https://esd.copernicus.org/articles/15/405/2024/
*Authors*
Anton Laakso, Daniele Visioni, Ulrike Niemeier, Simone Tilmes, and Harri
Kokkola
https://doi.org/10.5194/esd-15-405-2024
*24 April 2024*
*Abstract*
This is the second of two papers in which we study the dependency of the
impacts of stratospheric sulfur injections on the model and injection
strategy used. Here, aerosol optical properties from simulated
stratospheric aerosol injections using two aerosol models (modal scheme M7
and sectional scheme SALSA), as described in Part 1 (Laakso et al., 2022),
are implemented consistently into the EC-Earth, MPI-ESM and CESM Earth
system models (ESMs) to simulate the climate impacts of different injection
rates ranging from 2 to 100 Tg(S) yr−1. Two sets of simulations were run
with the three ESMs: (1) regression simulations, in which an abrupt change
in CO2 concentration or stratospheric aerosols over pre-industrial
conditions was applied to quantify global mean fast temperature-independent
climate responses and quasi-linear dependence on temperature, and (2)
equilibrium simulations, in which radiative forcing of aerosol injections
with various magnitudes compensated for the corresponding radiative forcing
of CO2 enhancement to study the dependence of precipitation on the
injection magnitude. The latter also allow one to explore the regional
climatic responses. Large differences in SALSA- and M7-simulated radiative
forcing in Part 1 translated into large differences in the estimated
surface temperature and precipitation changes in ESM simulations; for
example, an injection rate of 20 Tg(S) yr−1 in CESM using M7-simulated
aerosols led to only 2.2 K global mean cooling, while EC-Earth–SALSA
combination produced a 5.2 K change. In equilibrium simulations, where
aerosol injections were utilized to offset the radiative forcing caused by
an atmospheric CO2 concentration of 500 ppm, the decrease in global mean
precipitation varied among models, ranging from −0.7 % to −2.4 % compared
with the pre-industrial climate. These precipitation changes can be
explained by the fast precipitation response due to radiation changes
caused by the stratospheric aerosols and CO2, as the global mean fast
precipitation response is shown to be negatively correlated with global
mean atmospheric absorption. Our study shows that estimating the impact of
stratospheric aerosol injection on climate is not straightforward. This is
because the simulated capability of the sulfate layer to reflect solar
radiation and absorb long-wave radiation is sensitive to the injection rate
as well as the aerosol model used to simulate the aerosol field. These
findings emphasize the necessity for precise simulation of aerosol
microphysics to accurately estimate the climate impacts of stratospheric
sulfur intervention. This study also reveals gaps in our understanding and
uncertainties that still exist related to these controversial techniques.
*Source: EGU *
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