A graph showing the monthly global temperature anomalies

In September, global temperatures skyrocketed to an unprecedented record, leaving scientists astounded.

This scorching September marked the continuation of a concerning trend, following the hottest August and July on record, with the latter being the hottest month ever documented.

What’s particularly striking is that September 2023 shattered the previous record for that month by a staggering 0.5 degrees Celsius, representing the most substantial temperature increase ever recorded. In comparison to pre-industrial levels, September was approximately 1.8 degrees Celsius warmer. This remarkable leap in temperature is supported by datasets from both European and Japanese agencies.

“September was in my professional opinion as a climate scientist – absolutely gobsmackingly bananas” wrote Zeke Hausfather, climate scientist on the Βerkley Earth project. “JRA-55 beat the prior monthly record by over 0.5C, and was around 1.8C warmer than preindustrial levels.”

September 2023 data

Zeke goes on to compare the temperature of September to a typical July from the past decade.

He finally posts a heat map of the temperature anomaly1 of every day of the year so far which basically puts all the previous years to shame.

I’m still struggling to comprehend how a single year can jump so much compared to previous years.

Mika Rantanen, climate researcher at the Finnish Meteorological Institute

Mika uses data from ERA5 to create an animated illustration that visualises that, just by adding the 2023 data, the linear warming trend since 1979 is increased by 10%.

In August, the Guardian asked 45 leading climate scientists about the record-breaking temperatures. They said that, although the recent events might have felt alarming, the broad global heating observed thus far aligns perfectly with the scientific predictions made over the past three decades.

What is JRA-55

JRA-55, short for Japanese 55-year Reanalysis, is a global, widely used atmospheric and oceanic dataset that provides a comprehensive historical record of weather and climate information. It is essentially a reanalysis product that assimilates various types of observational data, such as surface weather observations, satellite data, and balloon measurements, into a numerical weather model to create a consistent and continuous dataset.

It covers a time span of 1958 to the present and it’s a valuable resource for climate research, weather forecasting, and understanding long-term climate trends. Researchers and meteorologists use JRA-55 to study past climate variations, analyze weather patterns, and improve our understanding of how the Earth’s climate system works.

What is ERA5

ERA5, short for the Fifth Generation of the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis, is a state-of-the-art climate dataset. It provides comprehensive information on various atmospheric and surface parameters over a global scale, including temperature, humidity, wind, pressure, and more.

  1. A heat map of temperature anomalies for every day of the year is a representation of how daily temperatures deviate from the long-term average over a specific period. ↩︎

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