CO2-eq Yr Research Articles

Long-term changes in greenhouse gas emissions from French agriculture and livestock (1852–2014): From traditional agriculture to conventional intensive systems

France was a traditionally agricultural country until the first half of the 20th century. Today, it is the first European cereal producer, with cereal crops accounting for 40% of the agricultural surface area used, and is also a major country for livestock breeding with 25% of the European cattle livestock. This major socioecological transition, with rapid intensification and specialisation in an open global market, has been accompanied by deep environmental changes. To explore the changes in agricultural GHG emissions over the long term (1852–2014), we analysed the emission factors of N2O from field experiments covering major land uses, in a gradient of fertilisation and within a range of temperature and rainfall, and used CH4 emission coefficients for livestock categories, in terms of enteric and manure management, considering the historical changes in animal excretion rates. We also estimated indirect CO2 emissions, rarely accounted for in agricultural emissions, using coefficients found in the literature for the dominant energy consumption items (fertiliser production, field work and machinery, and feed import). From GHG emissions of ~30,000 ktons CO2 Eq yr−1 in 1852, reaching 54,000 ktons CO2 Eq yr−1 in 1955, emissions more than doubled during the ‘Glorious thirties’ (1950–1980), and peaked around 120,000 ktons CO2 Eq yr−1 in the early 2000s. For the 2010–2014 period, French agriculture GHG emissions stabilised at ~114,000 ktons CO2 Eq yr−1, distributed into 49% methane (CH4), 22% carbon dioxide (CO2) and 29% nitrous oxide (N2O). A regional approach through 33 regions in France shows a diversity of agriculture reflecting the hydro-ecoregion distribution and the agricultural specialisation of local areas. Exploring contrasting scenarios at the 2040 horizon suggests that only deep changes in the structure of the agro-food system would double the reduction of GHG emissions by the agricultural sector.

Food security and sustainable agriculture in Lebanon: An environmental accounting framework

World population is expected to approach 9.7 billion by 2050. This scenario will lead to an increase in food demand, worsening environmental problems due to intensive agricultural productions. For this reason, one of the major challenges is to attain both food security and sustainable agriculture worldwide. While food security is aimed at ensuring a constant and healthy food supply over time, sustainable agriculture plays a key role for the maintenance of resilient agroecosystems. In this study, we implemented a multicriteria accounting framework to explore the environmental performance and sustainability of agricultural production in Lebanon at both farm and national level. An extensive field study was conducted to collect data on natural and human-driven flows supporting nine main agricultural production systems in different Lebanese regions. The investigated cropping systems were assessed in terms of environmental costs and impacts by jointly applying the following environmental accounting methods: gross energy requirement (GER), material flow accounting (MFA), emergy accounting, and emissions accounting and contribution to impact categories. At national level, the total emergy demand resulted 5.46⋅1021 sej yr−1, while the total GER was 1.81⋅1010 MJ yr−1. The total water and abiotic demand resulted 6.27⋅108 t yr −1 and 2.64⋅106 t yr−1, respectively. Finally, the total contribution to global warming potential (GWP) resulted 1.45⋅1012 g CO2 eq yr−1, while the acidification potential (AP) and the human toxicity (HT) resulted 5.79⋅109 g SO2 eq yr−1 and 6.88⋅109 g 1,4-DCB eq yr−1. At farm level, orange production showed the lowest environmental performance due to a high use of water, diesel, and fertilizers. Instead, olive production showed the best environmental performance thanks to a low requirement of mass and energy inputs, and human labour, confirming the advantages of environmental friendly practices. The results of this study can help both farmers and policy makers in charge for ensuring a sustainable management of agricultural production while providing access to safe, healthy, and nutritious food for a growing population. Finally, a set of biophysical and socio-economic indicators is proposed for integrating the environmental accounting with a socio-economic perspective on food security and sustainable agriculture.

Carbon dioxide, methane and nitrous oxide emissions from the human-impacted Seine watershed in France

Greenhouse gas (GHG) emissions from rivers and lakes have been shown to contribute significantly to global carbon and nitrogen cycling. In temperate and human-impacted regions, simultaneous carbon dioxide, methane and nitrous oxide emissions from aquatic systems are poorly documented. We estimated carbon dioxide (CO2) concentrations in the Seine hydrosystem (71,730 km2, France) using direct measurements, and calculations of CO2 partial pressures from 14 field campaigns conducted between 2010 and 2017, and compared them to methane (CH4) and nitrous oxide (N2O) concentrations.In the main stem of the Seine River, CO2 showed the same spatial gradient as N2O and CH4 with peaks in concentration downstream from the arrival of effluents from wastewater treatment plants enriched in organic matter, thus favoring mineralization. It is likely that high CO2 concentrations upstream were due to organic carbon inputs from soils and enriched CO2 groundwater discharges, whereas high N2O and CH4 upstream values were likely due to denitrification in riparian wet areas and anoxic decomposition of organic matter-rich wetlands, respectively. In addition, seasonal variations in all three GHGs were observed with higher concentrations in summer when higher temperatures promote mineralization and low water reduces the dilution of organic matter mainly originating from WWTP effluents.GHG emissions were calculated and compared with agricultural and nonagricultural (urban, transport) fluxes in the basin. In the Seine River network, CO2 emissions dominated riverine GHG emissions, reaching 95.3%, while N2O and CH4 emissions accounted for 4.4% and 0.3%, respectively. These indirect emissions from the hydrosystem were estimated to account for 3.7% of the total GHG emissions from the basin that amounted to 61,284 Gg CO2eq yr−1. Comparatively, direct agricultural and nonagricultural GHG emissions were estimated at 23.3% and 73.0%., respectively.

Abundance and sources of atmospheric halocarbons in the Eastern Mediterranean

Abstract. A wide range of anthropogenic halocarbons is released to the atmosphere, contributing to stratospheric ozone depletion and global warming. Using measurements of atmospheric abundances for the estimation of halocarbon emissions on the global and regional scale has become an important top-down tool for emission validation in the recent past, but many populated and developing areas of the world are only poorly covered by the existing atmospheric halocarbon measurement network. Here we present 6 months of continuous halocarbon observations from Finokalia on the island of Crete in the Eastern Mediterranean. The gases measured are the hydrofluorocarbons (HFCs), HFC-134a (CH2FCF3), HFC-125 (CHF2CF3), HFC-152a (CH3CHF2) and HFC-143a (CH3CF3) and the hydrochlorofluorocarbons (HCFCs), HCFC-22 (CHClF2) and HCFC-142b (CH3CClF2). The Eastern Mediterranean is home to 250 million inhabitants, consisting of a number of developed and developing countries, for which different emission regulations exist under the Kyoto and Montreal protocols. Regional emissions of halocarbons were estimated with Lagrangian atmospheric transport simulations and a Bayesian inverse modeling system, using measurements at Finokalia in conjunction with those from Advanced Global Atmospheric Gases Experiment (AGAGE) sites at Mace Head (Ireland), Jungfraujoch (Switzerland) and Monte Cimone (Italy). Measured peak mole fractions at Finokalia showed generally smaller amplitudes for HFCs than at the European AGAGE sites except for periodic peaks of HFC-152a, indicating strong upwind sources. Higher peak mole fractions were observed for HCFCs, suggesting continued emissions from nearby developing regions such as Egypt and the Middle East. For 2013, the Eastern Mediterranean inverse emission estimates for the four analyzed HFCs and the two HCFCs were 13.9 (11.3–19.3) and 9.5 (6.8–15.1) Tg CO2eq yr−1, respectively. These emissions contributed 16.8 % (13.6–23.3 %) and 53.2 % (38.1–84.2 %) to the total inversion domain, which covers the Eastern Mediterranean as well as central and western Europe. Greek bottom-up HFC emissions reported to the UNFCCC were higher than our top-down estimates, whereas for Turkey our estimates agreed with UNFCCC-reported values for HFC-125 and HFC-143a, but were much and slightly smaller for HFC-134a and HFC-152a, respectively. Sensitivity estimates suggest an improvement of the a posteriori emission estimates, i.e., a reduction of the uncertainties by 40–80 % in the entire inversion domain, compared to an inversion using only the existing central European AGAGE observations.

Evaluation of greenhouse gas emissions from industrial parks using criteria air pollutants: a case study of Taiwan

An innovative greenhouse gas (GHG) inventory using criteria air pollutants (CAPs) was constructed to evaluate GHG emissions from industrial parks. The inventory included both on- (CAPs from air quality monitoring stations) and off-site GHG emissions from waste generation, wastewater treatment, electricity consumption and transportation. According to the inventory, the total GHG emissions from the industrial parks in Taiwan were ranged from 899.41 to 1,329.69 ppmv CO2-eq yr–1 for on-site emissions and 2.19 × 104 to 1.22 × 107 t CO2-eq yr–1 for off-site emissions. Electricity consumption was the most important factor contributing to higher GHG emissions in the industrial parks. Methane was found to contribute the highest GHG emissions in the wastewater treated. GHG emissions from transportation can be expected to undergo a 1.9–15.4% reduction from the industrial parks in this study. The results of this study have great implications for low-carbon development in other industrial parks worldwide.

Evaluation of Greenhouse Gas Emissions from Industrial Parks Using Criteria Air Pollutants: A Case Study of Taiwan

An innovative greenhouse gas (GHG) inventory using criteria air pollutants (CAPs) was constructed to evaluate GHG emissions from industrial parks. The inventory included both on- (CAPs from air quality monitoring stations) and off-site GHG emissions from waste generation, wastewater treatment, electricity consumption and transportation. According to the inventory, the total GHG emissions from the industrial parks in Taiwan were ranged from 899.41 to 1,329.69 ppmv CO2-eq yr–1 for on-site emissions and 2.19 × 104 to 1.22 × 107 t CO2-eq yr–1 for off-site emissions. Electricity consumption was the most important factor contributing to higher GHG emissions in the industrial parks. Methane was found to contribute the highest GHG emissions in the wastewater treated. GHG emissions from transportation can be expected to undergo a 1.9–15.4% reduction from the industrial parks in this study. The results of this study have great implications for low-carbon development in other industrial parks worldwide.

Impacts of nationally determined contributions on 2030 global greenhouse gas emissions: uncertainty analysis and distribution of emissions

Nationally Determined Contributions (NDCs), submitted by Parties to the United Nations Framework Convention on Climate Change before and after the 21st Conference of Parties, summarize domestic objectives for greenhouse gas (GHG) emissions reductions for the 2025–2030 time horizon. In the absence, for now, of detailed guidelines for the format of NDCs, ancillary data are needed to interpret some NDCs and project GHG emissions in 2030. Here, we provide an analysis of uncertainty sources and their impacts on 2030 global GHG emissions based on the sole and full achievement of the NDCs. We estimate that NDCs project into 56.8–66.5 Gt CO2eq yr−1 emissions in 2030 (90% confidence interval), which is higher than previous estimates, and with a larger uncertainty range. Despite these uncertainties, NDCs robustly shift GHG emissions towards emerging and developing countries and reduce international inequalities in per capita GHG emissions. Finally, we stress that current NDCs imply larger emissions reduction rates after 2030 than during the 2010–2030 period if long-term temperature goals are to be fulfilled. Our results highlight four requirements for the forthcoming ‘climate regime’: a clearer framework regarding future NDCs’ design, an increasing participation of emerging and developing countries in the global mitigation effort, an ambitious update mechanism in order to avoid hardly feasible decarbonization rates after 2030 and an anticipation of steep decreases in global emissions after 2030.

Emission of greenhouse gases from waste incineration in Korea

Greenhouse gas (GHG) emission factors previously reported from various waste incineration plants have shown significant variations according to country-specific, plant-specific, and operational conditions. The purpose of this study is to estimate GHG emissions and emission factors at nine incineration facilities in Korea by measuring the GHG concentrations in the flue gas samples. The selected incineration plants had different operation systems (i.e., stoker, fluidized bed, moving grate, rotary kiln, and kiln & stoker), and different nitrogen oxide (NOx) removal systems (i.e., selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR)) to treat municipal solid waste (MSW), commercial solid waste (CSW), and specified waste (SW). The total mean emission factors for A and B facilities for MSW incineration were found to be 134 ± 17 kg CO2 ton−1, 88 ± 36 g CH4 ton−1, and 69 ± 16 g N2O ton−1, while those for CSW incineration were 22.56 g CH4 ton−1 and 259.76 g N2O ton−1, and for SW incineration emission factors were 2959 kg CO2 ton−1, 43.44 g CH4 ton−1 and 401.21 g N2O ton−1, respectively. Total emissions calculated using annual incineration for MSW were 3587 ton CO2-eq yr−1 for A facility and 11,082 ton CO2-eq yr−1 for B facility, while those of IPCC default values were 13,167 ton CO2-eq yr−1 for A facility and 32,916 ton CO2-eq yr−1, indicating that the emissions of IPCC default values were estimated higher than those of the plant-specific emission factors. The emission of CSW for C facility was 1403 ton CO2-eq yr−1, while those of SW for D to I facilities was 28,830 ton CO2-eq yr−1. The sensitivity analysis using a Monte Carlo simulation for GHG emission factors in MSW showed that the GHG concentrations have a greater impact than the incineration amount and flow rate of flue gas. For MSW incineration plants using the same stoker type in operation, the estimated emissions and emission factors of CH4 showed the opposite trend with those of NO2 when the NOx removal system was used, whereas there was no difference in CO2 emissions.

Orchard and horticulture systems in Spanish Mediterranean coastal areas: Is there a real possibility to contribute to C sequestration?

Agriculture in the Mediterranean basin is currently contributing to greenhouse gas emissions (GHG) and in the future is expected to be strongly affected by climate change. Increasing soil organic carbon (SOC) via soil organic matter (SOM) improvement is widely regarded as a way to both mitigate and adapt to climate change. Using as a case study the Mediterranean coastal area in Spain, which is regarded as one of the most intensively managed areas in Europe for orchards and horticultural cropping, we analyzed the potential for climate change mitigation of introducing different practices that are expected to increase SOC. We selected both as a single measure and in combination, cover cropping and application to the soil of the available underutilized exogenous organic matter (EOM), treated (e.g. composted or digested) or non-treated. These practices were compared against a baseline scenario that intended to reflect the current practices in the area (e.g. all livestock manure produced in the area is applied to the agricultural soil). We carried out a modelling exercise at the regional scale using the agricultural activity data and current climatic conditions as inputs. Modelling runs were performed coupling a widely used dynamic model of SOC turnover (RothC) with a model to simulate the GHG emissions from EOM processing or storage prior to soil application (SIMSWASTE).Results indicate that the most promising practice, considered as a single measure and with respect to the baseline, was introducing cover crops in woody cropping systems. This practice resulted in an increase of 0.44MgCha−1 yr−1 during the first 20 years (range 0.41–0.52MgCha−1 yr−1) and led to a total SOC accumulation of about 30TgC after 100 years. Amendment of all agricultural land with available underutilized EOM resulted in an increase of up to 0.09MgCha−1 yr−1 (range 0.07–0.16MgCha−1 yr−1) as a single measure (urban waste) and 0.13MgCha−1 yr−1 (range 0.11–0.21MgCha−1 yr−1) as a combined measure (urban waste and composted agroindustry by-products), leading to a total SOC accumulation of about 7TgC (urban waste) and 10Tg C (urban waste and composted agroindustry by-products) after 100 years. Manure anaerobic digestion or composting as a single measure did not result in significant SOC changes but, if GHG emissions and savings from manure storage and processing management stages are considered, they could help to reduce about 4.3 (anaerobic digestion) or 1.1Tg CO2eq yr−1 (composting) in the study area, which represents a significant amount compared with total agricultural emissions in Spain.

FAOSTAT estimates of greenhouse gas emissions from biomass and peat fires

The Global Fire Emissions Database (GFED3) and the FAOSTAT Emissions database, containing estimates of greenhouse gas (GHG) emissions from biomass burning and peat fires, are compared. The two datasets formed the basis for several analyses in the fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5), and thus represent a critical source of information for emissions inventories at national, regional and global level. The two databases differ in their level of computational complexity in estimating emissions. While both use the same burned area information from remote sensing, estimates of available biomass are computed in GFED3 at tier 3 using a complex dynamic vegetation model, while they are computed in FAOSTAT using default, tier 1 parameters from the Intergovernmental Panel on Climate Change (IPCC). Over the analysis period 1997–2011, the two methods were found to produce very similar global GHG emissions estimates for each of the five GFED aggregated biomass fire classes: i) Savanna; ii) Woodland; iii) Forest; iv) Deforestation; v) Peatlands; with total emissions ranging 6–8 Gt CO2eq yr-1. The main differences between the two datasets were found with respect to peat fires, with FAOSTAT showing a lower 1997–1998 peak in emissions compared with GFED3, within an otherwise good agreement for the rest of the study period, when limited to the three tropical countries covered by GFED. Conversely, FAOSTAT global emissions from peat fires, including both boreal and tropical regions, were several times larger than those currently estimated by GFED3. Results show that FAOSTAT activity data and emission estimates for biomass fires offer a robust alternative to the more sophisticated GFED data, representing a valuable resource for national GHG inventory experts, especially in countries where technical and institutional constraints may limit access, generation and maintenance of more complex methodologies and data.

Quantifying changes to the global warming potential of rice wheat systems with the adoption of conservation agriculture in northwestern India

Field trials were conducted in Haryana representing the northwestern Indo-Gangetic Plains (IGP) to assess the changes brought about by management, including conservation agriculture (CA) practices, in the global warming potential (GWP) of conventional rice–wheat systems. Conservation agriculture is an approach to managing agro-ecosystems for improved and sustained productivity, by way of minimal soil disturbance, permanent soil cover with organic matter or cover crops and crop rotation. Methane (CH4) and nitrous oxide (N2O) fluxes were measured using static chambers. Experiments involved four cropping system scenarios with different CA components, and different N rates. In addition, emissions of CH4 and N2O fluxes were measured in farmers’ fields to establish baselines. The dynamics of CH4 emissions were controlled by floodwater levels, and fertilizer N had no effect. On the other hand, N application rates and timing in relation to soil water status determined the N2O emissions in rice fields. Nitrous oxide fluxes could be avoided by applying N fertilizer to wet soil or by irrigating the field not later than 1 day after N application. Applying crop residues on soil surface had no significant effect on the seasonal CH4 and N2O emissions. It was estimated that switching rice crop establishment method from conventional to CA-based practices in Haryana could reduce GWP for rice by 23% or by 1.26 Tg CO2 eqyr−1. An intensive CA-based rice–wheat and maize–wheat system reduced GWP by 16–26% or by 1.3–2.0 Tg CO2 eqyr−1 compared with the conventional rice–wheat system. However, this reduction in GWP would be from a decrease in diesel and electricity consumption and not from direct emissions of CH4 and N2O, which were higher in the maize–wheat system than in the rice–wheat system.

The Contribution of Agriculture, Forestry and other Land Use activities to Global Warming, 1990-2012.

We refine the information available through the IPCC AR5 with regard to recent trends in global GHG emissions from agriculture, forestry and other land uses (AFOLU), including global emission updates to 2012. Using all three available AFOLU datasets employed for analysis in the IPCC AR5, rather than just one as done in the IPCC AR5 WGIII Summary for Policy Makers, our analyses point to a down-revision of global AFOLU shares of total anthropogenic emissions, while providing important additional information on subsectoral trends. Our findings confirm that the share of AFOLU emissions to the anthropogenic total declined over time. They indicate a decadal average of 28.7±1.5% in the 1990s and 23.6±2.1% in the 2000s and an annual value of 21.2±1.5% in 2010. The IPCC AR5 had indicated a 24% share in 2010. In contrast to previous decades, when emissions from land use (land use, land use change and forestry, including deforestation) were significantly larger than those from agriculture (crop and livestock production), in 2010 agriculture was the larger component, contributing 11.2±0.4% of total GHG emissions, compared to 10.0±1.2% of the land use sector. Deforestation was responsible for only 8% of total anthropogenic emissions in 2010, compared to 12% in the 1990s. Since 2010, the last year assessed by the IPCC AR5, new FAO estimates indicate that land use emissions have remained stable, at about 4.8Gt CO2 eqyr-1 in 2012. Emissions minus removals have also remained stable, at 3.2Gt CO2 eqyr-1 in 2012. By contrast, agriculture emissions have continued to grow, at roughly 1% annually, and remained larger than the land use sector, reaching 5.4Gt CO2 eqyr-1 in 2012. These results are useful to further inform the current climate policy debate on land use, suggesting that more efforts and resources should be directed to further explore options for mitigation in agriculture, much in line with the large efforts devoted to REDD+ in the past decade.

Environmental footprints show China and Europe’s evolving resource appropriation for soybean production in Mato Grosso, Brazil

Mato Grosso has become the center of Brazil’s soybean industry, with production located across an agricultural frontier expanding into savanna and rainforest biomes. We present environmental footprints of soybean production in Mato Grosso and resource flows accompanying exports to China and Europe for the 2000s using five indicators: deforestation, land footprint (LF), carbon footprint (CF), water footprint (WF), and nutrient footprints. Soybean production was associated with 65% of the state’s deforestation, and 14–17% of total Brazilian land use change carbon emissions. The decade showed two distinct production systems illustrated by resources used in the first and second half of the decade. Deforestation and carbon footprint declined 70% while land, water, and nutrient footprints increased almost 30% between the two periods. These differences coincided with a shift in Mato Grosso’s export destination. Between 2006 and 2010, China surpassed Europe in soybean imports when production was associated with 97 m2 deforestation yr−1 ton−1 of soybean, a LF of 0.34 ha yr−1 ton−1, a carbon footprint of 4.6 ton CO2-eq yr−1 ton−1, a WF of 1908 m3 yr−1 ton−1, and virtual phosphorous and potassium of 5.0 kg P yr−1 ton−1 and 0.0042 g K yr−1 ton−1. Mato Grosso constructs soil fertility via phosphorous and potassium fertilizer sourced from third party countries and imported into the region. Through the soybean produced, Mato Grosso then exports both water derived from its abundant, seasonal precipitation and nutrients obtained from fertilizer. In 2010, virtual water flows were 10.3 km3 yr−1 to China and 4.1 km3 yr−1 to Europe. The total embedded nutrient flows to China were 2.12 Mtons yr−1 and 2.85 Mtons yr−1 to Europe. As soybean production grows with global demand, the role of Mato Grosso’s resource use and production vulnerabilities highlight the challenges with meeting future international food security needs.

The potential use of heather, Calluna vulgaris, as a bioenergy crop

Calluna vulgaris can and does grow in areas considered unsuitable for production of biomass crops. In the UK, Calluna vegetation is regularly controlled by burn management and if instead the lost biomass could be harvested would it represent a viable energy crop? This study used established techniques for other energy crops to assess the energy yield, energy efficiency and the greenhouse gas savings represented by cropping of Calluna under two scenarios; only harvested on the area currently under burn management; and harvested on the present total area of Calluna in the UK. The study can consider biomass potential across the UK and can include altitude changes. The study can show that Calluna would represent an efficient energy crop in areas where it would not be possible to revert to functioning peat bogs. The energy efficiency was 65±19GJoutputGJinput−1 with GHG savings of up to 11 tonnes CO2eq ha−1 yr−1. When considered across the UK the potential energy production was up to 40.7 PJ yr−1 and the potential greenhouse gas saving was upto −2061 ktonnes CO2eq yr−1 if the all Calluna could be brought into production and substituted for coal.

HFC-43-10mee atmospheric abundances and global emission estimates

We report in situ atmospheric measurements of hydrofluorocarbon HFC-43-10mee (C5H2F10; 1,1,1,2,2,3,4,5,5,5-decafluoropentane) from seven observatories at various latitudes, together with measurements of archived air samples and recent Antarctic flask air samples. The global mean tropospheric abundance was 0.21 ± 0.05 ppt (parts per trillion, dry air mole fraction) in 2012, rising from 0.04 ± 0.03 ppt in 2000. We combine the measurements with a model and an inverse method to estimate rising global emissions—from 0.43 ± 0.34 Gg yr−1 in 2000 to 1.13 ± 0.31 Gg yr−1 in 2012 (~1.9 Tg CO2-eq yr−1 based on a 100 year global warming potential of 1660). HFC-43-10mee—a cleaning solvent used in the electronics industry—is currently a minor contributor to global radiative forcing relative to total HFCs; however, our calculated emissions highlight a significant difference from the available reported figures and projected estimates.

A multitower measurement network estimate of California's methane emissions

AbstractWe present an analysis of methane (CH4) emissions using atmospheric observations from five sites in California's Central Valley across different seasons (September 2010 to June 2011). CH4 emissions for spatial regions and source sectors are estimated by comparing measured CH4 mixing ratios with transport model (Weather Research and Forecasting and Stochastic Time‐Inverted Lagrangian Transport) predictions based on two 0.1° CH4 (seasonally varying “California‐specific” (California Greenhouse Gas Emission Measurements, CALGEM) and a static global (Emission Database for Global Atmospheric Research, release version 42, EDGAR42)) prior emission models. Region‐specific Bayesian analyses indicate that for California's Central Valley, the CALGEM‐ and EDGAR42‐based inversions provide consistent annual total CH4 emissions (32.87 ± 2.09 versus 31.60 ± 2.17 Tg CO2eq yr−1; 68% confidence interval (CI), assuming uncorrelated errors between regions). Summing across all regions of California, optimized CH4 emissions are only marginally consistent between CALGEM‐ and EDGAR42‐based inversions (48.35 ± 6.47 versus 64.97 ± 11.85 Tg CO2eq), because emissions from coastal urban regions (where landfill and natural gas emissions are much higher in EDGAR than CALGEM) are not strongly constrained by the measurements. Combining our results with those from a recent study of the South Coast Air Basin narrows the range of estimates to 43–57 Tg CO2eq yr−1 (1.3–1.8 times higher than the current state inventory). These results suggest that the combination of rural and urban measurements will be necessary to verify future changes in California's total CH4 emissions.

Contemporary and projected biogenic fluxes of methane and nitrous oxide in North American terrestrial ecosystems

Accurately estimating biogenic methane (CH4) and nitrous oxide (N2O) fluxes in terrestrial ecosystems is critical for resolving global budgets of these greenhouse gases (GHGs) and continuing to mitigate climate warming. Here, we assess contemporary biogenic CH4 and N2O budgets and probable climate‐change‐related impacts on CH4 and N2O emissions in terrestrial North America. Multi‐approach estimations show that, during 1990–2010, biogenic CH4 emissions ranged from 0.159 to 0.502 petagrams of carbon dioxide (CO2) equivalents per year (Pg CO2eq yr−1, where 1 Pg = 1 × 1015 g) and N2O emissions ranged from 0.802 to 1.016 Pg CO2eq yr−1, which offset 47–166% of terrestrial CO2 sequestration (0.915–2.040 Pg CO2eq yr−1, as indicated elsewhere in this Special Issue). According to two future climate scenarios, CH4 and N2O emissions are projected to continue increasing by 137–151% and 157–227%, respectively, by the end of this century, as compared with levels during 2000–2010. Strategies to mitigate climate change must account for non‐CO2 GHG emissions, given their substantial warming potentials.

Net greenhouse gas balance in response to nitrogen enrichment: perspectives from a coupled biogeochemical model

Increasing reactive nitrogen (N) input has been recognized as one of the important factors influencing climate system through affecting the uptake and emission of greenhouse gases (GHG). However, the magnitude and spatiotemporal variations of N-induced GHG fluxes at regional and global scales remain far from certain. Here we selected China as an example, and used a coupled biogeochemical model in conjunction with spatially explicit data sets (including climate, atmospheric CO2 , O3 , N deposition, land use, and land cover changes, and N fertilizer application) to simulate the concurrent impacts of increasing atmospheric and fertilized N inputs on balance of three major GHGs (CO2 , CH4 , and N2 O). Our simulations showed that these two N enrichment sources in China decreased global warming potential (GWP) through stimulating CO2 sink and suppressing CH4 emission. However, direct N2 O emission was estimated to offset 39% of N-induced carbon (C) benefit, with a net GWP of three GHGs averaging -376.3±146.4Tg CO2 eqyr(-1) (the standard deviation is interannual variability of GWP) during 2000-2008. The chemical N fertilizer uses were estimated to increase GWP by 45.6±34.3Tg CO2 eqyr(-1) in the same period, and C sink was offset by 136%. The largest C sink offset ratio due to increasing N input was found in Southeast and Central mainland of China, where rapid industrial development and intensively managed crop system are located. Although exposed to the rapidly increasing N deposition, most of the natural vegetation covers were still showing decreasing GWP. However, due to extensive overuse of N fertilizer, China's cropland was found to show the least negative GWP, or even positive GWP in recent decade. From both scientific and policy perspectives, it is essential to incorporate multiple GHGs into a coupled biogeochemical framework for fully assessing N impacts on climate changes.

Net exchanges of CO2, CH4 and N2O between marshland and the atmosphere in Northeast China as influenced by multiple global environmental changes

Natural wetland ecosystem plays an important role in global climate change due to its large amounts of stored carbon and nitrogen. The Sanjiang Plain, Northeast China, encompasses large area of natural freshwater marshy wetlands. However, the magnitude and temporal patterns of major greenhouse gases (GHGs: CO2, CH4 and N2O) in this region remain far from certain. Here we used a process-based ecosystem model to examine GHGs fluxes and their underlying mechanisms in the marshland across the Sanjiang Plain over the period 1949–2008. Simulation results indicated that during the past 60 years, the Sanjiang Plain's marshland acted as a net CO2 sink of 4.20 ± 0.44 Tg C yr−1, while approximately 0.46 ± 0.02 Tg C yr−1 for CH4 and 0.02 ± 0.00 Tg N yr−1 for N2O were released to the atmosphere. Land cover and land use change (LCLUC) was the primary driver for GHGs changes. Climate change and tropospheric ozone (O3) pollution decreased CO2 uptakes, yet elevated CO2 concentration and nitrogen deposition increased CO2 uptake. Tropospheric O3 pollution and nitrogen deposition decreased CH4 emission by 7.94 Gg C and 0.41 Gg C, respectively, while elevated CO2 concentration increased the CH4 emission by 133.81 Gg C. Accumulatively, tropospheric O3 pollution and climate change contributed approximately 5.37% and 4.89% to the increased N2O emission, respectively, while elevated CO2 concentration reduced 2.81% of the N2O emission. The global warming potential (GWP) ranged from −1.81 Tg CO2eq yr−1 in the 1970s to 29.15 Tg CO2eq yr−1 in the 2000s. The decadal GWP by CO2 fluxes shifted from negative values between the 1950s and the 1990s to positive values in the 2000s, while CH4 and N2O emissions enhanced GWP from the 1950s to the 2000s. The total GWP decreased from the 1950s to the 1970s, but increased from the 1980s to the 2000s. This suggested that the reduced GWP by decreased CH4 emissions was gradually offset by the increased GWP by increased N2O emissions and decreased CO2 sink from the 1980s to the 2000s, implying that a full accounting of the greenhouse gas balance is essential in assessing global change impacts.

The European land and inland water CO<sub>2</sub>, CO, CH<sub>4</sub> and N<sub>2</sub>O balance between 2001 and 2005

Abstract. Globally, terrestrial ecosystems have absorbed about 30% of anthropogenic greenhouse gas emissions over the period 2000–2007 and inter-hemispheric gradients indicate that a significant fraction of terrestrial carbon sequestration must be north of the Equator. We present a compilation of the CO2, CO, CH4 and N2O balances of Europe following a dual constraint approach in which (1) a land-based balance derived mainly from ecosystem carbon inventories and (2) a land-based balance derived from flux measurements are compared to (3) the atmospheric data-based balance derived from inversions constrained by measurements of atmospheric GHG (greenhouse gas) concentrations. Good agreement between the GHG balances based on fluxes (1294 ± 545 Tg C in CO2-eq yr−1), inventories (1299 ± 200 Tg C in CO2-eq yr−1) and inversions (1210 ± 405 Tg C in CO2-eq yr−1) increases our confidence that the processes underlying the European GHG budget are well understood and reasonably sampled. However, the uncertainty remains large and largely lacks formal estimates. Given that European net land to atmosphere exchanges are determined by a few dominant fluxes, the uncertainty of these key components needs to be formally estimated before efforts could be made to reduce the overall uncertainty. The net land-to-atmosphere flux is a net source for CO2, CO, CH4 and N2O, because the anthropogenic emissions by far exceed the biogenic sink strength. The dual-constraint approach confirmed that the European biogenic sink removes as much as 205 ± 72 Tg C yr−1 from fossil fuel burning from the atmosphere. However, This C is being sequestered in both terrestrial and inland aquatic ecosystems. If the C-cost for ecosystem management is taken into account, the net uptake of ecosystems is estimated to decrease by 45% but still indicates substantial C-sequestration. However, when the balance is extended from CO2 towards the main GHGs, C-uptake by terrestrial and aquatic ecosystems is offset by emissions of non-CO2 GHGs. As such, the European ecosystems are unlikely to contribute to mitigating the effects of climate change.