| 1. |
- Claesson, Jonas, et al.
(författare)
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Combined effect of global warming and increased CO2-concentration on vegetation growth in water-limited conditions
- 2013
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Ingår i: Ecological Modelling. - : Elsevier BV. - 0304-3800 .- 1872-7026. ; 256, s. 23-30
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Tidskriftsartikel (refereegranskat)abstract
- The most severe impact of climate change on vegetation growth and agriculture is likely to occur under water-limited conditions. Under such conditions the plants optimize the inward flux of CO2 and the outward flux of water vapor (the transpiration) by regulating the size of the stomatal openings. Higher temperature increases water loss through transpiration, forcing the plants to diminish the stomatal openings, which decreases photosynthesis. This is counteracted by higher CO2 concentration, which allows plants to maintain the inward flux of CO2 through the smaller openings. These two counteracting effects, combined with the change in precipitation, determine the net change of biological productivity. Here, a vegetation sensitivity approximation (VSA) is introduced, in order to understand and estimate the combined effect of changed temperature, CO2 and precipitation to first order. The VSA is based on the physical laws of gas flux through the stomatal openings, and is only valid under water-limited conditions. It assumes that the temperature depends logarithmically on the CO2 concentration with a given climate sensitivity. Precipitation is included by assuming that it is proportional to the transpiration. This is reasonable underwater-limited conditions, when transpiration is often a large fraction of the precipitation. The VSA is compared to simulations with the dynamic vegetation model LPJ. The agreement is reasonable, and the deviations can be understood by comparison with Koppen's definition of arid climate: in an arid climate growth increases more according to LPJ than according to the VSA, and in non-arid conditions the reverse is true. Both the VSA and the LPJ simulations generally show increased growth with increasing CO2 levels and the resulting temperature increase, assuming precipitation to be unchanged. Thus, in this case the negative temperature effect is more than compensated by the positive effect of CO2.
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| 2. |
- Hassler, John, et al.
(författare)
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SNS Economic Policy Council Report 2020 : Swedish Policy for Global Climate
- 2020
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Climate policy is a complex area that requires input from many different perspectives. The sns Economic Policy Council 2020 comprises nine researchers from a range of disciplines, with different backgrounds and with varied opinions on the debate surrounding climate policy. They analyse Swedish climate policy in a global context, describing the causes and consequences of climate change and focusing on how policy can achieve the desired reductions in carbon emissions. The report also provides answers to questions that are frequently discussed in the Swedish debate, such as the effectiveness of climate aid and whether Sweden should generate a larger surplus of fossil-free electricity for export.
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| 3. |
- Hassler, John, et al.
(författare)
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Svensk politik för globalt klimat
- 2020
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- Nio forskare från olika discipliner ingår i SNS Konjunkturråd 2020. Forskarna har bred bakgrund inom nationalekonomi, juridik, naturvetenskap och ingenjörsvetenskap. Tillsammans har de skrivit SNS Konjunkturrådsrapport 2020: Svensk politik för globalt klimat, där de fokuserar på hur politiken ska utformas för att bromsa och till slut stoppa klimatförändringarna. Några av deras viktigaste förslag och rekommendationer: Låt kolet stanna i marken. Det är kolet, inte konventionell olja, som är det centrala hotet mot klimatet. Om klimatförändringarna ska hejdas måste Kina bli av med sitt kolberoende. Indien och Afrika kan inte heller följa Kinas kolkraftsbaserade utvecklingsstrategi. Merparten av världens kolreserver måste stanna i marken.Inför globalt minimipris på koldioxidutsläpp och slopa fossilsubventioner. Det är två nödvändiga ingredienser i klimatpolitiken som måste diskuteras på FN:s nästa stora klimatkonferens COP26 i Glasgow.Gröna subventioner räcker inte för att minska utsläppen. Billig grön energi leder till ökad användning av sådan men inte automatiskt till att fossila bränslen utkonkurreras.Bidra till rätt global inriktning. Den svenska klimatpolitiken bör ha som överordnat mål att minska de globala utsläppen.Bidra finansiellt till andra länders omställning. Klokt och välavvägt klimatbistånd är både möjligt och önskvärt. Inom ramen för EU:s klimatpolitik finns fungerande sätt att finansera mindre rika medlemsländers utsläppsminskningar. Men eftersom även Sverige måste bli klimatneutralt bör ett ökat klimatbistånd inte minska de svenska klimatambitionerna.Klimatklubbar. Sverige bör driva frågan om att det ska vara tillåtet att införa klimattullar mot länder som inte har en acceptabel nivå på utsläppspriset. En modell är så kallade klimatklubbar där länder går ihop och sätter ett enhetligt utsläppspris. Import från länder som inte deltar i klubben beläggs med en tull.Fossilfri elexport kan ge betydande minskningar av utsläppen inom EU genom att pressa undan kolkraft där sådan fortfarande används.Finansiera insamling och lagring av koldioxid (CCS-teknik) med lagringspeng. Vi kan ta hand om koldioxid motsvarande hälften av Sveriges utsläpp till en kostnad motsvarande det som dras in till staten via koldioxidskatten. Det krävs dock en statlig finansiering som bör utformas som ett bidrag per ton insamlad och säkert lagrad koldioxid:– Motsvarande runt hälften av Sveriges koldioxidutsläpp kan tas bort om CCS-tekniken införs på de 27 industrianläggningar som släpper ut mest i Sverige. Detta är mer än utsläppen från hela den svenska vägtrafiken. Tekniken fungerar också i resten av världen och Sverige kan här bli ett föregångsland, säger John Hassler, ordförande i SNS Konjunkturråd 2020.
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| 4. |
- Aldama Campino, Aitor, et al.
(författare)
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Meridional Ocean Carbon Transport
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The ocean's ability to take up and store CO$_{2}$ is a key factor for understanding past and future climate variability. However, qualitative and quantitative understanding of surface-to-interior pathways, and how the ocean circulation affects the CO$_2$ uptake, is limited. Consequently, how changes in ocean circulation may influence carbon uptake and storage and therefore the future climate remains ambiguous.Here we quantify the roles played by ocean circulation and various water masses in the meridional redistribution of carbon.We do so by calculating stream functions defined in Dissolved Inorganic Carbon (DIC) and latitude coordinates, using output from a coupled biogeochemical-physical model. By further separating DIC into components originating from the solubility pump and a residual including the biological pump, air-sea disequilibrium and anthropogenic CO$_2$, we are able to distinguish the dominant pathways of how carbon enters particular water masses.With this new tool, we show that the largest meridional carbon transport occurs in a pole-to-equator transport in the subtropical gyres in the upper ocean. We are able to show that this pole-to-equator DIC transport, and the Atlantic Meridional Overturning Circulation (AMOC) related DIC transport, are mainly driven by the solubility pump. By contrast, the DIC transport associated with deep circulation, including that in Antarctic Bottom Water and Pacific Deep Water, is mostly driven by the biological pump. As these two pumps, as well as ocean circulation, are widely expected to be impacted by anthropogenic changes, these findings have implications for the future role of the ocean as a climate-buffering carbon reservoir.
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| 5. |
- Aldama-Campino, Aitor, et al.
(författare)
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Meridional Ocean Carbon Transport
- 2020
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Ingår i: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 34:9
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Tidskriftsartikel (refereegranskat)abstract
- The ocean's ability to take up and store CO2 is a key factor for understanding past and future climate variability. However, qualitative and quantitative understanding of surface‐to‐interior pathways, and how the ocean circulation affects the CO2 uptake, is limited. Consequently, how changes in ocean circulation may influence carbon uptake and storage and therefore the future climate remains ambiguous. Here we quantify the roles played by ocean circulation and various water masses in the meridional redistribution of carbon. We do so by calculating streamfunctions defined in dissolved inorganic carbon (DIC) and latitude coordinates, using output from a coupled biogeochemical‐physical model. By further separating DIC into components originating from the solubility pump and a residual including the biological pump, air‐sea disequilibrium, and anthropogenic CO2, we are able to distinguish the dominant pathways of how carbon enters particular water masses. With this new tool, we show that the largest meridional carbon transport occurs in a pole‐to‐equator transport in the subtropical gyres in the upper ocean. We are able to show that this pole‐to‐equator DIC transport and the Atlantic meridional overturning circulation (AMOC)‐related DIC transport are mainly driven by the solubility pump. By contrast, the DIC transport associated with deep circulation, including that in Antarctic bottom water and Pacific deep water, is mostly driven by the biological pump. As these two pumps, as well as ocean circulation, are widely expected to be impacted by anthropogenic changes, these findings have implications for the future role of the ocean as a climate‐buffering carbon reservoir.
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| 6. |
- Bahrami, Fariba, et al.
(författare)
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Existence of energy maximizing vortices in a three-dimensionalquasigeostrophic shear flow with bounded height
- 2010
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Ingår i: Nonlinear Analysis. - : Elsevier. - 1468-1218. ; 11:3, s. 1589-1599
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Tidskriftsartikel (refereegranskat)abstract
- The existence of an energy maximizer relative to a class of rearrangements of agiven function is proved. The maximizers are stationary and stable solutions of thequasigeostrophic equation, which governs the time evolution of large-scale threedimensionalgeophysical flow in a vertically bounded domain. The background flow isunidirectional, with linear horizontal shear. The theorem proved implies the existence of afamily of stationary and stable vortices that rotate in the same direction as the backgroundshear. It extends an earlier theorem by Burton and Nycander, which is valid for a verticallyunbounded domain.
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| 7. |
- Bahrami, Fariba, et al.
(författare)
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Existence of energy minimizing vortices attached to a flat-top seamount
- 2007
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Ingår i: Nonlinear Analysis. - : Elsevier BV. - 1468-1218. ; 8, s. 288-294
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Tidskriftsartikel (refereegranskat)abstract
- The existence of an energy minimizer relative to a class ofrearrangements of a given function is proved. The minimizers are stationary and stable solutions of the two-dimensional barotropic vorticity equation, governing the evolution of geophysical flow over a surface of variable height. The theorem proved implies the existence of a family of stable anticyclonic vortices with cyclonic potential vorticity over a seamount, and a corresponding family of cyclonic vortices with anticyclonic potential vorticity over a localized depression. The seamount is described by a characteristic function (corresponding to a flat top) with arbitrary shape.
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| 8. |
- Bahrami, Fariba, et al.
(författare)
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Stability investigation for steady solutions of the barotropic vorticity equation in R-2
- 2013
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Ingår i: Communications in nonlinear science & numerical simulation. - : Elsevier BV. - 1007-5704 .- 1878-7274. ; 18:3, s. 541-546
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we investigate the p-norm stability for vortices of geophysical flows over a surface of variable height that are strict maximizers of the kinetic energy relative to all isovortical flows. In this note, stability means nonlinear stability in the p-norm on the space of vorticity.
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| 9. |
- Ballarotta, Maxime, 1984-, et al.
(författare)
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The vigorous large-scale ocean circulations during the Last Glacial Maximum
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The representation of the ocean thermohaline circulation (THC) under glacial and interglacial climate conditions is investigated using a new global thermohaline stream function. Consequently, the interglacial and glacial THCs are compared from two experiments based on an ocean general circulation model forced at the surface by conditions representing the present-day and the period of the Last Glacial Maximum (LGM, ≈ 21kyr ago). It is shown that the LGM THC is amplified by the salinity/density contrast between the Atlantic and the Pacific basins, as well as in the abyss due to larger salinity gradients. Even though the circuit along the Conveyor Belt loop is not drastically changed, the water mass transformations can regionally differ between the two periods. Additionally, the LGM Conveyor Belt Cell is more isolated from the abyss and its turnover time is between two and three times shorter than in the present-day simulation, suggesting vigorous large-scale circulation.
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| 10. |
- Berglund, Sara, et al.
(författare)
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Lagrangian tracing of the water-mass transformations in the Atlantic Ocean
- 2017
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Ingår i: Tellus. Series A, Dynamic meteorology and oceanography. - : Stockholm University Press. - 0280-6495 .- 1600-0870. ; 69
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Tidskriftsartikel (refereegranskat)abstract
- The thermohaline stream function has previously been used to describe the ocean circulation in temperature and salinity space. In the present study, the Lagrangian thermohaline stream function is introduced and computed for northward flowing water masses in the Atlantic Ocean, using Lagrangian trajectories. The stream function shows the water-mass transformations in the Atlantic Ocean, where warm and saline water is converted to cold and fresh as it flows from 17 degrees S to 58 degrees N. By analysing the Lagrangian divergence of heat and salt flux, the conversion of temperature is found to take place in the Gulf Stream, the upper flank of the North Atlantic subtropical gyre and in the North Atlantic Drift, whereas the conversion of salinity rather occurs over a narrower band in the same regions. Thus, conversions of temperature and salinity as shown by the Lagrangian thermohaline stream function are confined to the same regions in the domain. The study of a specific, representative trajectory shows that, in the absence of air-sea interactions, a mixing process leads to the conversion of temperature and salinity from warm and saline to cold and fresh, and that this process is confined to the North Atlantic subtropical gyre. However, to define and to understand this process, further investigation is needed.
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