| 1. |
- Cheng, Y., et al.
(author)
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Indication of paleoecological evidence on the evolution of alpine vegetation productivity and soil erosion in central China since the mid-Holocene
- 2021
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In: Science China-Earth Sciences. - : Springer Science and Business Media LLC. - 1674-7313 .- 1869-1897. ; 64
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Journal article (peer-reviewed)abstract
- Although alpine ecosystems have been commonly recognized as sensitive to recent climate change, few studies have examined its impact on the long-term productivity of vegetation and soil erosion. Using paleoecological records, these two aspects were examined in the alpine zone of the Taibai Mountains (elevation, 3767 m) in monsoon-dominated East Asia since the middle Holocene. Proxies for the productivity of vegetation and severity of soil erosion from high-resolution alpine lacustrine records show that the productivity was closely related to mean annual temperature and soil erosion, to summer precipitation from the East Asian Summer Monsoon (EASM). Specifically, when the mean annual temperature was low and precipitation was abundant, during 5800-4000 calendar years before the present (cal. yr BP), the alpine ecosystem was characterized by low vegetation productivity and severe soil erosion. However, the productivity increased and soil erosion decreased from 4000 cal. yr BP onwards. These results highlight the role of paleoecological evidence in studying ecosystem services on longer time scales, which is significant in making policies for sustainable development under climate change in regions for which such long-term monitoring data are not available.
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| 2. |
- Li, Y., et al.
(author)
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Widespread spring phenology effects on drought recovery of Northern Hemisphere ecosystems
- 2023
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In: Nature Climate Change. - : Springer Science and Business Media LLC. - 1758-678X .- 1758-6798. ; 13
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Journal article (peer-reviewed)abstract
- The authors reveal complex drought recovery responses to phenology shifts, in that early spring can shorten or lengthen recovery, while delayed spring following drought events delays it. These effects suggest a need to incorporate phenology aspects into resilience models. The time required for an ecosystem to recover from severe drought is a key component of ecological resilience. The phenology effects on drought recovery are, however, poorly understood. These effects centre on how phenology variations impact biophysical feedbacks, vegetation growth and, ultimately, recovery itself. Using multiple remotely sensed datasets, we found that more than half of ecosystems in mid- and high-latitudinal Northern Hemisphere failed to recover from extreme droughts within a single growing season. Earlier spring phenology in the drought year slowed drought recovery when extreme droughts occurred in mid-growing season. Delayed spring phenology in the subsequent year slowed drought recovery for all vegetation types (with importance of spring phenology ranging from 46% to 58%). The phenology effects on drought recovery were comparable to or larger than other well-known postdrought climatic factors. These results strongly suggest that the interactions between vegetation phenology and drought must be incorporated into Earth system models to accurately quantify ecosystem resilience.
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| 3. |
- Shen, M., et al.
(author)
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Evaporative cooling over the Tibetan plateau induced by vegetation growth
- 2015
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In: Proceedings of the National Academy of Science of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 112:30, s. 9299-9304
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Journal article (peer-reviewed)abstract
- In the Arctic, climate warming enhances vegetation activity by extending the length of the growing season and intensifying maximum rates of productivity. In turn, increased vegetation productivity reduces albedo, which causes a positive feedback on temperature. Over the Tibetan Plateau (TP), regional vegetation greening has also been observed in response to recent warming. Here, we show that in contrast to arctic regions, increased growing season vegetation activity over the TP may have attenuated surface warming. This negative feedback on growing season vegetation temperature is attributed to enhanced evapotranspiration (ET). The extra energy available at the surface, which results from lower albedo, is efficiently dissipated by evaporative cooling. The net effect is a decrease in daily maximum temperature and the diurnal temperature range, which is supported by statistical analyses of in situ observations and by decomposition of the surface energy budget. A daytime cooling effect from increased vegetation activity is also modeled from a set of regional weather research and forecasting (WRF) mesoscale model simulations, but with a magnitude smaller than observed, likely because the WRF model simulates a weaker ET enhancement. Our results suggest that actions to restore native grasslands in degraded areas, roughly one-third of the plateau, will both facilitate a sustainable ecological development in this region and have local climate cobenefits. More accurate simulations of the biophysical coupling between the land surface and the atmosphere are needed to help understand regional climate change over the TP, and possible larger scale feedbacks between climate in the TP and the Asian monsoon system.
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| 4. |
- Shi, C. M., et al.
(author)
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Summer Temperature over the Tibetan Plateau Modulated by Atlantic Multidecadal Variability
- 2019
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In: Journal of Climate. - : American Meteorological Society. - 0894-8755 .- 1520-0442. ; 32:13, s. 4055-4067
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Journal article (peer-reviewed)abstract
- Rapid warming has led to an aggregated environmental degradation over the Tibetan Plateau (TP) in the last few decades, including accelerated glacier retreat, early snowmelt, permafrost degradation, and forest fire occurrence. Attribution of this warming in recent decades has mainly been focused on anthropogenic forcing. Yet, linkages to the Atlantic multidecadal variability (AMV), an essential part of the climate system causing decadal to centennial fluctuations of temperature, remains poorly understood for the TP, especially at long time scales. Using well-replicated tree-ring width records, we reconstructed 358 years of summer minimum temperature (MinT) of the whole TP. This reconstruction matches the recent warming signal recorded since the 1980s, and captures 63% of the variance in 1950-2005 instrumental records. A teleconnection from the North Atlantic to the TP is further identified based in observations and simulations with an atmospheric general circulation model (AGCM). We propose that half of the multidecadal variability of TP summer MinT can be explained by the AMV over the past three and a half centuries. Both observations and AGCM simulations indicate that the AMV warm phase induces a zonal dipole response in sea level pressure across the Atlantic-Eurasia region, with anomalously high surface pressure and corresponding downward atmospheric motion over the TP. We propose that the descending motion during warm AMV phases causes negative rainfall and positive temperature anomalies over the TP. Our findings highlight that the AMV plays a role in the multidecadal temperature variability over the TP.
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| 5. |
- Wu, X. C., et al.
(author)
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Timing and Order of Extreme Drought and Wetness Determine Bioclimatic Sensitivity of Tree Growth
- 2022
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In: Earth's Future. - : American Geophysical Union (AGU). - 2328-4277. ; 10:7
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Journal article (peer-reviewed)abstract
- Tree resistance to extreme droughts and post-drought recovery are sensitive to the drought timing. However, how the bioclimatic sensitivity of tree growth may vary with the timing and order of extreme droughts and wetness is still poorly understood. Here, we quantified the bioclimatic sensitivity of tree growth in the period of 1951-2013 under different seasonal extreme drought/wetness regimes over the extra-tropical Northern Hemisphere, using 1,032 tree ring chronologies from 121 gymnosperm and angiosperm species. We found a negative asymmetry in tree growth under regimes with seasonal extreme droughts. With extreme drought, tree growth in arid and temperate dry regions is more negatively impacted by pre-growing-season (PGS) extreme droughts. Clade-wise, angiosperms are more sensitive to PGS water availability, and gymnosperms to legacy effects of the preceding tree growth conditions in temperate dry and humid regions. Our finding of divergent bioclimatic legacy effects underscores contrasting trends in forest responses to drought across different ecoregions and functional groups in a more extreme climate.
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| 6. |
- Yun, H. B., et al.
(author)
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Warming, permafrost thaw and increased nitrogen availability as drivers for plant composition and growth across the Tibetan Plateau
- 2023
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In: Soil Biology and Biochemistry. - 0038-0717 .- 1879-3428. ; 182
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Journal article (peer-reviewed)abstract
- Permafrost-affected ecosystems are subject to warming and thawing, which can increase the availability of subsurface nitrogen (N) with consequences in otherwise N-limited tundra and alpine vegetation. Here, we quantify the extent of warming and permafrost thawing and the corresponding effects on nitrogen availability and plant growth based on a 20-year survey across 14 sites on the Tibetan Plateau. The survey showed that most sites have been subject to warming and thawing and that the upper permafrost zone across all sites was rich in inorganic N, mainly as ammonium. We further explore the efficiency of plants to utilize 15N-labelled inorganic N over five years following 15N addition at the permafrost table far below the main root zone. The 15N experiment showed that deep-rooted plant species were able to utilize the labelled N. A SEM model suggests that changes in vegetation can be explained by both active layer warming and permafrost thawing and the associated changes in inorganic nitrogen availability. Our results highlight a feedback mechanism of climate warming, in which released plant-available N may favour deep-rooted plants. This can explain important changes in plant composition and growth across the sites on the Tibetan Plateau.
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| 7. |
- Zeng, Z., et al.
(author)
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Deforestation-induced warming over tropical mountain regions regulated by elevation
- 2021
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In: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 14
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Journal article (peer-reviewed)abstract
- Agriculture is expanding in tropical mountainous areas, yet its climatic effect is poorly understood. Here, we investigate how elevation regulates the biophysical climate impacts of deforestation over tropical mountainous areas by integrating satellite-observed forest cover changes into a high-resolution land–atmosphere coupled model. We show that recent forest conversion between 2000 and 2014 increased the regional warming by 0.022 ± 0.002 °C in the Southeast Asian Massif, 0.010 ± 0.007 °C in the Barisan Mountains (Maritime Southeast Asia), 0.042 ± 0.010 °C in the Serra da Espinhaço (South America) and 0.047 ± 0.008 °C in the Albertine Rift mountains (Africa) during the local dry season. The deforestation-driven local temperature anomaly can reach up to 2 °C where forest conversion is extensive. The warming from mountain deforestation depends on elevation, through the intertwined and opposing effects of increased albedo causing cooling and decreased evapotranspiration causing warming. As the elevation increases, the albedo effect increases in importance and the warming effect decreases, analogous to previously highlighted decreases of deforestation-induced warming with increasing latitude. As most new croplands are encroaching lands at low to moderate elevations, deforestation produces higher warming from suppressed evapotranspiration. Impacts of this additional warming on crop yields, land degradation and biodiversity of nearby intact ecosystems should be incorporated into future assessments.
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| 8. |
- Zeng, Z. Z., et al.
(author)
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A reversal in global terrestrial stilling and its implications for wind energy production
- 2019
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In: Nature Climate Change. - : Springer Science and Business Media LLC. - 1758-678X .- 1758-6798. ; 9:12, s. 979-985
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Journal article (peer-reviewed)abstract
- Wind power, a rapidly growing alternative energy source, has been threatened by reductions in global average surface wind speed, which have been occurring over land since the 1980s, a phenomenon known as global terrestrial stilling. Here, we use wind data from in situ stations worldwide to show that the stilling reversed around 2010 and that global wind speeds over land have recovered. We illustrate that decadal-scale variations of near-surface wind are probably determined by internal decadal ocean-atmosphere oscillations, rather than by vegetation growth and/or urbanization as hypothesized previously. The strengthening has increased potential wind energy by 17 +/- 2% for 2010 to 2017, boosting the US wind power capacity factor by similar to 2.5% and explains half the increase in the US wind capacity factor since 2010. In the longer term, the use of ocean-atmosphere oscillations to anticipate future wind speeds could allow optimization of turbines for expected speeds during their productive life spans.
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| 9. |
- Zou, J. Y., et al.
(author)
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Rewetting global wetlands effectively reduces major greenhouse gas emissions
- 2022
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In: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 15:8, s. 627-
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Journal article (peer-reviewed)abstract
- Carbon and nitrogen losses from degraded wetlands and methane emissions from flooded wetlands are both important sources of greenhouse gas emissions. However, the net-exchange dependence on hydrothermal conditions and wetland integrity remains unclear. Using a global-scale in situ database on net greenhouse gas exchanges, we show diverse hydrology-influenced emission patterns in CO2, CH4 and N2O. We find that total CO2-equivalent emissions from wetlands are kept to a minimum when the water table is near the surface. By contrast, greenhouse gas exchange rates peak in flooded and drained conditions. By extrapolating the current trajectory of degradation, we estimate that between 2021 and 2100, wetlands could result in greenhouse gas emissions equivalent to around 408 gigatons of CO2. However, rewetting wetlands could reduce these emissions such that the radiative forcing caused by CH4 and N2O is fully compensated by CO2 uptake. As wetland greenhouse gas budgets are highly sensitive to changes in wetland area, the resulting impact on climate from wetlands will depend on the balance between future degradation and restoration. Global in situ observations show greenhouse gas emissions from wetlands are lowest when the water table is near the surface, and therefore rewetting wetlands could substantially reduce future emissions.
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