About This Data
This page shows historical weather data for nearly two hundred capital cities worldwide, going back to 1940. The figures come from the same meteorological source used by professional climatologists, and none of it is estimated or rounded. Daily temperature and precipitation readings have been aggregated into yearly totals, so long-term trends become visible without a single extreme day skewing the picture. Climate change can't be read from a single day or season. Only over a period of decades does a pattern emerge from the normal fluctuations in temperature and rainfall. This page makes that pattern visible city by city, rather than reducing it to an abstract global average.
Map and selection
The map at the top shows every capital city. Europe currently has a complete dataset, so its cities are clickable. Other continents will follow as their data is completed. Selecting a city opens a dashboard with the relevant figures. Amsterdam is selected by default, so the page is populated as soon as it loads.
How the dashboard is built
The dashboard covers three themes: heat, cold, and precipitation. For each one, it shows how often extremes occur, how the yearly average has developed over the full period, and a comparison between the earliest and most recent years on record. That comparison always uses a multi-year window on both ends, rather than two isolated years, to smooth out one-off outliers. Below that, a handful of key figures sum things up, such as the average rise in summer temperatures or the shift in when spring begins. These figures are drawn directly from the charts above them, not from a separate calculation.
Climate spiral and climate stripes
The climate spiral, based on a design by climate scientist Ed Hawkins, turns each year's monthly temperature deviation into a line drawn on a circle. The distance from the center reflects the deviation from the average of the earliest years in the series, and the line's color marks the year. As the lines drift outward, the warming shows up as a pattern rather than a set of isolated numbers.
The climate stripes present the same data differently: one solid block of color per year, with no axes or numbers attached. For temperature, blue marks a cooler year and red a warmer one. For precipitation, brown marks a drier year and green a wetter one. The intensity of the color shows the size of the deviation from the average across the full series.
Scope of the data
Every chart on this page is based on actual measurements, not models or estimates. In any single city, the weather can vary sharply from year to year; that's normal and doesn't disprove a long-term trend. What gives this dataset its value is the length of the record. Fifty years of daily measurements make it possible to tell chance apart from trend, city by city, using figures that can be checked and that will be expanded as more continents become available.
