Outlook Web Desk
On July 21, the world experienced its hottest day on record. But wait. The record was broken in just 24 hours as EU's Copernicus Climate Change Service (C3S) announced July 22 as the hottest day in thousands of years.
Despite not having thermometers placed everywhere, the scientists of C3S are now relying on a new technique to gauge the world's hottest day even without the monitors in every corner of the world. The method is called 'reanalysis'
Reanalysis or retrospective analysis is a technique that gathers data on temperature and utilises particular models to provide a nearly accurate global view of the climate.
In reanalysis method, a nearly real-time picture of the Earth’s climate is created based on several variables including temperature, wind and precipitation, for (roughly) every 30-square-kilometer chunk of the planet’s surface.
The data utilised by the ERA5 model in this reanalysis study dates back to 1940. Besides finding out the hottest day, this time data also showed that 2023 was the hottest year ever recorded.
According to European Centre for Medium-Range Weather Forecasts (ECMWF) Director Carlo Buontempo, EU's C3S aggregates 100 million readings per day about weather conditions from around the world and uses them for reanalysis.
Millions of data received from observations made by airplanes, satellites, ships, radar and surface-level weather stations are fed into a model, known as ERA5, which is equipped with historic information about the global climate to perform the reanalysis.
To cover the gaps in observations caused by several disruptions, the long-term ERA5 model also makes predictions for the scientists to use and test them against the observations.
The mixing of million of data with the super efficient ERA5 model makes it possible to create a complete picture that is as accurate as possible and thus allows scientists to confidently declare record like when the world experiences the hottest day in human history.
Five weather services across the world are constantly monitoring the changes in global temperatures. They are- US’s NOAA, NASA, Europe's ECMWF, China's Meteorological Administration, and the Japan Meteorological Agency.