Warming stripes are part art, part science. Each stripe represents a single year, colored to show how that year's average temperature compared to a long-term average — not the temperature itself. Blue stripes mark years that were cooler than the long-term average; red stripes mark years that were warmer than average. The deeper the shade, the larger the difference.
Because each stripe reflects a difference from a baseline rather than a raw temperature, how a graphic looks depends on choices like the data source, the baseline period, and the color scale. Two perfectly valid versions of the same location can look different but share the same underlying story. For our data sources, baseline periods, and other important caveats, please read the full methodology below.
Above all, warming stripes are a visual communication tool — designed to be simple and to spark conversations about our changing climate.
Data
Average annual temperature data for U.S. cities was obtained from NOAA's Applied Climate Information System. For U.S. counties, climate divisions, climate regions, states, and the contiguous United States, monthly average temperatures were obtained from the U.S. Climate Divisional Database, and annual averages were derived from the monthly data. Aggregated data can also be accessed directly through NCEI's Climate at a Glance tool. Global stripes were downloaded directly from ShowYourStripes.info.
Baselines
Each stripe represents a given year's average annual temperature anomaly — the difference from a long-term average, not the temperature itself. Most locations use the 20th-century average (1901–2000) as the baseline. For cities whose records begin after 1901, the first 100-year period is used instead. For Alaska's county, climate division, and state data, which begins in 1925, a 1925–2024 baseline is used. Global stripes use a 1961–2010 baseline.
Color scale
The scale uses 16 colors spanning ±2.6 standard deviations of the annual temperatures during the baseline period. Black stripes mark years with insufficient data (>10% daily data missing); white stripes mark years whose average temperature equaled the long-term average.
Other caveats
County, climate division, and state data for Hawaii is excluded, as records are only available from 1991 onward. Climate division data is not provided for Rhode Island, as the entire state is a single climate division — please use the state graphic instead. While Connecticut has recently shifted from counties to planning divisions, NCEI still provides its data at the county level.
Final notes
Warming stripes were originally created by climate scientist Ed Hawkins. Special thanks to Jared Rennie for his help with the warming stripes for U.S. counties. See Warming Stripes: Global to Local to learn more and download additional multimedia resources.