We summed 76 winters of ERA5 heating degree days across 25 European countries. The last five winters ran 9.3% milder than the 1991-2020 normal, the decline is accelerating, and every one of the ten mildest heating seasons on record has come since 2006. That is a structural cut to gas and electric heating demand — with a rising cooling season taking its place.
Latest complete heating season (July-June) versus each country's fixed 1991-2020 average. The latest winter is computed live from Copernicus ERA5 monthly heating degree days; the normal was computed from the full 1950-2026 archive on August 9, 2026. Sparklines show the last 12 winters.
Every autumn, European gas storage levels and weather forecasts start moving markets. The quiet structural story underneath is that the thing being forecast — winter cold itself — has been shrinking for decades. Measured in heating degree days (HDD, the standard yardstick of heating need: degrees below 18°C, summed daily), the average heating season across 25 European countries was 2,731 HDD over the last five winters (2021/22-2025/26) — 9.3% below the 1991-2020 climatological normal of 3,009, and 18.3% below the average winter of the 1950s.
This is not one lucky stretch. The Copernicus ERA5 record shows European heating demand potential falling by about 86 HDD per decade since 1951 — and the rate has accelerated to roughly 140 HDD per decade since the early 1990s, close to 5% of a normal winter lost every ten years. Because energy used for space heating scales almost linearly with degree days, that is a like-for-like decline in the heating fuel a fixed building stock needs — before any insulation, heat pumps or behaviour change, which compound it.
Below we quantify the trend country by country, verify the demand link in European grid data, and look at the flip side: cooling demand, which is growing three times faster in percentage terms than heating is fading.
1. The backdrop: the three hottest years on record, back to back
Europe's milder winters sit inside an unambiguous global signal. In the ERA5 reanalysis, which reconstructs world temperature back to 1940, the three hottest calendar years in the entire record are 2023, 2024 and 2025 — with 2024 the peak at a global mean of 15.09°C, 1.34°C above the 1951-1980 average. Through August 2, 2026 was running as the third-warmest year-to-date at 14.93°C, about 1.17°C above the same period of 1951-1980 (Copernicus/ECMWF ERA5).
Daily global mean air temperature since 2022, °C — the record years 2023-2025 and the current year, updating daily. Latest: 16.97°C (Aug 2, 2026).
2. Seventy-six winters, one direction
Summing ERA5 monthly heating degree days into July-June heating seasons gives 76 complete winters per country, 1950/51 through 2025/26. The chart shows six major markets; the pattern holds across all 25 countries analysed. Winter-to-winter noise is large — a cold snap like early 2021 still happens — but the floor keeps dropping: all ten of the mildest heating seasons in the record have occurred since 2006/07. The mildest was 2006/07 itself (16.2% below normal), followed by 2023/24 (-15.3%) and 2019/20 (-12.6%). The most recent complete winter, 2025/26, came in 7.0% below normal — the ninth-mildest in 76 years, and that now counts as an ordinary winter.
Heating degree days per season, 1950/51-2025/26
Annual HDD summed over each July-June heating season (18°C base), Copernicus ERA5 monthly data. History through winter 2025/26 computed from the full archive on August 9, 2026; newer complete winters are appended live. SEAS5 forecast points are excluded.
3. The south is losing winter fastest
The decline is universal but uneven. In percentage terms the Mediterranean is losing its heating season fastest — Portugal is down 20.1% and Italy 19.1% versus 1991-2020 — because a warm anomaly eats a bigger share of an already short winter. In absolute degree days, the biggest losses are in the cold mid-latitudes: Finland is shedding about 175 HDD per decade and Germany about 156 per decade since 1981. Nowhere in the 25-country panel is the last-five-winter average above its 1991-2020 normal.
Heating seasons (July-June); "last 5 winters" = 2021/22-2025/26. Copernicus ERA5, one representative location per country. Spain is excluded from aggregates (series updated through January 2026 at publication). Full 25-country table reproducible from the WorldPulse knowledge graph.
4. The grid confirms it: ~40 GWh per degree day in France
Degree days are not an abstraction — they show up in metered demand. France is the cleanest test because so much of its heating is electric: matching ENTSO-E daily load against ERA5 monthly HDD for 2015-2026 gives a correlation of 0.92, with each heating degree day adding roughly 40 GWh of monthly electricity demand. At that sensitivity, France's five-winter average deficit of about 330 HDD versus the 1991-2020 normal translates to roughly 13 TWh of heating electricity per winter that is simply no longer needed — about the annual output of two 900 MW nuclear reactors. In Germany, where heating is mostly gas, the electric signal is smaller (about 12 GWh per HDD, correlation 0.75) and the missing degree days land on gas demand instead.
Mean daily load per month since 2022, GWh/day, aggregated live from ENTSO-E daily data. The winter peaks are the heating season; their height tracks HDD almost exactly.
The demand curve is not just shrinking — it is migrating across the calendar. Cooling degree days (degrees above 18°C) across 24 European countries averaged 317 per year in 2021-2025, 32% above the 1991-2020 normal of 240 and 75% above the 1950s, rising at about 15% per decade since 1991 — three times the pace at which heating demand is falling. The level is still an order of magnitude below heating need, so in energy terms Europe remains a heating continent. But the growth is concentrated in the south — Greece, Turkey, Italy — and it arrives as sharp summer air-conditioning peaks, a very different problem for grids than the broad winter plateau it is replacing.
Cooling degree days per calendar year, 1950-2025
Annual CDD (18°C base), Copernicus ERA5 monthly data, computed from the full archive on August 9, 2026 (complete calendar years through 2025).
The verdict: a structural repricing of winter
Europe's heating season is in secular, accelerating decline: -9.3% over the last five winters versus the 1991-2020 normal, -18% versus the 1950s, and roughly -5% per decade at the post-1990 trend. Every one of the ten mildest winters in 76 years of ERA5 data falls in the last twenty. For a fixed building stock this maps almost one-for-one into heating energy — visible already as roughly 13 TWh per winter of electricity France no longer draws, and as a permanently lower baseline for European gas-for-heating demand.
The honest caveat is variance: the spread between a cold and a mild winter (several hundred HDD) is still larger than a decade of trend, so any single winter can spike demand and prices. The trend does not abolish cold winters — it makes the average winter milder and each "normal" one milder still. Meanwhile cooling demand, up 32% on its normal, is shifting the load toward summer peaks. Energy systems sized for the winters of 1990 are increasingly sized for a climate that no longer exists.
Frequently Asked Questions
What are heating degree days (HDD)?
Heating degree days measure how much heating a place needs. For each day, take how far the mean outdoor temperature falls below a base temperature (18°C in this analysis) and sum it over time: a day averaging 8°C contributes 10 HDD. Because buildings lose heat roughly in proportion to that temperature gap, energy used for space heating scales almost linearly with HDD — which is why gas and power traders watch degree-day forecasts as closely as prices.
Are winters getting warmer in Europe?
Yes, and measurably so. Copernicus ERA5 data across 25 European countries shows heating degree days falling by about 86 per decade since 1951, accelerating to about 140 per decade since the early 1990s. The last five winters (2021/22-2025/26) averaged 9.3% fewer HDD than the 1991-2020 normal, and all ten of the mildest heating seasons in the 76-year record have occurred since 2006.
How does warm weather affect gas and electricity demand?
Space heating is the single largest use of household energy in the EU — roughly two-thirds of it, per Eurostat — and heating need scales almost one-for-one with heating degree days. So a winter with 10% fewer HDD needs roughly 10% less heating fuel from the same building stock. The link is visible in grid data: in France, where electric heating is widespread, monthly electricity consumption and monthly HDD move together with a correlation of 0.92 (2015-2026, ENTSO-E), at roughly 40 GWh of extra demand per heating degree day.
Will rising cooling demand offset falling heating demand?
Not in energy terms, at least not in Europe. Cooling degree days across 24 European countries are up 32% in 2021-2025 versus the 1991-2020 normal — growing far faster in percentage terms than heating is declining. But the level remains small: about 317 CDD per year against roughly 2,700-3,000 HDD. The real effect is a reshaping of the demand curve — a shallower, shorter winter peak and a fast-growing summer air-conditioning peak, which stresses grids in new ways even as total heating energy falls.
Data & methodology. Recent data (the latest winters, world daily temperature and electricity load) is served live from the WorldPulse knowledge graph and redraws as new observations arrive; historical degree-day aggregates (pre-2021 seasons, climatological normals, the country table) were computed from the full 1950-2026 archive on August 9, 2026 and are fixed. Heating and cooling degree days are computed from the Copernicus Climate Change Service ERA5 reanalysis (ECMWF), monthly means at one representative location per country, 18°C base; heating seasons run July-June and only complete 12-month seasons are counted. The European aggregate is an unweighted mean of 25 countries with full 1950-2026 histories (Spain excluded — data through January 2026 at publication). SEAS5 seasonal-forecast points present on degree-day series are excluded from all historical figures. World daily 2m temperature is ERA5 (Copernicus/ECMWF). Electricity load is from the ENTSO-E Transparency Platform; the France regression uses monthly load sums against monthly HDD, 2015-2026. Analysis as of August 9, 2026; figures stated in prose reflect data available on that date. This article is analysis, not investment advice.