Environmental Science Laboratory, Central Research Institute of Electric Power Industry, Abiko-shi, Japan
Myles R. Allen
Department of Physics, Atmospheric Oceanic and Planetary Physics, University of Oxford, UK
Environmental Change Institute, University of Oxford, Oxford, UK
Abstract. Here we present a Generalised Impulse Response (GIR) model for use in probabilistic future climate and scenario exploration, integrated assessment, policy analysis and teaching. This model is based on a set of only six equations, which correspond to the standard Impulse Response model used for greenhouse gas metric calculations by the IPCC, plus one physically-motivated additional equation to represent state-dependent feedbacks on the response timescales of each greenhouse gas cycle. These six equations are simple and transparent enough to be easily understood and implemented in other models without reliance on the original source code, but flexible enough to reproduce observed well-mixed greenhouse gas (GHG) concentrations and atmospheric lifetimes, best-estimate effective radiative forcing, and temperature response. We describe the assumptions and methods used in selecting the default parameters, but emphasize that other methods would be equally valid: our focus here is on identifying a minimum level of structural complexity. The tunable nature of the model lends it to use as a fully transparent emulator of complex Earth System Models, such as those participating in CMIP6, while also reproducing the behaviour of other simple climate models. We argue that this GIR model is adequate to reproduce the global temperature response to global emissions and effective radiative forcing, and that it should be used as a lowest-common denominator to provide consistency and continuity between different climate assessments. The model design is such that it can be written in tabular data analysis software, such as Excel, increasing the potential user base considerably.
How to cite. Leach, N. J., Nicholls, Z., Jenkins, S., Smith, C. J., Lynch, J., Cain, M., Wu, B., Tsutsui, J., and Allen, M. R.: GIR v1.0.0: a generalised impulse-response model for climate uncertainty and future scenario exploration, Geosci. Model Dev. Discuss. [preprint], https://doi.org/10.5194/gmd-2019-379, 2020.
Received: 31 Dec 2019 – Discussion started: 27 Jan 2020
GIR is a simple climate model designed to make exploration of the impact of greenhouse gas and aerosol emissions on the climate easy and understandable for its users. It uses an intuitive input and output structure, and the model is itself a set of only six equations. This lends the model to applications such as teaching, or as a lowest common denominator model between groups in large-scale climate assessments. It could also be used to investigate more complex models through emulation.
GIR is a simple climate model designed to make exploration of the impact of greenhouse gas and...