is estimated at 247.2 Mt in terms of CO2 equivalent emissions. Although the Indian livestock contributes substantially to the methane budget, the per capita emission is only 24.23 kgCH4/animal/year. Using the remote sensing derived potential feed/fodder area available for livestock, the average methane flux was calculated as 74.4 kg/ha. The spatial patterns derived in GIS environment indicated the regions with high GHGs emissions that need to be focused subsequently for mitigation measures. The projected estimates indicate a likely increase of 40 % in methane emissions from buffalo population.  相似文献   

2.
A global three-dimensional chemical transport model has been used to identify and evaluate possible candidates for the `missing' surface source required to balance the atmospheric budget of methyl bromide. Both natural and anthropogenic emissions of methyl bromide are `coloured' in the model, thus allowing the global CH3Br distribution to be broken-down into its source components. These coloured CH3Br tracers are then combined in various ways to create one base-line emission scenario and five further plausible scenarios. The additional emission scenarios are specifically designed to test whether the geographical distribution and seasonal cycles of additional vegetation and/or increased biomass burning emissions are consistent with atmospheric observations of methyl bromide mixing ratios. Due to an imbalance in our current understanding of the methyl bromide budget, simulated CH3Br mixing ratios from the base-line emission scenario are significantly lower than atmospheric measurements. Both the inclusion of a vegetation source in the tropics and a double strength biomass burning source substantially improve the agreement between model simulations and atmospheric measurements compared with the base-line emission scenario. While measurement data provides useful information on global fluxes and regional CH3Br seasonal cycles, small differences between the simulated seasonal cycles of different emission scenarios makes it difficult to distinguish between the relative likelihoods of model scenarios containing a tropical vegetation source or an increased biomass burning source. Further measurements performed in continental mid-to-high northern latitudes, central-southern Africa and South America would be of particular benefit in future attempts to constrain the location and magnitude of the natural terrestrial sources of methyl bromide.  相似文献   

3.
Experimental data on the precipitation chemistry in the semi-arid savanna of South Africa is presented in this paper. A total of 901 rainwater samples were collected with automatic wet-only samplers at a rural site, Louis Trichardt, and at an industrial site, Amersfoort, from July 1986 to June 1999. The chemical composition of precipitation was analysed for seven inorganic and two organic ions, using ion chromatography. The most abundant ion was SO4 2 – and a large proportion of theprecipitation is acidic, with 98% of samples at Amersfoort and 94% at LouisTrichardt having a pH below 5.6 (average pH of 4.4 and 4.9, respectively). This acidity results from a mixture of mineral and organic acids, with mineral acids being the primary contributors to the precipitation acidity in Amersfoort, while at Louis Trichardt, organic and mineral acids contribute equal amounts of acidity. It was found that the composition of rainwater is controlled by five sources: marine, terrigenous, nitrogenous, biomass burning and anthropogenic sources. The relative contributions of these sources at the two sites were calculated. Anthropogenic sources dominate at Amersfoort and biomass burning at Louis Trichardt. Most ions exhibit a seasonal pattern at Louis Trichardt, with the highest concentrations occurring during the austral spring as a result of agricultural activities and biomass combustion, while at Amersfoort it is less pronounced due to the dominance of relatively constant industrial emissions. The results are compared to observations from other African regions.  相似文献   

4.
Increasing atmospheric concentrations of greenhouse gases are expected to result in global climatic changes over the next decades. Means of evaluating and reducing greenhouse gas emissions are being sought. In this study an existing simulation model of a tropical savanna woodland grazing system was adapted to account for greenhouse gas emissions. This approach may be able to be used in identifying ways to assess and limit emissions from other rangeland, agricultural and natural ecosystems.GRASSMAN, an agricultural decision-support model, was modified to include sources, sinks and storages of greenhouse gases in the tropical and sub-tropical savanna woodlands of northern Australia. The modified model was then used to predict the changes in emissions and productivity resulting from changes in stock and burning management in a hypothetical grazing system in tropical northeastern Queensland. The sensitivity of these results to different Global Warming Potentials (GWPs) and emission definitions was then tested.Management options to reduce greenhouse gas emissions from the tropical grazing system investigated were highly sensitive to the GWPs used, and to the emission definition adopted. A recommendation to reduce emissions by changing burning management would be toreduce fire frequency if both direct and indirect GWPs of CO2, CH4, N2O, CO and NO are used in evaluating emissions, but toincrease fire frequency if only direct GWPs of CO2, CH4 and N2O are used. The ability to reduce greenhouse gas emissions from these systems by reducing stocking rates was also sensitive to the GWPs used. In heavily grazed systems, the relatively small reductions in stocking rate needed to reduce emissions significantly should also reduce the degradation of soils and vegetation, thereby improving the sustainability of these enterprises.The simulation studies indicate that it is possible to alter management to maximise beef cattle production per unit greenhouse gases or per unit methane emitted, but that this is also dependent upon the emission definition used. High ratios of liveweight gain per unit net greenhouse gas emission were found in a broadly defined band covering the entire range of stocking rates likely to be used. In contrast, high values of liveweight gain per unit anthropogenic greenhouse gas emission were found only at very low stocking rates that are unlikely to be economically viable.These results suggest that policy initiatives to reduce greenhouse gas emissions from tropical grazing systems should be evaluated cautiously until the GWPs have been further developed and the implications of emission definitions more rigorously determined.  相似文献   

5.
We measured the emissions of volatile aliphatic amines and ammonia produced by the manure of beef cattle, dairy cows, swine, laying hens and horses in livestock buildings. The amine emissions consisted almost exclusively of the three methylamines and correlated with those of ammonia. The molar emission ratios of the methylamines to ammonia, and data on NH3 emissions from animal husbandry in Europe, together with global statistics on domestic animals, were used to estimate the global emissions of amines. Annual global methylamine-N input to the atmosphere from animal husbandry in 1988 was 0.15±0.06 TgN (Tg=1012 g). Almost 3/4 of these emissions consisted of trimethylamine-N. This represents about half of all methylamine emissions to the atmosphere. Other sources are marine coastal waters and biomass burning.Possible reaction pathways for atmospheric methylamines are shown. Among various speculative but possible products N2O and HCN are of interest because the emission of methylamines could contribute to the global budgets of these compounds. Maximum atmospheric N2O production from methylamines are below 0.4 Tg N/year, which is less than 10% of the annual N2O growth rate. Although we do not expect the methylamine emissions to contribute in a major way to the atmospheric N2O budget, more studies are needed to establish this conclusion beyond doubt. Similar conclusions hold for HCN.  相似文献   

6.
A field study of trace gas emissions from biomass burning in Equatorial Africa gave methyl chloride emission ratios of 4.3×10–5±0.8×10–5 mol CH3Cl/mol CO2. Based on the global emission rates for CO2 from biomass burning we estimate a range of 226–904×109 g/y as global emission rate with a best estimate of 515×109 g/y. This is somewhat lower than a previous estimate which has been based on laboratory studies. Nevertheless, our emission rate estimates correspond to 10–40% of the global turnover of methyl chloride and thus support the importance of biomass burning as methyl chloride source. The emission ratios for other halocarbons (CH2Cl2, CHCl3, CCl4, CH3CCl3, C2HCl3, C2Cl4, F-113) are lower. In general there seems to be a substantial decrease with increasing complexity of the compounds and number of halogen atoms. For dichloromethane biomass burning still contributes significantly to the total global budget and in the Southern Hemisphere biomass burning is probably the most important source for atmospheric dichloromethane. For the global budgets of other halocarbons biomass burning is of very limited relevance.  相似文献   

7.
Africa is one of the sources of biomass burning emissions. It is estimated that about 6 million tons of fuel per day is consumed in the southern hemisphere. Biomass burning has an important contribution on aerosol particle concentrations in the atmosphere. Efforts have been made to conduct research in Gaborone to monitor the concentration of atmospheric aerosol particles. These studies were mainly confined to measurement of concentration of aerosol particles and establishing a relation with determinants such as carbon dioxide concentration, biomass burning, and precipitation among others. However, very little seems to have been done in relating the empirical data to levels of aerosol concentrations through a mathematical model. In this paper an objective criterion of classifying levels of aerosol concentrations in terms of their severity is provided. A mathematical model for severity levels is built. Furthermore, two indices, namely, an index of dispersion when applied to the observed annual data indicated that intensity of atmospheric aerosol are on increase in the city of Gaborone, Botswana, and an index of drift which establishes that aerosol severity states showed larger drift during the year 2006–2007 than in the year 2007–2008.  相似文献   

8.
Presented is a detailed comparison of CH4 and δ13C–CH4 measurements with simulations of the global transport model TM3. Experimental data were obtained during campaigns along the Trans-Siberian railroad in the framework of the TROICA project. Two summer (1999 and 2001) and one spring (2003) expeditions are evaluated. Model simulations include sensitivity tests to further investigate the isotopic composition of natural gas and emissions from Siberian wetlands. Comparison of the average mixing ratio of methane and its isotopic composition (δ13C) has been performed for different geographic zones, including the European part of Russia, Western Siberia and Central Siberia. Simulations are in reasonable agreement with the measurements for the European part of Russia and confirm a high contribution of natural gas to the observed methane levels. An increase of emission from bogs shifts the simulated methane isotopic composition closer to the observations. The relative importance of the Western Siberia emissions in current inventories is underestimated in comparison with other wetland regions in the former USSR. Simulated average mixing ratios are in a good agreement with the observations in Central Siberia, while 13C(CH4) values tend to be higher than measured in all considered scenarios. These results point to a bias in the modeled source mixture over Russia, which could be repaired by shifting emissions from isotopically heavy methane sources (e.g. coal, oil or biomass burning) to light sources (e.g. wetlands, ruminants, waste treatment). Alternatively, the average isotopic signature of Siberian wetlands may be lighter than expected.  相似文献   

9.
Carried out are numerical experiments with the IAP RAS global climate model (IAP RAS CM) under new RCP scenarios of anthropogenic impact for the 18th–21st centuries taking account of the response of the methane emission from the soil to the atmosphere and effects of chemical processes in the atmosphere on the climate changes. The model generally simulates the preindustrial and present-day characteristics of the methane cycle. Methane emissions from the soil to the atmosphere (within the range of 150–160 Mt CH4/year for the present-day period) reach 170–230 Mt CH4/year by the late 21st century depending on the scenario of anthropogenic impact. The methane concentration under the most aggressive RCP 8.5 anthropogenic scenario increases up to 3900 ppb by the late 21st century. Under more moderate RCP 4.5 and 6.0 anthropogenic scenarios, it reaches 1850–1980 ppb in the second half of the 21st century and decreases afterwards. Under RCP 2.6 scenario, the methane concentration maximum of 1730 ppb in the atmosphere is reached in the second decade of the 21st century. The taking account of the interaction between the processes in the soils and the climate leads to the additional increase in the methane content in the atmosphere by 10–25% in the 21st century depending on the scenario of anthropogenic impact. The taking account of the methane oxidation in the atmosphere in the case of warming reduces the increase in its concentration by 5–40%. The associated changes in the surface air temperature turn out to be small (less than 0.1 K globally or 4% of the warming expected by the late 21st century).  相似文献   

10.
Trace elements in tropical African savanna biomass burning aerosols   总被引：2，自引：0，他引：2  
As a part of the FOS/DECAFE experiment, aerosol particles emitted during prescribed savanna fires were collected in January 1991 at Lamto (Ivory Coast), either close to the emission or in ambient air. Analytical transmission electron microscopy pointed out the presence of sub-micrometer soots, salt condensates, vegetation relicts and soil derived particles. The samples were also analyzed for their total particulate matter (TPM) content and elemental composition by PIXE or XRF. At the emission, high concentrations of soil derived elements (Fe and Al) pointed out an intense remobilization process during the fires. Biomass burning emissions contributed to more than 90% of the measured concentrations, of P, Cl, S, K, Cu and Zn, which were found primarily in the fine fraction with the exception of P. Near the emission, K was mainly present as KCl, evolving to K2SO4 in the ambient samples. Trace elements emission factors were obtained for the first time for the African savanna burning and their annual emissions were estimated: our median K emission factor (0.78 g/kg of C) is higher than estimates for other ecosystems (0.2–0.58 g/kg of C); Zn emissions (0.008 Tg/year) account for 4 to 11% of the global anthropogenic emissions.  相似文献   

11.
There are many indicators that human activity may change climate conditions all around the globe through emissions of greenhouse gases. In addition, aerosol particles are emitted from various natural and anthropogenic sources. One important source of aerosols arises from biomass burning, particularly in low latitudes where shifting cultivation and land degradation lead to enhanced aerosol burden. In this study the counteracting effects of greenhouse gases and aerosols on African climate are compared using climate model experiments with fully interactive aerosols from different sources. The consideration of aerosol emissions induces a remarkable decrease in short-wave solar irradiation near the surface, especially in winter and autumn in tropical West Africa and the Congo Basin where biomass burning is mainly prevailing. This directly leads to a modification of the surface energy budget with reduced sensible heat fluxes. As a consequence, temperature decreases, compensating the strong warming signal due to enhanced trace gas concentrations. While precipitation in tropical Africa is less sensitive to the greenhouse warming, it tends to decrease, if the effect of aerosols from biomass burning is taken into account. This is partly due to the local impact of enhanced aerosol burden and partly to modifications of the large-scale monsoon circulation in the lower troposphere, usually lagging behind the season with maximum aerosol emissions. In the model equilibrium experiments, the greenhouse gas impact on temperature stands out from internal variability at various time scales from daily to decadaland the same holds for precipitation under the additional aerosol forcing. Greenhouse gases and aerosols exhibit an opposite effect on daily temperature extremes, resulting in an compensation of the individual responses under the combined forcing. In terms of precipitation, daily extreme events tend to be reduced under aerosol forcing, particularly over the tropical Atlantic and the Congo basin. These results suggest that the simulation of the multiple aerosol effects from anthropogenic sources represents an important factor in tropical climate change, hence, requiring more attention in climate modelling attempts.  相似文献   

12.
Field measurements of N2O emission rates were carried out from August until October 1982 in a subtropical region in Europe, i.e. in Andalusia, Spain. The measurements were performed by using an automatic sampling and analysis technique allowing the semi-continuous determination of N2O emission rates. The N2O emission rates were positively correlated to the soil surface temperature and exhibited a diurnal rhythm with maximum rates in the afternoon and minimum rates in the early morning with average values of 1 g N2O–N/m2/h for the grass lawn and 15 g N2O–N/m2/h for cultivated land. Application of urea and ammonium nitrate resulted in elevated N2O emission rates when compared to the unfertilized control. The loss of fertilizer-nitrogen as N2O was 0.18% for urea and 0.04% for NH4NO3 which compares very well with data obtained in a temperate climate (Germany). The total source strength of fertilizer-derived N2O is estimated to be 0.01–2.2 Tg N2O–N per year. The N2O flux from unfertilized natural soils may be as high as 4.5 Tg N2O–N, indicating that the N2O emission from soils contributes significantly to the global N2O budget.  相似文献   

13.
Terrestrial carbon pools in southeast and south-central United States   总被引：1，自引：0，他引：1  
Analyses of regional carbon sources and sinks are essential to assess the economical feasibility of various carbon sequestration technologies for mitigating atmospheric CO2 accumulation and for preventing global warming. Such an inventory is a prerequisite for regional trading of CO2 emissions. As a U.S. Department of Energy Southeast Regional Carbon Sequestration Partner, we have estimated the state-level terrestrial carbon pools in the southeast and south-central US. This region includes: Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, Tennessee, Texas, and Virginia. We have also projected the potential for terrestrial carbon sequestration in the region. Texas is the largest contributor (34%) to greenhouse gas emission in the region. The total terrestrial carbon storage (forest biomass and soils) in the southeast and south-central US is estimated to be 130 Tg C/year. An annual forest carbon sink (estimated as 76 Tg C/year) could compensate for 13% of the regional total annual greenhouse gas emission (505 Tg C, 1990 estimate). Through proper policies and the best land management practices, 54 Tg C/year could be sequestered in soils. Thus, terrestrial sinks can capture 23% of the regional total greenhouse emission and hence are one of the most cost-effective options for mitigating greenhouse emission in the region.  相似文献   

14.
Particulate content of savanna fire emissions   总被引：9，自引：0，他引：9  
As part of the FOS-DECAFE experiment at Lamto (Ivory Coast) in January 1991, various aerosol samples were collected at ground level near prescribed fires or under local background conditions, to characterize the emissions of particulate matter from the burning of savanna vegetation. This paper deals with total aerosol (TPM) and carbon measurements. Detailed trace element and polycyclic hydrocarbon data are discussed in other papers presented in this issue.Near the fire plumes, the aerosols from biomass burning are primarily of a carbonaceous nature (C%70% of the aerosol mass) and consist predominantly of submicron particles (more than 90% in mass.) They are characterized by their organic nature (black to total carbon ratio Cb/Ct in the range 3–20%) and their high potassium content (K/Cb0.6). These aerosols undergo aging during their first minutes in the atmosphere causing slight alterations in their size distribution and chemical composition. However, they remain enriched in potassium (K/Cb=0.21) and pyrene, a polycyclic aromatic hydrocarbon, such that both of these species may be used as tracers of savanna burning aerosols. We show that during this period of the year, the background atmosphere experiences severe pollution from both terrigenous sources and regional biomass burning (44% of the aerosol). Daynight variations of the background carbon concentrations suggest that fire ignition and spreading occur primarily during the day. Simultaneous TPM and CO2 real-time measurements point to a temporal and spatial heterogeneity of the burning so that the ratio of the above background concentrations (TPM/CO2) varies from 2 to 400 g/kg C. Smoldering processes are intense sources of particles but particulate emissions may also be important during the rapidly spreading heading fires in connection with the generation of heavy brown smoke. We propose emission factor values (EF) for aerosols from the savanna biomass burning aerosols: EF (TPM)=11.4±4.6 and 69±25 g/kg Cdry plant and EF(Ct)=7.4±3.4 and 56±16 g C/kg Cdry plant for flaming and smoldering processes respectively. In these estimates, the range of uncertainty is mostly due to the intra-fire variability. These values are significantly lower than those reported in the literature for the combustion of other types of vegetation. But due to the large amounts of vegetation biomass being burnt in African savannas, the annual flux of particulate carbon into the atmosphere is estimated to be of the order of 8 Tg C, which rivals particulate carbon emissions from anthropogenic activities in temperate regions.  相似文献   

15.
The allocation of CO2 emissions to specific sources is a major policy issue for international aviation, especially for determining allocations for emissions trading schemes. This paper addresses the problem by recommending a possible methodology to allocate emissions to specific sources using detailed air traffic data. The basis for the calculations is an air traffic sample for one full-day of traffic from the UK. In order to analyse aircraft fuel burn use and hence CO2 emissions, the Reorganized Air Traffic Control Mathematical Simulator (RAMS Plus) and the Advanced Emission Model (AEM III) are used. The results from these detailed simulations are compared with two of the most widely-used aviation CO2 emission estimates to have been made for the UK: the SERAS study and NETCEN estimate. Their estimates for the year 2000 are 26.1 and 31.4 Mt, respectively. In addition, the most recent NETCEN estimate for the year 2003 is 34.1 Mt of CO2. Our estimate of total aviation CO2 emissions, using detailed simulations and real air traffic data, is 34.7 Mt for the year 2004. In addition, emission estimates are compared with two global aviation emission inventories: AERO2K and SAGE. Contributions of the highest-emitting flights and aircraft types are identified. International departures dominate; 6% of flights account for 50% of total emissions. The largest aircraft emit the most per flight-km, although not per passenger-km. Different methodologies and their implications are also discussed.  相似文献   

16.
A global data set on the geographic distribution and seasonality of freshwater wetlands and rice paddies has been compiled, comprising information at a spatial resolution of 2.5° by latitude and 5° by longitude. Global coverage of these wetlands total 5.7×106 km2 and 1.3×106 km2, respectively. Natural wetlands have been grouped into six categories following common terminology, i.e. bog, fen, swamp, marsh, floodplain, and shallow lake. Net primary productivity (NPP) of natural wetlands is estimated to be in the range of 4–9×1015 g dry matter per year. Rice paddies have an NPP of about 1.4×1015 g y–1. Extrapolation of measured CH4 emissions in individual ecosystems lead to global methane emission estimates of 40–160 Teragram (1 Tg=1012 g) from natural wetlands and 60–140 Tg from rice paddies per year. The mean emission of 170–200 Tg may come in about equal proportions from natural wetlands and paddies. Major source regions are located in the subtropics between 20 and 30° N, the tropics between 0 and 10° S, and the temperate-boreal region between 50 and 70° N. Emissions are highly seasonal, maximizing during summer in both hemispheres. The wide range of possible CH4 emissions shows the large uncertainties associated with the extrapolation of measured flux rates to global scale. More investigations into ecophysiological principals of methane emissions is warranted to arrive at better source estimates.  相似文献   

17.
An integrated assessment of carbon balance in biomass removed during lumbering and transformed into products of forest, woodworking, and pulp and paper industry is conducted. Carbon sequestration was calculated with the IPCC technique. Depending on the economic state of the forest complex, from 1961 to 2005, its products can be both a source of emission of about 15 Mt CO2 per year and a pool that can uptake up to 54.1 Mt CO2 per year. In 2004, 28.3 Mt CO2 or 1.4% equivalent emission from other national economy sectors came to forest products from the atmosphere. Rational use of forest products and reduced non-productive losses of raw wood can lead to a significant contribution of the forest complex to decrease in greenhouse gas emissions into the atmosphere.  相似文献   

18.
海南岛和厦门红树林湿地CH4 排放的时空变化   总被引：16，自引：0，他引：16  
叶勇  卢昌义  林鹏 《大气科学》2000,24(2):152-156
研究了海南岛和厦门的河口海岸红树林湿地、海岸光滩及红树林伐迹地CH4排放的时空变化。海南岛长宁站位海莲林连续两年的CH4排放率均表现为外滩>中滩>内滩的空间变化模式,与土壤含水量的空间变化一致,而与土壤盐度的空间变化相反;但1997年在其余五个红树林湿地的CH4排放率表现出不同的空间变化规律,且大多与土壤理化因子不呈对应关系。各红树林湿地的最低CH4排放率均出现在冬季。红树林湿地年CH4排放率高于海岸光滩而低于红树林伐迹地。  相似文献   

19.
Measurements of nitrous oxide emission from agricultural lands were conducted. The results show that nitrous oxide fluxes on several soils are at the range of 2-60 μg . N / m2 h. Factors influencing the production rates of nitrous oxide from the soils, such as soil temperature, soil moisture and fertilization, are discussed. The calculated amount of nitrous oxide emission from China farmlands is 9.8 × 107 Kg . N per year, which accounts for about 10% of the total source strength in China areas.  相似文献   

20.
The U.K. has extensive databases on soils, land cover and historic land use change which have made it possible to construct a comprehensive inventory of the principal terrestrial sources and sinks of carbon for approximately the year 1990, using methods that are consistent with, and at least as accurate as, the revised 1996 guidelines recommended by IPCC where available – and including categories which are not currently considered under the UN Framework Convention on Climate Change. This country inventory highlights issues concerning methodology, uncertainty, double counting, the importance of soils and the relative magnitude of sources and sinks which are reported to the UNFCCC relative to other sources and sinks. The carbon sinks (negative values in MtC a-1) for categories reported to the UNFCCC, based on the IPCC categories, were estimated to be: forest trees and litter (–2.1), U.K. forest products (–0.5, ignoring imports and exports), non-forest biomass (–0.3), forest soils (–0.1) and soils on set-aside land (–0.4). The carbon sources (positive values) reported under the UNFCCC were estimated to be: losses of soil organic carbon resulting from cultivation of semi-natural land (6.2) and from urbanization (1.6), drainage of peatlands (0.3) and fenlands (0.5), and peat extraction (0.2). A range of other sources and sinks not covered by the IPCC guidelines were also quantified, namely, the accumulation of carbon in undrained peatlands (–0.7, ignoring methane emission), sediment accretion in coastal marshes (–0.1), the possible U.K. share of the CO2 and N fertilization carbon sink (–2.0) and riverine organic and particulate carbon export to the sea (1.4, which may be assumed to be a source if most of this carbon is released as CO2 in the sea). All sinks totalled –6.2 and sources 10.2, giving a net flux to the atmosphere in 1990 of 4.0 MtC a-1. Uncertainties associated with categories, mostly based on best guesses, ranged from ±15% for forest biomass and litter to ±60% for CO2 and N fertilization.  相似文献   

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