We are pleased to share the release of the new ERA Explorer web app powered by the Climate Data Store (CDS) of the Copernicus Climate Change Service (C3S). C3S is an EU service provided by ECMWF. ERA Explorer provides an interactive interface for exploring 85 years of global climate data from the ERA5 reanalysis: https://era-explorer.climate.copernicus.eu/. It replaces the previous ERA5 Explorer, which was introduced in 2019.
ERA Explorer is designed to demonstrate the power and richness of ERA5. It is deployed via the updated infrastructure in the C3S applications cluster. The app enables users to easily compare climate data across the globe, such as temperature, precipitation, wind and other climatological averages. For example, users can investigate local temperature thresholds or understand how the climate has changed in the last 85 years by generating warming stripes.
ERA Explorer has been designed from the ground up to be mobile-first and responsive, offering an optimal experience across devices, from smartphones to desktops. It offers a modern search and map navigation system, allowing users to quickly retrieve climate data by selecting locations or typing place names. It also facilitates deeper data exploration, allowing users to download CSV files to work with locally or access Python notebooks for more advanced analysis. In keeping with the mobile-first approach, the app also supports the creation and sharing of images directly, allowing easy sharing via social media.
Zarr: revolutionising data processing
Behind the scenes, the newly implemented Data Stores ARCO (Analysis Ready, Cloud Optimised) Data Lake based on Zarr technology optimises data processing for ERA Explorer. Zarr is a modern storage format designed for large, multidimensional datasets like ERA5. It stores data in ‘chunks’, allowing efficient, on‑the‑fly access to specific subsets of data. The app uses two Zarr storage formats – one chunked by time and another by space – enabling rapid retrieval of time-series data for a single location or spatial data for broader regions. This enables ERA Explorer to process and display grid-point daily, monthly, and annual statistics, derived from ERA5’s hourly data, in a matter of seconds. The use of Zarr is integral to modernising the C3S Climate Data Store (CDS), significantly enhancing the scalability and speed of climate data analysis. As an extension to the ERA Explorer and powered by the same underlying ARCO data, a new entry has been published on the CDS Catalogue, providing improved access to ERA5 point time-series: https://cds.climate.copernicus.eu/datasets/reanalysis-era5-single-levels-timeseries.
Powerful features
Although using modern, minimalist design standards, ERA Explorer offers a wealth of powerful features. The base map can display temperature or precipitation based on 30‑year averages, with features like month-by-month visualisations and animated wind layers. An interactive onboarding feature guides users into the app, inviting them to explore deeper and more advanced options, such as comparing locations side by side, choosing which climatologies to display, and toggling locations on and off. ERA Explorer provides explanations about the data and data provider, including detailed discussion of the caveats and considerations when interpreting ERA5 data. The accompanying Python notebooks, where users can recreate the same plots themselves, provide a jumping off point for a longer scientific journey.
All told, the design, implementation, technical infrastructure, and dissemination of ERA Explorer represents a significant collaborative effort by many colleagues across ECMWF, supported by the Copernicus Climate Change Service (C3S), external contractor Lobelia for the ARCO implementation, and the Horizon Europe ASPECT project. We welcome any feedback.