| 1. |
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| 2. |
- Bender, Frida A-M, 1978-
(författare)
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Earth's albedo in a changing climate
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The albedo is a key parameter in the radiative budget of the Earth and a primary determinant of the planetary temperature and is therefore also central to questions regarding climate stability, climate change and climate sensitivity. Climate models and satellite observations are essential for studying the albedo, and the parameters determining it, on large spatial and temporal scales. Although climate models are able to capture the large-scale characteristics of the albedo, a bias is found between modelled and observed global albedo estimates, and on a regional scale particular problematic regions can be identified. Cloud parameters, that are of great importance for determining the albedo, vary widely among models, but lack of observations makes constraining models, and even evaluating models, difficult. The freedom of variability for cloud parameters can be used to make models agree with observations of the better constrained radiative budget. It is shown that tuning a model to different radiative budget estimates by altering cloud parameters can influence the climate sensitivity of the model, but the effect seen is small, compared to the range of climate sensitivities estimated by different models. Despite their different parameterizations of clouds, aerosols etc., models do have fundamental features in common, which can further the understanding of the real climate system. For instance it is found that sensitivity to volcanic forcing is related to climate sensitivity in an ensemble of models. If this relation is valid for the real climate as well, observations of the volcanic sensitivity can help restrict the climate sensitivity. The range of climate sensitivity estimates in models can largely be attributed to variations in cloud response to forcing. It is found that in models with high climate sensitivity changes in cloud cover and cloud reflectivity enhance a positive radiative forcing due to increased CO2 concentrations, feeding back on the warming and in models with low climate sensitivity, cloud response counteracts the positive radiative forcing and warming induced by the same forcing. As a consequence the total albedo response to increased CO2 forcing is found to be stronger (more negative) in high sensitivity models and vice versa. Cloud albedo and its variation between different cloud regimes, is important in this regard, yet not well known. A method based on the relation between cloud fraction and albedo is presented, giving a way to estimate regional cloud albedo, primarily for homogeneous cloud regimes, but possibly also extended to a global scale.
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| 3. |
- Bender, Frida, et al.
(författare)
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Al Gore är inte forskare
- 2008
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Ingår i: Svenska Dagbladet. ; :2008-10-25
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 4. |
- Bender, Frida, et al.
(författare)
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Response to the eruption of Mount Pinatubo in relation to climate sensitivity in the CMIP3 models
- 2010
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Ingår i: Climate Dynamics. - : Springer. - 0930-7575 .- 1432-0894. ; 35:5, s. 875-886
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Tidskriftsartikel (refereegranskat)abstract
- The radiative flux perturbations and subsequent temperature responses in relation to the eruption of Mount Pinatubo in 1991 are studied in the ten general circulation models incorporated in the Coupled Model Intercomparison Project, phase 3 (CMIP3), that include a parameterization of volcanic aerosol. Models and observations show decreases in global mean temperature of up to 0.5 K, in response to radiative perturbations of up to 10 W m−2, averaged over the tropics. The time scale representing the delay between radiative perturbation and temperature response is determined by the slow ocean response, and is estimated to be centered around 4 months in the models. Although the magniude of the temperature response to a volcanic eruption has previously been used as an indicator of equilibrium climate sensitivity in models, we find these two quantities to be only weakly correlated. This may partly be due to the fact that the size of the volcano-induced radiative perturbation varies among the models. It is found that the magnitude of the modelled radiative perturbation increases with decreasing climate sensitivity, with the exception of one outlying model. Therefore, we scale the temperature perturbation by the radiative perturbation in each model, and use the ratio between the integrated temperature perturbation and the integrated radiative perturbation as a measure of sensitivity to volcanic forcing. This ratio is found to be well correlated with the model climate sensitivity, more sensitive models having a larger ratio. Further, if this correspondence between “volcanic sensitivity” and sensitivity to CO2 forcing is a feature not only among the models, but also of the real climate system, the alleged linear relation can be used to estimate the real climate sensitivity. The observational value of the ratio signifying volcanic sensitivity is hereby estimated to correspond to an equilibrium climate sensitivity, i.e. equilibrium temperature increase due to a doubling of the CO2 concentration, between 1.7 and 4.1 K. Several sources of uncertainty reside in the method applied, and it is pointed out that additional model output, related to ocean heat storage and radiative forcing, could refine the analysis, as could reduced uncertainty in the observational record, of temperature as well as forcing.
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| 5. |
- Bender, Frida, et al.
(författare)
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Vem ska man tro på om klimatet?
- 2008
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Ingår i: Svenska Dagbladet. ; :2008-10-17
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 6. |
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| 7. |
- Björck, S, et al.
(författare)
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Uttalande från klimatgruppen inom akademiens klass för geovetenskaper angående Climate Change 2007: The Physical Science Basis
- 2007
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Annan publikation (populärvet., debatt m.m.)abstract
- Björck S., Backman J., Bengtsson S., Destouni G., Rodhe H., Uttalande från klimatgruppen inom akademiens klass för geovetenskaper angående Climate Change 2007: The Physical Science Basis (Statement on Climate Change 2007: The Physical Science Basis; in Swedish), Climate Group of the Class of Geosciences at the Royal Swedish Academy of Sciences, 5 June, 2007.
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| 8. |
- Budhavant, K. B., et al.
(författare)
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Black carbon in cloud-water and rain water during monsoon season at a high altitude station in India
- 2016
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 129, s. 256-264
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Tidskriftsartikel (refereegranskat)abstract
- We present results of measurements of black carbon (BC) from ground-based wet-only rainwater (RW) and cloud-water (CW) sampling at a mountain field station, Sinhagad, situated in south western India during the period from June 2008 to October 2010. The amount of BC in the sample was determined by photometry at a wavelength of 528 nm after a procedure including the filtration through a 0.4 mu m polycarbonate membrane filter. Water soluble concentrations of major anions in RW and CW were also determined. The average concentration of BC in RW (16 mu mol dm(-3)) is higher by at least a factor 2 than that found in similar studies reported from other parts of the world. On the other hand, the average concentration of BC in CW (47 mu mol dm(-3)) is lower by about a factor of 2 than that found at other sites. The ratio between the average concentrations in CW and RW varies from 2 (K+) to 7 (SO42-). The ratio for BC was about 3. No significant difference was observed for pH. Analysis of air mass back trajectories and of correlations between the various components indicates that long range transport of pollutants and dust from East Africa and Southern part of the Arabian peninsula might contribute to the high concentrations of BC and some of the ionic constituents at Sinhagad during the monsoon season.
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| 9. |
- Budhavant, K. B., et al.
(författare)
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Chemical composition of the inorganic fraction of cloud-water at a high altitude site in West India
- 2014
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Ingår i: Atmospheric Environment. - : Elsevier BV. - 1352-2310 .- 1873-2844. ; 88, s. 59-65
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Tidskriftsartikel (refereegranskat)abstract
- Data from a ground-based cloud-water collection system intercepting water from clouds at a mountain field station, Sinhagad near Pune in India are presented. This study was part of an Indo-Swedish Collaboration Project on Atmospheric Brown Cloud-Asia (ABC-A). Cloud-water and rainwater (wet-only) samples were collected during June 2007-Dec. 2010. Concentrations of major anions and cations were determined. Ion concentrations were generally higher (NO3-, about 8 times; SO42- and K+, 5 times; NH4+ times and Cl-, Na+, Ca2+, Mg2+ 3 times) in cloud-water samples than in rainwater samples collected during the same days. The average pH of cloud-water samples was 6.0 with about 20% of the values below 5.6 and only 4% less than 5.0. Despite high concentrations of SO42- and NO3- the cloud water samples were on average not more acidic than rainwater samples. This is different from most of the other studies of cloud-water composition which have noted a substantially higher acidity (i.e. lower pH) in cloud-water than in rainwater. The slightly alkaline (pH > 5.6) nature of the cloud-water samples is mainly due to the presence of soil derived calcium carbonate in quantities more than enough to neutralize the acids or their precursors. A separation of the cloud-water data into trajectory groups showed that samples in air-masses having spent the last few days over the Indian sub-continent were in general more acidic (due to anthropogenic emissions) than those collected during days with air-masses of marine origin. A high correlation mutually between Ca2+, Na+, NO3- and SO42- makes it difficult to estimate the contribution to SO42- from different sources. Anthropogenic SO2- emissions and soil dust may both give important contributions.
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| 10. |
- Chen, Deliang, 1961, et al.
(författare)
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Summary of a workshop on extreme weather events in a warming world organized by the Royal Swedish Academy of Sciences
- 2020
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Ingår i: Tellus Series B-Chemical and Physical Meteorology. - : Stockholm University Press. - 1600-0889 .- 0280-6509. ; 72:1
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Tidskriftsartikel (refereegranskat)abstract
- Climate change is not only about changes in means of climatic variables such as temperature, precipitation and wind, but also their extreme values which are of critical importance to human society and ecosystems. To inspire the Swedish climate research community and to promote assessments of international research on past and future changes in extreme weather events against the global climate change background, the Earth Science Class of the Royal Swedish Academy of Sciences organized a workshop entitled 'Extreme weather events in a warming world' in 2019. This article summarizes and synthesizes the key points from the presentations and discussions of the workshop on changes in floods, droughts, heat waves, as well as on tropical cyclones and extratropical storms. In addition to reviewing past achievements in these research fields and identifying research gaps with a focus on Sweden, future challenges and opportunities for the Swedish climate research community are highlighted.
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| 11. |
- Das, Ruby, et al.
(författare)
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Chemical composition of rainwater at Maldives Climate Observatory at Hanimaadhoo (MCOH)
- 2011
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 11:8, s. 3743-3755
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Tidskriftsartikel (refereegranskat)abstract
- Water-soluble inorganic components in rain deposited at the Maldives Climate Observatory Hanimaadhoo (MCOH) were examined to determine seasonality and possible source regions. The study, which is part of the Atmospheric Brown Cloud (ABC) project, covers the period June 2005 to December 2007. Air mass trajectories were used to separate the data into situations with transport of air from India and adjacent parts of the Asian continent during the months December and January (Indian group) and those with southerly flow from the Indian Ocean during the summer monsoon season June to September (Marine group). A third trajectory group was identified with transport from the northern parts of the Arabian Sea and adjacent land areas during the months March, April and October (Arabian Sea group). The concentrations of nss-SO(4)(2-), NH(4)(+) and NO(3)(-) were more than a factor of 4 higher in the Indian group than in the Marine group. The average rainwater pH was significantly lower in the Indian group (4.7) than in the Marine group (6.0). This shows a pronounced influence of continental pollutants during December and January. The origin of the very high concentration of nss-Ca(2+) found in the Marine group - a factor of 7 higher than in the Indian group - is unclear. We discuss various possibilities including long-range transport from the African or Australian continents, local dust from nearby islands and calcareous plankton debris and exopolymer gels emitted from the ocean surface. The occurrence of NO(3)(-) and NH(4)(+) in the Marine group suggests emissions from the ocean surface. Part of the NO(3)(-) could also be associated with lightning over the ocean. Despite the fact that the concentrations of nss-SO(4)(2-), NO(3)(-), and NH(4)(+) were highest in the Indian group the wet deposition was at least as big in the Marine group reflecting the larger amount of rainfall during the monsoon season. The annual wet deposition of NO(3)(-), NH(4)(+) and nss-SO(4)(2-) at MCOH is about a factor of three lower than observed at rural sites in India.
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| 12. |
- De Geer, Lars-Erik, et al.
(författare)
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A Nuclear Jet at Chernobyl Around 21:23:45 UTC on April 25, 1986
- 2018
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Ingår i: Nuclear Technology. - : Informa UK Limited. - 0029-5450 .- 1943-7471. ; 201:1, s. 11-22
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Tidskriftsartikel (refereegranskat)abstract
- The nature of two explosions that were witnessed within 3 s at the Chernobyl-4 reactor less than a minute after 21:23:00 UTC on April 25, 1986, have since then been the subject of sprawling interpretations. This paper renders the following hypothesis. The first explosion consisted of thermal neutron mediated nuclear explosions in one or rather a few fuel channels, which caused a jet of debris that reached an altitude of some 2500 to 3000 m. The second explosion would then have been the steam explosion most experts believe was the first one. The solid support for this new scenario rests on two pillars and three pieces of corroborating evidence. The first pillar is that a group at the V. G. Khlopin Radium Institute in then Leningrad on April 29, 1986, detected newly produced, or fresh, xenon fission products at Cherepovets, 370 km north of Moscow and far away from the major track of Chernobyl debris ejected by the steam explosion and subsequent fires. The second pillar is built on state-of-the-art meteorological dispersion calculations, which show that the fresh xenon signature observed at Cherepovets was only possible if the injection altitude of the fresh debris was considerably higher than that of the bulk reactor core releases that turned toward Scandinavia and central Europe. These two strong pieces of evidence are corroborated by what were manifest physical effects of a downward jet in the southeastern part of the reactor, by seismic measurements some 100 km west of the reactor, and by observations of a blue flash above the reactor a few seconds after the first explosion.
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| 13. |
- Engström, Erik J., 1976-
(författare)
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Characterization of soot in air and rain over southern Asia
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Filter-based optical measurements of light absorbing particulate matter at awavelength of about 550 nm, here referred to as soot, in air and rainwaterhave been performed during the period from 1st June 2005 to 31th May 2009at Godavari in Nepal, Sinhagad in India and Hanimaadhoo in The Maldives.A method for determination of water-insoluble light absorbing matter inrainwater has been developed. Analysis of environmental samples has beensuccessfully performed with the described method on samples collected atHanimaadhoo and Godavari. At Hanimaadhoo the average soot concentrationin rainwater was 48 mgl-1 and at Godavari 86 mgl-1.In order to reduce systematic errors at optical determination of soot due tothe light scattering of non-absorbing particles co-deposited on the filter, suchas inorganic salts and mineral dust, an additional sensor recording backscatteredlight was used. Two alternative protocols of corrections (optical andchemical) were applied to the samples. Simultaneous measurements of sootand inorganic ions in aerosol and precipitation at Hanimaadhoo during theperiod May 2005 to February 2007 made it possible to calculate the washoutratio (WR) of these components as a measure of how efficiently they are scavengedby precipitation. During the monsoon season the WR for soot was similarto that of sulphate and other fine mode aerosol components, indicating thatsoot containing particles in these situations were efficient as cloud condensationnuclei. During the polluted winter days, on the other hand, the WR forsoot was 3 times smaller than that of sulphate, showing that the soot containingparticles had retained a hydrophobic character even after a travel time ofseveral days.The Indian monsoon circulation with its two annual phases in combinationwith the location of the main combustion source areas dominated the observedpatterns of soot at the observatories in India and Maldives. Godavari in Nepalwas however mainly influenced by combustion sources all year around concealingpossible variability related to the monsoon circulation. At Hanimaadhoo,peak values in the soot concentration occurred during the winter season(December to April) when air was transported from the polluted Indian subcontinentout over the Indian Ocean. At least a factor of ten lower values wererecorded in air that had spent more than 10-days over the Indian Ocean duringthe monsoon season (July to September).
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| 14. |
- Granat, Lennart, et al.
(författare)
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Light Absorbing Material ("Soot") in Rainwater and in aerosol particles in the Maldives
- 2010
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Ingår i: Journal of Geophysical Research. - : American Geophysical Union.. - 0148-0227 .- 2156-2202. ; 115, s. D16307-
-
Tidskriftsartikel (refereegranskat)abstract
- Simultaneous measurements of soot (absorbing material at 528 nm) and inorganic ions in aerosol and precipitation at the Maldives Climate Observatory Hanimaadhoo during the period May 2005 to February 2007 have made it possible to calculate the washout ratio (WR) of these components as a measure of how efficiently they are scavenged by precipitation. Based on air trajectories the data have been separated into days with polluted air arriving from the Indian subcontinent in a north-easterly sector during winter and clean monsoon days with southerly flow from the Indian Ocean. The average soot concentration was a factor of ten higher in the former situations. Despite considerable scatter for individual days a systematic pattern emerged when the WR for the different components were compared with each other. During the monsoon season the WR for soot was similar to that of sulphate and other fine mode aerosol components, indicating that soot containing particles in these situations were efficient as cloud condensation nuclei. The origin of the light absorbing material during the monsoon season is unclear. We speculate that light absorbing material from the tropical ocean surface could contribute to the concentration of "soot" during the monsoon season. During the polluted winter days, on the other hand, the WR for soot was 3 times smaller than that of sulphate. This indicates that, even after a travel time of several days, the soot containing particles from India have retained much of their hydrophobic property and that the soot must be mainly externally mixed. The low WR and the infrequent rain during this season probably contribute to extending the atmospheric lifetime of soot well beyond several days. Surprisingly high concentrations of non sea salt calcium were measured during the monsoon season, substantially higher than during the winter season. The origin of these high values might be long-range transport from the Australian or African continents. Another possibility might be exopolymer gels derived from the ocean surface micro-layer.
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| 15. |
- Grennfelt, Peringe, et al.
(författare)
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Acid rain and air pollution : 50 years of progress in environmental science and policy
- 2020
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Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 49:4, s. 849-864
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Forskningsöversikt (refereegranskat)abstract
- Because of its serious large-scale effects on ecosystems and its transboundary nature, acid rain received for a few decades at the end of the last century wide scientific and public interest, leading to coordinated policy actions in Europe and North America. Through these actions, in particular those under the UNECE Convention on Long-range Transboundary Air Pollution, air emissions were substantially reduced, and ecosystem impacts decreased. Widespread scientific research, long-term monitoring, and integrated assessment modelling formed the basis for the policy agreements. In this paper, which is based on an international symposium organised to commemorate 50 years of successful integration of air pollution research and policy, we briefly describe the scientific findings that provided the foundation for the policy development. We also discuss important characteristics of the science-policy interactions, such as the critical loads concept and the large-scale ecosystem field studies. Finally, acid rain and air pollution are set in the context of future societal developments and needs, e.g. the UN's Sustainable Development Goals. We also highlight the need to maintain and develop supporting scientific infrastructures.
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| 16. |
- Gustafsson, Örjan, et al.
(författare)
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Brown clouds over South Asia: Biomass or fossil fuel combustion?
- 2009
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 323:23 January, s. 495-498
-
Tidskriftsartikel (refereegranskat)abstract
- Carbonaceous aerosols cause strong atmospheric heating and large surface cooling that is as important to South Asian climate forcing as greenhouse gases, yet the aerosol sources are poorly understood. Emission inventory models suggest that biofuel burning accounts for 50 to 90% of emissions, whereas the elemental composition of ambient aerosols points to fossil fuel combustion. We used radiocarbon measurements of winter monsoon aerosols from western India and the Indian Ocean to determine that biomass combustion produced two-thirds of the bulk carbonaceous aerosols, as well as one-half and two-thirds of two black carbon subfractions, respectively. These constraints show that both biomass combustion (such as residential cooking and agricultural burning) and fossil fuel combustion should be targeted to mitigate climate effects and improve air quality.
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| 17. |
- Hicks, Kevin, et al.
(författare)
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Soil sensitivity to acidification in Asia : Status and prospects
- 2008
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Ingår i: Ambio. ; 37:4, s. 295-303
-
Tidskriftsartikel (refereegranskat)abstract
- Exceedance of steady-state critical loads for soil acidification is consistently found in southern China and parts of SE Asia, but there is no evidence of impacts outside of China. This study describes a methodology for calculating the time to effects for soils sensitive to acidic deposition in Asia under potential future sulfur (S), nitrogen (N), and calcium (Ca) emission scenarios. The calculations are matched to data availability in Asia to produce regional-scale maps that provide estimates of the time (y) it will take for soil base saturation to reach a critical limit of 20% in response to acidic inputs. The results show that sensitive soil types in areas of South, Southeast, and East Asia, including parts of southern China, Burma, Hainan, Laos, Thailand, Vietnam, and the Western Ghats of India, may acidify to a significant degree on a 0–50 y timescale, depending on individual site management and abiotic and biotic characteristics. To make a clearer assessment of risk, site-specific data are required for soil chemistry and deposition (especially base cation deposition); S and N retention in soils and ecosystems; and biomass harvesting and weathering rates from sites across Asia representative of different soil and vegetation types and management regimes. National and regional assessments of soils using the simple methods described in this paper can provide an appreciation of the time dimension of soil acidification–related impacts and should be useful in planning further studies and, possibly, implementing measures to reduce risks of acidification
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| 18. |
- Karlsson, Johannes, et al.
(författare)
-
Cloud radiative forcing of subtropical low level clouds in global models
- 2008
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 30:7-8, s. 779-788
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Tidskriftsartikel (refereegranskat)abstract
- Simulations of subtropical marine low clouds and their radiative properties by nine coupled oceanatmosphere climate models participating in the fourth assesment report (AR4) of the intergovernmental panel on climate change (IPCC) are analyzed. Satellite observations of cloudiness and radiative fluxes at the top of the atmosphere (TOA) are utilized for comparison. The analysis is confined to the marine subtropics in an attempt to isolate low cloudiness from tropical convective systems. All analyzed models have a negative bias in the low cloud fraction (model mean bias of –15%). On the other hand, the models show an excess of cloud radiative cooling in the region (model mean excess of 13 W m–2). The latter bias is shown to mainly originate from too much shortwave reflection by the models clouds rather than biases in the clear-sky fluxes. These results confirm earlier studies, thus no major progress in simulating the marine subtropical clouds is noted. As a consequence of the combination of these two biases, this study suggests that all investigated models are likely to overestimate the radiative response to changes in low level subtropical cloudiness.
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| 19. |
- Karlsson, Johannes, 1978-
(författare)
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The influence of clouds on Earth's radiation budget in global climate models
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Considering the high sensitivity of climate to changes in cloudiness, the way clouds might change in a perturbed climate is important for the total temperature response. In fact, the cloud feedback has been identified as the main uncertainty in future projections, as simulated by global climate models. To increase the confidence of future scenario simulations it is necessary, although not sufficient, that the models manage to represent the present-day climate in a realistic manner. We compare the simulations of cloudiness to available observations in the marine subtropics and the Arctic, two regions in which changes in cloudiness are believed to have large impact on the climate. In terms of the annual cycle of Arctic cloud properties, climate models show large disagreement with each other and with observations. There exists a tentative across-model relationship, such that models with higher amounts of clouds in the winter are also associated with larger surface cloud forcing. However, across-model differences in the wintertime surface cloud forcing cannot explain differences in the simulated surface temperatures. Rather, we identify across-model differences in temperature and moisture properties of the air entering the Arctic region to be of greater importance. We find that climate models in general underestimate the amount of low clouds in the marine subtropics but still overestimate the regional averaged cloud radiative cooling. As a consequence we suggest that models are likely to overestimate the radiative response to changes in the cloudiness. We also demonstrate the potential of satellite derived cloud top heights to be used as model diagnostics in the climatologically important transition from stratus-topped to cumulus-topped marine boundary layers in the subtropics.
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| 20. |
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| 21. |
- Kleman, Johan, et al.
(författare)
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Rubbat förtroende för forskarna
- 2010
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Ingår i: Svenska Dagbladet. - 1101-2412. ; :25 maj
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 22. |
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| 23. |
- Rockström, Johan, et al.
(författare)
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A safe operating space for humanity
- 2009
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 461:7263, s. 472-475
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Tidskriftsartikel (refereegranskat)
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| 24. |
- Rockström, Johan, et al.
(författare)
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Planetary Boundaries : Exploring the Safe Operating Space for Humanity
- 2009
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Ingår i: Ecology and Society. - 1708-3087. ; 14:2, s. 32-
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Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic pressures on the Earth System have reached a scale where abrupt global environmental change can no longer be excluded. We propose a new approach to global sustainability in which we define planetary boundaries within which we expect that humanity can operate safely. Transgressing one or more planetary boundaries may be deleterious or even catastrophic due to the risk of crossing thresholds that will trigger non-linear, abrupt environmental change within continental- to planetary-scale systems. We have identified nine planetary boundaries and, drawing upon current scientific understanding, we propose quantifications for seven of them. These seven are climate change (CO2 concentration in the atmosphere <350 ppm and/or a maximum change of +1 W m(-2) in radiative forcing); ocean acidification (mean surface seawater saturation state with respect to aragonite >= 80% of pre-industrial levels); stratospheric ozone (<5% reduction in O-3 concentration from pre-industrial level of 290 Dobson Units); biogeochemical nitrogen (N) cycle (limit industrial and agricultural fixation of N-2 to 35 Tg N yr(-1)) and phosphorus (P) cycle (annual P inflow to oceans not to exceed 10 times the natural background weathering of P); global freshwater use (<4000 km(3) yr(-1) of consumptive use of runoff resources); land system change (<15% of the ice-free land surface under cropland); and the rate at which biological diversity is lost (annual rate of <10 extinctions per million species). The two additional planetary boundaries for which we have not yet been able to determine a boundary level are chemical pollution and atmospheric aerosol loading. We estimate that humanity has already transgressed three planetary boundaries: for climate change, rate of biodiversity loss, and changes to the global nitrogen cycle. Planetary boundaries are interdependent, because transgressing one may both shift the position of other boundaries or cause them to be transgressed. The social impacts of transgressing boundaries will be a function of the social-ecological resilience of the affected societies. Our proposed boundaries are rough, first estimates only, surrounded by large uncertainties and knowledge gaps. Filling these gaps will require major advancements in Earth System and resilience science. The proposed concept of "planetary boundaries" lays the groundwork for shifting our approach to governance and management, away from the essentially sectoral analyses of limits to growth aimed at minimizing negative externalities, toward the estimation of the safe space for human development. Planetary boundaries define, as it were, the boundaries of the "planetary playing field" for humanity if we want to be sure of avoiding major human-induced environmental change on a global scale.
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| 25. |
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