No description available.

Thesis (Ph.D.) -- McMaster University, 2001. / Includes bibliographical references (leaves 240-249). Also available via World Wide Web.

Lake Victoria (LV), is the largest tropical fresh water lake. It is however facing a myriad of challenges like eutrophication, introducing species, mass extinction and climate change. Eutrophication has mostly been seen as a result of non-point pollution from upstream agricultural areas. However, studies have found that atmospheric deposition could perhaps be the greatest cause of nutrient loading in the lake. Our study looked at black carbon as one of the factors favoring eutrophication in LV. Black carbon is a product of incomplete combustion of biomass or fossil fuel. Biomass burning is prevalent in many areas of Africa and our results have shown a great spatial and temporal variability in its concentration in sediments. The sedimentation rates calculated after analyzing 210Pb activity were 0.87, 0.53 and 0.35 g cm-2 yr-1 while the average black carbon concentrations were 4.6, 2.1 and 6.9 mg g-1 for Siaya, Kisumu and Busia, respectively. These results provided valuable information when compared to past historical events in the Lake region especially eutrophication. The study also found that soot BC has been increasing in the past 100 years suggesting the input from fossil fuels. This study elucidates the complexity of drivers of eutrophication in Lake Victoria. Nitrogen and Phosphorous from the upstream agricultural sites has long been seen as the main cause of eutrophication. Through this study we find that soot deposition in the lake coincides with the period of increased primary productivity. The Total Organic Carbon and Total Nitrogen were also analyzed and have shown increased remarkable increase with time. All these geochemical variables are a testament to the increased role of human activities on the lake’s productivity. While other studies on soot in marine environments have associated bacterial growth to nutrients attached to soot black carbon. We correlate the concentration of soot in Lake Victoria basin to blooming of cyanobacteria.

No description available.

In this research work, the relationships between structure and properties in micro-composites and nano-composites of polyurethane (PU) and conductive carbon particles have been studied. PU is a class of block copolymers containing the urethane linkage (-NHCO-O-) within its structure. Most PU block copolymers consist of alternating ‘soft’ and ‘hard’ segments. The hard segment used in this study was based on 4,4’-methylenebisphenylisocyanate (MDI) and 2-methyl 1,3 propanediol (MP-Diol) which produced a stiff aromatic polyurethane. Two soft segments; poly(tetrahydofuran) (PTHF) and poly(propylene oxide) based polyol end-capped with ethylene oxide (PPO-EO) were used to study the effects of soft segment structure on PU properties. DMTA, DSC and modulated-DSC indicated that PU-PTHF had higher microphase separation due to greater immiscibility between PTHF and the MDI/MP-Diol hard segments. In order to improve the electrical and mechanical properties of PU, conductive carbon particles were incorporated. The critical factor was the dispersion of these conductive fillers in the PU matrix to obtain optimum properties. The first carbon filler studied was carbon black (CB). PU composites prepared by the adding of MP-Diol plus ultrasonication (MU) gave the best dispersion of CB aggregates resulting in higher thermal decomposition temperature and good conductivity. However, the mechanical toughness was reduced. In subsequent studies, PU composites incorporating three different treated multiwalled carbon nanotubes (MWCNT) were investigated. MWCNT were disentangled and shortened by ultrasonication and acid cutting treatments. The ultrasonicated MWCNT (MWCNT_U) had longer length than the acid-cut MWCNT (MWCNT_AC). Ultrasonication was the best technique for dispersing MWCNT since the storage modulus was increased by ~200% at low MWCNT_U loading and the toughness remained the same as unfilled PU. PU/MWCNT_AC nanocomposites at 1 – 3 wt% of MWCNT_AC exhibited similar electrical conductivities to unfilled PU at an order of 10-8 S/cm, implying that the acid cutting treatment might disturb the inherent conductivity in MWCNT. The conductive percolation thresholds of composites were determined following the percolation theory. It was found that the percolation thresholds for MWCNT-filled composites were significantly lower than that of CB-filled composites. The lowest percolation threshold was observed in MWCNT_U-filled composite at 0.31 wt%.

A matéria orgânica do solo (MOS) representa um importante reservatório de carbono (C) nos ecossistemas terrestres. O conteúdo de C estocado no solo pode ser liberado para a atmosfera na forma de CO2, com a decomposição da MOS, ou pode ser aumentado com a entrada de resíduos e retenção da MOS. Nesse sentido, é importante entender os mecanismos de estabilidade e retenção da MOS para predizer como os solos respondem a mudanças, quer sejam elas induzidas por alterações climáticas ou por práticas de manejo. Dentro dos Latossolos, classe que ocupa cerca de 32 % do território brasileiro, há aqueles que possuem horizonte A húmico hiper espesso e, portanto, com maior estoque de C. Aspectos sobre a origem, formação e preservação do horizonte A húmico destes solos em suas ocorrências em diferentes biomas ainda não foram completamente elucidados e estão estritamente ligados à fonte, dinâmica e mecanismos de preservação e distribuição da MOS no solo. O objetivo deste trabalho é entender a gênese da MO dos Latossolos húmicos que ocorrem no Bioma Cerrado, por meio da caracterização molecular pela técnica da pirólise acoplada à cromatografia gasosa e espectroscopia de massas (pirólise - CG/EM). Para isso, foram coletadas amostras dos horizontes A em dois perfis de Latossolos com horizonte A húmico (LH1, LH2) e um perfil de Latossolo com horizonte A moderado (solo de referência; LNH) situados em superfície de aplanamento adjacente à Serra do Espinhaço, no município de Grão Mogol - MG, sob clima tropical semi-úmido e vegetação de cerrado sensu strictu. Por meio da descrição morfológica dos solos em diferentes níveis de observação (campo, lupa e microscópio) procurou-se entender melhor os mecanismos de espessamento do horizonte A e a distribuição de partículas de carvão ao longo do perfil. As amostras dos horizontes foram submetidas ao fracionamento físico e extração da MOS, gerando as seguintes frações: fração leve livre (FLL); fração leve oclusa (FLO), fração extraível com NaOH (EXT) e resíduo (RES). A morfologia dos perfis evidencia a intensa e longa atividade biológica (fauna e raízes) a que esses solos foram e estão submetidos. Isso explica a abundância de microagregados e a consequente macropososidade elevada, assim como a ampla distribuição de fragmentos de carvão em todo o horizonte A, e parte do B, com dimensões milimétricas a submilimétricas, sugerindo a fragmentação destes ao longo do tempo. Foi evidenciado o maior conteúdo de carvões nos dois LHs em comparação ao LNH. A distribuição da MOS nas frações estudadas foi a mesma para os três perfis estudados: RES>EXT>FLL>FLO, que mostra a importância da fração RES para estes solos. Produtos da carbonização (Black carbon; BC: hidrocarbonetos poliaromáticos) foram mais abundantes na fração RES e FLO, no entanto, a maior diferença qualitativa entre a MOS de LHs e LNH diz respeito à abundância de BC na fração RES, que é maior em LHs do que LNH; confirmando a maior quantidade de carvões em LHs verificada na morfologia. Um índice de degradação do BC foi estabelecido com base em análise fatorial com os todas as frações estudadas e produtos poliaromáticos. Este índice, aplicado às frações EXT e RES, mostrou que a degradação do BC aumenta com a profundidade/idade, e não houve diferenças significativas entre os perfis estudados. Portanto, LHs provavelmente tem maior entrada de carvões, o que deve estar ligado a um histórico de maior incidência de incêndios ou maior abundância local de espécies arbóreas. / Soil organic matter (SOM) is an important carbon (C) stock in terrestrial ecosystems. C in soils can be released to the atmosphere in CO2 form by SOM decomposition, or can be stored with residue inputs and SOM retention in the soils. In this sense, it is important to understand the SOM stability mechanisms to predict how soils behave under climatic or human management induced environmental changes. Latosols occupy 40% of the national territory in Brazil. Some of them have a hyper thick A horizon with a major C stock, Humic Latasols. Aspects that underlie the formation of humic A horizon are still unclear, and mainly concern SOM dynamics, SOM preservation mechanisms, and SOM distribution with depth. The aim of this work is to understand the genesis of Humic Latosols through molecular characterization of SOM by pyrolysis coupled to gas chromatography and mass spectrometry (pyrolysis - GC/MS). For this purpose samples from two profiles (LH1, LH2) were collected, and in addition a reference profile was sampled (Latosol without humic characteristics, LNH). All profiles were located near Grão Mogol city (MG) under a semi-humid tropical climate and Cerrado vegetation. Morphology at different levels (field, bloom and microscope) showed that charcoal was abundant in all three profiles, and an extremely high biological activity. Profiles were sampled in detail and all samples were submitted to sequential physical fractionation and chemical extraction, generating the following SOM fractions: free light fraction (FLF); occluded light fraction (OLF); NaOH extractable fraction (EXT) and residue (RES). The molecular composition of the samples was studied by pyrolysis-GC/MS. Profile morphology evidence the long and intense biological activity (faunal and roots) in this soils, in the past and present time. This explains the microaggregate abundance and consequent macroporosity, and also the distribution of charcoal fragments in all of A and part of B horizon. These fragments have submilimetrical a milimetrical dimensions, suggests its fragmentation along the time. It was evidenced too, the bigger charcoal content in LHs than LNH. The C distribution in the fractions was the same for all the studied profiles: RES>EXT>FLL>FLO, which shows the importance of the RES fraction for these soils. Pyrolysis products derived from black carbon (BC; polyaromatics hydrocarbons) were most abundant in RES and FLO. In the RES, PAHs were more abundant in the LH than LNH; confirming the biggest quantity of charcoals in LHs verified in morphology. A BC degradation index was established using factor analysis with all PAH and all fractions studied. Depth records of these parameter showed an increase with depth in both EX and RES, and showed no differences between the studied profiles. It is concluded, therefore, that the LH had a larger input of charcoal. It is hypothesized that the larger contribution from BC in LHs is related to local differences in fire intensity and/or more trees in the vegetation.

A matéria orgânica do solo (MOS) representa um importante reservatório de carbono (C) nos ecossistemas terrestres. O conteúdo de C estocado no solo pode ser liberado para a atmosfera na forma de CO2, com a decomposição da MOS, ou pode ser aumentado com a entrada de resíduos e retenção da MOS. Nesse sentido, é importante entender os mecanismos de estabilidade e retenção da MOS para predizer como os solos respondem a mudanças, quer sejam elas induzidas por alterações climáticas ou por práticas de manejo. Dentro dos Latossolos, classe que ocupa cerca de 32 % do território brasileiro, há aqueles que possuem horizonte A húmico hiper espesso e, portanto, com maior estoque de C. Aspectos sobre a origem, formação e preservação do horizonte A húmico destes solos em suas ocorrências em diferentes biomas ainda não foram completamente elucidados e estão estritamente ligados à fonte, dinâmica e mecanismos de preservação e distribuição da MOS no solo. O objetivo deste trabalho é entender a gênese da MO dos Latossolos húmicos que ocorrem no Bioma Cerrado, por meio da caracterização molecular pela técnica da pirólise acoplada à cromatografia gasosa e espectroscopia de massas (pirólise - CG/EM). Para isso, foram coletadas amostras dos horizontes A em dois perfis de Latossolos com horizonte A húmico (LH1, LH2) e um perfil de Latossolo com horizonte A moderado (solo de referência; LNH) situados em superfície de aplanamento adjacente à Serra do Espinhaço, no município de Grão Mogol - MG, sob clima tropical semi-úmido e vegetação de cerrado sensu strictu. Por meio da descrição morfológica dos solos em diferentes níveis de observação (campo, lupa e microscópio) procurou-se entender melhor os mecanismos de espessamento do horizonte A e a distribuição de partículas de carvão ao longo do perfil. As amostras dos horizontes foram submetidas ao fracionamento físico e extração da MOS, gerando as seguintes frações: fração leve livre (FLL); fração leve oclusa (FLO), fração extraível com NaOH (EXT) e resíduo (RES). A morfologia dos perfis evidencia a intensa e longa atividade biológica (fauna e raízes) a que esses solos foram e estão submetidos. Isso explica a abundância de microagregados e a consequente macropososidade elevada, assim como a ampla distribuição de fragmentos de carvão em todo o horizonte A, e parte do B, com dimensões milimétricas a submilimétricas, sugerindo a fragmentação destes ao longo do tempo. Foi evidenciado o maior conteúdo de carvões nos dois LHs em comparação ao LNH. A distribuição da MOS nas frações estudadas foi a mesma para os três perfis estudados: RES>EXT>FLL>FLO, que mostra a importância da fração RES para estes solos. Produtos da carbonização (Black carbon; BC: hidrocarbonetos poliaromáticos) foram mais abundantes na fração RES e FLO, no entanto, a maior diferença qualitativa entre a MOS de LHs e LNH diz respeito à abundância de BC na fração RES, que é maior em LHs do que LNH; confirmando a maior quantidade de carvões em LHs verificada na morfologia. Um índice de degradação do BC foi estabelecido com base em análise fatorial com os todas as frações estudadas e produtos poliaromáticos. Este índice, aplicado às frações EXT e RES, mostrou que a degradação do BC aumenta com a profundidade/idade, e não houve diferenças significativas entre os perfis estudados. Portanto, LHs provavelmente tem maior entrada de carvões, o que deve estar ligado a um histórico de maior incidência de incêndios ou maior abundância local de espécies arbóreas. / Soil organic matter (SOM) is an important carbon (C) stock in terrestrial ecosystems. C in soils can be released to the atmosphere in CO2 form by SOM decomposition, or can be stored with residue inputs and SOM retention in the soils. In this sense, it is important to understand the SOM stability mechanisms to predict how soils behave under climatic or human management induced environmental changes. Latosols occupy 40% of the national territory in Brazil. Some of them have a hyper thick A horizon with a major C stock, Humic Latasols. Aspects that underlie the formation of humic A horizon are still unclear, and mainly concern SOM dynamics, SOM preservation mechanisms, and SOM distribution with depth. The aim of this work is to understand the genesis of Humic Latosols through molecular characterization of SOM by pyrolysis coupled to gas chromatography and mass spectrometry (pyrolysis - GC/MS). For this purpose samples from two profiles (LH1, LH2) were collected, and in addition a reference profile was sampled (Latosol without humic characteristics, LNH). All profiles were located near Grão Mogol city (MG) under a semi-humid tropical climate and Cerrado vegetation. Morphology at different levels (field, bloom and microscope) showed that charcoal was abundant in all three profiles, and an extremely high biological activity. Profiles were sampled in detail and all samples were submitted to sequential physical fractionation and chemical extraction, generating the following SOM fractions: free light fraction (FLF); occluded light fraction (OLF); NaOH extractable fraction (EXT) and residue (RES). The molecular composition of the samples was studied by pyrolysis-GC/MS. Profile morphology evidence the long and intense biological activity (faunal and roots) in this soils, in the past and present time. This explains the microaggregate abundance and consequent macroporosity, and also the distribution of charcoal fragments in all of A and part of B horizon. These fragments have submilimetrical a milimetrical dimensions, suggests its fragmentation along the time. It was evidenced too, the bigger charcoal content in LHs than LNH. The C distribution in the fractions was the same for all the studied profiles: RES>EXT>FLL>FLO, which shows the importance of the RES fraction for these soils. Pyrolysis products derived from black carbon (BC; polyaromatics hydrocarbons) were most abundant in RES and FLO. In the RES, PAHs were more abundant in the LH than LNH; confirming the biggest quantity of charcoals in LHs verified in morphology. A BC degradation index was established using factor analysis with all PAH and all fractions studied. Depth records of these parameter showed an increase with depth in both EX and RES, and showed no differences between the studied profiles. It is concluded, therefore, that the LH had a larger input of charcoal. It is hypothesized that the larger contribution from BC in LHs is related to local differences in fire intensity and/or more trees in the vegetation.

The baseline of uncertainty in aerosol radiative forcing is large and depends on aerosol characteristics (e.g. size and composition), which can vary significantly on a regional scale. Sources (natural and anthropogenic) can be directly linked to the aerosol characteristics of a region, making monitoring campaigns to determine aerosol composition in different regions very important. Limited data currently exists for atmospheric aerosol black carbon (BC) and organic carbon (OC) in South Africa. In this study, BC and OC concentrations were explored in terms of spatial and temporal patterns, mass fractions of BC and OC of the overall aerosol mass, as well as possible sources. Primary pollutants, of which BC is an example, are emitted directly from the source. Certain primary pollutants can react with other pollutants to form secondary pollutants. OC can either be a primary or secondary pollutant, e.g. formed by gas-to-particle conversion of volatile organic compounds (VOCs) in the atmosphere (nucleation and condensation of gaseous precursors). Greenhouse gases (GHG) and BC absorb terrestrial long wave radiation causing an increase of atmospheric temperature. In contrast, OC generally reflects incoming radiation, cooling the atmosphere. GHGs have a long residence time in the atmosphere (10 to 100 years), while the residence time of aerosols is usually only a week or more. The climatic effects of aerosols are therefore particularly important from a regional perspective. Aerosols are also important from an air quality perspective, especially since ultrafine particles (diameter smaller than 100nm) are small enough to go through the membranes of the respiratory tract and into the blood stream. They can then be transported to the brain. Up to 2005, DEBITS (Deposition of Biogeochemical Import Trace Species) activities in South Africa did not include aerosol measurements. In order to initiate aerosol monitoring, campaigns were launched during the 2005 to 2007 period. Additionally, OC and BC measurements for the PM10 and PM2.5 (particulate matter smaller than or equal to 10 and 2.5 μm, respectively) fractions were started in 2009. PM10 and PM2.5 samples were collected at five sampling sites in South Africa operated within the DEBITS network, i.e. Louis Trichardt, Skukuza, Vaal Triangle, Amersfoort and Botsalano, with MiniVol samplers. The selected sites are mostly located in rural areas, but with the surrounding atmosphere influenced by industries, transportation, biomass burning, etc. Winters are characterised by an increase in biomass burning (fires) and combustion for domestic use (cooking and space heating). Samples were analysed with a Thermal/Optical Carbon analyser (Desert Research Institute). OC and BC results showed that the total carbonaceous content decreased during the summer due to less biomass burning (fires). BC was the highest at the industrially influenced sites, while OC was highest at regional background sites. OC was higher than BC concentrations at all sites in both size fractions. Most OC and BC occurred in the PM2.5 fraction. OC/BC ratios reflected the setting of the different DEBITS sites, with sites in or close to anthropogenic source regions having the lowest OC/BC ratios, while background sites had the highest OC/BC ratios. The OC mass fraction percentage of the total aerosol weight varied up to 24% and the BC up to 12%. The highest OC mass fraction was found at Skukuza, which was attributed to both natural (lies within the savannah biome) and anthropogenic (dominant path of air mass movement from the anthropogenic industrial hub of South Africa) reasons. The highest mass fraction of BC was found in the Vaal Triangle, since it is situated within a well-known anthropogenic source region. Household combustion for space heating and cooking also seemed to make a significant contribution to BC at this site in the cold winter months. A relatively well-defined seasonal pattern was observed, with higher OC and BC concentrations measured from May to October, which coincides with the dry season in the interior of South Africa. Positive correlations between OC and BC concentrations with the distance back trajectories passed fires were observed, indicating that fires contribute significantly to both atmospheric OC and BC during the burning season. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2014

The baseline of uncertainty in aerosol radiative forcing is large and depends on aerosol characteristics (e.g. size and composition), which can vary significantly on a regional scale. Sources (natural and anthropogenic) can be directly linked to the aerosol characteristics of a region, making monitoring campaigns to determine aerosol composition in different regions very important. Limited data currently exists for atmospheric aerosol black carbon (BC) and organic carbon (OC) in South Africa. In this study, BC and OC concentrations were explored in terms of spatial and temporal patterns, mass fractions of BC and OC of the overall aerosol mass, as well as possible sources. Primary pollutants, of which BC is an example, are emitted directly from the source. Certain primary pollutants can react with other pollutants to form secondary pollutants. OC can either be a primary or secondary pollutant, e.g. formed by gas-to-particle conversion of volatile organic compounds (VOCs) in the atmosphere (nucleation and condensation of gaseous precursors). Greenhouse gases (GHG) and BC absorb terrestrial long wave radiation causing an increase of atmospheric temperature. In contrast, OC generally reflects incoming radiation, cooling the atmosphere. GHGs have a long residence time in the atmosphere (10 to 100 years), while the residence time of aerosols is usually only a week or more. The climatic effects of aerosols are therefore particularly important from a regional perspective. Aerosols are also important from an air quality perspective, especially since ultrafine particles (diameter smaller than 100nm) are small enough to go through the membranes of the respiratory tract and into the blood stream. They can then be transported to the brain. Up to 2005, DEBITS (Deposition of Biogeochemical Import Trace Species) activities in South Africa did not include aerosol measurements. In order to initiate aerosol monitoring, campaigns were launched during the 2005 to 2007 period. Additionally, OC and BC measurements for the PM10 and PM2.5 (particulate matter smaller than or equal to 10 and 2.5 μm, respectively) fractions were started in 2009. PM10 and PM2.5 samples were collected at five sampling sites in South Africa operated within the DEBITS network, i.e. Louis Trichardt, Skukuza, Vaal Triangle, Amersfoort and Botsalano, with MiniVol samplers. The selected sites are mostly located in rural areas, but with the surrounding atmosphere influenced by industries, transportation, biomass burning, etc. Winters are characterised by an increase in biomass burning (fires) and combustion for domestic use (cooking and space heating). Samples were analysed with a Thermal/Optical Carbon analyser (Desert Research Institute). OC and BC results showed that the total carbonaceous content decreased during the summer due to less biomass burning (fires). BC was the highest at the industrially influenced sites, while OC was highest at regional background sites. OC was higher than BC concentrations at all sites in both size fractions. Most OC and BC occurred in the PM2.5 fraction. OC/BC ratios reflected the setting of the different DEBITS sites, with sites in or close to anthropogenic source regions having the lowest OC/BC ratios, while background sites had the highest OC/BC ratios. The OC mass fraction percentage of the total aerosol weight varied up to 24% and the BC up to 12%. The highest OC mass fraction was found at Skukuza, which was attributed to both natural (lies within the savannah biome) and anthropogenic (dominant path of air mass movement from the anthropogenic industrial hub of South Africa) reasons. The highest mass fraction of BC was found in the Vaal Triangle, since it is situated within a well-known anthropogenic source region. Household combustion for space heating and cooking also seemed to make a significant contribution to BC at this site in the cold winter months. A relatively well-defined seasonal pattern was observed, with higher OC and BC concentrations measured from May to October, which coincides with the dry season in the interior of South Africa. Positive correlations between OC and BC concentrations with the distance back trajectories passed fires were observed, indicating that fires contribute significantly to both atmospheric OC and BC during the burning season. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2014

Black carbon affects the atmosphere, clouds, and the albedo of snow. These effects of black carbon are a fact but exactly what they entail is not well known. The atmosphere, the albedo in ice crystals and snow (due to warming of the snows’ surface), clouds’ life time and cloud cover are all influenced because black carbon absorbs radiation, thus altering the radiative forcing (RF).Many models and measurements have been done to evaluate the effects of black carbon but they show very different results. This literature study examines papers and articles to see what and how much we know about black carbon and its climate effects. I conclude that there have been great differences in results that are evident due to the span that black carbon is thought to change the RF in the atmosphere (results ranging from +0.4 to +1.2 Wm-2), and snow (+0.007 to +0.054 Wm-2), as well as the albedo in snow (results ranging from -0.02 to -0.17, only including the results from studies with BC concentration of 1000 ng/g for increased comparability). I as well as many others suggest that models tend to get very different results because they use different starting conditions and equations and because models handle aerosols and clouds in different ways. This is largely because of a lack of information, especially concerning aerosols and clouds. / Sot påverkar atmosfären, moln och albedot i snö. Dessa effekter av sot är ett faktum, men exakt vad de innebär är inte väl känt. Atmosfären, albedo i iskristaller och snö, uppvärmningen av snö och isytor, molns livstid och molntäckets utbredning påverkas av sot eftersom sot absorberar strålning, vilket förändra strålningsdrivningen och kan förånga moln, och att sot kan vara nuklider som kan skapa moln.Många modeller och mätningar har gjorts för att utvärdera effekterna av sot men de visar mycket olika resultat. Denna litteraturstudie undersöker artiklar för att se vad och hur mycket vi vet om sot och dess klimatpåverkan. Jag drar slutsatsen att det har finns stora skillnader i resultat vilket återspeglas i det stora intervall som sot tros ändra strålningsdrivningen i atmosfären (resultat som sträcker sig från 0,4 till 1,2 Wm-2) och snö (0,007 till 0.054 Wm-2), liksom albedo i snö (resultat som sträcker sig från -0,02 till -0,17 Wm-2). Jag samt mång andra föreslår att modeller tenderar att få väldigt olika resultat eftersom de använder olika startvillkor, ekvationer och eftersom modellerna hanterar aerosoler och moln på olika sätt. Detta är till stor del på grund av bristande information, särskilt när det gäller aerosoler och moln.