https://egusphere.copernicus.org/preprints/2026/egusphere-2026-1004/
*Authors: *Walker Raymond Lee, Simone Tilmes, and Ewa M. Bednarz
*11 March 2026*
*Abstract*
Stratospheric aerosol injection (SAI) simulations are often short relative
to climatic timescales and conducted against a background that evolves due
to changes in anthropogenic greenhouse gas emissions and other forcings.
This can cause challenges in assessing certain impacts of the intervention,
especially for aspects of the climate that respond slowly to such changes.
The early Geoengineering Model Intercomparison Project (GeoMIP) G2
experiment prescribes solar dimming to offset 1%CO2 forcing in a
preindustrial control background. Here we propose a new G2-SAI experiment,
in which SAI is applied in the same scenario, to isolate SAI climate
responses from transient changes other than CO2. Using the Community Earth
System Model (CESM2), we present three 150-year "G2-SAI" simulations which
use contemporary SAI strategies: two use the commonly-used "three
degree-of-freedom" ("3DOF") strategy, in which independent injections at
30° N, 15° N, 15° S, and 30° S are used to manage global mean temperature
(T0) and large-scale meridional temperature gradients (T1, T2). Our third
G2-SAI simulation uses a "1DOF" strategy that injects at 30°N and 30°S to
manage global mean temperature only. Our two 3DOF simulations both maintain
the same temperature targets; however, one simulation, which injects mostly
at 15° S, slows but does not prevent the decline of the Atlantic Meridional
Overturning Circulation (AMOC) compared to the baseline simulation, while
the other, which injects mostly at 30° N and 30° S, stops the decline of
AMOC entirely, similarly to the 1DOF simulation. These results demonstrate
that multiple distinct Earth system states can satisfy the same temperature
targets, challenging the assumption of linearity commonly used in strategy
design. In addition, the results highlight that long simulations are
required to identify some of the long-term impacts of SAI, such as AMOC
changes. Using this knowledge, we revisit the ARISE-SAI-1.5 experiment and
modify the injection strategy without changing the temperature targets,
producing an "ARISE-hybrid" ensemble. We demonstrate that this results in
some significant differences in the climate response to SAI, with
implications for the perceived effects of the intervention.
*Source: EGUsphere*
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