| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- Alexander, Peter, et al.
(författare)
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Assessing uncertainties in land cover projections
- 2017
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013. ; 23:2, s. 767-781
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Tidskriftsartikel (refereegranskat)abstract
- Understanding uncertainties in land cover projections is critical to investigating land-based climate mitigation policies, assessing the potential of climate adaptation strategies and quantifying the impacts of land cover change on the climate system. Here, we identify and quantify uncertainties in global and European land cover projections over a diverse range of model types and scenarios, extending the analysis beyond the agro-economic models included in previous comparisons. The results from 75 simulations over 18 models are analysed and show a large range in land cover area projections, with the highest variability occurring in future cropland areas. We demonstrate systematic differences in land cover areas associated with the characteristics of the modelling approach, which is at least as great as the differences attributed to the scenario variations. The results lead us to conclude that a higher degree of uncertainty exists in land use projections than currently included in climate or earth system projections. To account for land use uncertainty, it is recommended to use a diverse set of models and approaches when assessing the potential impacts of land cover change on future climate. Additionally, further work is needed to better understand the assumptions driving land use model results and reveal the causes of uncertainty in more depth, to help reduce model uncertainty and improve the projections of land cover.
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| 5. |
- Arneth, Almut, et al.
(författare)
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Clean the Air, Heat the Planet?
- 2009
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 326:5953, s. 672-673
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Measures to control emissions of air pollutants may have unintended climatic consequences.
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| 6. |
- Arneth, Almut, et al.
(författare)
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Climate-fire interactions and Savanna ecosystems : A dynamic vegetation modeling study for the African Continent
- 2010
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Ingår i: Ecosystem Function in Savannas : Measurement and Modeling at Landscape to Global Scales - Measurement and Modeling at Landscape to Global Scales. - : CRC Press. - 9781439804704 - 9781439804711 ; , s. 463-478
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Bokkapitel (refereegranskat)abstract
- Savannas are inherently “disturbed” ecosystems, but the regularly recurring disruptions play such a fundamental ecological role (Scholes and Archer, 1997) that “episodic events” rather than “disturbance” may the more apt terminology. From an atmospheric perspective, fire is the most significant of these episodic events. Fires shape community species composition; tree to grass ratio and nutrient redistribution; and biosphere-atmosphere exchange of trace gases, aerosols, momentum, and energy. Savannas’ estimated mean NPP of 7.2 ± 2.0 t C ha-1 year-1 amounts to nearly two thirds of tropical forest NPP (Grace et al., 2006); but remarkably little is known about Savanna net carbon balance, especially for the African continent (Williams et al., 2007). In the absence of transient changes in the fire regime, such as could be introduced by climate change or fire-driven changes in land cover, Savanna fires do not affect average annual net carbon uptake much, as the carbon released.
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| 7. |
- Arneth, Almut, et al.
(författare)
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CO2 inhibition of terrestrial isoprene production stabilises tropospheric oxidation capacity
- 2007
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Ingår i: Geophysical Research Letters. - 1944-8007. ; 34, L18813:18
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Tidskriftsartikel (refereegranskat)abstract
- [1] Isoprene is the dominant volatile organic compound produced by the terrestrial biosphere and fundamental for atmospheric composition and climate. It constrains the concentration of tropospheric oxidants, affecting the lifetime of other reduced species such as methane and contributing to ozone production. Oxidation products of isoprene contribute to aerosol growth. Recent consensus holds that emissions were low during glacial periods ( helping to explain low methane concentrations), while high emissions ( contributing to high ozone concentrations) can be expected in a greenhouse world, due to positive relationships with temperature and terrestrial productivity. However, this response is offset when the recently demonstrated inhibition of leaf isoprene emissions by increasing atmospheric CO2 concentration is accounted for in a process-based model. Thus, isoprene may play a small role in determining pre-industrial tropospheric OH concentration and glacial-interglacial methane trends, while predictions of high future tropospheric O-3 concentrations partly driven by isoprene emissions may need to be revised.
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| 8. |
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| 9. |
- Arneth, Almut, et al.
(författare)
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From biota to chemistry and climate: towards a comprehensive description of trace gas exchange between the biosphere and atmosphere
- 2010
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Ingår i: Biogeosciences. - 1726-4189. ; 7:1, s. 121-149
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Forskningsöversikt (refereegranskat)abstract
- Exchange of non-CO2 trace gases between the land surface and the atmosphere plays an important role in atmospheric chemistry and climate. Recent studies have highlighted its importance for interpretation of glacial-interglacial ice-core records, the simulation of the pre-industrial and present atmosphere, and the potential for large climate-chemistry and climate-aerosol feedbacks in the coming century. However, spatial and temporal variations in trace gas emissions and the magnitude of future feedbacks are a major source of uncertainty in atmospheric chemistry, air quality and climate science. To reduce such uncertainties Dynamic Global Vegetation Models (DGVMs) are currently being expanded to mechanistically represent processes relevant to non-CO2 trace gas exchange between land biota and the atmosphere. In this paper we present a review of important non-CO2 trace gas emissions, the state-of-the-art in DGVM modelling of processes regulating these emissions, identify key uncertainties for global scale model applications, and discuss a methodology for model integration and evaluation.
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| 10. |
- Arneth, Almut, et al.
(författare)
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Future vegetation-climate interactions in Eastern Siberia: an assessment of the competing effects of CO2 and Secondary Organic Aerosols
- 2016
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7324. ; 16:8, s. 5243-5262
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Tidskriftsartikel (refereegranskat)abstract
- Abstract. Disproportional warming in the northern high latitudes and large carbon stocks in boreal and (sub)arctic ecosystems have raised concerns as to whether substantial positive climate feedbacks from biogeochemical process responses should be expected. Such feedbacks occur when increasing temperatures lead, for example, to a net release of CO2 or CH4. However, temperature-enhanced emissions of biogenic volatile organic compounds (BVOCs) have been shown to contribute to the growth of secondary organic aerosol (SOA), which is known to have a negative radiative climate effect. Combining measurements in Eastern Siberia with model-based estimates of vegetation and permafrost dynamics, BVOC emissions, and aerosol growth, we assess here possible future changes in ecosystem CO2 balance and BVOC–SOA interactions and discuss these changes in terms of possible climate effects. Globally, the effects of changes in Siberian ecosystem CO2 balance and SOA formation are small, but when concentrating on Siberia and the Northern Hemisphere the negative forcing from changed aerosol direct and indirect effects become notable – even though the associated temperature response would not necessarily follow a similar spatial pattern. While our analysis does not include other important processes that are of relevance for the climate system, the CO2 and BVOC–SOA interplay serves as an example for the complexity of the interactions between emissions and vegetation dynamics that underlie individual terrestrial processes and highlights the importance of addressing ecosystem–climate feedbacks in consistent, process-based model frameworks.
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