| 1. |
- Ciais, Philippe, et al.
(författare)
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Definitions and methods to estimate regional land carbon fluxes for the second phase of the REgional Carbon Cycle Assessment and Processes Project (RECCAP-2)
- 2022
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Ingår i: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 15:3, s. 1289-1316
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Tidskriftsartikel (refereegranskat)abstract
- Regional land carbon budgets provide insights into the spatial distribution of the land uptake of atmospheric carbon dioxide and can be used to evaluate carbon cycle models and to define baselines for land-based additional mitigation efforts. The scientific community has been involved in providing observation-based estimates of regional carbon budgets either by downscaling atmospheric CO2 observations into surface fluxes with atmospheric inversions, by using inventories of carbon stock changes in terrestrial ecosystems, by upscaling local field observations such as flux towers with gridded climate and remote sensing fields, or by integrating data-driven or process-oriented terrestrial carbon cycle models. The first coordinated attempt to collect regional carbon budgets for nine regions covering the entire globe in the RECCAP-1 project has delivered estimates for the decade 2000–2009, but these budgets were not comparable between regions due to different definitions and component fluxes being reported or omitted. The recent recognition of lateral fluxes of carbon by human activities and rivers that connect CO2 uptake in one area with its release in another also requires better definitions and protocols to reach harmonized regional budgets that can be summed up to a globe scale and compared with the atmospheric CO2 growth rate and inversion results. In this study, using the international initiative RECCAP-2 coordinated by the Global Carbon Project, which aims to be an update to regional carbon budgets over the last 2 decades based on observations for 10 regions covering the globe with a better harmonization than the precursor project, we provide recommendations for using atmospheric inversion results to match bottom-up carbon accounting and models, and we define the different component fluxes of the net land atmosphere carbon exchange that should be reported by each research group in charge of each region. Special attention is given to lateral fluxes, inland water fluxes, and land use fluxes.
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| 2. |
- Ehlers, Todd A., et al.
(författare)
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Past, present, and future geo-biosphere interactions on the Tibetan Plateau and implications for permafrost
- 2022
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Ingår i: Earth-Science Reviews. - : Elsevier BV. - 0012-8252. ; 234
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Tidskriftsartikel (refereegranskat)abstract
- Interactions between the atmosphere, biosphere, cryosphere, hydrosphere, and geosphere are most active in the critical zone, a region extending from the tops of trees to the top of unweathered bedrock. Changes in one or more of these spheres can result in a cascade of changes throughout the system in ways that are often poorly understood. Here we investigate how past and present climate change have impacted permafrost, hydrology, and ecosystems on the Tibetan Plateau. We do this by compiling existing climate, hydrologic, cryosphere, biosphere, and geologic studies documenting change over decadal to glacial-interglacial timescales and longer. Our emphasis is on showing present-day trends in environmental change and how plateau ecosystems have largely flourished under warmer and wetter periods in the geologic past. We identify two future pathways that could lead to either a favorable greening or unfavorable degradation and desiccation of plateau ecosystems. Both paths are plausible given the available evidence. We contend that the key to which pathway future generations experience lies in what, if any, human intervention measures are implemented. We conclude with suggested management strategies that can be implemented to facilitate a future greening of the Tibetan Plateau.
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| 3. |
- Geng, Xiaojun, et al.
(författare)
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Contrasting phenology responses to climate warming across the northern extra-tropics
- 2022
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Ingår i: Fundamental Research. - : Elsevier BV. - 2667-3258. ; 2:5, s. 708-715
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Tidskriftsartikel (refereegranskat)abstract
- Climate warming has substantially advanced the timing of spring leaf-out of woody species at middle and high latitudes, albeit with large differences. Insights in the spatial variation of this climate warming response may therefore help to constrain future trends in leaf-out and its impact on energy, water and carbon balances at global scales. In this study, we used in situ phenology observations of 38 species from 2067 study sites, distributed across the northern hemisphere in China, Europe and the United States, to investigate the latitudinal patterns of spring leaf-out and its sensitivity (ST, advance of leaf-out dates per degree of warming) and correlation (RT, partial correlation coefficient) to temperature during the period 1980–2016. Across all species and sites, we found that ST decreased significantly by 0.15 ± 0.02 d °C−1 °N−1, and RT increased by 0.02 ± 0.001 °N−1 (both at P < 0.001). The latitudinal patterns in RT and ST were explained by the differences in requirements of chilling and thermal forcing that evolved to maximize tree fitness under local climate, particularly climate predictability and summed precipitation during the pre-leaf-out season. Our results thus showed complicated spatial differences in leaf-out responses to ongoing climate warming and indicated that spatial differences in the interactions among environmental cues need to be embedded into large-scale phenology models to improve the simulation accuracy.
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| 4. |
- He, Bin, et al.
(författare)
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Worldwide impacts of atmospheric vapor pressure deficit on the interannual variability of terrestrial carbon sinks
- 2022
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Ingår i: National Science Review. - : Oxford University Press (OUP). - 2095-5138 .- 2053-714X. ; 9:4
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Tidskriftsartikel (refereegranskat)abstract
- Interannual variability of the terrestrial ecosystem carbon sink is substantially regulated by various environmental variables and highly dominates the interannual variation of atmospheric carbon dioxide (CO2) concentrations. Thus, it is necessary to determine dominating factors affecting the interannual variability of the carbon sink to improve our capability of predicting future terrestrial carbon sinks. Using global datasets derived from machine-learning methods and process-based ecosystem models, this study reveals that the interannual variability of the atmospheric vapor pressure deficit (VPD) was significantly negatively correlated with net ecosystem production (NEP) and substantially impacted the interannual variability of the atmospheric CO2 growth rate (CGR). Further analyses found widespread constraints of VPD interannual variability on terrestrial gross primary production (GPP), causing VPD to impact NEP and CGR. Partial correlation analysis confirms the persistent and widespread impacts of VPD on terrestrial carbon sinks compared to other environmental variables. Current Earth system models underestimate the interannual variability in VPD and its impacts on GPP and NEP. Our results highlight the importance of VPD for terrestrial carbon sinks in assessing ecosystems' responses to future climate conditions.
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| 5. |
- Shen, Zexi, et al.
(författare)
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Mining Can Exacerbate Global Degradation of Dryland
- 2021
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 48:21
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Tidskriftsartikel (refereegranskat)abstract
- Groundwater storage (GS) is the major water resource for vegetation in drylands. Thus, positive relationships between vegetative growth condition (VGC) and GS are expected in drylands. Since mining-induced dewatering tends to deplete GS surrounding mine sites, VGC should become less favorable due to a shortage of accessible water. However, quantitative analysis repealed the opposite. We found that global annual mineral production in drylands increased by 24%, while GS decreased by 22% but the VGC improved by 37% (2002–2010). And negative relationships between VGC and GS were detected in 84.7% of global dryland mine sites. We concluded that irrigation supported by mining-induced dewatering promoted the vegetation growth surrounding mine sites. However, since the GS is limited, irrigation-supported vegetation growth is unsustainable. This study elucidates the reason behind these abnormal negative relationships and highlights the potential risk of vegetation degradation induced by unsustainable groundwater depletion in global dryland mine sites.
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| 6. |
- Wang, Chenzhi, et al.
(författare)
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Occurrence of crop pests and diseases has largely increased in China since 1970
- 2022
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Ingår i: Nature Food. - : Springer Science and Business Media LLC. - 2662-1355. ; 3:1, s. 57-65
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Tidskriftsartikel (refereegranskat)abstract
- Crop pests and diseases (CPDs) are emerging threats to global food security, but trends in the occurrence of pests and diseases remain largely unknown due to the lack of observations for major crop producers. Here, on the basis of a unique historical dataset with more than 5,500 statistical records, we found an increased occurrence of CPDs in every province of China, with the national average rate of CPD occurrence increasing by a factor of four (from 53% to 218%) during 1970–2016. Historical climate change is responsible for more than one-fifth of the observed increment of CPD occurrence (22% ± 17%), ranging from 2% to 79% in different provinces. Among the climatic factors considered, warmer nighttime temperatures contribute most to the increasing occurrence of CPDs (11% ± 9%). Projections of future CPDs show that at the end of this century, climate change will lead to an increase in CPD occurrence by 243% ± 110% under a low-emissions scenario (SSP126) and 460% ± 213% under a high-emissions scenario (SSP585), with the magnitude largely dependent on the impacts of warmer nighttime temperatures and decreasing frost days. This observation-based evidence highlights the urgent need to accurately account for the increasing risk of CPDs in mitigating the impacts of climate change on food production.
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| 7. |
- Wang, Xuhui, et al.
(författare)
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Global irrigation contribution to wheat and maize yield
- 2021
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Irrigation is the largest sector of human water use and an important option for increasing crop production and reducing drought impacts. However, the potential for irrigation to contribute to global crop yields remains uncertain. Here, we quantify this contribution for wheat and maize at global scale by developing a Bayesian framework integrating empirical estimates and gridded global crop models on new maps of the relative difference between attainable rainfed and irrigated yield (ΔY). At global scale, ΔY is 34 ± 9% for wheat and 22 ± 13% for maize, with large spatial differences driven more by patterns of precipitation than that of evaporative demand. Comparing irrigation demands with renewable water supply, we find 30–47% of contemporary rainfed agriculture of wheat and maize cannot achieve yield gap closure utilizing current river discharge, unless more water diversion projects are set in place, putting into question the potential of irrigation to mitigate climate change impacts.
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| 8. |
- Yan, Yanzi, et al.
(författare)
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Increasing riverine export of dissolved organic carbon from China
- 2023
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Ingår i: Global Change Biology. - 1354-1013. ; 29:17, s. 5014-5032
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Tidskriftsartikel (refereegranskat)abstract
- River transport of dissolved organic carbon (DOC) to the ocean is a crucial but poorly quantified regional carbon cycle component. Large uncertainties remaining on the riverine DOC export from China, as well as its trend and drivers of change, have challenged the reconciliation between atmosphere-based and land-based estimates of China's land carbon sink. Here, we harmonized a large database of riverine in-situ measurements and applied a random forest model, to quantify riverine DOC fluxes (FDOC) and DOC concentrations (CDOC) in rivers across China. This study proposes the first DOC modeling effort capable of reproducing well the magnitude of riverine CDOC and FDOC, as well as its trends, on a monthly scale and with a much wider spatial distribution over China compared to previous studies that mainly focused on annual-scale estimates and large rivers. Results show that over the period 2001–2015, the average CDOC was 2.25 ± 0.45 mg/L and average FDOC was 4.04 ± 1.02 Tg/year. Simultaneously, we found a significant increase in FDOC (+0.044 Tg/year2, p =.01), but little change in CDOC (−0.001 mg/L/year, p >.10). Although the trend in CDOC is not significant at the country scale, it is significantly increasing in the Yangtze River Basin and Huaihe River Basin (0.005 and 0.013 mg/L/year, p <.05) while significantly decreasing in the Yellow River Basin and Southwest Rivers Basin (−0.043 and −0.014 mg/L/year, p =.01). Changes in hydrology, play a stronger role than direct impacts of anthropogenic activities in determining the spatio-temporal variability of FDOC and CDOC across China. However, and in contrast with other basins, the significant increase in CDOC in the Yangtze River Basin and Huaihe River Basin is attributable to direct anthropogenic activities. Given the dominance of hydrology in driving FDOC, the increase in FDOC is likely to continue under the projected increase in river discharge over China resulting from a future wetter climate.
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