The past 12 months in 87 cities: 74 ran warmer than normal, French cities furthest of all

Over the twelve months from 12 September 2025 to 9 September 2026, 74 of the 86 cities where our two data sources agree were warmer than their normal, 9 were cooler and the rest finished level. Averaged across all of them, the year ran +0.9 °C above normal (ERA5: +1.0 °C), and 63% of all city-days were warmer than normal for their date (ERA5: 64%).

The figures come from OpenWeather’s hourly observation history, aggregated into local days and compared with OpenWeather’s normal for each calendar date, then recomputed with the ERA5 reanalysis against its 2011–2025 average. A city is ranked only when the two anomalies agree within 1.5 °C; 86 of 87 did. The methodology sets out every definition.

74 / 86

cities warmer than normal over the year

+0.9 °C

average anomaly across those cities

+2.7 °C

Phoenix, the largest anomaly

63%

of city-days warmer than normal

Key findings

• 74 of 86 cities were warmer than normal in OpenWeather’s record, 79 in ERA5’s; 42 were at least 1 °C above.
• All 25 French cities ran warm, by +1.4 °C on average — against +0.8 °C for the rest of Europe and +0.6 °C for the cities outside Europe.
• Phoenix had the largest anomaly, +2.7 °C (+4.9 °F); Johannesburg the smallest, −0.7 °C.
• January 2026 was the only month when the average across cities fell below normal (−0.2 °C). August 2026 ran furthest above (+1.5 °C).
• The hottest reading was 47.1 °C (116.8 °F) in Dubai on 13 August; the coldest −22.6 °C (−8.7 °F) in Chicago on 23 January.

A warm year, but not everywhere equally

At the top of the table, Phoenix ran +2.7 °C above its normal over the year (ERA5: +2.2 °C), followed by Nice (+2.4 °C), Lima (+2.3 °C) and Valletta (+2.3 °C). Paris finished at +1.8 °C, London at +1.6 °C, New York at +0.2 °C and Tokyo at +0.6 °C.

France stands out as a group. Its 25 cities averaged +1.4 °C, and even the least anomalous of them, Strasbourg, was +0.8 °C above normal. The other 30 European cities averaged +0.8 °C, pulled down by the north and east: Berlin (−0.1 °C), Helsinki (−0.1 °C), Kyiv (−0.4 °C), Warsaw (−0.4 °C) finished below normal. The 5 cities south of the tropics — Melbourne, Sydney, Buenos Aires, São Paulo, Johannesburg — stayed close to their normals, at +0.2 °C on average (ERA5: +0.5 °C).

Month by month

The heatmap shows where the year’s warmth and cold came from. Averaged across cities, the last months of 2025 ran mildly warm (Oct +0.2 °C, Nov +0.4 °C, Dec +0.8 °C). January 2026 then dipped below, when only 36 of 86 cities were warmer than normal. The cold sat over northern and eastern Europe, with Toronto (−2.0 °C), Chicago (−1.7 °C) and New York (−1.5 °C) also below normal, and it lingered into February in the Nordic and Baltic region: the three coldest city-months of the year relative to normal were Helsinki in February 2026 (−6.4 °C), Kyiv in January 2026 (−5.2 °C), Kyiv in February 2026 (−5.2 °C).

From February 2026 to August 2026, the cross-city average stayed above +1 °C in every month. August 2026 was the warmest relative to normal in OpenWeather’s data (+1.5 °C), June 2026 in ERA5’s (+2.0 °C). The single most anomalous city-month was Phoenix in March 2026, at +7.2 °C.

The year’s extremes

Dubai recorded the year’s highest temperature among these cities, 47.1 °C on 13 August, ahead of Phoenix (46.5 °C) and Delhi (45.5 °C). Dubai spent 165 days (ERA5: 161) and Phoenix 147 (ERA5: 146) at 35 °C or more. At the other end, Chicago fell to −22.6 °C on 23 January and Kyiv to −22.5 °C on 2 February. ERA5, which averages over a grid of about 30 km, puts both peaks and troughs slightly differently, so its values sit beside OpenWeather’s.

What this does and does not show

The normal is the average of recent years, not a pre-industrial baseline, so a city at +1 °C here was one degree warmer than a period that was itself already warm. Twelve months is a short window for any single city, and the figures describe these cities, not the planet. Reykjavik is not ranked: OpenWeather puts its anomaly at −3.7 °C, ERA5 at ±0.0 °C.

For the seasons in detail, see summer 2026 in 32 European cities and winter 2025–26. The CSV below has every city’s annual and monthly anomalies from both sources.