Permafrost carbon cycle and its dynamics on the Tibetan Plateau

Our knowledge on permafrost carbon(C)cycle is crucial for understanding its feedback to climate warming and developing nature-based solutions for mitigating climate change.To understand the characteristics of permafrost C cycle on the Tibetan Plateau,the largest alpine permafrost region around the world,we summarized recent advances including the stocks and fluxes of permafrost C and their responses to thawing,and depicted permafrost C dynamics within this century.We find that this alpine permafrost region stores approximately 14.1 Pg(1 Pg=1015g)of soil organic C(SOC)in the top 3 m.Both substantial gaseous emissions and lateral C transport occur across this permafrost region.Moreover,the mobilization of frozen C is expedited by permafrost thaw,especially by the formation of thermokarst landscapes,which could release significant amounts of C into the atmosphere and surrounding water bodies.This alpine permafrost region nevertheless remains an important C sink,and its capacity to sequester C will continue to increase by 2100.For future perspectives,we would suggest developing long-term in situ observation networks of C stocks and fluxes with improved temporal and spatial coverage,and exploring the mechanisms underlying the response of ecosystem C cycle to permafrost thaw.In addition,it is essential to improve the projection of permafrost C dynamics through in-depth model-data fusion on the Tibetan Plateau.

中国草地生态系统固碳能力及其提升途径

准确评估草地生态系统固碳速率、提升其碳汇能力对于深入认识国家尺度陆地生态系统碳源汇特征及其固碳潜力具有重要意义。通过梳理文献,本文总结了我国草地碳汇大小、空间格局及其未来趋势,并提出了提升草地碳汇的可能途径。结果发现,不同研究对我国草地碳源汇特征的估算差异较大,大小介于-3.4~17.6 Tg C year^(-1)(1 Tg=10^(12)g),中值为13.0 Tg C year^(-1)。模型预测未来全球变化背景下我国草地碳汇呈增加趋势,由1970s—2010s的12.8 Tg C year^(-1)(不同研究结果的范围:-3.6~18.0 Tg C year^(-1))增加至2050s的29.0 Tg C year^(-1)(10.3~50.0 Tg C year^(-1))。通过构建退化草地恢复技术体系、加强重大生态工程、自然保护区和人工草地建设、利用碳汇植物提升荒漠化草地碳汇、以及实施有效的生态奖补政策等手段,有望进一步提升草地固碳能力。未来亟需在草地碳通量长期联网观测、碳循环关键过程对全球变化响应和反馈机制、数据—模型融合等方面加强研究,以降低草地碳汇估算中的不确定性。此外,还需加强草地退化和恢复过程中碳循环观测和模拟研究,从而针对性地恢复退化草地碳汇功能,为我国实现“碳中和”国家战略目标提供科技支撑。

Changes in productivity and carbon storage of grasslands in china under future global warming scenarios of 1.5℃ and 2℃

Aims the impacts of future global warming of 1.5℃ and 2℃ on the productivity and carbon(c)storage of grasslands in china are not clear yet,although grasslands in china support~45 million agricultural populations and more than 238 million livestock populations,and are sensitive to global warming.Methods this study used a process-based terrestrial ecosystem model named ORcHIDEE to simulate c cycle of alpine meadows and temperate grasslands in china.this model was driven by high-resolution(0.5°×0.5°)climate of global specific warming levels(SWL)of 1.5℃ and 2℃(warmer than pre-industrial level),which is downscaled by Ec-EARtH3-HR v3.1 with sea surface temperature and sea-ice concentration as boundary conditions from IPSL-cM5-LR(low spatial resolution,2.5°×1.5°)Earth system model(ESM).Important Findingscompared with baseline(1971-2005),the mean annual air temperature over chinese grasslands increased by 2.5℃ and 3.7℃ under SWL1.5 and SWL2,respectively.the increase in temperature in the alpine meadow was higher than that in the temperate grassland under both SWL1.5 and SWL2.Precipitation was also shown an increasing trend under SWL2 over most of the chinese grasslands.Strong increases in gross primary productivity(GPP)were simulated in the chinese grasslands,and the mean annual GPP(GPP_(MA))increased by 19.32%and 43.62%under SWL1.5 and SWL2,respectively.the c storage increased by 0.64 Pg c and 1.37 Pg c under SWL1.5 and SWL2 for 50 years simulations.the GPP_(MA) was 0.67_(0.39)^(0.88)(0.82)(model mean_(min) ^(max) (this study)),0.85_(0.45)^(1.24)(0.97)and 0.94_(0.61)^(1.30)(1.17)Pg C year^(−1) under baseline,SWL1.5 and SWL2 modeled by four cMIP5 ESMs(phase 5 of the coupled Model Inter-comparison Project Earth System Models).In contrast,the mean annual net biome productivity was−18.55_(−40.37)^(4.47)(−3.61),18.65_(−2.03)^(64.03)(10.29)and 24.15_(8.38)^(38.77)(24.93)Tg C year^(−1) under base-line,SWL1.5 and SWL2 modeled by the four cMIP5 ESMs.Our results indicated that the chinese grasslands would have higher productivity than the baseline and can mitigate climate change through increased C sequestration under future global warming of 1.5℃ and 2℃ with the increase of precipitation and the global increase of atmospheric CO_(2) concentration.

Terrestrial carbon sinks in China and around the world and their contribution to carbon neutrality

Enhancing the terrestrial ecosystem carbon sink(referred to as terrestrial C sink) is an important way to slow down the continuous increase in atmospheric carbon dioxide(CO_(2)) concentration and to achieve carbon neutrality target.To better understand the characteristics of terrestrial C sinks and their contribution to carbon neutrality,this review summarizes major progress in terrestrial C budget researches during the past decades,clarifies spatial patterns and drivers of terrestrial C sources and sinks in China and around the world,and examines the role of terrestrial C sinks in achieving carbon neutrality target.According to recent studies,the global terrestrial C sink has been increasing from a source of (-0.2±0.9) Pg C yr^(-1)(1 Pg=1015g)in the 1960s to a sink of (1.9±1.1) Pg C yr^(-1) in the 2010s.By synthesizing the published data,we estimate terrestrial C sink of 0.20–0.25 Pg C yr^(-1) in China during the past decades,and predict it to be 0.15–0.52 Pg C yr^(-1) by 2060.The terrestrial C sinks are mainly located in the mid-and high latitudes of the Northern Hemisphere,while tropical regions act as a weak C sink or source.The C balance differs much among ecosystem types:forest is the major C sink;shrubland,wetland and farmland soil act as C sinks;and whether the grassland functions as C sink or source remains unclear.Desert might be a C sink,but the magnitude and the associated mechanisms are still controversial.Elevated atmospheric CO_(2) concentration,nitrogen deposition,climate change,and land cover change are the main drivers of terrestrial C sinks,while other factors such as fires and aerosols would also affect ecosystem C balance.The driving factors of terrestrial C sink differ among regions.Elevated CO_(2) concentration and climate change are major drivers of the C sinks in North America and Europe,while afforestation and ecological restoration are additionally important forcing factors of terrestrial C sinks in China.For future studies,we recommend the necessity for intensive and long-term ecosystem C monitoring over broad geographic scale to improve terrestrial biosphere models for accurately evaluating terrestrial C budget and its dynamics under various climate change and policy scenarios.

China’s low-emission pathways toward climate-neutral livestock production for animal-derived foods

Animal-derived food production accounts for 19%of global anthropogenic greenhouse gas(GHG)emissions.Diet followed in China is ranked as lowcarbon emitting(i.e.,0.21 t CO_(2-)eq per capita in 2018,ranking at 145^(th) of 168 countries)due to the low average animal-derived food consumption rate,and preferential consumption of animal-derived foods with lower GHG emissions(i.e.,pork and eggs versus beef and milk).

Use,calibration and verification of agroecologicalmodels for boreal environments:A review

Past assessments report negative impacts of the climate crisis in boreal areas;but milder and shorter winters and elevated atmospheric CO_(2) may provide opportunities for agricultural productivity potentially playing a significant role in future food security.Arable cropping systems are expanding in boreal areas,but the regional mainstay will likely continue to be livestock production.Agroecological models can when appropriately calibrated and evaluated,facilitate improved productivity while minimising environmental impacts by identifying system interactions,and quantifying greenhouse gas emissions,soil carbon stocks and fertiliser use.While models designed for temperate and tropical zones abound,few are developed specifically for boreal zones,and there is uncertainty around the performance of existing models in boreal areas.We reviewed model performance across boreal environments and management systems.We identified a dearth of modelling studies in boreal regions,with the publication of three or less papers per year since the year 2000,constituting a significant research gap.Models IFSM and BASGRA_N performed best in grassland production,DNDC best in predicting soil N_(2)O and NH_(3) emissions.No model outperformed all others,strengthening the case for ensemble modelling.Existing agroecological models would be worthy of further evaluation,providing model improvements designed for boreal systems.