August 2026 ties July 2023 as the hottest month in the Copernicus record

August 2026 was the warmest August in the Copernicus ERA5 record and, by a margin of less than 0.01C, the joint-hottest calendar month ever measured, matching July 2023.

Global mean surface air temperature in August was 16.96C. That is 0.85C above the 1991-2020 August average and 1.65C above the 1850-1900 pre-industrial baseline. The previous August peaks, in 2023 and 2024, both sat at 16.82C. July 2023, the previous all-month record, was 16.95C. August 2026 was also 0.06C warmer than July 2026. In ERA5, which starts in 1940, August has beaten July in the same year only four times before: 1945, 1951, 1955 and 1985.

The month was the first since November 2025 to sit more than 1.5C above the pre-industrial August average. Land areas set an August record at 15.73C, a sliver above August 2024's 15.71C. Extra-polar sea surface temperature averaged 21.07C, an August record above the 20.98C mark from 2023, and tied March 2024 for the highest extra-polar ocean reading in any month. A daily extra-polar SST of 21.1C on 22 August edged past the previous daily peak of 21.09C.

Samantha Burgess, strategic lead for climate at ECMWF, called August both the warmest August and the warmest month in the record. The June-to-August mean tied 2024 as the joint-warmest boreal summer, at 0.69C above the 1991-2020 summer average. In Europe the summer was the third-warmest for the continent and the warmest on record for western Europe. European land averaged 20.26C in August, the fourth-warmest August there. The Rhine, Danube, Vistula, Rhone and Po ran at exceptionally low levels.

The 12 months from September 2025 to August 2026 averaged 0.60C above 1991-2020 and 1.48C above 1850-1900. Copernicus attributes the spike to the long rise in greenhouse gases plus a strong El Nino that has pushed warm water back into the eastern tropical Pacific. Burgess has said some coming months could run as much as 2C above the old baselines if that El Nino keeps building toward December.

Arctic sea ice extent in August averaged 6.1 million square kilometres, 0.6 million square kilometres or 9.2 percent below the 1991-2020 August mean, twelfth-lowest for the month. Cover was particularly thin north of two island groups on the Russian side. Antarctic extent was fourth-lowest for August, with the weakest ice in the Amundsen Sea and the Indian Ocean sector.

A single month above 1.5C is not the Paris Agreement's long-term metric. The Agreement speaks about multi-decade averages. The operational fact is simpler. After a dip below the line through much of late 2025, the planet has printed another month that sits 1.65C above the nineteenth-century August, with oceans outside the polar belts at a record for the month and western Europe coming off its hottest summer. The next Copernicus bulletin will show whether September holds that height or drops as the calendar turns.

The United Nations said last week that a durable rise through 1.5C is now unavoidable. August's 1.65C print does not by itself prove that sentence. It is consistent with it. El Nino is adding heat on top of the multi-decade rise. Burgess has already warned that the records will keep arriving as the Pacific event strengthens toward December.

Western Europe's hottest summer is the regional expression of the same file. Low rivers are not an abstract index. They cut barge traffic on the Rhine and the Danube and raise intake temperatures at plants that use river water for cooling. Those are August consequences that sit inside the 16.96C global mean.

Those details are now part of the public record of 10 September 2026 and can be checked against the primary notices issued the same week.