| 1. |
- Metcalfe, Daniel B., et al.
(författare)
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Patchy field sampling biases understanding of climate change impacts across the Arctic
- 2018
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Ingår i: Nature Ecology and Evolution. - : Springer Science and Business Media LLC. - 2397-334X. ; 2:9, s. 1443-1448
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Tidskriftsartikel (refereegranskat)abstract
- Effective societal responses to rapid climate change in the Arctic rely on an accurate representation of region-specific ecosystem properties and processes. However, this is limited by the scarcity and patchy distribution of field measurements. Here, we use a comprehensive, geo-referenced database of primary field measurements in 1,840 published studies across the Arctic to identify statistically significant spatial biases in field sampling and study citation across this globally important region. We find that 31% of all study citations are derived from sites located within 50 km of just two research sites: Toolik Lake in the USA and Abisko in Sweden. Furthermore, relatively colder, more rapidly warming and sparsely vegetated sites are under-sampled and under-recognized in terms of citations, particularly among microbiology-related studies. The poorly sampled and cited areas, mainly in the Canadian high-Arctic archipelago and the Arctic coastline of Russia, constitute a large fraction of the Arctic ice-free land area. Our results suggest that the current pattern of sampling and citation may bias the scientific consensuses that underpin attempts to accurately predict and effectively mitigate climate change in the region. Further work is required to increase both the quality and quantity of sampling, and incorporate existing literature from poorly cited areas to generate a more representative picture of Arctic climate change and its environmental impacts.
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| 2. |
- Ahlström, Anders, et al.
(författare)
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GCM characteristics explain the majority of uncertainty in projected 21st century terrestrial ecosystem carbon balance
- 2012
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Ingår i: Biogeosciences Discussions. - : Copernicus GmbH. - 1810-6277. ; 9, s. 13685-13712
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- One of the largest sources of uncertainties in modelling of the future global climate is the response of the terrestrial carbon cycle. Studies have shown that it is likely that the extant land sink of carbon will weaken in a warming climate. Should this happen, a larger portion of the annual carbon dioxide emissions will remain in the atmosphere, and further increase global warming, which in turn may further weaken the land sink. We investigate the potential sensitivity of global terrestrial ecosystem carbon balance to differences in future climate simulated by four general circulation models (GCMs) under three different CO2 concentration scenarios. We find that the response in simulated carbon balance is more influenced by GCMs than CO2 concentration scenarios. Empirical orthogonal function (EOF) analysis of sea surface temperatures (SSTs) reveals differences among GCMs in simulated SST variability leading to decreased tropical ecosystem productivity in two out of four GCMs. We extract parameters describing GCM characteristics by parameterizing a statistical emulator mimicking the carbon balance response simulated by a full dynamic ecosystem model. By sampling two GCM-specific parameters and global temperatures we create 60 new "artificial" GCMs and investigate the extent to which the GCM characteristics may explain the uncertainty in global carbon balance under future radiative forcing. Differences among GCMs in the representation of SST variability and ENSO and its effect on precipitation and temperature patterns explain the majority of the uncertainty in the future evolution of global terrestrial ecosystem carbon in our analysis. We suggest that the characterisation and evaluation of patterns and trends in simulated SST variability should be a priority for the further development of GCMs, in particular as vegetation dynamics and carbon cycle feedbacks are incorporated.
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| 3. |
- Ahlström, Anders, et al.
(författare)
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GCM characteristics explain the majority of uncertainty in projected 21st century terrestrial ecosystem carbon balance
- 2013
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4189. ; 10:3, s. 1517-1528
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Tidskriftsartikel (refereegranskat)abstract
- One of the largest sources of uncertainties in modelling of the future global climate is the response of the terrestrial carbon cycle. Studies have shown that it is likely that the extant land sink of carbon will weaken in a warming climate. Should this happen, a larger portion of the annual carbon dioxide emissions will remain in the atmosphere, and further increase global warming, which in turn may further weaken the land sink. We investigate the potential sensitivity of global terrestrial ecosystem carbon balance to differences in future climate simulated by four general circulation models (GCMs) under three different CO2 concentration scenarios. We find that the response in simulated carbon balance is more influenced by GCMs than CO2 concentration scenarios. Empirical orthogonal function (EOF) analysis of sea surface temperatures (SSTs) reveals differences among GCMs in simulated SST variability leading to decreased tropical ecosystem productivity in two out of four GCMs. We extract parameters describing GCM characteristics by parameterizing a statistical emulator mimicking the carbon balance response simulated by a full dynamic ecosystem model. By sampling two GCM-specific parameters and global temperatures we create 60 new "artificial" GCMs and investigate the extent to which the GCM characteristics may explain the uncertainty in global carbon balance under future radiative forcing. Differences among GCMs in the representation of SST variability and ENSO and its effect on precipitation and temperature patterns explain the majority of the uncertainty in the future evolution of global terrestrial ecosystem carbon in our analysis. We suggest that the characterisation and evaluation of patterns and trends in simulated SST variability should be a priority for the further development of GCMs, in particular as vegetation dynamics and carbon cycle feedbacks are incorporated.
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| 4. |
- Harden, Jennifer W., et al.
(författare)
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Networking our science to characterize the state, vulnerabilities, and management opportunities of soil organic matter
- 2018
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 24:2, s. e705-e718
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Tidskriftsartikel (refereegranskat)abstract
- Soil organic matter (SOM) supports the Earth's ability to sustain terrestrial ecosystems, provide food and fiber, and retains the largest pool of actively cycling carbon. Over 75% of the soil organic carbon (SOC) in the top meter of soil is directly affected by human land use. Large land areas have lost SOC as a result of land use practices, yet there are compensatory opportunities to enhance productivity and SOC storage in degraded lands through improved management practices. Large areas with and without intentional management are also being subjected to rapid changes in climate, making many SOC stocks vulnerable to losses by decomposition or disturbance. In order to quantify potential SOC losses or sequestration at field, regional, and global scales, measurements for detecting changes in SOC are needed. Such measurements and soil-management best practices should be based on well established and emerging scientific understanding of processes of C stabilization and destabilization over various timescales, soil types, and spatial scales. As newly engaged members of the International Soil Carbon Network, we have identified gaps in data, modeling, and communication that underscore the need for an open, shared network to frame and guide the study of SOM and SOC and their management for sustained production and climate regulation.
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| 5. |
- Pellegrini, Adam F.A., et al.
(författare)
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Soil carbon storage capacity of drylands under altered fire regimes
- 2023
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Ingår i: Nature Climate Change. - 1758-678X. ; 13:10, s. 1089-1094
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Tidskriftsartikel (refereegranskat)abstract
- The determinants of fire-driven changes in soil organic carbon (SOC) across broad environmental gradients remains unclear, especially in global drylands. Here we combined datasets and field sampling of fire-manipulation experiments to evaluate where and why fire changes SOC and compared our statistical model to simulations from ecosystem models. Drier ecosystems experienced larger relative changes in SOC than humid ecosystems—in some cases exceeding losses from plant biomass pools—primarily explained by high fire-driven declines in tree biomass inputs in dry ecosystems. Many ecosystem models underestimated the SOC changes in drier ecosystems. Upscaling our statistical model predicted that soils in savannah–grassland regions may have gained 0.64 PgC due to net-declines in burned area over the past approximately two decades. Consequently, ongoing declines in fire frequencies have probably created an extensive carbon sink in the soils of global drylands that may have been underestimated by ecosystem models.
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| 6. |
- Ahlström, Anders, et al.
(författare)
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Importance of vegetation dynamics for future terrestrial carbon cycling
- 2015
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 10:5
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Tidskriftsartikel (refereegranskat)abstract
- Terrestrial ecosystems currently sequester about one third of anthropogenic CO 2 emissions each year, an important ecosystem service that dampens climate change. The future fate of this net uptake of CO 2 by land based ecosystems is highly uncertain. Most ecosystem models used to predict the future terrestrial carbon cycle share a common architecture, whereby carbon that enters the system as net primary production (NPP) is distributed to plant compartments, transferred to litter and soil through vegetation turnover and then re-emitted to the atmosphere in conjunction with soil decomposition. However, while all models represent the processes of NPP and soil decomposition, they vary greatly in their representations of vegetation turnover and the associated processes governing mortality, disturbance and biome shifts. Here we used a detailed second generation dynamic global vegetation model with advanced representation of vegetation growth and mortality, and the associated turnover. We apply an emulator that describes the carbon flows and pools exactly as in simulations with the full model. The emulator simulates ecosystem dynamics in response to 13 different climate or Earth system model simulations from the Coupled Model Intercomparison Project Phase 5 ensemble under RCP8.5 radiative forcing. By exchanging carbon cycle processes between these 13 simulations we quantified the relative roles of three main driving processes of the carbon cycle; (I) NPP, (II) vegetation dynamics and turnover and (III) soil decomposition, in terms of their contribution to future carbon (C) uptake uncertainties among the ensemble of climate change scenarios. We found that NPP, vegetation turnover (including structural shifts, wild fires and mortality) and soil decomposition rates explained 49%, 17% and 33%, respectively, of uncertainties in modelled global C-uptake. Uncertainty due to vegetation turnover was further partitioned into stand-clearing disturbances (16%), wild fires (0%), stand dynamics (7%), reproduction (10%) and biome shifts (67%) globally. We conclude that while NPP and soil decomposition rates jointly account for 83% of future climate induced C-uptake uncertainties, vegetation turnover and structure, dominated by biome shifts, represent a significant fraction globally and regionally (tropical forests: 40%), strongly motivating their representation and analysis in future C-cycle studies.
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| 7. |
- Ahlström, Anders, et al.
(författare)
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Improved accessibility modeling and its relation to poverty - A case study in Southern Sri Lanka
- 2011
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Ingår i: Habitat International. - : Elsevier BV. - 0197-3975. ; 35:2, s. 316-326
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Tidskriftsartikel (refereegranskat)abstract
- Many studies have found close relationships between accessibility and various socio-economic indicators. Yet, since accessibility tends to have differentiated effects, both socially and spatially, there is a need for a model which allows for a disaggregated analysis of accessibility. The model should be possible to use in areas where road network data is incomplete. In this paper such an accessibility model is developed, using a raster-based approach in a Geographical Information System (GIS). One important factor in accessibility modeling is to estimate the traveling speed on different landscape entities. This paper develops a method where local knowledge and physical geographical data are integrated in the GIS model. From the interview data the best door-to-door traveling speeds of three road classes were estimated. The results from these calculations have been used as frictions for a cost surface. The analysis shows strong relationships between poverty indicators and estimated spatial accessibility, stronger than the commonly used accessibility measure of Euclidian distance. (C) 2010 Elsevier Ltd. All rights reserved.
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| 8. |
- Ahlström, Anders, et al.
(författare)
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Robustness and uncertainty in terrestrial ecosystem carbon response to CMIP5 climate change projections
- 2012
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 7:4
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the spatio-temporal carbon balance patterns resulting from forcing a dynamic global vegetation model with output from 18 climate models of the CMIP5 (Coupled Model Intercomparison Project Phase 5) ensemble. We found robust patterns in terms of an extra-tropical loss of carbon, except for a temperature induced shift in phenology, leading to an increased spring uptake of carbon. There are less robust patterns in the tropics, a result of disagreement in projections of precipitation and temperature. Although the simulations generally agree well in terms of the sign of the carbon balance change in the middle to high latitudes, there are large differences in the magnitude of the loss between simulations. Together with tropical uncertainties these discrepancies accumulate over time, resulting in large differences in total carbon uptake over the coming century (−0.97–2.27 Pg C yr −1 during 2006–2100). The terrestrial biosphere becomes a net source of carbon in ten of the 18 simulations adding to the atmospheric CO 2 concentrations, while the remaining eight simulations indicate an increased sink of carbon.
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| 9. |
- Ahlström, Anders
(författare)
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Terrestrial Ecosystem Interactions with Global Climate and Socio-Economics
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The global terrestrial carbon cycle plays a pivotal role in regulating the atmospheric composition of greenhouse gases. Currently it is responsible for removing 25-30% of our emissions every year, an important ecosystem service that may not persist in the long term. Global warming tends to decrease the CO2 sink capacity of the world’s oceans and ecosystems leading to a larger fraction of our emissions remaining in the atmosphere contributing to further warming, which in turn further decreases the sink capacity. Here past, present and future variations and drivers of terrestrial ecosystem fluxes are analysed and projected. Uncertainties and robustness as well as their origin are assessed. It is shown that short term variations such as droughts significantly influence global fluxes even though occurring in limited regions. Additionally, seasonal changes may alter the present balance between uptake and release of carbon by stimulating the process of release of carbon through respiration dominating in the winter more than the photosynthesis and net uptake of carbon in the growing season. These variations may be more important for the carbon cycle than long term trends. Ecosystem models represents powerful tools to further our understanding of the functioning of terrestrial ecosystems as well as allowing for projections of the potential future evolution of the carbon cycle. It is demonstrated that ecosystem models generally capture the main global spatial and temporal distributions of carbon fluxes. However, future projections are accompanied by large uncertainties, a result of a combination of uncertainties in climate predictions by climate models and uncertainties in the response of ecosystems to changes in the drivers. It is shown that uncertainties arising from differences in climate projections in terms of seasonal changes and short term variability dominate uncertainties arising from different scenarios of future atmospheric CO2 concentrations. Additionally, representation of sea surface temperature variations and especially variations associated with El Niño-Southern Oscillation in climate models stands out as particularly important for accurate predictions of future carbon fluxes. Human activity contributes with a significant perturbation of the carbon-cycle and the climate system. Climate-economy models have the potential to supply direct policy-relevant estimates for climate mitigation. Here it is demonstrated that correct representation of the climate system and the carbon cycle in climate-economy models is important for making accurate estimates of future economy.
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| 10. |
- Ahlström, Anders, et al.
(författare)
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The dominant role of semi-arid ecosystems in the trend and variability of the land CO2 sink
- 2015
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 348:6237, s. 895-899
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Tidskriftsartikel (refereegranskat)abstract
- The growth rate of atmospheric carbon dioxide (CO2) concentrations since industrialization is characterized by large interannual variability, mostly resulting from variability in CO2 uptake by terrestrial ecosystems (typically termed carbon sink). However, the contributions of regional ecosystems to that variability are not well known. Using an ensemble of ecosystem and land-surface models and an empirical observation-based product of global gross primary production, we show that the mean sink, trend, and interannual variability in CO2 uptake by terrestrial ecosystems are dominated by distinct biogeographic regions. Whereas the mean sink is dominated by highly productive lands (mainly tropical forests), the trend and interannual variability of the sink are dominated by semi-arid ecosystems whose carbon balance is strongly associated with circulation-driven variations in both precipitation and temperature.
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