GeoMIP Simulations: Testbed

The GeoMIP Testbed was introduced by Kravitz et al. (2015) as a way for other communities to participate in GeoMIP. The idea is that individuals can propose potential GeoMIP experiments to be performed by a small number of models. If these experiments turn out to be fruitful, they can then be considered for adoption by GeoMIP as official core experiments.

All current testbed experiments will be listed here as they are added:


Experiment G6sulfur is designed to reduce radiative forcing in a high emissions scenario to that of a moderate emissions scenario via simulation of stratospheric sulfate aerosol injection. This experiment would be useful in assessing the effectiveness of geoengineering as part of a portfolio of responses to climate change. However, this experiment only addresses one potential scenario, i.e., using geoengineering to achieve the forcing from a “medium” scenario. Increasing amounts of stratospheric SO2 injection would cause particles to coagulate and fall out more rapidly. Therefore, the relationship between the amount of injection and the resulting radiative forcing is projected to be sublinear. This problem prompts a natural question: how would the injection amount and the results from that injection differ if geoengineering were used to achieve a larger radiative forcing? This question is the first step in assessing any potential practical limits to stratospheric aerosol injection.

A natural first step in addressing this problem would in- volve a similar setup to that of G6sulfur. Against a background of the ScenarioMIP Tier 1 high forcing scenario, sulfate aerosol precursors would be injected into the stratosphere in sufficient amounts to reduce anthropogenic radiative forcing from the levels in the high forcing scenario to levels in the low forcing scenario.

GeoSulfur5, GeoSulfur20, GeoSulfur50

A different way of quantifying the effects of stratospheric aerosol geoengineering is to perform a series of experiments in which the hypothetical rate of injection of stratospheric sulfate aerosols is constrained. Such a simulation would be well suited to ascertain the range of model responses to a fixed amount of SO2 injection, highlighting model diversity. Against a background of the ScenarioMIP Tier 1 high forcing scenario, the modeling groups will inject 10, 20, or 50 Tg SO2 per year into the lower stratosphere, in a similar setup to experiment G4.


Experiment G1ocean-albedo has simulated the effects of marine cloud brightening by increasing ocean albedo by a constant multiplication factor. However, GeoMIP has not yet explored land-based approaches towards solar radiation management. Such approaches could readily be implemented on the regional scale, as human activities already control the albedo of a significant fraction of the land surface. We therefore propose an alternative experiment in which the land surface albedo is increased.

A protocol for this experiment has been designed and is available by clicking here. This experiment has specific model output requirements, which can be found by clicking here. For further details, please contact Annette Hirsch.


The G4Foam Experiment involves ocean albedo increases in several localized regions to take advantage of the power of climate system feedbacks in providing more broad-scale cooling. A formal protocol has not yet been established, but initial results from a single-model study are discussed by Gabriel et al. (2017).


Instead of using SO2 injection, a different injection strategy could be direct condensation of H2SO4. This method is hypothesized to have numerous advantages over SO2 injection, but it has not been tested in state-of-the-art Earth System Models, nor in a multi-model context. Details of the experimental protocol are provided here.