Atmospheric CO2 Growth Research Articles

High predictability of terrestrial carbon fluxes from an initialized decadal prediction system

Interannual variations in the flux of carbon dioxide (CO2) between the land surface and the atmosphere are the dominant component of interannual variations in the atmospheric CO2 growth rate. Here, we investigate the potential to predict variations in these terrestrial carbon fluxes 1–10 years in advance using a novel set of retrospective decadal forecasts of an Earth system model. We demonstrate that globally-integrated net ecosystem production (NEP) exhibits high potential predictability for 2 years following forecast initialization. This predictability exceeds that from a persistence or uninitialized forecast conducted with the same Earth system model. The potential predictability in NEP derives mainly from high predictability in ecosystem respiration, which itself is driven by vegetation carbon and soil moisture initialization. Our findings unlock the potential to forecast the terrestrial ecosystem in a changing environment.

Wintertime fCO2 Variability in the Subpolar North Atlantic Since 2004

AbstractWinter data of surface ocean temperature (SST), salinity (SSS) and CO2 fugacity (fCO2) collected on the VOS M/V Nuka Arctica in the subpolar North Atlantic between 2004 and 2017 are used to establish trends, drivers, and interannual variability. Over the period, waters cooled and freshened, and the fCO2 increased at a rate similar to the atmospheric CO2 growth rate. When accounting for the freshening, the inferred increase in dissolved inorganic carbon (DIC) was found to be approximately twice that expected from atmospheric CO2 alone. This is attributed to the cooling. In the Irminger Sea, fCO2 exhibited additional interannual variations driven by atmospheric forcing through winter mixing. As winter fCO2 in the region is close to the atmospheric, the subpolar North Atlantic has varied between being slightly supersaturated and slightly undersaturated over the investigated period.

Linkage between tropical terrestrial carbon cycle and precipitation: The two anomalous years of 1979 and 1996

Tropical terrestrial ecosystems are the critical driver of the land carbon cycle and climate change. Previous studies have reported strong response in the tropical land carbon cycle to precipitation anomalies in post‐La Niña years. We show that among the post‐La Niña years, 1979 and 1996 stand out strikingly different from other years. 1979 has one of the largest atmospheric CO2 growth rate (CGR) while 1996 has one of the smallest CGR, despite that their annual tropical precipitation anomalies are small. We show that these 2 years correspond to opposite seasonal precipitation anomalies over tropical vegetated lands in the wet‐to‐dry transition seasons in which negative correlation between precipitation and CGR is the strongest. 1979 has large dry anomaly during the transition season, inhibiting land carbon uptake, while 1996 has large wet anomaly during the transition season, favoring more carbon uptake by the tropical ecosystem. Results here highlight the importance of seasonality of climate anomalies and their timing of occurrences with the rhythm of the carbon–climate coupling.

Correlation between the Fluctuations in Worldwide Seismicity and Atmospheric Carbon Pollution

The crucial stages in the geochemical evolution of the Earth’s crust, ocean, and atmosphere could be explained by the assumed low-energy nuclear reactions (LENR) that are triggered by seismic activity. LENR result in the fission of medium-weight elements accompanied by neutron emissions, involving Fe and Ni as starting elements, and C, N, O as resultants. Geochemical data and experimental evidences support the LENR hypothesis. A spectral analysis of the period 1955-2013 shows common cycles between interannual changes in atmospheric CO2 growth rate and global seismic-moment release, whereas the trending behavior of the atmospheric CO2 was in response to the anthropogenic emissions. Assuming a correlation between such seismic and atmospheric fluctuations, the latter could be explained by cycles of worldwide seismicity, which would trigger massively LENR in the Earth’s Crust. In this framework, LENR from active faults could be considered as a relevant cause of carbon formation and degassing of freshly-formed CO2 during seismic activity. However, further studies are necessary to validate the present hypothesis which, at the present time, mainly aims to stimulate debate on the models which regulates atmospheric CO2.

Correlation between the Fluctuations in Worldwide Seismicity and Atmospheric Carbon Pollution

The crucial stages in the geochemical evolution of the Earth’s crust, ocean, and atmosphere could be explained by the assumed low-energy nuclear reactions (LENR) that are triggered by seismic activity. LENR result in the fission of medium-weight elements accompanied by neutron emissions, involving Fe and Ni as starting elements, and C, N, O as resultants. Geochemical data and experimental evidences support the LENR hypothesis. A spectral analysis of the period 1955-2013 shows common cycles between interannual changes in atmospheric CO2 growth rate and global seismic-moment release, whereas the trending behavior of the atmospheric CO2 was in response to the anthropogenic emissions. Assuming a correlation between such seismic and atmospheric fluctuations, the latter could be explained by cycles of worldwide seismicity, which would trigger massively LENR in the Earth’s Crust. In this framework, LENR from active faults could be considered as a relevant cause of carbon formation and degassing of freshly-formed CO2 during seismic activity. However, further studies are necessary to validate the present hypothesis which, at the present time, mainly aims to stimulate debate on the models which regulates atmospheric CO2.

Large influence of soil moisture on long-term terrestrial carbon uptake.

The terrestrial biosphere absorbs about 25% of anthropogenic CO2 emissions, yet the rate of land carbon uptake remains highly uncertain, leading to uncertainties in climate projections1,2. Understanding the factors that are limiting or driving land carbon storage is therefore important for improved climate predictions. One potential limiting factor for land carbon uptake is soil moisture, which can reduce gross primary production due to ecosystem water stress3,4, cause vegetation mortality5, and further exacerbate climate extremes due to land-atmosphere feedbacks6. Previous work has explored the impact of soil moisture availability on past carbon flux variability3,7,8. However, the magnitude of the effect of soil moisture variability and trends on the long-term carbon sink and the mechanisms responsible for associated carbon losses remain uncertain. Here we use four global land-atmosphere models9, and find that soil moisture variability and trends induce large CO2 sources (~2–3 GtC/year) throughout the twenty-first century; on the order of the land carbon sink itself1. Subseasonal and interannual soil moisture variability generates a CO2 source as a result of the nonlinear response of photosynthesis and net ecosystem exchange to soil water availability and the increased temperature and vapour pressure deficit caused by land-atmosphere interactions. Soil moisture variability reduces the present land carbon sink while soil moisture variability and its drying trend reduce it in the future. Our results emphasize that the capacity of continents to act as a future carbon sink critically depends on the nonlinear response of carbon fluxes to soil moisture and on land-atmosphere interactions. This suggests that with the drying trend and increase in soil moisture variability projected in several regions, the current carbon uptake rate may not be sustained past mid-century and could result in an accelerated atmospheric CO2 growth rate.

Relationship between the Atmospheric CO<sub>2</sub> and Climate Indices by Wavelet-Based Multifractal Analysis

Atmospheric concentrations of greenhouse gases are rising, leading to a positive radiative forcing of climate and an expected warming of surface temperatures. In general, fractal properties may be observed in the time series of the dynamics of complex systems. To study the relation between the atmospheric CO2 concentration and the climate indices, we investigated the change of fractal behavior of the CO2, the carbon isotope ratio (δ13C) of atmospheric CO2, the El Nino-Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and the North Atlantic Oscillation (NAO) indices using the multifractal analysis. When the atmospheric CO2 growth rate was large, the multifractality of CO2, δ13C in CO2, ENSO, and NAO was large and the changes were large from the change of fractality. The changes of CO2 and ENSO were closely related and the influence of the CO2 on the ENSO was strong from the change in fractality and wavelet coherence. When the El Nino occurred, the CO2 growth rate was large. The CO2 related to PDO, NAO, and global temperature from the change in fractality and wavelet coherence. Especially, the changes of CO2 and global temperature were closely related. When the global warming hiatus occurred, the multifractality of the global temperature was weaker than that of CO2 and the change of the global temperature was stable. These findings will contribute to the research of the relation between the atmospheric CO2 and climate change.

Trade-offs in using European forests to meet climate objectives.

The Paris Agreement advances forest management as one of the pathways to halt climate warming through carbon dioxide (CO2) emission reduction1. The climate benefits from carbon sequestration from forest management may, however, be reinforced, counteracted, or even offset by concurrent management-induced changes in surface albedo, surface roughness, biogenic volatile organic compound emissions, transpiration, and sensible heat flux2–4. Forest management could, thus, offset CO2 emissions without halting global temperature rise. It remains, therefore, to be confirmed that sustainable forest management portfolios for the end of the 21st-century for Europe would comply with the Paris Agreement, i.e., reduce the growth rate of atmospheric CO2, reduce the radiative imbalance at the top of the atmosphere, and neither increase the near-surface air temperature nor decrease precipitation. Here we show that a spatially-optimized portfolio that maximises the carbon sink through carbon sequestration, wood use and product and energy substitution, reduces the growth rate of atmospheric CO2 but does not meet any of the other criteria. The portfolios that maximise the carbon sink or forest albedo pass only one, albeit different, criterion. Managing the European forests with the objective to reduce near-surface air temperature, on the other hand, will also reduce the atmospheric CO2 growth rate, thus meeting two out of four criteria. Our results demonstrate that if present-day forest cover is sustained, the additional climate benefits through forest management would be modest and local rather than global. Based on these findings we argue that if adaptation would require large-scale changes in species composition and silvicultural systems over Europe5,6, these changes could be implemented with little unintended climate effects.

Correlation between the Fluctuations in Worldwide Seismicity and in Atmospheric Carbon Pollution

The crucial stages in the geochemical evolution of the Earth’s crust, ocean, and atmosphere could be explained by the assumed low-energy nuclear reactions (LENR) that are triggered by seismic activity. LENR result in the fission of medium-weight elements accompanied by neutron emissions, involving Fe and Ni as starting elements, and C, N, O as resultants. Geochemical data and experimental evidences support the LENR hypothesis. The time series analysis highlighted significant correlation between the atmospheric CO2 growth rate and the global seismic-moment release rate, whereas the trending behavior was in response to the anthropogenic emissions. The fluctuations in the atmospheric CO2 growth rate time series were inexplicable in terms of anthropogenic emissions, but could be explained by the cycles of worldwide seismicity, which massively trigger LENR in the Earth’s crust. In this framework, LENR from active faults must be considered as a relevant cause of carbon formation and degassing of freshly-formed CO2 during seismic activity.

Correlation between the Fluctuations in Worldwide Seismicity and Atmospheric Carbon Pollution

The crucial stages in the geochemical evolution of the Earth’s crust, ocean, and atmosphere could be explained by the assumed low-energy nuclear reactions (LENR) that are triggered by seismic activity. LENR result in the fission of medium-weight elements accompanied by neutron emissions, involving Fe and Ni as starting elements, and C, N, O as resultants. Geochemical data and experimental evidences support the LENR hypothesis. A spectral analysis of the period 1955-2013 shows common cycles between interannual changes in atmospheric CO2 growth rate and global seismic-moment release, whereas the trending behavior of the atmospheric CO2 was in response to the anthropogenic emissions. Assuming a correlation between such seismic and atmospheric fluctuations, the latter could be explained by cycles of worldwide seismicity, which would trigger massively LENR in the Earth’s Crust. In this framework, LENR from active faults could be considered as a relevant cause of carbon formation and degassing of freshly-formed CO2 during seismic activity. However, further studies are necessary to validate the present hypothesis which, at the present time, mainly aims to stimulate debate on the models which regulates atmospheric CO2.

Detecting drought impact on terrestrial biosphere carbon fluxes over contiguous US with satellite observations

With projections of increasing drought in the future, understanding how the natural carbon cycle responds to drought events is needed to predict the fate of the land carbon sink and future atmospheric CO2 concentrations and climate. We quantified the impacts of the 2011 and 2012 droughts on terrestrial ecosystem carbon uptake anomalies over the contiguous US (CONUS) relative to non-drought years during 2010–2015 using satellite observations and the carbon monitoring system—flux inversion modeling framework. Soil moisture and temperature anomalies are good predictors of gross primary production anomalies (R2 > 0.6) in summer but less so for net biosphere production (NBP) anomalies, reflecting different respiration responses. We showed that regional responses combine in complicated ways to produce the observed CONUS responses. Because of the compensating effect of the carbon flux anomalies between northern and southern CONUS in 2011 and between spring and summer in 2012, the annual NBP decreased by 0.10 ± 0.16 GtC in 2011, and increased by 0.10 ± 0.16 GtC in 2012 over CONUS, consistent with previous reported results. Over the 2011 and 2012 drought-impacted regions, the reductions in NBP were ∼40% of the regional annual fossil fuel emissions, underscoring the importance of quantifying natural carbon flux variability as part of an overall observing strategy. The NBP reductions over the 2011 and 2012 CONUS drought-impacted region were opposite to the global atmospheric CO2 growth rate anomaly, implying that global atmospheric CO2 growth rate is an offsetting effect between enhanced uptake and emission, and enhancing the understanding of regional carbon-cycle climate relationship is necessary to improve the projections of future climate.

Sensitivity of atmospheric CO2 growth rate to observed changes in terrestrial water storage.

Land ecosystems absorb on average 30 per cent of anthropogenic carbon dioxide (CO2) emissions, thereby slowing the increase of CO2 concentration in the atmosphere1. Year-to-year variations in the atmospheric CO2 growth rate are mostly due to fluctuating carbon uptake by land ecosystems1. The sensitivity of these fluctuations to changes in tropical temperature has been well documented2-6, but identifying the role of global water availability has proved to be elusive. So far, the only usable proxies for water availability have been time-lagged precipitation anomalies and drought indices3-5, owing to a lack of direct observations. Here, we use recent observations of terrestrial water storage changes derived from satellite gravimetry7 to investigate terrestrial water effects on carbon cycle variability at global to regional scales. We show that the CO2 growth rate is strongly sensitive to observed changes in terrestrial water storage, drier years being associated with faster atmospheric CO2 growth. We demonstrate that this global relationship is independent of known temperature effects and is underestimated in current carbon cycle models. Our results indicate that interannual fluctuations in terrestrial water storage strongly affect the terrestrial carbon sink and highlight the importance of the interactions between the water and carbon cycles.

Divergent response of seasonally dry tropical vegetation to climatic variations in dry and wet seasons.

Interannual variations of photosynthesis in tropical seasonally dry vegetation are one of the dominant drivers to interannual variations of atmospheric CO2 growth rate. Yet, the seasonal differences in the response of photosynthesis to climate variations in these ecosystems remain poorly understood. Here using Normalized Difference Vegetation Index (NDVI), we explored the response of photosynthesis of seasonally dry tropical vegetation to climatic variations in the dry and the wet seasons during the past three decades. We found significant (p<0.01) differences between dry and wet seasons in the interannual response of photosynthesis to temperature (γint ) and to precipitation (δint ). γint is ~1%°C-1 more negative and δint is ~8% 100mm-1 more positive in the dry season than in the wet season. Further analyses show that the seasonal difference in γint can be explained by background moisture and temperature conditions. Positive γint occurred in wet season where mean temperature is lower than 27°C and precipitation is at least 60mm larger than potential evapotranspiration. Two widely used Gross Primary Productivity (GPP) estimates (empirical modeling by machine-learning algorithm applied to flux tower measurements, and nine process-based carbon cycle models) were examined for the GPP-climate relationship over wet and dry seasons. The GPP derived from empirical modeling can partly reproduce the divergence of γint , while most process models cannot. The overestimate by process models on negative impacts by warmer temperature during the wet season highlights the shortcomings of current carbon cycle models in representing interactive impacts of temperature and moisture on photosynthesis. Improving representations on soil water uptake, leaf temperature, nitrogen cycling, and soil moisture may help improve modeling skills in reproducing seasonal differences of photosynthesis-climate relationship and thus the projection for impacts of climate change on tropical carbon cycle.

Influence of high-latitude warming and land-use changes in the early 20th century northern Eurasian CO2 sink

While the global carbon budget (GCB) is relatively well constrained over the last decades of the 20th century [], observations and reconstructions of atmospheric CO2 growth rate present large discrepancies during the earlier periods []. The large uncertainty in GCB has been attributed to the land biosphere, although it is not clear whether the gaps between observations and reconstructions are mainly because land-surface models (LSMs) underestimate inter-annual to decadal variability in natural ecosystems, or due to inaccuracies in land-use change reconstructions.As Eurasia encompasses about 15% of the terrestrial surface, 20% of the global soil organic carbon pool and constitutes a large CO2 sink, we evaluate the potential contribution of natural and human-driven processes to induce large anomalies in the biospheric CO2 fluxes in the early 20th century. We use an LSM specifically developed for high-latitudes, that correctly simulates Eurasian C-stocks and fluxes from observational records [], in order to evaluate the sensitivity of the Eurasian sink to the strong high-latitude warming occurring between 1930 and 1950. We show that the LSM with improved high-latitude phenology, hydrology and soil processes, contrary to the group of LSMs in [], is able to represent enhanced vegetation growth linked to boreal spring warming, consistent with tree-ring time-series []. By compiling a dataset of annual agricultural area in the Former Soviet Union that better reflects changes in cropland area linked with socio-economic fluctuations during the early 20th century, we show that land-abadonment during periods of crisis and war may result in reduced CO2 emissions from land-use change (44%–78% lower) detectable at decadal time-scales.Our study points to key processes that may need to be improved in LSMs and LUC datasets in order to better represent decadal variability in the land CO2 sink, and to better constrain the GCB during the pre-observational record.

Vegetation greenness and land carbon-flux anomalies associated with climate variations: a focus on the year 2015

Abstract. Understanding the variations in global land carbon uptake, and their driving mechanisms, is essential if we are to predict future carbon-cycle feedbacks on global environmental changes. Satellite observations of vegetation greenness have shown consistent greening across the globe over the past three decades. Such greening has driven the increasing land carbon sink, especially over the growing season in northern latitudes. On the other hand, interannual variations in land carbon uptake are strongly influenced by El Niño–Southern Oscillation (ENSO) climate variations. Marked reductions in land uptake and strong positive anomalies in the atmospheric CO2 growth rates occur during El Niño events. Here we use the year 2015 as a natural experiment to examine the possible response of land ecosystems to a combination of vegetation greening and an El Niño event. The year 2015 was the greenest year since 2000 according to satellite observations, but a record atmospheric CO2 growth rate also occurred due to a weaker than usual land carbon sink. Two atmospheric inversions indicate that the year 2015 had a higher than usual northern land carbon uptake in boreal spring and summer, consistent with the positive greening anomaly and strong warming. This strong uptake was, however, followed by a larger source of CO2 in the autumn. For the year 2015, enhanced autumn carbon release clearly offset the extra uptake associated with greening during the summer. This finding leads us to speculate that a long-term greening trend may foster more uptakes during the growing season, but no large increase in annual carbon sequestration. For the tropics and Southern Hemisphere, a strong transition towards a large carbon source for the last 3 months of 2015 is discovered, concomitant with El Niño development. This transition of terrestrial tropical CO2 fluxes between two consecutive seasons is the largest ever found in the inversion records. The strong transition to a carbon source in the tropics with the peak of El Niño is consistent with historical observations, but the detailed mechanisms underlying such an extreme transition remain to be elucidated.

Influence of El Niño on atmospheric CO2 over the tropical Pacific Ocean: Findings from NASA's OCO-2 mission.

Spaceborne observations of carbon dioxide (CO2) from the Orbiting Carbon Observatory-2 are used to characterize the response of tropical atmospheric CO2 concentrations to the strong El Niño event of 2015-2016. Although correlations between the growth rate of atmospheric CO2 concentrations and the El Niño-Southern Oscillation are well known, the magnitude of the correlation and the timing of the responses of oceanic and terrestrial carbon cycle remain poorly constrained in space and time. We used space-based CO2 observations to confirm that the tropical Pacific Ocean does play an early and important role in modulating the changes in atmospheric CO2 concentrations during El Niño events-a phenomenon inferred but not previously observed because of insufficient high-density, broad-scale CO2 observations over the tropics.

Contrasting carbon cycle responses of the tropical continents to the 2015-2016 El Niño.

The 2015-2016 El Niño led to historically high temperatures and low precipitation over the tropics, while the growth rate of atmospheric carbon dioxide (CO2) was the largest on record. Here we quantify the response of tropical net biosphere exchange, gross primary production, biomass burning, and respiration to these climate anomalies by assimilating column CO2, solar-induced chlorophyll fluorescence, and carbon monoxide observations from multiple satellites. Relative to the 2011 La Niña, the pantropical biosphere released 2.5 ± 0.34 gigatons more carbon into the atmosphere in 2015, consisting of approximately even contributions from three tropical continents but dominated by diverse carbon exchange processes. The heterogeneity of the carbon-exchange processes indicated here challenges previous studies that suggested that a single dominant process determines carbon cycle interannual variability.

Cellular trade-offs and optimal resource allocation during cyanobacterial diurnal growth

Cyanobacteria are an integral part of Earth's biogeochemical cycles and a promising resource for the synthesis of renewable bioproducts from atmospheric CO2 Growth and metabolism of cyanobacteria are inherently tied to the diurnal rhythm of light availability. As yet, however, insight into the stoichiometric and energetic constraints of cyanobacterial diurnal growth is limited. Here, we develop a computational framework to investigate the optimal allocation of cellular resources during diurnal phototrophic growth using a genome-scale metabolic reconstruction of the cyanobacterium Synechococcus elongatus PCC 7942. We formulate phototrophic growth as an autocatalytic process and solve the resulting time-dependent resource allocation problem using constraint-based analysis. Based on a narrow and well-defined set of parameters, our approach results in an ab initio prediction of growth properties over a full diurnal cycle. The computational model allows us to study the optimality of metabolite partitioning during diurnal growth. The cyclic pattern of glycogen accumulation, an emergent property of the model, has timing characteristics that are in qualitative agreement with experimental findings. The approach presented here provides insight into the time-dependent resource allocation problem of phototrophic diurnal growth and may serve as a general framework to assess the optimality of metabolic strategies that evolved in phototrophic organisms under diurnal conditions.

The CarbonTracker Data Assimilation Shell (CTDAS) v1.0: implementation and global carbon balance 2001–2015

Abstract. Data assimilation systems are used increasingly to constrain the budgets of reactive and long-lived gases measured in the atmosphere. Each trace gas has its own lifetime, dominant sources and sinks, and observational network (from flask sampling and in situ measurements to space-based remote sensing) and therefore comes with its own optimal configuration of the data assimilation. The CarbonTracker Europe data assimilation system for CO2 estimates global carbon sources and sinks, and updates are released annually and used in carbon cycle studies. CarbonTracker Europe simulations are performed using the new modular implementation of the data assimilation system: the CarbonTracker Data Assimilation Shell (CTDAS). Here, we present and document this redesign of the data assimilation code that forms the heart of CarbonTracker, specifically meant to enable easy extension and modification of the data assimilation system. This paper also presents the setup of the latest version of CarbonTracker Europe (CTE2016), including the use of the gridded state vector, and shows the resulting carbon flux estimates. We present the distribution of the carbon sinks over the hemispheres and between the land biosphere and the oceans. We show that with equal fossil fuel emissions, 2015 has a higher atmospheric CO2 growth rate compared to 2014, due to reduced net land carbon uptake in later year. The European carbon sink is especially present in the forests, and the average net uptake over 2001–2015 was 0. 17 ± 0. 11 PgC yr−1 with reductions to zero during drought years. Finally, we also demonstrate the versatility of CTDAS by presenting an overview of the wide range of applications for which it has been used so far.

Decreasing net primary production due to drought and slight decreases in solar radiation in China from 2000 to 2012

AbstractTerrestrial ecosystems have continued to provide the critical service of slowing the atmospheric CO2growth rate. Terrestrial net primary productivity (NPP) is thought to be a major contributing factor to this trend. Yet our ability to estimate NPP at the regional scale remains limited due to large uncertainties in the response of NPP to multiple interacting climate factors and uncertainties in the driver data sets needed to estimate NPP. In this study, we introduced an improved NPP algorithm that used local driver data sets and parameters in China. We found that bias decreased by 30% for gross primary production (GPP) and 17% for NPP compared with the widely used global GPP and NPP products, respectively. From 2000 to 2012, a pixel‐level analysis of our improved NPP for the region of China showed an overall decreasing NPP trend of 4.65 Tg C a−1. Reductions in NPP were largest for the southern forests of China (−5.38 Tg C a−1), whereas minor increases in NPP were found for North China (0.65 Tg C a−1). Surprisingly, reductions in NPP were largely due to decreases in solar radiation (82%), rather than the more commonly expected effects of drought (18%). This was because for southern China, the interannual variability of NPP was more sensitive to solar radiation (R2in 0.29–0.59) relative to precipitation (R2 &lt; 0.13). These findings update our previous knowledge of carbon uptake responses to climate change in terrestrial ecosystems of China and highlight the importance of shortwave radiation in driving vegetation productivity for the region, especially for tropical forests.