Quantifying the Impact of Internal Variability on the CESM2 Control
Algorithm for Stratospheric Aerosol Injection
Abstract
Earth system models are a powerful tool to simulate the response to
hypothetical climate intervention strategies, such as stratospheric
aerosol injection (SAI). Recent simulations of SAI implement tools from
control theory, called “controllers”, to determine the quantity of
aerosol to inject into the stratosphere to reach or maintain specified
global temperature targets, such as limiting global warming to
1.5\textdegree C above pre-industrial temperatures. This
work explores how internal (unforced) climate variability can impact
controller-determined injection amounts using the Assessing Responses
and Impacts of Solar climate intervention on the Earth system with
Stratospheric Aerosol Injection (ARISE-SAI) simulations. Since the
ARISE-SAI controller determines injection amounts by comparing global
annual-mean surface temperature to predetermined temperature targets,
internal variability that impacts temperature can impact the total
injection amount as well. Using an offline version of the ARISE-SAI
controller and data from CESM2 earth system model simulations, we
quantify how internal climate variability and volcanic eruptions impact
injection amounts. While idealized, this approach allows for the
investigation of a large variety of climate states without additional
simulations and can be used to attribute controller sensitivities to
specific modes of internal variability.