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Causal links of past climate change in Coupled Model Intercomparison Project Phase 5 climate models

Le, Thanh LU (2016)
Abstract (Swedish)
Klimatsystemet påverkas av diverse externa faktorer (vulkanism, solaktivitet och förändringar i växthusgaskoncentration) och dess eget interna klimatvariabilitet. När man utvärderar orsakerna till tidigare klimatförändringar är det viktigt att öka vår kunskap om påverkan från externa faktorer samt förstå sambandet mellan de större interna faktorer som styr klimatet för att kunna förutsäga framtida klimatextremer.
Denna avhandling använder Grangers kausalitetstest för att undersöka effekterna av externa faktorer på lufttemperaturen nära markytan (SAT) under kortare tidsskalor (kortare än 10 år) för det senaste årtusendet (850-1850 e.Kr.). Dessutom undersöks solens påverkan på lågfrekvensvariabilitet för Nordatlanten. Också det... (More)
Klimatsystemet påverkas av diverse externa faktorer (vulkanism, solaktivitet och förändringar i växthusgaskoncentration) och dess eget interna klimatvariabilitet. När man utvärderar orsakerna till tidigare klimatförändringar är det viktigt att öka vår kunskap om påverkan från externa faktorer samt förstå sambandet mellan de större interna faktorer som styr klimatet för att kunna förutsäga framtida klimatextremer.
Denna avhandling använder Grangers kausalitetstest för att undersöka effekterna av externa faktorer på lufttemperaturen nära markytan (SAT) under kortare tidsskalor (kortare än 10 år) för det senaste årtusendet (850-1850 e.Kr.). Dessutom undersöks solens påverkan på lågfrekvensvariabilitet för Nordatlanten. Också det dubbelriktade kausala förhållandet mellan El Niño – sydlig oscillation (ENSO) och den Indiska oceanen dipolen (IOD) utvärderas. Den huvudsakliga data som används i denna avhandling är från "Coupled Model Intercomparison Project 5” (CMIP5) simuleringarna.
Resultaten i denna avhandling stöder slutsatsen om en robust påverkan från vulkanism på SAT i förindustriella tider under de senaste 1000 åren. Dessutom visar resultaten att det finns en solsignal i SAT i tropiska och subtropiska regioner medan påverkan från växthusgaser på regional SAT är svag och osäker. Utöver det kan solen eventuellt ha en påverkan på vintertemperaturen vid havsytan (SST) i Nordatlanten, på tidsskalor över flera århundraden, medan sambandet mellan solens påverkan och den Nordatlantiska oscillationen är svagt. Resultaten visar att påverkan från ENSO på IOD är svagare i flera modeller än resultatet i återanalyserad data samtidigt som påverkan från IOD på ENSO är robust i de flesta modeller och även i återanalyserad data.
Övergripande bidrar resultaten i denna avhandling till ökad kunskap om påverkan från externa faktorer på regionala klimatförändringar och ökar förståelsen för orsaksambandet mellan ENSO och IOD. (Less)
Abstract
The climate system is influenced by various external forcings (e.g. volcanic forcing, solar forcing and change of greenhouse gas concentrations) and its own internal climate variability. While evaluating the causes of past climate change is important to expand our knowledge of the impacts of different external forcings, understanding the coupling between major internal climate drivers is crucial for the prediction of future climate.
This thesis uses the Granger causality test to investigate the impacts of external forcings on subdecadal variability of regional near-surface air temperature (SAT) during the past millennium (period 850-1850). In addition, the role of solar forcing on low-frequency variability of the North Atlantic is... (More)
The climate system is influenced by various external forcings (e.g. volcanic forcing, solar forcing and change of greenhouse gas concentrations) and its own internal climate variability. While evaluating the causes of past climate change is important to expand our knowledge of the impacts of different external forcings, understanding the coupling between major internal climate drivers is crucial for the prediction of future climate.
This thesis uses the Granger causality test to investigate the impacts of external forcings on subdecadal variability of regional near-surface air temperature (SAT) during the past millennium (period 850-1850). In addition, the role of solar forcing on low-frequency variability of the North Atlantic is examined and the two-way causal relationship between the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) is evaluated. The investigations are mainly based on the output from the Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations.
The results of this thesis support the conclusion for robust impact of volcanic forcing on SAT during preindustrial times of the past 1000 years. Besides, the results indicate that there is solar signal in SAT response of the tropical and subtropical regions whereas the influence of greenhouse gases radiative forcing on regional SAT is weak and uncertain. In addition, solar forcing might have an influence, at multi-centennial time scales, on the North Atlantic winter sea surface temperatures while the connection between solar forcing and the North Atlantic Oscillation is weak in the models. The results for the investigation of the causal impact of ENSO on the IOD show that this impact is weaker in numerous models than the result in reanalysis datasets, whereas the influence of the IOD on ENSO is robust for most models and reanalysis datasets.
Overall, the findings in this thesis contribute to the knowledge of the influence of external forcings on regional climate change and help us to better understand the two-way causal relationship between ENSO and the IOD. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Senior lecturer Zhang, Qiong, Bolin Centre for Climate Research, Stockholm University
organization
publishing date
type
Thesis
publication status
published
subject
keywords
solar forcing, volcanic forcing, greenhouse gases radiative forcing, Granger causality, near-surface air temperature, ENSO, IOD, CMIP5, North Atlantic
pages
88 pages
publisher
Lund University, Faculty of Science, Department of Geology, Quaternary Sciences
defense location
Geocentre II, lecture hall “Pangea”, Sölvegatan 12, Lund
defense date
2016-10-21 13:15
ISBN
ISBN 978-91-87847-24-0
ISBN 978-91-87847-25-7
language
English
LU publication?
yes
id
5a4a7a43-1449-4d20-a894-2891c17f4f2f
date added to LUP
2016-09-28 17:11:33
date last changed
2016-10-07 15:59:33
@phdthesis{5a4a7a43-1449-4d20-a894-2891c17f4f2f,
  abstract     = {The climate system is influenced by various external forcings (e.g. volcanic forcing, solar forcing and change of greenhouse gas concentrations) and its own internal climate variability. While evaluating the causes of past climate change is important to expand our knowledge of the impacts of different external forcings, understanding the coupling between major internal climate drivers is crucial for the prediction of future climate. <br/>This thesis uses the Granger causality test to investigate the impacts of external forcings on subdecadal variability of regional near-surface air temperature (SAT) during the past millennium (period 850-1850). In addition, the role of solar forcing on low-frequency variability of the North Atlantic is examined and the two-way causal relationship between the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) is evaluated. The investigations are mainly based on the output from the Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations.<br/>The results of this thesis support the conclusion for robust impact of volcanic forcing on SAT during preindustrial times of the past 1000 years. Besides, the results indicate that there is solar signal in SAT response of the tropical and subtropical regions whereas the influence of greenhouse gases radiative forcing on regional SAT is weak and uncertain. In addition, solar forcing might have an influence, at multi-centennial time scales, on the North Atlantic winter sea surface temperatures while the connection between solar forcing and the North Atlantic Oscillation is weak in the models. The results for the investigation of the causal impact of ENSO on the IOD show that this impact is weaker in numerous models than the result in reanalysis datasets, whereas the influence of the IOD on ENSO is robust for most models and reanalysis datasets.<br/>Overall, the findings in this thesis contribute to the knowledge of the influence of external forcings on regional climate change and help us to better understand the two-way causal relationship between ENSO and the IOD.},
  author       = {Le, Thanh},
  isbn         = {ISBN 978-91-87847-24-0},
  keyword      = {solar forcing,volcanic forcing,greenhouse gases radiative forcing,Granger causality,near-surface air temperature,ENSO,IOD,CMIP5,North Atlantic},
  language     = {eng},
  pages        = {88},
  publisher    = {Lund University, Faculty of Science, Department of Geology, Quaternary Sciences},
  school       = {Lund University},
  title        = {Causal links of past climate change in Coupled Model Intercomparison Project Phase 5 climate models},
  year         = {2016},
}