Seasonal compensation implied no weakening of the land carbon sink in the Northern Hemisphere under the 2015/2016 El Niño

The recurrent extreme El Niño events are commonly linked to reduced vegetation growth and the land carbon sink over many but discrete regions of the Northern Hemisphere(NH).However,we reported here a pervasive and continuous vegetation greening and no weakened land carbon sink in the maturation phase of the 2015/2016 El Niño event over the NH(mainly in the extra-tropics),based on multiple evidences from remote sensing observations,global ecosystem model simulations and atmospheric CO_(2)inversions.We discovered a significant compensation effect of the enhanced vegetation growth in spring on subsequent summer/autumn vegetation growth that sustained vegetation greening and led to a slight increase in the land carbon sink over the spring and summer of 2015(average increases of 23.34%and 0.63%in net ecosystem exchange from two independent datasets relative to a 5-years average before the El Niño event,respectively)and spring of 2016(6.82%),especially in the extra-tropics of the NH,where the water supply during the pre-growing-season(November of the previous year to March of the current year)had a positive anomaly.This seasonal compensation effect was much stronger than that in 1997 and 1998 and significantly alleviated the adverse impacts of the 2015/2016 El Niño event on vegetation growth during its maturation phase.The legacy effect of water supply during the pre-growing-season on subsequent vegetation growth lasted up to approximately six months.Our findings highlight the role of seasonal compensation effects on mediating the land carbon sink in response to episodic extreme El Niño events.

全球变暖和厄尔尼诺导致青藏高原中部湿地迅速扩张

阐明青藏高原湿地的时空变化规律和驱动因素,对理解青藏高原湿地对气候变化的响应及保护其生态系统和生物多样性至关重要.由于湿地边界的不确定性、遥感数据光谱和纹理特征的复杂性,湿地的智能识别监测面临许多技术挑战.本研究提出了一种面向遥感场景分类的深度学习框架,实现了基于Landsat遥感图像的青藏高原湿地智能提取.结果表明,近30年(1990~2019年)青藏高原湿地面积增加了31.2%,其中青藏高原中部,即羌塘高原、柴达木盆地和三江源地区的湿地面积增长最明显.气温升高引起的多年冻土融化是该地区湿地面积增长的主要驱动力.因厄尔尼诺而导致的气温和降水异常进一步加剧了湿地面积的增长.

The impacts of climate extremes on the terrestrial carbon cycle:A review

The increased frequency of climate extremes in recent years has profoundly affected terrestrial ecosystem functions and the welfare of human society. The carbon cycle is a key process of terrestrial ecosystem changes. Therefore, a better understanding and assessment of the impacts of climate extremes on the terrestrial carbon cycle could provide an important scientific basis to facilitate the mitigation and adaption of our society to climate change. In this paper, we systematically review the impacts of climate extremes(e.g. drought, extreme precipitation, extreme hot and extreme cold) on terrestrial ecosystems and their mechanisms. Existing studies have suggested that drought is one of the most important stressors on the terrestrial carbon sink, and that it can inhibit both ecosystem productivity and respiration. Because ecosystem productivity is usually more sensitive to drought than respiration, drought can significantly reduce the strength of terrestrial ecosystem carbon sinks and even turn them into carbon sources. Large inter-model variations have been found in the simulations of drought-induced changes in the carbon cycle, suggesting the existence of a large gap in current understanding of the mechanisms behind the responses of ecosystem carbon balance to drought, especially for tropical vegetation. The effects of extreme precipitation on the carbon cycle vary across different regions. In general, extreme precipitation enhances carbon accumulation in arid ecosystems, but restrains carbon sequestration in moist ecosystems. However, current knowledge on the indirect effects of extreme precipitation on the carbon cycle through regulating processes such as soil carbon lateral transportation and nutrient loss is still limited. This knowledge gap has caused large uncertainties in assessing the total carbon cycle impact of extreme precipitation. Extreme hot and extreme cold can affect the terrestrial carbon cycle through various ecosystem processes. Note that the severity of such climate extremes depends greatly on their timing, which needs to be investigated thoroughly in future studies. In light of current knowledge and gaps in the understanding of how extreme climates affect the terrestrial carbon cycle, we strongly recommend that future studies should place more attention on the long-term impacts and on the driving mechanisms at different time scales.Studies based on multi-source data, methods and across multiple spatial-temporal scales, are also necessary to better characterize the response of terrestrial ecosystems to climate extremes.

Multimodel projections and uncertainties of net ecosystem production in China over the twenty-first century

Ecosystems in China have been absorbing anthropogenic CO2 over the last three decades. Here, we assess future carbon uptake in China using models from phase 5 of Coupled Model Intercomparison Project under four socio-economic scenarios. The average of China's carbon sink from 2006 to 2100 represented by multimodel mean net ecosystem production(NEP) is projected to increase(relative to averaged NEP from 1976 to 2005) in the range of 0.137 and 0.891 Pg C a-1across differentscenarios. Increases in NEP are driven by increases in net primary production exceeding increases in heterotrophic respiration, and future carbon sink is mainly attributed to areas located in eastern China. However, there exists a considerable model spread in the magnitude of carbon sink and model spread tends to be larger when future climate change becomes more intense. The model spread may result from intermodel discrepancy in the magnitude of CO2 fertilization effect on photosynthesis, soil carbon turnover time, presence of carbon-nitrogen cycle and interpretation of land-use changes. For better quantifying future carbon cycle, a research priority toward improving model representation of these processes is recommended.

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.

Mapping global forest biomass and its changes over the first decade of the 21st century

Forests played an important role in carbon sequestration during the past two decades. Using a model tree ensemble method(MTE) to regress the seven reflectance bands of EOS-Terra-MODIS satellite data against country level forest biomass carbon density(BCD) of 2001–2005 provided by United Nations' s Forest Resource Assessment(FRA), we developed a global map of forest BCD at 1 km×1 km resolution for both 2001–2005 and 2006–2010. For 2006–2010, the total global forest biomass carbon stock is estimated as 279.6±7.1 Pg C, and the tropical forest biomass carbon stock is estimated as 174.4±5.4 Pg C. During the first decade of the 21 st century, we estimated an increase of global forest biomass of 0.28±0.75 Pg C yr^(-1). Tropical forest biomass carbon stock slightly decreased(-0.31±0.60 Pg C yr^(-1)); by contrast, temperate and boreal forest biomass increased(0.58±0.28 Pg C yr^(-1)) during the same period. Our estimation of the global forest biomass carbon stock and its changes is subject to uncertainties due to lack of extensive ground measurements in the tropics, spatial heterogeneity in large countries, and different definitions of forest. The continuously monitoring of forest biomass carbon stock with MODIS satellite data will provide useful information for detecting forest changes.