Why August 2026 Became the Hottest and Most Humid Month on Record

August 2026 stood out not only for global heat, but for the amount of water held in the atmosphere. An ERA5 analysis reported the warmest August in that dataset’s record—1.65°C above the pre-industrial baseline, or 0.14°C above August 2024—alongside the planet’s moistest month on record. The analysis reported global precipitable water of 2.74 cm and unusually widespread extreme August rainfall. 16

The best-supported interpretation is a compound one: persistent human-driven warming elevated the background temperature and moisture conditions, while a rapidly developing El Niño added a short-term boost to global heat and altered large-scale weather patterns. That combination raises the potential for dangerous heat and, where storms develop, intense rainfall. It does not mean that global temperature alone explains a particular flood, heatwave or storm.

Heat and humidity rose together

A warmer atmosphere changes the starting point for weather. More heat supports greater evaporation from oceans and land, while a warmer atmosphere can contain more water vapour. That extra moisture can intensify humidity and provide more water for precipitation when weather systems force air to rise and condense.

In August, the ERA5-based assessment found both components at exceptional levels: a record global temperature for August and record atmospheric water vapour. 16 That pairing is especially consequential because heat risk is not determined by air temperature alone. High humidity makes it harder for sweat to evaporate, reducing the body’s ability to cool itself.

The record should be interpreted carefully. The 1.65°C figure is a monthly anomaly in one dataset, not a declaration that the Paris Agreement’s long-term temperature threshold has been permanently crossed. Dataset choice, reference period and averaging period all matter when comparing climate records.

The Bright Angel Canyon flood: a local disaster in a warmer, wetter backdrop

The August 29 flash flood in the Grand Canyon illustrates why a moisture-loaded atmosphere can be dangerous when local ingredients line up. Researchers at the Center for Western Weather and Water Extremes reported that tropical moisture associated with Tropical Storm Karina was transported northward into the eastern Grand Canyon, fueling monsoonal rainfall and flash flooding along Bright Angel Creek. At least two deaths were reported and at least 80 people required rescue. 1

The immediate causes were regional and local: monsoonal moisture, intense short-duration rain, steep canyon topography and catchment conditions. Reporting also identified drought and a previous wildfire burn scar as factors that could leave soils more susceptible to rapid runoff and debris flows. 15

That distinction matters. Climate-scale warming can make a hot, moisture-rich backdrop more likely, but it is not a substitute for explaining the storm track, rainfall timing, terrain and land-surface conditions that turned rainfall into a deadly canyon flood.

Why El Niño became a major part of the outlook

El Niño is a recurring Pacific Ocean–atmosphere pattern that can raise global average temperatures and shift seasonal weather probabilities. In early September, the World Meteorological Organization said the developing event was expected to intensify and had a near-100% likelihood of persisting through February 2027; it cautioned that, if its trajectory continued, it could be stronger than any event in the modern monitoring record.

This was a forecast, not a settled fact. But it helps explain why scientists expected the global heat signal to remain elevated and why 2027 could become especially warm: the atmosphere often feels the full global-temperature influence of an El Niño after the ocean warming has developed.

Would 2026 become the warmest year on record?

The answer depended on the dataset and the date of the estimate. Berkeley Earth’s June update put the chance of a record-warm 2026 at about 12%, before lifting it to roughly 69% in its July update as the El Niño outlook strengthened. A subsequent estimate cited by climate scientist Zeke Hausfather put the chance near 75% after August.

Those shifts are a reminder that annual-ranking probabilities are model-based estimates, not final observations. A more defensible conclusion at the time was that August and the evolving El Niño materially increased the chance of a record year, while the final ranking still awaited the remaining months and independent dataset updates.

Europe’s heat toll underscored the stakes

Europe experienced severe heat impacts well before August ended. France reported its hottest summer on record, according to its environment minister and Météo-France reporting. Italy’s National Research Council said the country had its hottest summer since 1950, with a June-to-August average temperature of 24.3°C.

Early mortality data also showed how dangerous prolonged heat can be. EuroMOMO-based reporting found more than 10,000 excess deaths across Europe during the early heatwave period, but this measure covers deaths from all causes above an expected baseline; it is not the same as a confirmed count of deaths directly attributable to heat. The figures were also still emerging.

Claims about specific September French national temperature records were not sufficiently corroborated in the supplied evidence, so they should not be treated as established here.

What a strong El Niño could mean for winter

El Niño changes odds; it does not produce the same outcome everywhere or guarantee a season’s weather. In the United States, a strong event generally favors a more active southern storm track, with wetter and cooler conditions more likely across parts of the South and warmer, drier conditions more likely across parts of the northern tier.

Broader claims of an unusually wet or stormy winter across all of Europe and eastern Asia deserve more caution. Seasonal outcomes depend on the jet stream, regional ocean conditions and other circulation patterns in addition to El Niño. The practical takeaway is not that any one place is certain to flood or receive above-normal rain, but that a very strong El Niño can meaningfully shift risk—and warrants close attention to official regional forecasts.

The larger lesson

August 2026 was notable because extreme heat and record atmospheric moisture arrived together. The event did not create every local disaster, but it raised the background risk environment in which heat stress, heavy rainfall and fast-moving floods can become more damaging. With El Niño expected to persist into early 2027, the key question was no longer whether climate variability or long-term warming mattered. It was how their interaction would play out in specific regions, seasons and vulnerable communities. 16