Our goal is to help support future informed decisions surrounding climate engineering (or solar geoengineering), and stratospheric aerosol injection (SAI) in particular.  A hypothetical decision-maker (whether a policy-maker or public more broadly) will want to know answers to questions such as: What are my choices?  What will happen if we make any given choice?  How confident are we?   Making informed choices thus requires viewing SAI not as “one thing” with one best guess of outcomes, but rather requires a more holistic assessment, for a range of possible future scenarios, for different possible strategies on how deployment might be done, and furthermore an assessment that captures uncertainty.    This is the goal of GAUSS: assessing geoengineering across these three dimensions.  Simulations that span this space will be available to the broader research community for understanding how the impacts depend on these dimensions.

We plan to produce a collection of simulations of stratospheric aerosol intervention in several climate models that span different scenarios for possible implementation (i.e., different amounts of background CO2, different amounts of cooling), different strategies (e.g., different latitudes of injection and different goals), and for different uncertainties (both in several models, and using perturbed physics in a single model).  Furthermore, we hope to create an “open-source” framework wherein other researchers can suggest additional simulations and other modelers can add to the database.  The details of this remain TBD but we welcome input.

Current plans:

  1. We have considered a “moderate” (SSP2-45) emission scenario.
  2. We have considered not only a goal of constant global-mean-temperature (at roughly 1.5C above pre-industrial, i.e., ~2030 conditions), but one that only slows the rate of warming, one that restores to an earlier temperature (0.5C or 1.0C), and a “delayed start”.  Most simulations start in 2035 and run for 35 years.  (Note that the longer-term trajectory is relevant, but not necessary to simulate in an ESM.)
  3. We have included some departures from these trajectories (termination, phase-out,…).
  4. We will include more than one strategy for latitudes of injection and goals.  The main simulations will use injections at 15º and 30º N/S, based on preparatory simulations we performed in multiple climate models. We are also exploring other strategies, such as ones aimed at the Arctic. This could include in the future multiple uncoordinated efforts as well.
  5. We have conducted simulations in CESM2(WACCM6-MA), with a larger ensemble (and a smaller amounts of cases) in CESM2(WACCM6-TSMLT).
  6. Simulations are underway with other models (UKESM, GISS).

All simulations will use a feedback algorithm so that comparisons can be made in terms of what is needed to achieve given goals rather than comparing similar injection rates.

Figure representing the idea behind the main GAUSS simulations

A first set of simulations has been performed (figure above). An overview paper has been published in PNAS. Please contact Dan if you are interested in using output from GAUSS simulations. An overview talk of GAUSS was given by Dan at NCAR in November 2022 and can be find here.