The browser you are using is not supported by this website. All versions of Internet Explorer are no longer supported, either by us or Microsoft (read more here: https://www.microsoft.com/en-us/microsoft-365/windows/end-of-ie-support).

Please use a modern browser to fully experience our website, such as the newest versions of Edge, Chrome, Firefox or Safari etc.

Raimund Muscheler

Raimund Muscheler

Professor

Raimund Muscheler

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

Author

  • Thanh Le

Summary, in English

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.

Department/s

  • Quaternary Sciences
  • MERGE: ModElling the Regional and Global Earth system

Publishing year

2016

Language

English

Publication/Series

Lundqua thesis

Issue

83

Document type

Dissertation

Publisher

Lund University, Faculty of Science, Department of Geology, Quaternary Sciences

Topic

  • Climate Research
  • Meteorology and Atmospheric Sciences
  • Geosciences, Multidisciplinary

Keywords

  • solar forcing
  • volcanic forcing
  • greenhouse gases radiative forcing
  • Granger causality
  • near-surface air temperature
  • ENSO
  • IOD
  • CMIP5
  • North Atlantic

Status

Published

Project

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

Supervisor

  • Jesper Sjolte
  • Raimund Muscheler
  • Dan Hammarlund
  • Svante Björck

ISBN/ISSN/Other

  • ISSN: 0281-3033
  • ISBN: 978-91-87847-25-7
  • ISBN: 978-91-87847-24-0

Defence date

21 October 2016

Defence time

13:15

Defence place

Geocentre II, lecture hall “Pangea”, Sölvegatan 12, Lund

Opponent

  • Qiong Zhang (Senior lecturer)