Natural Climate Solutions for China:The Last Mile to Carbon Neutrality

“I call on all leaders worldwide to declare a State of Climate Emergency in their own countries until carbon neutrality is reached.”–António GUTERRES(United Nations Secretary General),12 December,2020 There is no shortcut to a carbon neutral society;solutions are urgently required from both energy&industrial sectors and global ecosystems.While the former is often held accountable and emphasized in terms of its emissions reduction capability,the latter(recently termed natural climate solutions)should also be assessed for potential and limitations by the scientific community,the public,and policy makers.

中国碳收支:1980~2021年

As one of the world's largest emitters of greenhouse gases,China has set itself the ambitious goal of achieving carbon peaking and carbon neutrality.Therefore,it is crucial to quantify the magnitude and trend of sources and sinks of atmospheric carbon dioxide(CO_(2)),and to monitor China's progress toward these goals.Using state-of-the-art datasets and models,this study comprehensively estimated the anthropogenic CO_(2)emissions from energy,industrial processes and product use,and waste along with natural sources and sinks of CO_(2)for all of China during 1980-2021.To recognize the differences among various methods of estimating greenhouse emissions,the estimates are compared with China's National Greenhouse Gas Inventories(NGHGIs)for 1994,2005,2010,2012,and 2014.Anthropogenic CO_(2)emissions in China have increased by 7.39 times from 1980 to 12.77 Gt CO_(2)a^(-1)in 2021.While benefiting from ecological projects(e.g.,Three Norths Shelter Forest System Project),the land carbon sink in China has reached 1.65 Gt CO_(2)a^(-1)averaged through 2010-2021,which is almost 15.81 times that of the carbon sink in the 1980s.On average,China's terrestrial ecosystems offset 14.69%±2.49%of anthropogenic CO_(2)emissions through 2010-2021.Two provincial-level administrative regions of China,Xizang and Qinghai,have achieved carbon neutrality according to our estimates,but nearly half of the administrative regions of China have terrestrial carbon sink offsets of less than 10%of anthropogenic CO_(2)emissions.This study indicated a high level of consistency between NGHGIs and various datasets used for estimating fossil CO_(2)emissions,but found notable differences for land carbon sinks.Future estimates of the terrestrial carbon sinks of NGHGIs urgently need to be verified with process-based models which integrate the comprehensive carbon cycle processes.

Global and regional soil organic carbon estimates:Magnitudes and uncertainties

Globally,soil is the largest terrestrial carbon(C)reservoir.Robust quantification of soil organic C(SOC)stocks in existing global observation-based estimates avails accurate predictions in carbon-climate feedbacks and future climate trends.We investigated the magnitudes and distributions of global and regional SOC estimates(i.e.,density and stocks)based on five widely used global gridded SOC datasets,a regional permafrost dataset developed in 2021(UM2021),and a global-scale soil profile database(World Soil Information Service)reporting measurements of a series of physical and chemical edaphic attributes.The five global gridded SOC datasets were the Harmonized World Soil Database(HWSD),World Inventory of Soil Emission Potentials at 30 arc-second resolution(WISE30sec),Global Soil Dataset for Earth System Models(GSDE),Global Gridded Soil Information at 250-m resolution(SoilGrids250m),and Global Soil Organic Carbon Map(GSOCmap).Our analyses showed that the magnitude and distribution of SOC varied widely among datasets,with certain datasets showing region-specific robustness.At the global scale,SOC stocks at the top 30 and 100 cm were estimated to be 828(range:577–1171)and 1873(range:1086–2678)Pg C,respectively.The estimates from GSDE,GSOCmap,and WISE30sec were comparable,and those of SoilGrids250m and HWSD were at the upper and lower ends.The spatial SOC distribution varied greatly among datasets,especially in the northern circumpolar and Tibetan Plateau permafrost regions.Regionally,UM2021 and WISE30sec performed well in the northern circumpolar permafrost regions,and GSDE performed well in China.The estimates of SOC by different datasets also showed large variabilities across different soil layers and biomes.The discrepancies were generally smaller for the 0–30 cm soil than the 0–100 cm soil.The datasets demonstrated relatively higher agreement in grasslands,croplands,and shrublands/savannas than in other biomes(e.g.,wetlands).The users should be mindful of the gaps between regions and biomes while choosing the most appropriate SOC dataset for specific uses.Large uncertainties in existing global gridded SOC estimates were generally derived from soil sampling density,different sources,and various mapping methods for soil datasets.We call for future efforts for standardizing soil sampling efforts,cross-dataset comparison,proper validation,and overall global collaboration to improve SOC estimates.

What can the Glasgow Declaration on Forests bring to global emission reduction?

The Glasgow Declaration on Forests signed at the recent UN Climate Change Conference(COP 26)committed to halting forest loss by 2030.141 countries and regions,collectively covering over 90%of global forest,endorsed this declaration.Avoiding forest loss can generally contribute to climate change mitigation;however,the impacts of the declaration on global carbon dioxide(CO_(2))emission reduction are still unclear.Here we show that the Glasgow Declaration,if implemented fully and in a timely fashion,could reduce 123 Gt CO_(2) of emission from 2021 to 2050.This study also highlights that any delays in implementing the declaration would decrease the avoided emission.Although the Glasgow Declaration is a milestone for mitigating climate change,the more ambitious afforestation plan is urgently needed to keep the global temperature rise to below 1.5
C relative to pre-industrial levels.

Offshore wind power in China:A potential solution to electricity transformation and carbon neutrality

China is likely to lead global offshore wind power development,in the hope of transforming the coal-based electricity system and reducing greenhouse gas emissions.However,the potential of power generation and emissions mitigation is largely unknown,and the contribution of offshore wind utilization to regional carbon neutrality needs to be further clarified.Here,we reveal that offshore wind energy resources are abundant in China,with an estimated power generation potential of about 17.5 PWh,more than doubling the current power consumption nationwide.Although current utilization of offshore wind energy in China accounts for 21%of global overall capacity,the total share is still limited,supplying just 0.4%of national electricity needs(2019).With the increasing use of offshore wind,by 2050,the planned installation along China coast would be nearly five times as much as current(2019)global capacity,or 25 times of current national offshore wind power generation.The total CO_(2)emissions reduction in 2050 due to the decrease in coal use is projected to be 294.3 Tg CO_(2)-eq yr^(-1),equivalent to 20%of current emissions from coal-fired power in the coastal region.The size of reduced emissions is higher than current CO_(2)emissions in about 90%of countries.Our results highlight the important role of offshore wind power in upgrading the energy system and achieving carbon neutrality.Future studies are encouraged to further explore technological,economic and institutional challenges facing offshore wind energy deployment and low-carbon energy system development.