Abstract
AbstractWe describe the scientific and technical implementation of two models for a core set of experiments contributing to the sixth phase of the Coupled Model Intercomparison Project (CMIP6). The models used are the physical atmosphere‐land‐ocean‐sea ice model HadGEM3‐GC3.1 and the Earth system model UKESM1 which adds a carbon‐nitrogen cycle and atmospheric chemistry to HadGEM3‐GC3.1. The model results are constrained by the external boundary conditions (forcing data) and initial conditions. We outline the scientific rationale and assumptions made in specifying these. Notable details of the implementation include an ozone redistribution scheme for prescribed ozone simulations (HadGEM3‐GC3.1) to avoid inconsistencies with the model's thermal tropopause, and land use change in dynamic vegetation simulations (UKESM1) whose influence will be subject to potential biases in the simulation of background natural vegetation. We discuss the implications of these decisions for interpretation of the simulation results. These simulations are expensive in terms of human and CPU resources and will underpin many further experiments; we describe some of the technical steps taken to ensure their scientific robustness and reproducibility.
Highlights
Complex models of the Earth system are valuable tools for understanding the processes responsible for our changing climate
We describe the scientific and technical implementation of two models for a core set of experiments contributing to the sixth phase of the Coupled Model Intercomparison Project (CMIP6)
The most common method for generating such an ensemble is to ensure that the initial conditions used to start each historical simulation sample the major modes of variability in the model's preindustrial control, from which each historical member is initialized
Summary
Complex models of the Earth system are valuable tools for understanding the processes responsible for our changing climate. Journal of Advances in Modeling Earth Systems of the World Climate Research Programme that brings together results from these models to better understand their process representation and to pool their projections for robust understanding of future climate pathways. The U.K. contribution to CMIP6 is a collaborative endeavor, with model development and simulation shared between the Met Office Hadley Centre and a number of research centers under the auspices of the Natural Environment Research Council (NERC) and the Science and Technology Facilities Council. Contributions with U.K. models are not limited to the United Kingdom: Key simulations are being performed by the Korean Meteorological Administration and New Zealand's National Institute of Water and Atmospheric Research
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