Greenhouse Gas Emissions from Hydroelectric Reservoirs in Tropical Regions

This paper discusses emissions by power-dams in the tropics. Greenhouse gas emissions from tropical power-dams are produced underwater through biomass decomposition by bacteria. The gases produced in these dams are mainly nitrogen, carbon dioxide and methane. A methodology was established for measuring greenhouse gases emitted by various power-dams in Brazil. Experimental measurements of gas emissions by dams were made to determine accurately their emissions of methane (CH₄) and carbon dioxide (CO₂) gases through bubbles formed on the lake bottom by decomposing organic matter, as well as rising up the lake gradient by molecular diffusion.The main source of gas in power-dams reservoirs is the bacterial decomposition (aerobic and anaerobic) of autochthonous and allochthonous organic matter that basically produces CO₂ and CH₄. The types and modes of gas production and release in the tropics are reviewed.     

Climate change in Yellowstone National Park: Is the drought-related risk of wildfires increasing?

The increased frequency of wildfires in the United States has become a common prediction associated with the build-up of greenhouse gases. In this investigation, variations in annual wildfire data in Yellowstone National Park are compared to variations in historical climate conditions for the area. Univariate and multivariate analytical techniques reveal that (a) summer temperatures in the Park are increasing, (b) January-June precipitation levels are decreasing, and (c) variations in burn area within the Park are significantly related to the observed variations in climate. Outputs from four different general circulation model simulations for 2 × CO₂ are included in the analyses; model predictions for increasing aridity in the Yellowstone Park area are generally in agreement with observed trends in the historical climate records.     

A Local-Scale Study of the Trace Gas Emissions from Vegetation Burning around the Village of Dalun, Ghana, with Respect to Seasonal Vegetation Changes and Burning Practices

The annual trace gas emissions from a West African rural region were calculated using direct observations of gas emissions and burning practices, and the findings compared to the guidelines published by the IPCC. This local-scale study was conducted around the village of Dalun in the Northern Region of Ghana, near the regional capital of Tamale. Two types of fires were found in the region – agricultural fires andwildfires. Agricultural fires are intentionally set in order to remove shrub and crop residues; wildfires are mostly ignited by herders to remove inedible grasses and to promote the growth of fresh grass. An agricultural fire is ignited with a fire front moving against the wind (backfire), whereas a wildfire moves with the wind (headfire). Gas emissions (CO₂, CO and NO) weremeasured by burning eight experimental plots, simulating both headfires and backfires. A common method of evaluating burning conditions is to calculate modified combustion efficiency (MCE), which expresses the percentage of the trace gases released as CO₂. Modified combustion efficiency was95% in the wildfires burned as headfires, but only 90% in the backfires.The burned area in the study region was determined by classifying a SPOT HRV satellite image taken about two months into the dry season. Fires were classified as either old burned areas or new burned areas as determined by the gradient in moisture content in the vegetation from the onset of the dry season. Classified burned areas were subsequently divided into two classes depending on whether the location was in the cultivated area or in the rangeland area, this sub-classification thus indicating whether the fire had been burned as a backfire or headfire. Findings showed that the burned area was 48% of the total region, and that the ratio of lowland wildfiresto agricultural fires was 3:1. The net trace gas release from the classified vegetation burnings were extrapolated to 26–46×10⁸ gCO₂, 78–302×10⁶ g CO,17–156×10⁵ g CH₄,16–168×10⁵ g NMHC and 11–72×10³ NO_x. Calculation of the emissionsusing proposed IPCC default values on burned area and average biomass resulted in a net emission 5 to 10 times higher than the measured emission values. It was found that the main reason for this discrepancy was not the emission factorsused by the IPCC, but an exaggerated fuel load estimate.     

The model study of the wildfire impact on the spatial distribution of deposition of sulfur and nitrogen compounds in Siberia

Presented are the results of the model study of wildfire impact on the spatial distribution of deposition fields of sulfur and nitrogen compounds in the regions of Siberia and the Russian Far East. The CHIMERE chemistry transport model was used for computing the deposition fields taking account of pyrogenic emissions specified using satellite measurements of intensity of wildfire heat radiation. Carried out is the model validation using the data of ground-based measurements of nitrate and sulfate concentrations in precipitation at the Russian EANET stations as well as the data of satellite measurements of carbon dioxide content in the troposphere and aerosol optical depth carried out by IASI and MODIS instruments, respectively. It is demonstrated that wildfires considerably influence deposition of sulfur and nitrogen compounds and redistribution of nitrogen compounds assimilated by plants within the regions under consideration.     

Relative radiative forcing consequences of global emissions of hydrocarbons, carbon monoxide and NOx from human activities estimated with a zonally-averaged two-dimensional model

A global two-dimensional (altitude-latitude) chemistry transport model is used to follow the changes in the tropospheric distribution of the two major radiatively active trace gases, methane and ozone, following step changes to the sustained emissions of the short-lived trace gases methane, carbon monoxide and non-methane hydrocarbons. The radiative impacts were dependent on the latitude chosen for the applied change in emissions. Step change global warming potentials (GWPs) were derived for a range of short-lived trace gases to describe their time-integrated radiative forcing impacts for unit emissions relative to that of carbon dioxide. The GWPs show that the tropospheric chemistry of the hydrocarbons can produce significant indirect radiative impacts through changing the tropospheric distributions of hydroxyl radicals, methane and ozone. For aircraft, the indirect radiative forcing impact of the NO _x emissions appears to be greater than that from their carbon dioxide emissions. Quantitative results from this two-dimensional model study must, however, be viewed against the known inadequacies of zonally-averaged models and their poor representation of many important tropospheric processes.     

Emissions, Concentrations, & Temperature: A Time Series Analysis

We use recent advances in time series econometrics to estimate the relation among emissions of CO₂ and CH₄, the concentration of these gases, and global surface temperature. These models are estimated and specified to answer two questions; (1) does human activity affect global surface temperature and; (2) does global surface temperature affect the atmospheric concentration of carbon dioxide and/or methane. Regression results provide direct evidence for a statistically meaningful relation between radiative forcing and global surface temperature. A simple model based on these results indicates that greenhouse gases and anthropogenic sulfur emissions are largely responsible for the change in temperature over the last 130 years. The regression results also indicate that increases in surface temperature since 1870 have changed the flow of carbon dioxide to and from the atmosphere in a way that increases its atmospheric concentration. Finally, the regression results for methane hint that higher temperatures may increase its atmospheric concentration, but this effect is not estimated precisely.     

Temperature extremes and wildfires in Siberia in the 21st century: the MGO regional climate model simulation

Possible changes in temperature extremes and wildfires in the 21st century in the regions of Russia are analyzed using a regional climate model (RCM) with high space-time resolution. The IPCC A2 scenario of greenhouse gas and aerosol concentration increase in the atmosphere is used. It is shown that changes in extreme wildfires appear to be in the 21st century most pronounced relative to changes in moderate and high wildfires. In some areas, along with decreased moderate and high wildfires, a significant increase in extreme wildfires is expected. Further studies should be associated both with RCM development, aimed at improving simulation of the wildfire atmospheric condition, and with enlarging the parameter set for wildfire analysis. Not only seasonal mean, but also monthly mean wildfire conditions should be studied, along with the use of statistical methods of model data interpretation to analyze intraseasonal and interannual variability of wildfire characteristics.     

Simulation of regional temperature change effect of land cover change in agroforestry ecotone of Nenjiang River Basin in China

Currently, US forests constitute a large carbon sink, comprising about 9 % of the global terrestrial carbon sink. Wildfire is the most significant disturbance influencing carbon dynamics in US forests. Our objective is to estimate impacts of climate change, CO₂ concentration, and nitrogen deposition on the future net biome productivity (NBP) of US forests until the end of twenty-first century under a range of disturbance conditions. We designate three forest disturbance scenarios under one future climate scenario to evaluate factor impacts for the future period (2011–2100): (1) no wildfires occur but forests continue to age (S_aging), (2) no wildfires occur and forest ages are fixed in 2010 (S_{fixed_nodis}), and (3) wildfires occur according to a historical pattern, consequently changing forest age (S_{dis_age_change}). Results indicate that US forests remain a large carbon sink in the late twenty-first century under the S_{fixed_nodis} scenario; however, they become a carbon source under the S_aging and S_{dis_age_change} scenarios. During the period of 2011 to 2100, climate is projected to have a small direct effect on NBP, while atmospheric CO₂ concentration and nitrogen deposition have large positive effects on NBP regardless of the future climate and disturbance scenarios. Meanwhile, responses to past disturbances under the S_{fixed_nodis} scenario increase NBP regardless of the future climate scenarios. Although disturbance effects on NBP under the S_aging and S_{dis_age_change} scenarios decrease with time, both scenarios experience an increase in NBP prior to the 2050s and then a decrease in NBP until the end of the twenty-first century. This study indicates that there is potential to increase or at least maintain the carbon sink of conterminous US forests at the current level if future wildfires are reduced and age structures are maintained at a productive mix. The effects of CO₂ on the future carbon sink may overwhelm effects of other factors at the end of the twenty-first century. Although our model in conjunction with multiple disturbance scenarios may not reflect the true conditions of future forests, it provides a range of potential conditions as well as a useful guide to both current and future forest carbon management.     

Estimation of Nocturnal Area Fluxes of Carbon Cycle Gases in Saint Petersburg Suburbs

Carbon dioxide, methane, and carbon monoxide are the carbon cycle gases, the data on their emissions are needed when monitoring air pollution and developing methods for reducing anthropogenic emissions to the atmosphere and for climate forecasting. The estimates of nocturnal area fluxes for CO₂, CH₄, and CO presented for a suburb of Saint Petersburg (Peterhof) are obtained using the box model and continuous observations of concentration of these gases. The mean values of CH₄, CO₂, and CO fluxes estimated for Peterhof for 2014–2015 are 44 ± 27, 6100 ± 4000, and 90 ± 100 t/(km² year), respectively. The intensity of the CO area flux has pronounced seasonal variations characterized by the maximum of ~(160 ± 120) t/(km² year) in November—February and by the minimum of ~(30 ± 20) t/(km² year) in June-July. The analysis of the ratio of CO/CO₂ fluxes identified the main types of anthropogenic sources typical of Peterhof: motor transport, natural gas combustion, and the use of wood stoves for the heating of private low-rise buildings (in the cold season).     

Impacts from decommissioning of hydroelectric dams: a life cycle perspective

Greenhouse gas (GHG) emissions from hydroelectric dams are often portrayed as nonexistent by the hydropower industry and have been largely ignored in global comparisons of different sources of electricity. However, the life cycle assessment (LCA) of any hydroelectric plant shows that GHG emissions occur at different phases of the power plant’s life. This work examines the role of decommissioning hydroelectric dams in greenhouse gas emissions. Accumulated sediments in reservoirs contain noticeable levels of carbon, which may be released to the atmosphere upon decommissioning of the dam. The rate of sediment accumulation and the sediment volume for six of the ten largest United States hydroelectric power plants is surveyed. The amount of sediments and the respective carbon content at the moment of dam decommissioning (100 years after construction) was estimated. The released carbon is partitioned into CO₂ and CH₄ emissions and converted to CO₂ equivalent emissions using the global warming potential (GWP) method. The global warming effect (GWE) due to dam decommissioning is normalized to the total electricity produced over the lifetime of each power plant. The estimated GWE of the power plants range from 128–380 g of CO₂eq./kWh when 11% of the total available sediment organic carbon (SOC) is mineralized and between 35 and 104 g of CO₂eq./kWh when 3% of the total SOC is mineralized. Though these values are below emission factors for coal power plants (890 g of CO₂eq./kWh), the amount of greenhouse gases emitted by the sediments upon dam decommissioning is a notable amount that should not be ignored and must be taken into account when considering construction and relicensing of hydroelectric dams.     

Using Remote Sensing to Assess Russian Forest Fire Carbon Emissions

Russian boreal forests are subject to frequent wildfires. The resulting combustion of large amounts of biomass not only transforms forest vegetation, but it also creates significant carbon emissions that total, according to some authors, from 35–94 Mt C per year. These carbon emissions from forest fires should be considered an important part of the forest ecosystem carbon balance and a significant influence on atmospheric trace gases. In this paper we discuss a new method to assess forest fire damage. This method is based on using multi-spectral high-resolution satellite images, large-scale aerial photography, and declassified images obtained from the space-borne national security systems. A normalized difference vegetation index (NDVI) difference image was produced from pre- and post-fire satellite images from SPOT/HRVIR and RESURS-O/MSU-E images. A close relationship was found between values of the NDVI difference image and forest damage level. High-resolution satellite data and large-scale aerial-photos were used to calibrate the NDVI-derived forest damage map. The method was used for mapping of forest fire extent and damage and for estimating carbon emissions from burned forest areas.     

The RCP greenhouse gas concentrations and their extensions from 1765 to 2300

We present the greenhouse gas concentrations for the Representative Concentration Pathways (RCPs) and their extensions beyond 2100, the Extended Concentration Pathways (ECPs). These projections include all major anthropogenic greenhouse gases and are a result of a multi-year effort to produce new scenarios for climate change research. We combine a suite of atmospheric concentration observations and emissions estimates for greenhouse gases (GHGs) through the historical period (1750?C2005) with harmonized emissions projected by four different Integrated Assessment Models for 2005?C2100. As concentrations are somewhat dependent on the future climate itself (due to climate feedbacks in the carbon and other gas cycles), we emulate median response characteristics of models assessed in the IPCC Fourth Assessment Report using the reduced-complexity carbon cycle climate model MAGICC6. Projected ??best-estimate?? global-mean surface temperature increases (using inter alia a climate sensitivity of 3°C) range from 1.5°C by 2100 for the lowest of the four RCPs, called both RCP3-PD and RCP2.6, to 4.5°C for the highest one, RCP8.5, relative to pre-industrial levels. Beyond 2100, we present the ECPs that are simple extensions of the RCPs, based on the assumption of either smoothly stabilizing concentrations or constant emissions: For example, the lower RCP2.6 pathway represents a strong mitigation scenario and is extended by assuming constant emissions after 2100 (including net negative CO₂ emissions), leading to CO₂ concentrations returning to 360 ppm by 2300. We also present the GHG concentrations for one supplementary extension, which illustrates the stringent emissions implications of attempting to go back to ECP4.5 concentration levels by 2250 after emissions during the 21^st century followed the higher RCP6 scenario. Corresponding radiative forcing values are presented for the RCP and ECPs.     

Assessment of greenhouse gases emission from civil aviation in Russia

The greenhouse gases emission (CO₂, CH₄, and N₂O) from domestic and international aviation in the Russian Federation is assessed. In 2007, the total emission of CO₂, CH₄, and N₂O amounted to 18.4 million tons of CO₂-equivalent, which is 21% below the 1990 level. Carbon dioxide dominates in the component composition of the emissions, its part in 2007 accounted for 99.1% of the emission. Taking into account the tendency towards increasing fuel consumption due to intense aircraft traffic it can be expected that compared to the present level the greenhouse gases emissions in 2012 and 2020 will increase by 15 and 45%, respectively. Accounting for the increased aircraft emissions as well as plans of foreign countries to include the international aviation into the scheme of greenhouse gases emission allowance (trade credits) it is expedient to make more precise the greenhouse gases emissions from the Russian aviation based on the detailed flight data for all types of the aircraft.     

Carbon Sequestration in Arable Soils is Likely to Increase Nitrous Oxide Emissions,Offsetting Reductions in Climate Radiative Forcing

Strategies for mitigating the increasing concentration of carbon dioxide (CO₂) in the atmosphere include sequestering carbon (C) in soils and vegetation of terrestrial ecosystems. Carbon and nitrogen (N) move through terrestrial ecosystems in coupled biogeochemical cycles, and increasing C stocks in soils and vegetation will have an impact on the N cycle. We conducted simulations with a biogeochemical model to evaluate the impact of different cropland management strategies on the coupled cycles of C and N, with special emphasis on C-sequestration and emission of the greenhouse gases methane (CH₄) and nitrous oxide (N₂O). Reduced tillage, enhanced crop residue incorporation, and farmyard manure application each increased soil C-sequestration, increased N₂O emissions, and had little effect on CH₄ uptake. Over 20 years, increases in N₂O emissions, which were converted into CO₂-equivalent emissions with 100-year global warming potential multipliers, offset 75–310% of the carbon sequestered, depending on the scenario. Quantification of these types of biogeochemical interactions must be incorporated into assessment frameworks and trading mechanisms to accurately evaluate the value of agricultural systems in strategies for climate protection.     

The effect of nitrogen fertilization on the COS and CS2 emissions from temperature forest soils

The net fluxes of carbonyl sulfide (COS) and carbon disulfide (CS₂) to the atmosphere from nitrogen amended and unamended deciduous and coniferous forest soils were measured during the spring of 1986. We found that emissions of these gases from acidic forest soils were substantially increased after nitrogen fertilization. The total (COS+CS₂) emissions were increased by nearly a factor of three in the hardwood stand and were more than doubled in the pine stand. Furthermore, vegetation type appeared to have an influence on which was the dominant sulfur gas released from the forest soils. The added nitrogen caused a dramatic increase in COS emissions from the hardwood stand (a factor of three increase), while CS₂ emissions from this site were not affected. We observed the opposite response in the pine stand; that is, the nitrogen fertilization had no affect on COS emissions, but did stimulate CS₂ emissions (a factor of more than nine increase).     

A Model for Estimating Future Emissions of Sulfur Hexafluoride and Perfluorocarbons

Sulfur hexafluoride (SF₆), perfluoromethane (CF₄) and perfluoroethane (C₂F₆) are strong greenhouse gases with long (>1000 year) atmospheric residence times. We derive emission factors for the major anthropogenic sources and project future emissions for 5 regions and the world. Although firms in many industrialized countries are already limiting emissions, without further policy intervention global emissions will rise 150% (CF₄ and C₂F₆) and 210% (SF₆) between 1990 and 2050; radiative forcing will increase 0.026 W m^-2. Full application of available low-cost and costless policies in industrialized nations would cut that radiative forcing by one-quarter. Increased forcing due to these gases is small (<2%) relative to other gases but permanent on the timescale of human civilization. We also quantify plausible manipulations to governmental data that will be used to determine compliance with the 1997 Kyoto Protocol, which includes commitments for industrialized countries to regulate these and other greenhouse gases. More complete and transparent data are urgently needed. West European nations, for example, can cut their emissions of these gases by half by 2010 simply by manipulating emission factors within the current bounds of uncertainty.     

Competing impact of anthropogenic emissions and meteorology on the distribution of trace gases over Indian region

The spatial distribution of trace gases exhibit large spatial heterogeneity over the Indian region with an elevated pollution loading over densely populated Gangetic Plains (IGP). The contending role and importance of anthropogenic emissions and meteorology in deciding the trace gases level and distribution over Indian region, however, is poorly investigated. In this paper, we use an online regional chemistry transport model (WRF/Chem) to simulate the spatial distribution of trace gases over Indian region during one representative month of only three meteorological seasons namely winter, spring/summer and monsoon. The base simulation, using anthropogenic emissions from SEAC⁴RS inventory, is used to simulate the general meteorological conditions and the realistic spatial distribution of trace gases. A sensitivity simulation is conducted after removing the spatial heterogeneity in the anthropogenic emissions, i.e., with spatially uniform emissions to decouple the role of anthropogenic emissions and meteorology and their role in controlling the distribution of trace gases over India. The concentration levels of Ozone, CO, SO₂ and NO₂ were found to be lower over IGP when the emissions are uniform over India. A comparison of the base run with the sensitivity run highlights that meteorology plays a dominant role in controlling the spatial distribution of relatively longer-lived species like CO and secondary species like Ozone while short-lived species like NO_X and SO₂ are predominantly controlled by the spatial variability in anthropogenic emissions over the Indian region.     

Laboratory studies of some environmental variables controlling sulfur emissions from plants

Several trace sulfur gases that can have a significant influence on atmospheric chemistry are emitted from biological systems. In order to begin to address biological questions on the mechnisms of production of such gases, laboratory-scale experiments have been developed that reproduce such emissions under controlled conditions. Using a flux chamber technique, flats containing soil, or soil plus plants were sampled for the net fluxes of sulfur gases. The major sulfur gas emitted from all the plants tested (corn, alfalfa, and wheat) was dimethyl sulfide (DMS). Alfalfa and wheat also emitted lesser amounts of methanethiol, variable amounls of hydrogen sulfide, and in some experiments wheat emitted carbon disulfide. The use of a plant incubator allowed a systematic study of the effects of variables such as temperature, photon flux, and carbon dioxide levels, on these emissions. Fluxes of all the emitted sulfur gases increased exponentially with increasing air temperature, and increased with increasing photon flux up to a saturation level of \~300 E/m^–2 sec^-1. Three to four-fold changes in DMS flux were observed during light to dark or dark to light transitions. By varying the CO₂ content of the chamber flush gas, it was shown that the observed sulfur fluxes from corn and alfalfa were not related to the CO₂ concentration. Growing these crop plants through holes in a Teflon soil-covering film allowed a separate determination of soil and foliage emissions and substantiation of the light dependent uptake of COS by growing vegetation observed in previous field studies.     

Emissions from Russian domestic civil aviation in 2000–2012 and integrated assessment of their impact on the climate system

Emissions from Russian domestic civil aviation for the period of 2000–2012 are assessed for the following gases: carbon dioxide, methane, nitrous oxide, carbon monoxide, nitrogen oxides, and sulfur dioxide. The integrated assessment of their impact on the climate system is performed using the values of the global warming potential. The CO₂ equivalent was used as a common measure of emissions. It is established that the modern impact of Russian civil aviation on the Earth climate is insignificant.     

Abatement of Greenhouse Gases: Does Location Matter?

Today's climate policy is based on the assumption that the location of emissions reductions has no impact on the overall climate effect. However, this may not be the case since reductions of greenhouse gases generally will lead to changes in emissions of short-lived gases and aerosols. Abatement measures may be primarily targeted at reducing CO₂, but may also simultaneously reduce emissions of NO_x, CO, CH₄ and SO₂ and aerosols. Emissions of these species may cause significant additional radiative forcing. We have used a global 3-D chemical transport model and a radiative transfer model to study the impact on climate in terms of radiative forcing for a realistic change in location of the emissions from large-scale sources. Based on an assumed 10% reduction in CO₂ emissions, reductions in the emissions of other species have been estimated. Climate impact for the SRES A1B scenario is compared to two reduction cases, with the main focus on a case with emission reductions between 2010 and 2030, but also a case with sustained emission reductions. The emission reductions are applied to four different regions (Europe, China, South Asia, and South America). In terms of integrated radiative forcing (over 100 yr), the total effect (including only the direct effect of aerosols) is always smaller than for CO₂ alone. Large variations between the regions are found (53–86% of the CO₂ effect). Inclusion of the indirect effects of sulphate aerosols reduces the net effect of measures towards zero. The global temperature responses, calculated with a simple energy balance model, show an initial additional warming of different magnitude between the regions followed by a more uniform reduction in the warming later. A major part of the regional differences can be attributed to differences related to aerosols, while ozone and changes in methane lifetime make relatively small contributions. Emission reductions in a different sector (e.g. transportation instead of large-scale sources) might change this conclusion since the NO_x to SO₂ ratio in the emissions is significantly higher for transportation than for large-scale sources. The total climate effect of abatement measures thus depends on (i) which gases and aerosols are affected by the measure, (ii) the lifetime of the measure implemented, (iii) time horizon over which the effects are considered, and (iv) the chemical, physical and meteorological conditions in the region. There are important policy implications of the results. Equal effects of a measure cannot be assumed if the measure is implemented in a different region and if several gases are affected. Thus, the design of emission reduction measures should be considered thoroughly before implementation.