Identification

Title

Upper tropospheric ice sensitivity to sulfate geoengineering

Abstract

Aside from the direct surface cooling that sulfate geoengineering (SG) would produce, investigations of the possible side effects of this method are still ongoing, such as the exploration of the effect that SG may have on upper tropospheric cirrus cloudiness. The goal of the present study is to better understand the SG thermodynamical effects on the freezing mechanisms leading to ice particle formation. This is undertaken by comparing SG model simulations against a Representative Concentration Pathway 4.5 (RCP4.5) reference case. In the first case, the aerosol-driven surface cooling is included and coupled to the stratospheric warming resulting from the aerosol absorption of terrestrial and solar near-infrared radiation. In a second SG perturbed case, the surface temperatures are kept unchanged with respect to the reference RCP4.5 case. When combined, surface cooling and lower stratospheric warming tend to stabilize the atmosphere, which decreases the turbulence and updraft velocities (-10% in our modeling study). The net effect is an induced cirrus thinning, which may then produce a significant indirect negative radiative forcing (RF). This RF would go in the same direction as the direct effect of solar radiation scattering by aerosols, and would consequently influence the amount of sulfur needed to counteract the positive RF due to greenhouse gases. In our study, given an 8 Tg-SO2 yr(-1) equatorial injection into the lower stratosphere, an all-sky net tropopause RF of -1.46Wm(-2) is calculated, of which -0.3Wm(-2) (20 %) is from the indirect effect on cirrus thinning (6% reduction in ice optical depth). When surface cooling is ignored, the ice optical depth reduction is lowered to 3 %, with an all-sky net tropopause RF of -1.4Wm(-2), of which -0.14Wm(-2) (10 %) is from cirrus thinning. Relative to the clear-sky net tropopause RF due to SG aerosols (-2.1Wm(-2)), the cumulative effect of the background clouds and cirrus thinning accounts for +0.6Wm(-2), due to the partial compensation of large positive shortwave (+1.6Wm(-2)) and negative longwave adjustments (-1.0Wm(-2)). When surface cooling is ignored, the net cloud adjustment becomes +0.8Wm(-2), with the shortwave contribution (+1.5Wm(-2)) almost twice as much as that of the longwave (-0.7Wm(-2)). This highlights the importance of including all of the dynamical feedbacks of SG aerosols.

Resource type

document

Resource locator

Unique resource identifier

code

https://n2t.org/ark:/85065/d75h7k5s

codeSpace

Dataset language

eng

Spatial reference system

code identifying the spatial reference system

Classification of spatial data and services

Topic category

geoscientificInformation

Keywords

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keyword value

Text

originating controlled vocabulary

title

Resource Type

reference date

date type

publication

effective date

2016-01-01T00:00:00Z

Geographic location

West bounding longitude

East bounding longitude

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Temporal reference

Temporal extent

Begin position

End position

Dataset reference date

date type

publication

effective date

2018-10-17T00:00:00Z

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Conformity

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name of format

version of format

Constraints related to access and use

Constraint set

Use constraints

Limitations on public access

None

Responsible organisations

Responsible party

contact position

OpenSky Support

organisation name

UCAR/NCAR - Library

full postal address

PO Box 3000

Boulder

80307-3000

email address

opensky@ucar.edu

web address

http://opensky.ucar.edu/

name: homepage

responsible party role

pointOfContact

Metadata on metadata

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