Assessment And Future Prediction Of The Spatiotemporal Pattern Of Ecosystem Carbon Budget In China From 2000 To 2018

Global climate change depends on the climate change policies of countries around the world,including China and so on.Therefore,it is necessary to reasonably reduce carbon source emissions and increase carbon sink absorption in order to achieve the goal of carbon neutral as soon as possible.However,since the 21st century,the investigation and quantification of the carbon budget between anthropogenic carbon emissions(CEs)and terrestrial ecosystem carbon sinks(ECS)at the pixel scale in China has been unclear.And most scholars only considered the organic carbon sinks of terrestrial ecosystems or rock weathering carbon sink when calculating carbon sinks.The two are not comprehensively calculated,resulting in a slight deviation in the carbon sink calculation.Moreover,the future prediction of China carbon budget under different scenarios is also lacking.To this end,based on China's high-precision climate,hydrology,and vegetation data from 2000 to 2018,using the net ecosystem productivity(NEP)model and the GEM-CO₂ model,this paper created a spatial information map of organic-inorganic ECS for pixel-scale in China from 2000 to 2018 and clarified the spatiotemporal pattern and evolution trend of China ECS.On the premise of clarifying temporal and spatial pattern of ECS,combined with the pixel-scale CEs data,this paper quantified and evaluated China pixel-scale carbon neutral capacity(ECS—CEs)and its spatial pattern.Moreover,we compared the heterogeneity and temporal evolution of carbon neutral capacity in different comprehensive economic zones,provinces and cities.In addition,according to the"Special Report on Emission Scenarios"issued by the Intergovernmental Panel on Climate Change(IPCC)in 2000,two different carbon emission scenarios were selected,namely the A2 and B1 scenarios.Among them,Scenario A emphasizes the pursuit of economic development in the future,and Scenario A2 represents the scenario of economic development in only some regions.Scenario B emphasizes the future scenario of sustainable development,and B1 represents the situation of global sustainable development.Finally,based on the future2025-2060 climate,vegetation data,CEs data and their influencing factors,the Back Propagation neural network model was used to predict the carbon neutral potential in China.The results show:(1)Affected and restricted by the population structure,social economy and energy consumption development level,the spatial pattern of CEs in China showed obvious heterogeneity.Taking the Hu Huanyong Line as the boundary,the difference between the high and low levels of CEs on the east and west sides of my country was obvious.Among them,CEs fluxes on more than 90%of the western regions was less than 200t CO₂ km^-2 yr^-1.However,the CEs in these regions centered on the North China Plain,Yangtze River Delta and southeast coastal area gradually decreased to the periphery with a central magnitude greater than22.56×10~4 t CO₂ km^-2 yr^-1.From 2000 to 2018,China's CEs continued to rise,and the trend was obvious.After 2009,it has been higher than the annual average of CEs.In the future A2 scenario,China's CEs will still show an upward trend in the future,and the target of carbon peaking will still not be achieved in 2030.In 2060,China's CEs will exceed 59 Pg.In the B1 scenario,after the carbon emission peaks in 2029,it will drop to9.63Pg in 2060 and return to the 2010-2011 CEs level.So the B1 scenario will be more in line with the long-term development goals.(2)From 2000 to 2018,China terrestrial ecosystem was a huge carbon sink,with an average annual carbon sink of 1.78 Pg CO₂ yr^-1.Although vegetation in China mainly contributed to carbon sequestration,with the Hu Huanyong Line as the boundary,the effects of vegetation on both sides of the atmospheric CO₂ were in opposite states.In the southeastern part of the boundary,vegetation carbon sink was greater than respiration,showing the state of carbon sink as a whole,but the vegetation on the northwest side has become a huge carbon source.The law of its distribution is as follows:from the latitude level analysis-it decreased from low latitude to high latitude with the climate zone;from the sea and land position analysis-from the coastal area to the inland area,it decreased step by step.Over the entire study period,the ECS in China showed an increasing trend,and the area of increase accounted for78.31%,which was 3.6 times that of the other cases.The total change in ECS was 126.41 t km^-2,of which the rising change was 105.52 t km^-2and the drop change was-20.89 t km^-2.From a spatial point of view,the temperate region had the most obvious changes,especially the mid-temperate climate type,which increased the ECS by 34.16 t km^-2.(3)From 2000 to 2018,China annual CEs of 6.15Pg CO₂ were not absorbed,which was about 77.52%of CEs.The carbon surplus areas were distributed in the southwest,southeast and northeast of China.There were 87 cities(county-level cities)nationwide,which contributed 1.20 Pg of carbon sinks on the basis of achieving carbon neutral.Over the entire study period,the average change trend of China carbon neutral capacity was-21.57 Tg yr^-1,showing a weakening trend with large inter-annual fluctuations.Generally speaking,with the increase of carbon emissions,the carbon neutrality capacity continued to weaken.In addition,2004 was the time node,and the carbon neutral capacity of most provinces in China showed a significant downward trend.(4)By analyzing the Moran's I of the average carbon neutral capacity of Chinese cities from 2000 to 2018,the results showed that China carbon neutral capacity had a significant positive spatial correlation,with spatial agglomeration characteristics.The city-level regions in China were mainly dominated by high-value and high-value cluster and low-value and low-value cluster.The spatial boundaries between them were clear,and they were located in southern China(the high-value and high-value cluster),North China-East China(low-value and low-value cluster)and Western China(low-value and low-value cluster).And in most provinces,the carbon neutral capacity was at a relatively average level,following a certain rule.Cities in provinces with weak carbon neutral capacity in China also had the same capacity,that is,regions with cold capacity had lower Gini coefficient.(5)From 2025 to 2060,whether in the A2(regional economic development)or B1(Global sustainable Development)scenarios,the carbon sink capacity of China's terrestrial ecosystems will generally show a continuous upward trend in the future.And the growth trend of ECS in the B1 model will be greater than that in the A2 model.In terms of carbon neutral capacity,in the A2 scenario,China's carbon deficit will increase from 9.46 Pg in 2025 to 47.26 Pg in 2030.Eventually,China will have up to 57.44 Pg of carbon emissions that need to be absorbed to achieve carbon neutral by 2060.In the B1 scenario,by 2025,2030 and 2060,China carbon deficit will be 17.23 Pg,22.04 Pg and 7.37 Pg,respectively.In summary,this study believed that China terrestrial ecosystem had a large carbon sink potential,which can absorb 1.78 Pg CO₂ per year.However,with the continuous growth of carbon emissions,its carbon sink contribution was also constantly weakened.This showed that although terrestrial ecosystems can alleviate the pressure of carbon neutral targets to a certain extent,the main focus should be on emission reduction.In 2060,China CEs need to be reduced to at least 2.63Pg to achieve carbon neutral.Therefore,this work has clarified China carbon budget from the past to the future,as well as its spatial distribution and changing trends.This provided theoretical and data support for China to introduce corresponding zero-carbon solutions based on its understanding of CNC.