CMIP6 data usage: lessons learned from more than 200 million downloads

Earth system simulations from the Coupled Model Intercomparison Project (CMIP) are considered the gold standard in terms of representation of the Earth's climate system, its past and present states, and possible future evolution. As CMIP moves into its seventh phase, the increasing complexity of Earth system models (ESMs) means that there is a greater need for infrastructure resources to store, distribute and utilize CMIP simulations. Statistics on the usage of data during CMIP6 has the potential of offering guidance to prepare for CMIP7. Here, we analyse the downloads of CMIP6 data and propose recommendations for optimizing the production and accessibility of future CMIP data. Our analysis focuses on CMIP6 data downloads statistics from the Earth System Grid Federation (ESGF), the main database of CMIP and other ESMs simulation data. We perform an analysis of CMIP6 ESGF data downloads statistics, with a focus on variables, experiments, individual thematic Model Intercomparison Projects (MIPs), sources and institutions, and related geographical download trends. We further complement the ESGF analysis with statistics on access from other sources hosting CMIP6 data, including some curated by community portals (Pangeo) through commercial clouds (Google Cloud and Amazon Web Services) and by climate services (Copernicus Climate Change Service). We conclude with recommendations for centres involved in the production and distribution of data to optimise resources based on download statistics, to perform stronger quality checks, and to implement improved approaches to track usage.