The European Climate Change Service (C3S), managed by the European Center for Medium-Range Weather Forecasts (ECMWF), has just made an impressive new application available to the general public. Named “ Weather Replay », it acts like a real time machine, giving access to archives of the planet hour by hour, from January 1940 until a few days before today. It is a unique gateway to more than eight decades of atmospheric data.
How does this real time machine work?
The Weather Replay interface is designed to be intuitive et accessible. The user simply chooses a date in the calendar and a location on the globe, either by navigating the map or using the search bar. In a few seconds, the application displays the most relevant variables to understand the weather report of this precise moment: temperature, wind speed, atmospheric pressure or even cumulative precipitation.
To provide such a wealth of information, the tool leverages the power of the reanalysis dataset ERA5 of Copernicus, combined with a robust network of satellites and archives. This infrastructure makes it possible to generate visualisations complexes almost instantly, offering even expert users the ability to track variables in the upper atmosphere, such as the jet stream (altitude wind) 10 km above the ground.
What types of historical events can we explore?
The application highlights a selection ofmajor historical events to illustrate its capabilities. It is thus possible to relive the slow and devastating trajectory of Hurricane Katrina in August 2005, the European heatwave of 2003 or even Cyclone Nargis which struck Myanmar in 2008. These examples allow us to better understand the scale of extreme phenomena.
Beyond these textbook cases, Weather Replay invites a more personal exploration, such as discovering what the weather was like on the day of your birth. One of the most advanced functions is its comparison toolwhich allows two events to be viewed side by side, such as the Scandinavian heat waves of 2018 and 2025. This functionality is crucial for analyzing the evolution of the climate change.
What is the objective behind this innovative tool?
According to Chiara Cagnazzo, senior scientist at C3S, this application is a real « game changer » that can transform the way the public and media explore and understand climate data. The objective is to make this information, often complex, much more digestible and engaging, by banking on the old adage “ a picture is worth a thousand words “. This tool is part of a larger effort of data democratization.
This initiative aims to transform the program’s immense volume of data Copernicus into practical instruments for citizens. The application also includes a direct link to its sister application, Thermal Tracewhich focuses on more than eighty years of data relating to thermal comfort. By directly exploring the past, users can better understand the evolution of our climate.
