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dc.contributor.author
Gasparini, Blaž
dc.contributor.supervisor
Lohmann, Ulrike
dc.contributor.supervisor
Peter, Thomas
dc.contributor.supervisor
Leisner, Thomas
dc.date.accessioned
2017-05-30T07:07:04Z
dc.date.available
2017-05-17T09:11:51Z
dc.date.available
2017-05-17T09:52:07Z
dc.date.available
2017-05-17T09:57:44Z
dc.date.available
2017-05-17T10:07:13Z
dc.date.available
2017-05-17T10:08:32Z
dc.date.available
2017-05-17T13:37:30Z
dc.date.available
2017-05-19T07:29:08Z
dc.date.available
2017-05-30T07:07:04Z
dc.date.issued
2016
dc.identifier.uri
http://hdl.handle.net/20.500.11850/52
dc.identifier.doi
10.3929/ethz-b-000000052
dc.description.abstract
This thesis evaluates the option of modifying cirrus clouds in order to counteract part of the anthropogenic global warming, also known as cirrus seeding. The feasibility of cirrus seeding is assessed with the general circulation model ECHAM6-HAM with coupled aerosol-cloud interactions. The warming effect of cirrus clouds on climate led part of the research community to the idea of artificially decreasing their frequency and optical thickness by seeding them with ice nucleating particles. Cirrus seeding re- lies on the competition between two distinct cirrus formation pathways: homogeneous nucleation of soluble aerosols and heterogeneous ice crystal nucleation with the help of solid ice nucleating particles. Seeding attempts to transform optically thicker, longer lived homogeneously nucleated cirrus clouds to thinner and shorter lived heteroge- neously nucleated cirrus clouds. The cirrus seeding effectiveness depends on the correct representation of cirrus clouds in climate models. We evaluated the ECHAM6-HAM model against CALIPSO satellite data and found that the model reproduces the cirrus cloud occurrence fraction and ice water content well, but overestimates their extinction. Most importantly, we found that a large fraction of cirrus clouds formed in environments with liquid water, which cannot be modified by cirrus seeding. Moreover, modelled in situ cirrus formed by heterogenous ice nucleation on dust aerosols in most of the world, limiting the cir- rus geoengineering potential. Meanwhile, homogeneous cirrus were dominant only in the tropical tropopause layer and over mountain regions. Seeding cirrus clouds with ice nucleating particles of radii below 10 μm did not lead to a significant cooling effect on climate, due to radiative warming effects of increasing cir- rus cloud cover and decreasing ice crystal radius, which neutralized the cooling gained by the ice crystal number decrease. However, when seeding with larger ice nucleating particles, cirrus cloud cover, ice crystal number concentration, and ice water content decreased, due to increased ice crystal sedimentation velocity, leading to a cooling of up to 0.7◦ C globally. In addition, an idealized cirrus geoengineering setup with in- creased ice crystal sedimentation velocities at temperatures colder than -35◦ C could fully counteract the temperature increase by 1.5 x CO2 concentrations. Furthermore, seeding with ice nucleating particles larger than 10 μm could counteract up to 55% of the temperature and precipitation damage caused by a 1.5 x CO2 increase, without causing negative side effects in any of the analysed regions. Thus, cirrus geoengi- neering was found to be, not considering its problematic engineering details and large modelling uncertainties, an attractive method to counteract part of the anthropogenic warming.
en_US
dc.format
application/pdf
en_US
dc.language.iso
en
en_US
dc.publisher
ETH Zurich
en_US
dc.rights.uri
http://rightsstatements.org/page/InC-NC/1.0/
dc.subject
climate modelling
en_US
dc.subject
cirrus clouds
en_US
dc.subject
geoengineering
en_US
dc.subject
aerosol-cloud interactions
en_US
dc.subject
cloud radiative effects
en_US
dc.subject
climate engineering
en_US
dc.title
Cirrus clouds and their geoengineering potential
en_US
dc.type
Doctoral Thesis
dc.rights.license
In Copyright - Non-Commercial Use Permitted
dc.date.published
2017-05
ethz.size
178 p.
en_US
ethz.code.ddc
DDC - DDC::5 - Science::500 - Natural sciences
en_US
ethz.identifier.diss
23921
en_US
ethz.publication.place
Zurich
en_US
ethz.publication.status
published
en_US
ethz.leitzahl
ETH Zürich::00002 - ETH Zürich::00012 - Lehre und Forschung::00007 - Departemente::02350 - Dep. Umweltsystemwissenschaften / Dep. of Environmental Systems Science::02717 - Institut für Atmosphäre und Klima / Inst. Atmospheric and Climate Science::03690 - Lohmann, Ulrike / Lohmann, Ulrike
en_US
ethz.leitzahl.certified
ETH Zürich::00002 - ETH Zürich::00012 - Lehre und Forschung::00007 - Departemente::02350 - Dep. Umweltsystemwissenschaften / Dep. of Environmental Systems Science::02717 - Institut für Atmosphäre und Klima / Inst. Atmospheric and Climate Science::03690 - Lohmann, Ulrike / Lohmann, Ulrike
en_US
ethz.relation.cites
10.1002/2015JD024666
ethz.relation.cites
10.5194/acp-17-4871-2017
ethz.date.deposited
2017-05-17T09:11:52Z
ethz.source
FORM
ethz.eth
yes
en_US
ethz.availability
Open access
en_US
ethz.rosetta.installDate
2017-06-02T00:00:00Z
ethz.rosetta.lastUpdated
2020-02-14T04:00:18Z
ethz.rosetta.exportRequired
true
ethz.rosetta.versionExported
true
ethz.COinS
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