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Disputation: Zachary Scott McGraw

Doctoral candidate Zachary Scott McGraw at the Department of Geosciences, Faculty of Mathematics and Natural Sciences, is defending the thesis Global radiative impacts of aerosol variations through mixed-phase and cirrus clouds for the degree of Philosophiae Doctor.

Zachary Scott McGraw. Photo: Private

Zachary Scott McGraw. Photo: Private

The PhD defence and trial lecture are fully digital and streamed using Zoom. The host of the session will moderate the technicalities while the chair of the defence will moderate the disputation.

Ex auditorio questions: the chair of the defence will invite the audience to ask ex auditorio questions either written or oral. This can be requested by clicking 'Participants -> Raise hand'. 

Trial lecture

30.11.2020, 14:00, Zoom (videolink)

The Role of Clouds in Polar Amplification

Conferral summary (in Norwegian)

Aerosoler er samlinger med små luftbårne partikler av for eksempel sot og ørkenstøv. Aerosoler i atmosfæren kan endre jordens klima i en grad som er ukjent, og de gir store usikkerheter ved klimafremskrivninger. Blant annet kan de endre skyenes evner til å reflektere og absorbere stråling. I dette doktorgradsarbeidet er det utført simuleringer av aerosolers klimapåvirkning ved skyer som inneholder is. Studien viser at aerosoler har potensiale for å gi betydelig påvirkning, med naturlige grenser for størrelsen.

Main research findings

Popular scientific article about McGraw’s dissertation:

Global radiative impacts of aerosol variations through mixed-phase and cirrus clouds

Aerosols can warm or cool the Earth by affecting clouds’ abilities to reflect and absorb radiation. This influence is one of the greatest uncertainties in projections of future climate and limits the ability for the scientific community to bound greenhouse gas impacts.

This dissertation focuses on the potential for aerosol changes to alter Earth’s global climate, particularly by influencing the abilities of ice-containing clouds to form and interact with radiation. Associated impacts are evaluated for the presence of man-made soot aerosol, changes in naturally emitted dust from deserts, and a combination of aerosol changes since the pre-industrial era. Here, global-scale aerosol impacts are quantified and constrained using computer simulations of Earth’s climate system. Findings suggest that man-made soot aerosol may cool the Earth through its influence on ice clouds, while substantial changes to desert dust in clouds may have limited global impacts due to opposing influences on different regions and types of radiation.

As greenhouse emissions continue to pose a global threat, creative ways to offset the resulting warming – known as geoengineering strategies – have been sought. One proposal has been to harness the ability for aerosols to influence ice clouds’ abilities to interact with radiation. An additional component of the dissertation supports the potential for deliberate aerosol injections in ice clouds to counteract the damage from climate change.

Photo and other information:

Press photo: Zachary Scott McGraw, portrait; 280px. Photo: Private

Published Nov. 18, 2020 11:39 AM - Last modified Oct. 4, 2021 12:54 PM