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Asymmetric and Non-Monotonic Response of the Climate System to Idealized CO2 Forcing.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	Asymmetric and Non-Monotonic Response of the Climate System to Idealized CO2 Forcing./
Author:	Mitevski, Ivan.
Description:	1 online resource (159 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 85-02, Section: B.
Contained By:	Dissertations Abstracts International85-02B.
Subject:	Atmospheric sciences. -
Online resource:	click for full text (PQDT)
ISBN:	9798380134729

Asymmetric and Non-Monotonic Response of the Climate System to Idealized CO2 Forcing.
Mitevski, Ivan.

Asymmetric and Non-Monotonic Response of the Climate System to Idealized CO2 Forcing. - 1 online resource (159 pages)

Source: Dissertations Abstracts International, Volume: 85-02, Section: B.

Thesis (Ph.D.)--Columbia University, 2023.

Includes bibliographical references

In this thesis, I explore the climate system's response to symmetric abrupt and transient CO2 forcing across a range of concentrations, from 1/8x to 8xCO2, relative to pre-industrial levels. I use two CMIP6 class models: the CESM Large Ensemble (CESM-LE) model configuration and the NASA Goddard Institute for Space Studies Model E2.1-G (GISS-E2.1-G). I use a hierarchy of (1) fully coupled atmosphere-ocean-sea-ice-land, (2) slab ocean, and (3) prescribed sea surface temperature simulations to analyze and support the findings.First, I find an asymmetric response in global mean surface air temperature (∆Ts) and effective climate sensitivity (EffCS) between colder and warmer experiments. The ∆Ts response at 8xCO2 is more than a third larger than the corresponding cooling at 1/8xCO2. I attribute this assymetry primarily due to the non-logarithmic CO2 forcing, not to changes in the radiative feedbacks.Second, I identify a non-monotonic response of EffCS in the warmer scenarios, with a minimum occurring at 4xCO2 (3xCO2) in CESM-LE (GISS-E2.1-G). This minimum in the warming simulations is associated with a non-monotonicity in the radiative feedback. Similar non-monotonic responses in Northern Hemisphere sea-ice, precipitation, the latitude of zero precipitation-minus-evaporation, and the strength of the Hadley cell are also identified. Comparing the climate response over the same CO2 range between fully coupled and slab-ocean versions of the same models, I demonstrate that the climate system's non-monotonic response is linked to changes in ocean dynamics, associated with a collapse of the Atlantic Meridional Overturning Circulation (AMOC).Third, to establish the significance of North Atlantic cooling in driving the non-monotonic changes in the radiative feedback, I conducted additional atmosphere-only (AMIP) simulations using the same models but with prescribed sea surface temperatures (SSTs) restricted to different regions. Through these simulations, I uncovered that the minimum EffCS value, characterized by notably negative radiative feedbacks, primarily originates from relative cooling of the sea surface temperature (SST) in the tropical and subtropical North Atlantic. This cooling of SSTs contributes to an increase in low-level cloud content in the eastern region of the North Atlantic, subsequently leading to a pronounced negative (stabilizing) feedback response.Furthermore, I investigated the state dependence of the effective radiative forcing (ERF) from 1/16x to 16xCO2. I found that ERF increases with CO2 concentration due to the increase in Instantaneous Radiative Forcing (IRF). Specifically, the IRF increases at higher CO2 values primarily due to stronger stratospheric cooling induced by CO2 forcing. On the other hand, the radiative adjustments counteract the IRF increase, causing the ERF to rise at a slower pace compared to the corresponding increase in IRF induced by higher CO2 concentrations.Lastly, I studied the winter storm tracks in the Southern Hemisphere, focusing on experiments up to 8xCO2. Through this analysis, I identified a non-linear response in the low latitude storm tracks. It is projected that the storm tracks will experience an intensification by the end of the century. However, my findings reveal that this intensification does not scale linearly with CO2 forcing. In fact, the storm tracks shift poleward, including a reduction of the storm tracks at low-mid latitudes and intensification at mid-high latitudes.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798380134729Subjects--Topical Terms:

1179392
Atmospheric sciences.
Subjects--Index Terms:

CO2 dependenceIndex Terms--Genre/Form:

554714
Electronic books.

Asymmetric and Non-Monotonic Response of the Climate System to Idealized CO2 Forcing.
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520 $a In this thesis, I explore the climate system's response to symmetric abrupt and transient CO2 forcing across a range of concentrations, from 1/8x to 8xCO2, relative to pre-industrial levels. I use two CMIP6 class models: the CESM Large Ensemble (CESM-LE) model configuration and the NASA Goddard Institute for Space Studies Model E2.1-G (GISS-E2.1-G). I use a hierarchy of (1) fully coupled atmosphere-ocean-sea-ice-land, (2) slab ocean, and (3) prescribed sea surface temperature simulations to analyze and support the findings.First, I find an asymmetric response in global mean surface air temperature (∆Ts) and effective climate sensitivity (EffCS) between colder and warmer experiments. The ∆Ts response at 8xCO2 is more than a third larger than the corresponding cooling at 1/8xCO2. I attribute this assymetry primarily due to the non-logarithmic CO2 forcing, not to changes in the radiative feedbacks.Second, I identify a non-monotonic response of EffCS in the warmer scenarios, with a minimum occurring at 4xCO2 (3xCO2) in CESM-LE (GISS-E2.1-G). This minimum in the warming simulations is associated with a non-monotonicity in the radiative feedback. Similar non-monotonic responses in Northern Hemisphere sea-ice, precipitation, the latitude of zero precipitation-minus-evaporation, and the strength of the Hadley cell are also identified. Comparing the climate response over the same CO2 range between fully coupled and slab-ocean versions of the same models, I demonstrate that the climate system's non-monotonic response is linked to changes in ocean dynamics, associated with a collapse of the Atlantic Meridional Overturning Circulation (AMOC).Third, to establish the significance of North Atlantic cooling in driving the non-monotonic changes in the radiative feedback, I conducted additional atmosphere-only (AMIP) simulations using the same models but with prescribed sea surface temperatures (SSTs) restricted to different regions. Through these simulations, I uncovered that the minimum EffCS value, characterized by notably negative radiative feedbacks, primarily originates from relative cooling of the sea surface temperature (SST) in the tropical and subtropical North Atlantic. This cooling of SSTs contributes to an increase in low-level cloud content in the eastern region of the North Atlantic, subsequently leading to a pronounced negative (stabilizing) feedback response.Furthermore, I investigated the state dependence of the effective radiative forcing (ERF) from 1/16x to 16xCO2. I found that ERF increases with CO2 concentration due to the increase in Instantaneous Radiative Forcing (IRF). Specifically, the IRF increases at higher CO2 values primarily due to stronger stratospheric cooling induced by CO2 forcing. On the other hand, the radiative adjustments counteract the IRF increase, causing the ERF to rise at a slower pace compared to the corresponding increase in IRF induced by higher CO2 concentrations.Lastly, I studied the winter storm tracks in the Southern Hemisphere, focusing on experiments up to 8xCO2. Through this analysis, I identified a non-linear response in the low latitude storm tracks. It is projected that the storm tracks will experience an intensification by the end of the century. However, my findings reveal that this intensification does not scale linearly with CO2 forcing. In fact, the storm tracks shift poleward, including a reduction of the storm tracks at low-mid latitudes and intensification at mid-high latitudes.
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