Variability Of CO2 Fluxes Research Articles

СЕЗОННАЯ ИЗМЕНЧИВОСТЬ ПОТОКОВ ДИОКСИДА УГЛЕРОДА, ЯВНОГО И СКРЫТОГО ТЕПЛА В СЕВЕРОТАЕЖНОМ ЛИСТВЕННИЧНОМ ЛЕСУ СРЕДНЕЙ СИБИРИ ПО ДАННЫМ ПУЛЬСАЦИОННЫХ ИЗМЕРЕНИЙ

The seasonal and daily variability of sensible and latent heat and carbon dioxide (CO2) fluxes, as well as the sensitivity of the fluxes to changing environmental conditions were derived by the eddy covariance flux measurements in an undisturbed northern-taiga larch forest on continuous permafrost in Central Siberia from the end of May to the end of September in 2013 and 2015. The measurements showed a high seasonal and daily variability of CO2, sensible and latent heat fluxes. It was found that whereas dry and sunny weather conditions of June and July in 2013 and 2015 resulted in lower daily latent heat fluxes as compared to sensible ones, mostly cloudy and rainy weather in the second half of the summer led to the reduced net radiation and increased latent heat fluxes. The daily values of gross primary production from the beginning of June to mid-August in 2013 and 2015 exceeded the values of the ecosystem respiration, and the forest ecosystem was the sink of CO2 from the atmosphere. The maximum CO2 uptake was observed in late June and early July, primarily due to high photosynthesis rates influenced by high incoming solar radiation, optimal air temperature, and soil moisture conditions. Since mid-August, the balance between the CO2 uptake and release was close to zero. The total net ecosystem CO2 exchange during the growing season of 2013 was -76.5 g C/m2, while it was slightly higher (-103.6 g C/m2) during the growing season of 2015, primarily due to higher air temperatures in June and greater precipitation in the summer months of 2015.

Spring soil CO2 and CH4 emissions in the Yellow River Delta wetland, China

Climate change has become a global concern. Coastal wetlands play an important role in the global carbon cycle and significantly contribute to the emission and absorption of the greenhouse gases CO2 and CH4. In this study, the temporal and spatial variations of soil CO2 and CH4 emission fluxes, soil total carbon, total organic carbon, and carbon and nitrogen stable isotopes of four vegetation areas (Suaeda salsa, Phragmites australis, Tamarix chinensis, and farmland) and a bare beach in the Yellow River Delta wetland were observed in the spring of 2011–2013. Soil organic carbon δ13C ranged from −25.43–-23.69‰ and soil organic carbon content from 0.311 to 1.42%, and the two were significantly negatively correlated, indicating a low decomposition degree of soil organic matter. The soil CO2 emission fluxes in the study period were carbon emissions. In the area with mainly Tamarix chinensis, the 3-year average CO2 emission flux was the highest, in the area with predominantly Phragmites australisthe lowest. The soil CH4 emission flux in the spring of 2011 was a carbon absorption, whereas it was a carbon emission in the spring of 2012 and 2013. Its 3-year average was the highest in the bare beach area and the lowest in the Tamarix ramosissima area. Based on Pearson correlation analysis combined with RDA and multiple linear regression analysis, we found that the main factors affecting soil CO2 and CH4 emission fluxes may be the fast decomposition rate of soil organic matter, the content of soil carbon and organic carbon, and the low degree of soil organic matter decomposition.

Significant diurnal variation of CO2 flux from a shallow eutrophic lake: effects of submerged aquatic vegetation and algae bloom

Significant diurnal variation of CO2 flux from a shallow eutrophic lake: effects of submerged aquatic vegetation and algae bloom

Effects of long-term climate trends on the methane and CO2 exchange processes of Toolik Lake, Alaska

Methane and carbon dioxide effluxes from aquatic systems in the Arctic will affect and likely amplify global change. As permafrost thaws in a warming world, more dissolved organic carbon (DOC) and greenhouse gases are produced and move from soils to surface waters where the DOC can be oxidized to CO2 and also released to the atmosphere. Our main study objective is to measure the release of carbon to the atmosphere via effluxes of methane (CH4) and carbon dioxide (CO2) from Toolik Lake, a deep, dimictic, low-arctic lake in northern Alaska. By combining direct eddy covariance flux measurements with continuous gas pressure measurements in the lake surface waters, we quantified the k600 piston velocity that controls gas flux across the air–water interface. Our measured k values for CH4 and CO2 were substantially above predictions from several models at low to moderate wind speeds, and only converged on model predictions at the highest wind speeds. We attribute this higher flux at low wind speeds to effects on water-side turbulence resulting from how the surrounding tundra vegetation and topography increase atmospheric turbulence considerably in this lake, above the level observed over large ocean surfaces. We combine this process-level understanding of gas exchange with the trends of a climate-relevant long-term (30 + years) meteorological data set at Toolik Lake to examine short-term variations (2015 ice-free season) and interannual variability (2010–2015 ice-free seasons) of CH4 and CO2 fluxes. We argue that the biological processing of DOC substrate that becomes available for decomposition as the tundra soil warms is important for understanding future trends in aquatic gas fluxes, whereas the variability and long-term trends of the physical and meteorological variables primarily affect the timing of when higher or lower than average fluxes are observed. We see no evidence suggesting that a tipping point will be reached soon to change the status of the aquatic system from gas source to sink. We estimate that changes in CH4 and CO2 fluxes will be constrained with a range of +30% and −10% of their current values over the next 30 years.

Consistency of seasonal variability in regional CO2 fluxes from GOSAT-IM, NASA-GEOS, and NOAA-CT

Consistency of seasonal variability in regional CO2 fluxes from GOSAT-IM, NASA-GEOS, and NOAA-CT

Different variations in soil CO2, CH4, and N2O fluxes and their responses to edaphic factors along a boreal secondary forest successional trajectory

Forest succession is an important process regulating the carbon and nitrogen budgets in forest ecosystems. However, little is known about how and extent by which vegetation succession predictably affects soil CO2, CH4, and N2O fluxes, especially in boreal forest. Here, a field study was conducted along a secondary forest succession trajectory from Betula platyphylla forest (early stage), then Betula platyphylla-Larix gmelinii forest (intermediate stage), to Larix gmelinii forest (late stage) to explore the effects of forest succession on soil greenhouse gas fluxes and related soil environmental factors in Northeast China. The results showed significant differences in soil greenhouse gas fluxes during the forest succession. During the study period, the average soil CO2 flux was greatest at mid-successional stage (444.72 mg m-2 h-1), followed by the late (341.81 mg m-2 h-1) and the early-successional (347.12 mg m-2 h-1) stages. The average soil CH4 flux increased significantly during succession, ranging from -0.062 to -0.036 mg m-2 h-1. The average soil N2O flux was measured as 17.95 μg m-2 h-1 at intermediate successional stage, significantly lower than that at late (20.71 μg m-2 h-1) and early-successional (20.85 μg m-2 h-1) stages. During forest succession, soil greenhouse gas fluxes showed significant correlations with soil and environmental factors at both seasonal and successional time scales. The seasonal variations of soil GHG fluxes were mainly influenced by soil temperature and water content. Meanwhile, soil MBN and soil NO3--N content were also important factors for soil N2O fluxes. Structural equation modelling showed that forest succession affected soil CO2 fluxes by changing soil temperature and microbial biomass carbon, affected soil CH4 fluxes mainly by changing soil water content and soil pH value, and affected soil N2O fluxes mainly by changing soil temperature, microbial biomass nitrogen, and soil NO3--N content. Our study suggests that forest succession mainly alters soil nutrient and soil environment/chemical properties affecting soil CO2 and N2O fluxes and soil CH4 fluxes, respectively, in the secondary forest succession process.

Toward a long-term atmospheric CO2 inversion for elucidating natural carbon fluxes: technical notes of NISMON-CO2 v2021.1

Accurate estimates of the carbon dioxide (CO2) fluxes at the earth’s surface are imperative for comprehending the carbon cycle mechanisms and providing reliable global warming predictions. Furthermore, they can also provide valuable science-based information that will be helpful in reducing human-induced CO2 emissions. Inverse analysis is a prominent method of quantitatively estimating spatiotemporal variations in CO2 fluxes; however, it involves a certain level of uncertainty and requires technical refinement, specifically to improve the horizontal resolution so that local fluxes can be compared with other estimates made at the regional or national level. In this study, a novel set of inversion schemes was incorporated into a state-of-the-art inverse analysis system named NISMON-CO2. The introduced schemes include a grid conversion, observational weighting, and anisotropic prior error covariance, the details of which are described. Moreover, pseudo-observation experiments were performed to examine the effect of the new schemes and to assess the reliability of NISMON-CO2 for long-term analysis with practical inhomogeneous observations. The experiment results evidently demonstrate the advantages of the grid conversion scheme for high-resolution flux estimates (1° × 1°), with notable improvements being achieved through the observational weighting and anisotropic prior error covariance. Furthermore, the estimated seasonal and interannual variations in regional CO2 fluxes were confirmed to be reliable, although some potential bias in terms of global land–ocean partitioning was observed. Thus, these results are useful for interpreting the flux variations that result from real-observation inverse analysis by NISMON-CO2 ver. 2021.1.

Disparate responses of soil-atmosphere CO2 exchange to biophysical and geochemical factors over a biocrust ecological succession in the Tabernas Desert

There is growing evidence that dryland soils could act as substantial but so far disregarded carbon sinks at the global scale. In drylands, potential abiotic processes of CO2 uptake are still debated while estimates of the biotic contribution of photosynthetizing biocrusts to the net carbon uptake remain uncertain. This uncertainty is partly attributable to a common neglect of the underlying soil and spatiotemporal variability of soil CO2 fluxes. Moreover, it is still unknown how those fluxes evolve during the ecological succession of biocrusts and which factors control them. Therefore, in this study, we aimed to (1) identify those factors and use them for predictions, and (2) explain the inter-annual variation of cumulative CO2 fluxes over the succession. We conducted 2 years of continuous measurements of the topsoil CO2 molar fraction (χs) and microclimatic variables and estimated the soil-atmosphere CO2 flux using the gradient method. Statistical spatiotemporal models were developed of χs dynamics and cumulative annual fluxes. A soil CO2 uptake potentially due to coupled gypsum dissolution-calcite precipitation was consistently detected at night, with cumulative values ranging from −4 to −65 gC m−2 depending on succession stage. In comparison, cumulative soil CO2 emissions ranged from 101 to 307 gC m−2 depending on succession stage. The succession stage, soil water content (ϑw), and temperature (Ts) and the interactions of these variables explained and efficiently predicted the daily averaged χs dynamics. Soil CO2 emissions were more sensitive to ϑw and Ts in late successional stages, apparently because of organic carbon accumulation and higher porosity. Our measurements suggest that CO2 consumption processes were progressively counterbalanced by the increase in biological CO2 production during succession. That is probably why those processes could mainly be detected in early successional stages and more generally in drylands, as they sustain a low biological activity. However, such processes could be ubiquitous in ecosystems but difficult to detect. We discuss the implication of those results for the extensive dryland soils in the context of climate change.

Daily, seasonal and inter-annual variations in CO2 fluxes and carbon budget in a winter-wheat and summer-maize rotation system in the North China Plain

Investigating CO2 fluxes and carbon budget in agro-ecosystems is essential to develop climate smart agriculture. Here, we conducted a thorough analysis on the daily, seasonal and inter-annual variations in CO2 fluxes and carbon budget in a winter-wheat and summer-maize rotation system in the North China Plain (NCP) to better understand the CO2 flux exchange and the underlying mechanisms of carbon budget dynamics. During 2003-2010, the inter-annual variability of monthly gross primary productivity was significantly correlated with leaf area index (LAI), temperature and net radiation. The inter-annual variability of monthly ecosystem respiration was significantly correlated with LAI, soil temperature and moisture. Daily and monthly variability in net ecosystem exchange (NEE) was significantly correlated with LAI. At a seasonal scale, soil moisture was one of the primary factors controlling carbon sequestration of wheat system. Nitrogen application rate and water conditions were the primary factors controlling carbon sequestration of maize system. The NEE for winter wheat system, maize system, and winter wheat-maize rotation system in the NCP ranged from -418 to -29, -448 to -119, and -857 to -274 gCm−2, respectively. The net biome productivity (NBP) for winter wheat system, maize system, and winter wheat-maize rotation system in the NCP ranged from -223 to 151, -236 to 94, and -239 to 237 gCm−2, respectively. Taking greenhouse gas (GHG) emissions from irrigation, fertilization, herbicides, fungicide, insecticide, and field operations, the associated net GHG emissions ranged from -39 to 325 gCm−2 for wheat system and -22 to 287 gCm−2 for maize system. Wheat and maize systems in the region were a medium source of GHG emissions in most of years, mainly due to the large application rates of fertilization and irrigation. Our findings gain new insights into the mechanisms underlying the inter-annual variations in CO2 fluxes and carbon budget, highlighting the optimization of genotype, environment and management interactions to realize climate smart agriculture.

Environmental factors contributing to variations in CO2 flux over a barley-rice double-cropping paddy field in the Korean Peninsula.

Understanding the CO2 flux over agricultural crop fields is critical because the temporal cycle is driven by both ecological environment and anthropogenic change. We analyzed the net ecosystem exchange of CO2 measured over a barley-rice double-cropping field using the eddy covariance method for 5years. We conducted gap-filling based on u*-threshold criteria and partitioned the net ecosystem exchange into gross primary production and respiration. The relative importance analysis of solar radiation, temperature, soil heat flux, soil water content, and vapor deficit revealed that solar radiation and temperature were the dominant contributors to net ecosystem exchange. The annual variation in the net ecosystem exchange followed a bimodal pattern driven by CO2 uptake by both barley and rice, displaying two negative peaks in late April and mid-August. The elongation stages of the crops exhibited the highest flux. Gross primary production and respiration were closely related to solar radiation and nighttime temperature, respectively. The relative importance of the other environmental variables was affected by the cultivation season and irrigation water. In the period of rice cultivation, respiration was approximately 3µmolm-2s-1 higher during rice drainage than during the flooded period. The accumulated net ecosystem production was estimated to be 315 gC m-2 and 349 gC m-2 for the barley and rice growing periods, respectively, and 649 gC m-2 for the annual total. These values are comparable with the results of other studies on barley-rice double-cropping fields.

Seasonal Water Mass Evolution and Non-Redfield Dynamics Enhance CO2 Uptake in the Chukchi Sea.

The Chukchi Sea is an increasing CO2 sink driven by rapid climate changes. Understanding the seasonal variation of air-sea CO2 exchange and the underlying mechanisms of biogeochemical dynamics is important for predicting impacts of climate change on and feedbacks by the ocean. Here, we present a unique data set of underway sea surface partial pressure of CO2 (pCO2) and discrete samples of biogeochemical properties collected in five consecutive cruises in 2014 and examine the seasonal variations in air-sea CO2 flux and net community production (NCP). We found that thermal and non-thermal effects have different impacts on sea surface pCO2 and thus the air-sea CO2 flux in different water masses. The Bering summer water combined with meltwater has a significantly greater atmospheric CO2 uptake potential than that of the Alaskan Coastal Water in the southern Chukchi Sea in summer, due to stronger biological CO2 removal and a weaker thermal effect. By analyzing the seasonal drawdown of dissolved inorganic carbon (DIC) and nutrients, we found that DIC-based NCP was higher than nitrate-based NCP by 66%-84% and attributable to partially decoupled C and N uptake because of a variable phytoplankton stoichiometry. A box model with a non-Redfield C:N uptake ratio can adequately reproduce observed pCO2 and DIC, which reveals that, during the intensive growing season (late spring to early summer), 30%-46% CO2 uptake in the Chukchi Sea was supported by a flexible stoichiometry of phytoplankton. These findings have important ramification for forecasting the responses of CO2 uptake of the Chukchi ecosystem to climate change.

Drivers of spatial and seasonal variations of CO2 and CH4 fluxes at the sediment water interface in a shallow eutrophic lake

Shallow eutrophic lakes contribute disproportional to the emissions of CO2 and CH4 from inland waters. The processes that contribute to these fluxes, their environmental controls, and anthropogenic influences, however, are poorly constrained. Here, we studied the spatial variability and seasonal dynamics of CO2 and CH4 fluxes across the sediment-water interface, and their relationships to porewater nutrient concentrations in Lake Ulansuhai, a shallow eutrophic lake located in a semi-arid region in Northern China. The mean concentrations of CO2 and CH4 in porewater were 877.8 ± 31.0 µmol L−1 and 689.2 ± 45.0 µmol L−1, which were more than 50 and 20 times higher than those in the water column, respectively. The sediment was always a source of both gases for the water column. Porewater CO2 and CH4 concentrations and diffusive fluxes across the sediment-water interface showed significant temporal and spatial variations with mean diffusive fluxes of 887.3 ±124.7 µmol m−2 d−1 and 607.1 ± 68.0 µmol m−2 d−1 for CO2 and CH4, respectively. The temporal and spatial variations of CO2 and CH4 concentrations in porewater were associated with corresponding variations in dissolved organic carbon and dissolved nitrogen species. Temperature and dissolved organic carbon in surface porewater were the most important drivers of temporal variations in diffusive fluxes, whereas dissolved organic carbon and nitrogen were the main drivers of their spatial variations. Diffusive fluxes generally increased with increasing dissolved organic carbon and nitrogen in the porewater from the inflow to the outflow region of the lake. The estimated fluxes of both gases at the sediment-water interface were one order of magnitude lower than the emissions at the water surface, which were measured in a companion study. This indicates that diffusive fluxes across the sediment-water interface were not the main pathway for CO2 and CH4 emissions to the atmosphere. To improve the mechanistic understanding and predictability of greenhouse gas emissions from shallow lakes, future studies should aim to close the apparent gap in the CO2 and CH4 budget by combining improved flux measurement techniques with process-based modeling.

Contrasting projections of the ENSO-driven CO2flux variability in the equatorial Pacific under high-warming scenario

Abstract. The El Niño–Southern Oscillation (ENSO) widely modulates the global carbon cycle. More specifically, it alters the net uptake of carbon in the tropical ocean. Indeed, over the tropical Pacific less carbon is released by oceans during El Niño, while the opposite is the case for La Niña. Here, the skill of Earth system models (ESMs) from the latest Coupled Model Intercomparison Project (CMIP6) to simulate the observed tropical Pacific CO2 flux variability in response to ENSO is assessed. The temporal amplitude and spatial extent of CO2 flux anomalies vary considerably among models, while the surface temperature signals of El Niño and La Niña phases are generally well represented. Under historical conditions followed by the high-warming Shared Socio-economic Pathway (SSP5-8.5) scenarios, about half the ESMs simulate a reversal in ENSO–CO2 flux relationship. This gradual shift, which occurs as early as the first half of the 21st century, is associated with a high CO2-induced increase in the Revelle factor that leads to stronger sensitivity of partial pressure of CO2 (pCO2) to changes in surface temperature between ENSO phases. At the same time, uptake of anthropogenic CO2 substantially increases upper-ocean dissolved inorganic carbon (DIC) concentrations (reducing its vertical gradient in the thermocline) and weakens the ENSO-modulated surface DIC variability. The response of the ENSO–CO2 flux relationship to future climate change is sensitive to the contemporary mean state of the carbonate ion concentration in the tropics. We present an emergent constraint between the simulated contemporary carbonate concentration with the projected cumulated CO2 fluxes. Models that simulate shifts in the ENSO–CO2 flux relationship simulate positive bias in surface carbonate concentrations.

Seasonal Variability in Chlorophyll and Air-Sea CO2 Flux in the Sri Lanka Dome: Hydrodynamic Implications

Multiple upwelling systems develop in the Indian Ocean during the summer monsoon. The Sri Lanka dome (SLD), which occurs in the open ocean off the east coast of Sri Lanka from June to September, is distinct from those near the coast. The SLD is characterized by uplifted thermocline and increased chlorophyll concentration. Mechanisms of the upwelling and its biogeochemical response are not well understood. Here, we explored the dynamics of the chlorophyll and sea-to-air CO2 flux in the SLD using ocean color and altimetry remote sensing data, together with other reanalysis products. We found that the occurrence of high chlorophyll concentration and sea-to-air CO2 flux happens along the pathway of the southwest monsoon current (SMC). The annual cycle of chlorophyll in the SLD has a one-month lag relative to that in the southern coast of Sri Lanka. The positive wind stress curl that forms in the SLD during the summer does not fully explain the seasonal chlorophyll maximum. Transport of the SMC, eddy activity, and associated frontal processes also play an important role in regulating the variability in chlorophyll. In the SLD, upwelled subsurface water has excess dissolved inorganic carbon (DIC) relative to the conventional Redfield ratio between DIC and nutrients; thus, upwelling and sub-mesoscale processes determine this region to be a net carbon source to the atmosphere.

Impact of Changing Winds on the Mauna Loa CO2 Seasonal Cycle in Relation to the Pacific Decadal Oscillation.

Long‐term measurements at the Mauna Loa Observatory (MLO) show that the CO2 seasonal cycle amplitude (SCA) increased from 1959 to 2019 at an overall rate of 0.22 ± 0.034 ppm decade−1 while also varying on interannual to decadal time scales. These SCA changes are a signature of changes in land ecological CO2 fluxes as well as shifting winds. Simulations with the TM3 tracer transport model and CO2 fluxes from the Jena CarboScope CO2 Inversion suggest that shifting winds alone have contributed to a decrease in SCA of −0.10 ± 0.022 ppm decade−1 from 1959 to 2019, partly offsetting the observed long‐term SCA increase associated with enhanced ecosystem net primary production. According to these simulations and MIROC‐ACTM simulations, the shorter‐term variability of MLO SCA is nearly equally driven by varying ecological CO2 fluxes (49%) and varying winds (51%). We also show that the MLO SCA is strongly correlated with the Pacific Decadal Oscillation (PDO) due to varying winds, as well as with a closely related wind index (U‐PDO). Since 1980, 44% of the wind‐driven SCA decrease has been tied to a secular trend in the U‐PDO, which is associated with a progressive weakening of westerly winds at 700 mbar over the central Pacific from 20°N to 40°N. Similar impacts of varying winds on the SCA are seen in simulations at other low‐latitude Pacific stations, illustrating the difficulty of constraining trend and variability of land CO2 fluxes using observations from low latitudes due to the complexity of circulation changes.

Nitrogen fertilization decrease soil CO2 emission in a rainfed maize field in Northeast China.

Nitrogen fertilizer has considerable effects on soil carbon fluxes. However, the responses of soil CO2 emission to N fertilizer remain controversial. A field experiment was conducted to examine the effect of application of N fertilizer on soil CO2 emission in a maize (Zea mays L.) field in Northeast China. Soil CO2 emission was measured from May 2010 to April 2016. Soil CO2 emission during the growing season and non-growing season contributed 79.7-83.6% and 16.4-20.3%, respectively, to the total annual CO2 emission. Cumulative annual soil CO2 emissions were significantly higher in no-N addition treatment (CK) than that in N addition treatment (SU) from 2012/2013 to 2015/2016 (p < 0.05). Mean annual soil CO2 emission decreased on averaged by 21.2% after N fertilization (p < 0.05). 49.6-82.2% of CO2 flux variation was explained by soil temperature at 5cm depth. Q10 of soil CO2 emission in the annual scale was not significantly affected by N fertilizer. The results highlight the importance of N fertilizer on soil CO2 emission in agricultural ecosystem.

Response of vegetation and carbon fluxes to brown lemming herbivory in northern Alaska

Abstract. The warming of the Arctic is affecting the carbon cycle of tundra ecosystems. Most research on carbon fluxes from Arctic tundra ecosystems has focused on abiotic environmental controls (e.g., temperature, rainfall, or radiation). However, Arctic tundra vegetation, and therefore the carbon balance of these ecosystems, can be substantially impacted by herbivory. In this study we tested how vegetation consumption by brown lemmings (Lemmus trimucronatus) can impact carbon exchange of a wet-sedge tundra ecosystem near Utqiaġvik, Alaska during the summer and the recovery of vegetation during the following summer. We placed brown lemmings in individual enclosure plots and tested the impact of lemmings' herbivory on carbon dioxide (CO2) fluxes, methane (CH4) fluxes, and the normalized difference vegetation index (NDVI) immediately after lemming removal and during the following growing season. During the first summer of the experiment, lemmings' herbivory reduced plant biomass (as shown by the decrease in the NDVI) and decreased net CO2 uptake while not significantly impacting CH4 emissions. CH4 emissions were likely not significantly affected due to CH4 being produced deeper in the soil and escaping from the stem bases of the vascular plants. The summer following the lemming treatments, NDVI and net CO2 fluxes returned to magnitudes similar to those observed before the start of the experiment, suggesting a complete recovery of the vegetation and a transitory nature of the impact of lemming herbivory. Overall, lemming herbivory has short-term but substantial effects on carbon sequestration by vegetation and might contribute to the considerable interannual variability in CO2 fluxes from tundra ecosystems.

Alternate Histories: Synthetic Large Ensembles of Sea‐Air CO2 Flux

AbstractWe use a statistical emulation technique to construct synthetic ensembles of global and regional sea‐air carbon dioxide (CO2) flux from four observation‐based products over 1985–2014. Much like ensembles of Earth system models that are constructed by perturbing their initial conditions, our synthetic ensemble members exhibit different phasing of internal variability and a common externally forced signal. Our synthetic ensembles illustrate an important role for internal variability in the temporal evolution of global and regional CO2 flux and produce a wide range of possible trends over 1990–1999 and 2000–2009. We assume a specific externally forced signal and calculate the rank of the observed trends within the distribution of statistically modeled synthetic trends during these periods. Over the decade 1990–1999, three of four observation‐based products exhibit small negative trends in globally integrated sea‐air CO2 flux (i.e., enhanced ocean CO2 absorption with time) that are within one standard deviation of the mean in their respective synthetic ensembles. Over the decade 2000–2009, however, three products show large negative trends in globally integrated sea‐air CO2 flux that have a low rate of occurrence in their synthetic ensembles. The largest positive trends in global and Southern Ocean flux over 1990–1999 and the largest negative trends over 2000–2009 fall nearly two standard deviations away from the mean in their ensembles. Our approach provides a new perspective on the important role of internal variability in sea‐air CO2 flux trends, and furthers understanding of the role of internal and external processes in driving observed sea‐air CO2 flux variability.

Spatiotemporal variations in urban CO2 flux with land-use types in Seoul

BackgroundCities are a major source of atmospheric CO2; however, understanding the surface CO2 exchange processes that determine the net CO2 flux emitted from each city is challenging owing to the high heterogeneity of urban land use. Therefore, this study investigates the spatiotemporal variations of urban CO2 flux over the Seoul Capital Area, South Korea from 2017 to 2018, using CO2 flux measurements at nine sites with different urban land-use types (baseline, residential, old town residential, commercial, and vegetation areas).ResultsAnnual CO2 flux significantly varied from 1.09 kg C m− 2 year− 1 at the baseline site to 16.28 kg C m− 2 year− 1 at the old town residential site in the Seoul Capital Area. Monthly CO2 flux variations were closely correlated with the vegetation activity (r = − 0.61) at all sites; however, its correlation with building energy usage differed for each land-use type (r = 0.72 at residential sites and r = 0.34 at commercial sites). Diurnal CO2 flux variations were mostly correlated with traffic volume at all sites (r = 0.8); however, its correlation with the floating population was the opposite at residential (r = − 0.44) and commercial (r = 0.80) sites. Additionally, the hourly CO2 flux was highly related to temperature. At the vegetation site, as the temperature exceeded 24 ℃, the sensitivity of CO2 absorption to temperature increased 7.44-fold than that at the previous temperature. Conversely, the CO2 flux of non-vegetation sites increased when the temperature was less than or exceeded the 18 ℃ baseline, being three-times more sensitive to cold temperatures than hot ones. On average, non-vegetation urban sites emitted 0.45 g C m− 2 h− 1 of CO2 throughout the year, regardless of the temperature.ConclusionsOur results demonstrated that most urban areas acted as CO2 emission sources in all time zones; however, the CO2 flux characteristics varied extensively based on urban land-use types, even within cities. Therefore, multiple observations from various land-use types are essential for identifying the comprehensive CO2 cycle of each city to develop effective urban CO2 reduction policies.

Global Carbon Budget 2021

Abstract. Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesize datasets and methodology to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO2 emissions (EFOS) are based on energy statistics and cement production data, while emissions from land-use change (ELUC), mainly deforestation, are based on land use and land-use change data and bookkeeping models. Atmospheric CO2 concentration is measured directly, and its growth rate (GATM) is computed from the annual changes in concentration. The ocean CO2 sink (SOCEAN) is estimated with global ocean biogeochemistry models and observation-based data products. The terrestrial CO2 sink (SLAND) is estimated with dynamic global vegetation models. The resulting carbon budget imbalance (BIM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as ±1σ. For the first time, an approach is shown to reconcile the difference in our ELUC estimate with the one from national greenhouse gas inventories, supporting the assessment of collective countries' climate progress. For the year 2020, EFOS declined by 5.4 % relative to 2019, with fossil emissions at 9.5 ± 0.5 GtC yr−1 (9.3 ± 0.5 GtC yr−1 when the cement carbonation sink is included), and ELUC was 0.9 ± 0.7 GtC yr−1, for a total anthropogenic CO2 emission of 10.2 ± 0.8 GtC yr−1 (37.4 ± 2.9 GtCO2). Also, for 2020, GATM was 5.0 ± 0.2 GtC yr−1 (2.4 ± 0.1 ppm yr−1), SOCEAN was 3.0 ± 0.4 GtC yr−1, and SLAND was 2.9 ± 1 GtC yr−1, with a BIM of −0.8 GtC yr−1. The global atmospheric CO2 concentration averaged over 2020 reached 412.45 ± 0.1 ppm. Preliminary data for 2021 suggest a rebound in EFOS relative to 2020 of +4.8 % (4.2 % to 5.4 %) globally. Overall, the mean and trend in the components of the global carbon budget are consistently estimated over the period 1959–2020, but discrepancies of up to 1 GtC yr−1 persist for the representation of annual to semi-decadal variability in CO2 fluxes. Comparison of estimates from multiple approaches and observations shows (1) a persistent large uncertainty in the estimate of land-use changes emissions, (2) a low agreement between the different methods on the magnitude of the land CO2 flux in the northern extra-tropics, and (3) a discrepancy between the different methods on the strength of the ocean sink over the last decade. This living data update documents changes in the methods and datasets used in this new global carbon budget and the progress in understanding of the global carbon cycle compared with previous publications of this dataset (Friedlingstein et al., 2020, 2019; Le Quéré et al., 2018b, a, 2016, 2015b, a, 2014, 2013). The data presented in this work are available at https://doi.org/10.18160/gcp-2021 (Friedlingstein et al., 2021).