Earth’s atmosphere contained more water vapour in August than in any other month on record, according to the Copernicus Climate Change Service. The record could increase the risk of extreme heat and intense rainfall around the world.
C3S measured 27.35kg of water vapour per square metre, 0.04kg more than the previous record set in July 2024. The measure represents the water vapour contained in a column of air above each square metre of Earth’s surface, extending through the atmosphere.
Why water vapour reached a record
Climate scientists said global heating was a contributor because warmer air can hold more moisture. Dr Julien Nicolas, a senior scientist at C3S, said air can hold about 7% more water vapour for every degree of global warming. Read the context: Climate crisis intensifies Europe’s extreme drought by drying soils and water sources.
The tropical oceans are a major source of atmospheric moisture. Nicolas said exceptionally high sea-surface temperatures in those regions, partly linked to strengthening El Niño conditions, increased evaporation and were likely an important contributor to the August record. Related coverage: Sea temperatures reached a July record during Europe’s extreme heat.
Water vapour also reinforces warming because it is a greenhouse gas. Dr Kimberley Reid of the University of Melbourne said the underlying cause was additional carbon dioxide and methane from fossil-fuel emissions, alongside El Niño.
Key points
- The C3S estimates extend back to 1979 and combine humidity readings from satellites, weather balloons and other sources with a weather model.
- August was the joint hottest month in the ERA5 temperature record, which goes back to 1940, and the hottest month in the US National Oceanic and Atmospheric Administration dataset, which begins in 1850.
- A climate scientist calculated that the increase over the previous water vapour record represented about 20 trillion litres of additional water.
How extra moisture can affect people
Rising water vapour can increase the risk of intense rainfall, including rainfall associated with cyclones. When moisture condenses into cloud droplets, it releases heat that can provide extra energy to storms and potentially intensify them.
High humidity can also make heatwaves more dangerous by limiting night-time cooling. Prof Steven Sherwood of the University of New South Wales said this can make it harder for people to recover from very hot days, while moving moisture towards higher latitudes can add heat to the air there.
What scientists are watching next
The tropical Pacific’s current El Niño pattern is forecast to be the strongest on record. Climate scientists expect it could push global temperatures to record levels next year.
The water vapour estimates are part of the ERA5 dataset, with records extending back to 1979. Scientists compared the moisture peak with temperature records covering much longer periods, including NOAA’s dataset beginning in 1850.
What happens next
Scientists will continue monitoring the El Niño pattern and its influence on global temperatures, ocean temperatures and atmospheric moisture. Australian researchers have provisionally found that the expected peak in Pacific Ocean temperatures associated with El Niño was made six times more likely by global heating.
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