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🧪 Method and transparency

• Source: ERA5 reanalysis from ECMWF / Copernicus via Open-Meteo — the scientific standard for reconstructing past climate (2 m air temperature, from 1940).
• Anomalies, not absolute values: each year is compared against the 1961–1990 climate normal(the WMO reference period). Anomalies remove seasonal noise and make the underlying trend visible.
• Trend: computed by linear regression on annual means; R² indicates how much of the data the line explains (0 = no trend, 1 = perfect trend).
• Limitations: each city is a single point on the ERA5 grid. This data concerns these Italian cities (regional scale): it is consistent with the global warming measured by NASA, NOAA and Copernicus, but does not replace it.
• No cherry-picking: the entire available series is always shown, from the first to the last year.
• Daily records: exclude the last ~4 months. ERA5 publishes a preliminary version after a few days, but the final ("re-analyzed") version arrives later and can differ slightly: an absolute record is never declared on data that is still provisional.
• Highs and lows: shown separately from the mean (same two-normal comparison) because days and nights don't always warm at the same rate.
• Climate analog: compares this city's annual mean temperature with that of other monitored cities in past decades — not the full seasonal profile, which would require data not yet available at this level of detail.