Abstract:Global warming, which is caused by the rapid increase of atmospheric CO₂, has become an urgent problem for sustainable human development around the world.Terrestrial ecosystems have played an important carbon sink role over the past several decades, by absorbing about 30% of the CO₂ emitted by anthropogenic activities.This paper reviews the methods used to estimated the carbon sequestration rate of terrestrial ecosystems, including sampling inventory, flux monitoring, model simulation and remote sensing, and analyzes the progresses and challenges of the current approaches for calculating terrestrial carbon sequestration.Sampling inventory and flux observations can provide direct measurement of plot-scale carbon sequestration rate, yet there remain many problems, such as limited observation samples and insufficient spatial representation.Model simulation methods can describe the terrestrial carbon cycles and simulate the state and change of carbon sequestration rates in terrestrial ecosystems.However, using the approximating and simplifying processes of available models, together with the uncertainties introduced by model-driven data, it is very challenging to accurately model the carbon sequestration rate of terrestrial ecosystems.Satellite remote sensing, which possesses the advantages of global coverage, fine resolution and time-series observations, combined with machine learning methods, can provide a new approach for the estimation of the carbon sequestration rate of terrestrial ecosystems.At present, the various accounting methods that are available for carbon sequestration rates have yet to meet the needs of monitoring carbon sequestration in terrestrial ecosystems, due to the high spatial and temporal heterogeneity.In the future, it is of utmost importance to integrate various accounting approaches, such as ground observations, model simulations and satellite remote sensing, so as to provide an accurate estimation of terrestrial ecosystem carbon sinks at the regional and global scales.

Abstract:The terrestrial ecosystem carbon sink plays an important role in retarding the increase of atmospheric CO₂concentration and global warming.Affected by human activities and climate change, the terrestrial ecosystem carbon fluxes exhibit strong spatial and temporal variations.Their estimates still have large uncertainties, and the contributions of different factors to their variations are still unclear.Therefore, using the remote-sensing-driven terrestrial ecosystem process model BEPS, the temporal and spatial variation characteristics of global terrestrial ecosystem carbon fluxes from 1981 to 2019 are simulated and analyzed, and the contributions of atmospheric CO₂concentration, leaf area index (LAI), nitrogen deposition and climate change to the change of global terrestrial ecosystem carbon budget are evaluated.From 1981 to 2019, the average values of global terrestrial ecosystem GPP (Gross Primary Productivity), NPP (Net Primary Productivity) and NEP (Net Ecosystem Productivity) are 115.3, 51.3 and 2.7 Pg·a^-1 (in terms of carbon quality, the same below), and the rising rates are 0.47, 0.21 and 0.06 Pg·a^-1, respectively.GPP and NPP increase significantly in most regions of the world, and the regions where NEP increases significantly (p<0.05) are significantly less than those for GPP and NPP.From 1981 to 2019, the accumulative global NEP is 105.2 Pg.The contributions of forests, savanna and shrub, crop, and grass are 76.4, 15.8, 9.4 and 3.6 Pg, respectively.The accumulative contributions of CO₂ concentration, LAI, nitrogen deposition and climate change to NEP are 58.4, 20.6, 0.7 and -43.6 Pg, respectively.The accumulative contribution of all four factor changes to NEP is 39.8 Pg.The rise of CO₂ concentration is the main contributing factor to the increase of NEP in global terrestrial ecosystem in recent 40 years, followed by LAI.

Abstract:To combat the challenges posed by global climate change, in September 2020, China proposed to strive to achieve carbon neutrality by 2060.However, according to ecological theory, the carbon input and output of mature ecosystems tend to be in balance, and there is no net accumulation of carbon and no carbon sink function, while immature ecosystems have a net accumulation of carbon and a carbon sink function, but any immature ecosystem in nature has been continuously replacing the mature ecosystem since it was established, that is, the end result of any ecosystem succession must be that carbon input and output are in equilibrium.Since forest ecosystems are the largest carbon pools in terrestrial ecosystems, their contribution to carbon neutrality is highly expected.Therefore, taking mature forest ecosystems as an example, considering their biomass carbon pools and soil organic carbon pools respectively, and based on the latest global research results, this paper demonstrates that the soil carbon pool accumulation process of mature forest ecosystems has a long-term carbon sequestration function, and does not contradict the ecological theory that the carbon input and output of mature ecosystem tend to be in balance, and it can contribute to the goal of carbon neutrality.

Abstract:Ocean is the largest carbon pool on Earth and has huge potential for the carbon sink.The biologically-mediated transfer of particulate organic carbon (POC) to the deep sea, aka oceanic biological carbon pump, is a key pathway for oceanic carbon sequestration.The heterotrophic processes in the twilight zone (typically defined as the depth between the bottom of the euphotic zone and 1 000 m) consume more than 70% of the POC exported from the euphotic zone, and determine the carbon sequestration efficiency of the biological carbon pump.Therefore, quantification of the remineralization rate in the twilight zone is essential for the ocean budget assessment.Aiming at the carbon storage problem of marine biological pump, this paper focuses on the influence mechanism of heterotrophic processes in the twilight zone on marine carbon storage, reviews the global studies for remineralization rate estimation in the twilight zone, comprehensively analyzes the attenuation and remineralization of POC in the twilight zone, and looks forward to the application of relevant novel technologies.

Abstract:This paper presents projections of regional climate change over China under carbon neutrality against the historical reference period (1995-2014), based on an ensemble of nine model simulations from the Coupled Model Intercomparison Project Phase 6 (CMIP6).The time of carbon neutrality globally is determined by the time of peak CO2 concentration under two scenarios, namely SSP1-1.9 and SSP1-2.6.The results are compared with what produced by the SSP2-4.5 scenario, in which carbon neutrality cannot be achieved.The respective times to reach carbon neutrality under the SSP1-1.9 and SSP1-2.6 scenarios are 2041 and 2063.Compared with the reference period, the areal-mean annual temperature in China increases by 1.22/1.58℃ under the SSP1-1.9/SSP1-2.6 scenarios, and the areal-mean annual precipitation increases by 7.1%/9.9%.The areal-mean annual temperature increases by 0.36℃ under the SSP1-2.6 (late carbon neutrality) in comparison to the SSP1-1.9 (early carbon neutrality), with the strongest warming located in southwestern China and on the Tibet Plateau.For precipitation, the areal-mean annual precipitation increases by 2.7% in the later carbon neutral period compared to the earlier carbon neutral period.The annual and summer precipitations increase significantly in northwestern China, with an increase greater than 8% occurring in Xinjiang.In winter, the region that has an increase of precipitation above 8% is located in the middle and lower reaches of the Yellow River.The warming under the SSP2-4.5 scenario is significantly stronger than that under the SSP1-2.6 scenario, with the regional mean temperature being about 0.61℃ higher.The largest warming is located in northwestern China, with an increase of greater than 0.8℃ in some parts of Xinjiang.The annual precipitation increases more significantly in northwestern China under the SSP2-4.5 scenario than that under the SSP1-2.6 scenario, with a maximum increase of above 10% in northwestern Inner Mongolia.The winter precipitation increases by more than 20% in some areas of Xinjiang, and decreases by more than 15% in Yunnan.The results of this study show that the presence or absence of carbon neutrality has a much greater impact on climate than the time (early or late) of carbon neutrality.

Abstract:Air pollution has threatened the terrestrial ecosystem carbon sink capacity in China.With synergetic control of environmental pollution and carbon emission, mitigation of air pollution would drive improvements of terrestrial carbon sink and contribute to emission peak and carbon neutrality targets.To better understand the relationships between air pollution and terrestrial carbon sink, this review summarizes existing results related with tropospheric ozone (O₃) effects on plant carbon sequestration based on meta-analysis, dose-relative biomass/yield and earth system modeling.Responses of different crops, cultivars and plant functional types to elevated O₃ were significantly different.These effects were also changed by estimation approaches.Results indicated that ambient O₃ in China has induced losses of crop yield and forest productivity.Rising O₃ concentration has seriously threaten the terrestrial ecosystem carbon sink capacity in China.On the other hand, synergetic control of environmental pollution and carbon emission will increase forest productivity and crop yield in 2060 compared to 2020, estimated from the dose-relative biomass/yield relationship based on plants grown in China.The contributions of terrestrial ecosystem to carbon neutrality will be increased if ambient ozone is reduced.Lastly, we proposed how to improve the carbon sequestration under O₃ pollution.

Abstract:Under the background of "dual-carbon" goals, regional, urban and industrial enterprises are formulating and implementing the "dual-carbon" goals action plan from the national level to the local level.Because of its objectivity and high temporal and spatial resolution, CO₂ simulation is deeply valued in the research of urban carbon emission.This paper took Beijing-Tianjin-Hebei region as the research area, used the high-precision CO₂ data observed by Picarro instrument from 2019 to 2020, used WRF model to simulate CO₂ transmission, analyzed the seasonal characteristics of CO₂ concentration change, evaluated the simulation effect of the model in the urban center, suburbs and background stations, and studied the factors that may affect CO₂ concentration, such as planetary boundary layer height and fossil fuel carbon emission.The three observation stations are the 325 m meteorological tower observation station at Institute of Atmospheric Physics, Chinese Academy of Sciences (Beijing station), Hebei Xianghe observation station (Xianghe station) and Shangdianzi regional background observation station (Shangdianzi station).The simulation results show that:The effect of Shangdianzi station is better than that of Xianghe station, and the effect of Xianghe station is better than that of Beijing station, especially in winter.The high value areas of CO₂ concentration are mainly distributed in urban areas, power plants and industrial areas, especially in Tangshan, Shijiazhuang and Handan areas.A large number of traffic and industrial emissions lead to a significant increase in CO₂ concentration, and the range of high value area is the largest in winter.In terms of daily and diurnal variations, there is an opposite trend between the planetary boundary layer height and CO₂ concentration.There is a positive correlation between fossil fuel carbon emissions (FFECO2) and total CO₂ concentration near the surface at the three stations.The correlations in winter and spring are higher than that in summer and autumn, and the proportion of FFECO2 is Beijing station, Xianghe station and Shangdianzi station from large to small.There are spatial differences and seasonal variations in the uncertainty of CO₂ transport simulation.

Abstract:Scenario is an important tool for climate change projection.The Intergovernmental Panel on Climate Change (IPCC) developed the Shared Socioeconomic Pathways (SSPs) in 2010, aiming to scientifically support the Fifth Assessment Report (IPCC AR5), Coupled Model Intercomparison Project (CMIP), Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP), and other international programs.As climate scenarios developed from a socioeconomic perspective, SSPs facilitate climate change research including physical science, impacts, vulnerability, risk, adaptation and mitigation.In this paper, we first describe the development process of SSPs and their possible application.Next, the simulation and global and Chinese results of population and economy, land use, energy and carbon emissions are simulated and projected.In particular, the carbon emission trajectories under different SSPs and their relationship with the "two-carbon" target are also quantified on scales for both the world and China.Finally, a prospective application of SSPs is presented.

Abstract:The recently published IPCC AR6 once again emphasized the importance of CH₄ mitigation in global warming abatement.CH₄ is one of the most important short-life GHGs.Since many countries committed to the new CO₂ emission reduction targets of carbon neutrality either by 2050 or before 2060, programs focusing on CH₄ emission reduction have been increasing, and consequently CH₄ emission reduction is becoming one of the key areas for national and global GHG mitigation and international collaboration.This paper presents CH₄ emission scenarios for China based on the energy transition with the carbon neutrality target, together with mitigation technology options in other non-energy activities, by applying the IPAC model.With the two scenarios used in the modeling analysis, it is found that, with the energy transition, there will be significant CH₄ emission reduction by 2050.The reason for this is the reduced use of fossil fuels in the transition, with 67% CH₄ emission reduction compared with that in 2015.Compared with other sectors, CH₄ emission reduction in energy sector has better synergy.If more CH₄ mitigation is required, then reduced demand for nature gas may be a contributor.By combining this with O₃ reduction, and since NO_<i>x is a precursor of O₃, by 2050 NO_<i>x emission will mainly originate from natural gas combustion in the energy transition.In the meantime, CH₄ emission mitigation from non-energy sectors also bears great potential.In the low-CH₄ emission scenario, CH₄ emission could be reduced by 14.94 Mt by 2050, with 58% reduction compared with 2015.

Abstract:In this study, the impacts of stochastic tendency perturbations and stochastic parameter perturbations on the precipitation ensemble forecasts using the Betts-Miller-Janjic' (BMJ) scheme were investigated.Next, both stochastic perturbation approaches were implemented on the advanced regional prediction system (ARPS).Then, precipitation ensemble forecasts were evaluated using 10 cases that occurred in eastern China in June 2018 and July 2018.The tendency perturbations involved the temperature and specific humidity tendencies from the BMJ scheme, while the parameter perturbations were applied in the temperature and specific humidity reference profiles of the BMJ scheme.The results showed that the precipitation forecasts when using the BMJ scheme were characterized by wet bias at examined thresholds, thus signifying a greater number of forecast precipitation events than the corresponding observations.In addition, the bias issue remained after using wetter reference profiles, while the responses of the BMJ scheme to stochastic approaches differed substantially.The tendency perturbations bore little impact on the BMJ precipitation forecasts as the forecast precipitation frequency did not significantly change in comparison with the unperturbed BMJ scheme.In the case of using tendency perturbations, the ensemble spread is low.In contrast, perturbing the reference profiles bore great impacts on the precipitation ensemble forecasts.Symmetric perturbations of reference profiles produced a large ensemble spread, yet this approach also increased the wet bias at light rain thresholds, and yielded small improvement on the forecast skill scores.Compared to tendency perturbation approach, asymmetric perturbations (perturbation mean> 1.0) of the reference profiles were conducive to larger ensemble spread, higher forecast skill scores, and smaller wet bias, although the wet bias at large precipitation thresholds increased.Moreover, the asymmetric perturbations substantially improved the precipitation spatial distribution in early forecast stage (0-3 h) and the nocturnal precipitation intensity.The large area of spurious precipitation yielded by the BMJ scheme in the early stage of the forecast substantially dried the air, which in turn suppressed the precipitation intensity in subsequent forecast.Finally, the asymmetric perturbations effectively reduced the spurious precipitation and improved the precipitation intensity forecast.The quantities of temperature and specific humidity tendencies were both small, and this was likely the cause of small impact of tendency perturbations on the BMJ scheme.

Abstract:Based on the ERA5 hourly reanalysis dataset and the merged hourly precipitation products from National Meteorological Centre from May to June from 2010 to 2016, the low-level jet events affecting South China were selected and classified using an objective method.This paper also investigated the diurnal cycles of boundary layer jet (BLJ) and synoptic-system-related low-level jet (SLLJ) during early-summer, and analyzed their influences on temporal and spatial distributions of diurnal cycle of precipitation in South China.Results show that BLJ and SLLJ weaken during the day and increase at night, and reach the peak in the early morning.Their diurnal cycles are mainly related to the clockwise rotation of ageostrophic winds caused by inertial oscillations of boundary layer.The precipitation in South China increases significantly during the double low-level jet days, and the diurnal cycle of precipitation has obvious regional differences, which is closely related to the evolution and configuration of the double low-level jets.The precipitation in central and northern Guangxi is mainly concentrated over the mountainous area at the left anterior to the SLLJ at night and is characterized by only one single peak in the early morning.There are two peaks in the morning and afternoon in coastal Guangxi and Guangdong.The maintenance of convergence in BLJ exit area and divergence in SLLJ inlet area are conducive to the increase of precipitation frequency, resulting in the emergence of afternoon peak.In addition to the influence of the favorable configuration of the double low-level jets, the morning peak of precipitation is mainly due to the increase of the morning precipitation intensity.

Abstract:In this study, based on the daily ERA-Interim reanalysis data and daily precipitation data from 753 stations throughout China, the synoptic process of the northeast cold vortex during the period of March 23-28, 2008 was analyzed.In addition, the main factors influencing the cold vortex precipitation were also discussed.The results showed that, unlike the summer cold vortex, the upper-level circulation of the early spring cold vortex event underwent a transition from meridional circulation to zonal circulation.The establishment of the meridional circulation during the early stage guided the cold vortex to move southward, while the low trough to the rear (west) of the cold vortex supplied cold air for the development and maintenance of the cold vortex circulation.The blocking systems over the Eurasian continent were key factors influencing the early spring cold vortex.The Okhotsk Sea blocking high and Ural blocking high were respectively regulated by the tropical Pacific and preceding North Atlantic Sea surface temperature anomalies, which provided a beneficial background for the southward development and maintenance of the cold vortex.The jets at the lower and upper levels were also modulated by the Okhotsk blocking high, which was conducive to the formation of cold vortex precipitation.The configurations of the vorticity field and temperature field caused the cold vortex to develop into a deep circulation system, while the dry-air invasion also played an important role.The development of cold vortex circulation provided favorable vertical motion and water vapor conditions for precipitation in northeastern China.Finally, the frontal process induced by the cold and warm advection promoted the formation of large-scale precipitation.

Abstract:In this study, based on the average precipitation of the summer (July-August) and the NCEP/NCAR atmospheric circulation data of four stations (Lhasa, Shigatse, Zedang and Jiangzi) in the middle reaches of the Yarlung Zangbo River in the hinterland of the Tibet Plateau over the past 57 years (1961-2017), synthesis, correlation analysis and other methods are used to analyze the interannual variation characteristics of summer precipitation in the region, along with its possible causes.The results show the following:1) There is no significant linear trend in the summer precipitation in the region during the past 57 years, and the interannual oscillations of the significant period around 3 a are dominant.2) The interannual variation of summer precipitation in the region is directly related to the amount of the water vapor budget in the region.The anomalous anti-cyclonic water vapor flux transport in the Indian Peninsula-Southeast Asia and the dynamic process of water vapor in the plateau hinterland are the main reasons for the interannual oscillations of midsummer precipitation.3) The troposphere in the bottom of the Indian Peninsula-Southeast Asia anomalous anticyclonic circulation is an important water vapor transport channel for the interannual anomalies of midsummer precipitation in the region.The channel continuously transports water vapor to the plateau in the western Pacific, South China Sea and Bay of Bengal.During this period, large-scale system anomalies, such as the West Pacific subtropical high and the Iranian high pressure, played an important role in the water vapor transport process.At the same time, the plateau and the summer monsoon low pressure and South Asia high pressure provided the dynamic conditions for the water vapor to rise and rise in the plateau hinterland.