The role of atmospheric stability in the forcing-feedbacks-adjustments framework
File(s)
Author(s)
Salvi, Pietro
Type
Thesis
Abstract
One of the most recognised measures of climate change, global warming, is still subject
to significant uncertainty. Even with the best tools available in the form of climate
models, wide-ranging estimates are given of the increase in surface temperature for a given
emissions scenario. This thesis investigates various mechanisms by which temperature
change occurs as driven by energy imbalances introduced into the Earth system.
The focus of this work lies on atmospheric stability, a measure of vertical temperature
gradients that is well related to convection and thus in turn clouds. Greater stability
suppresses convection and encourages low cloud formation which provides a cooling effect
on the planet as these low clouds reflect incoming solar radiation. The structure of energy
imbalances induced by forcing agents is found to be significant for stability in many
ways, from the vertical structure of atmospheric heating, to the horizontal distribution
of radiative flux that affects the pattern of sea surface temperature (SST) change, to the
time-evolution of the forcing agents themselves. The result of analysing the impact of
these structures through stability is that stability is found to explain much in terms of
differences between forcing agents, as well as how temperatures evolve in the historical
period.
This thesis incorporates analysis of publicly available data from Climate Model Intercomparison Project 6 (CMIP6) historical experiments in order to compare and contrast
feedbacks from time-evolving aerosol, greenhouse gas (GHG), and natural forcings. Work
here shows that historical aerosols cause more amplifying feedbacks (higher effective climate sensitivity) than GHGs. Data from idealised computational experiments run for this
project demonstrate that this is due to the extra-tropical skew of aerosol forcing. Furthermore, the time-evolving feedbacks of the historical period are found to be explained
by the time-evolving feedbacks for the components of historical forcing.
to significant uncertainty. Even with the best tools available in the form of climate
models, wide-ranging estimates are given of the increase in surface temperature for a given
emissions scenario. This thesis investigates various mechanisms by which temperature
change occurs as driven by energy imbalances introduced into the Earth system.
The focus of this work lies on atmospheric stability, a measure of vertical temperature
gradients that is well related to convection and thus in turn clouds. Greater stability
suppresses convection and encourages low cloud formation which provides a cooling effect
on the planet as these low clouds reflect incoming solar radiation. The structure of energy
imbalances induced by forcing agents is found to be significant for stability in many
ways, from the vertical structure of atmospheric heating, to the horizontal distribution
of radiative flux that affects the pattern of sea surface temperature (SST) change, to the
time-evolution of the forcing agents themselves. The result of analysing the impact of
these structures through stability is that stability is found to explain much in terms of
differences between forcing agents, as well as how temperatures evolve in the historical
period.
This thesis incorporates analysis of publicly available data from Climate Model Intercomparison Project 6 (CMIP6) historical experiments in order to compare and contrast
feedbacks from time-evolving aerosol, greenhouse gas (GHG), and natural forcings. Work
here shows that historical aerosols cause more amplifying feedbacks (higher effective climate sensitivity) than GHGs. Data from idealised computational experiments run for this
project demonstrate that this is due to the extra-tropical skew of aerosol forcing. Furthermore, the time-evolving feedbacks of the historical period are found to be explained
by the time-evolving feedbacks for the components of historical forcing.
Version
Open Access
Date Issued
2022-09
Date Awarded
2023-03
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Ceppi, Paulo
Gregory, Jonathan
Sponsor
Imperial College London
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)