Warming Stripes

Warming Stripes

Overview

Warming Stripes are a heatmap-style visualization that shows the temperature anomaly for each year relative to the average of the first 20 years of available data. Each vertical stripe represents one year: blue stripes indicate years cooler than the baseline, white stripes indicate years near the average, and red stripes indicate warmer years. The progression from blue to red across the timeline makes the local warming trend immediately visible without requiring any technical expertise.

This visualization was conceived by Prof. Ed Hawkins (University of Reading, UK, 2018) as a science communication tool for climate change, and has since become one of the most recognizable symbols in international climate communication. Warming Stripes are today displayed worldwide on public buildings, scientific publications, and climate campaigns.

The platform shows Warming Stripes in one context: the Microclimate section of the Site Assessment, where the chart supports both a historical view (from approximately 1940 to the present year) and a future view (SSP climate scenario projections to 2050). This is a visualization-only KPI — there is no A–E quality grade; the anomaly calculation and colorization happen entirely in the frontend.

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Calculation Methodology

The Warming Stripes are computed entirely in the browser from two data sources:

$$\text{Annual anomaly} = T_{\text{year}} − T_{\text{baseline}}$$

where $T_{\text{year}}$ = annual mean temperature for year X (°C), $T_{\text{baseline}}$ = mean temperature of the first 20 years of available data for the site

The baseline is site-specific (not the WMO standard period 1961–1990). Each year's anomaly is mapped to a color from a fixed 15-stop gradient spanning −1.5 °C (deep blue) to +4.5 °C (black). When the Future toggle is active, SSP scenario projections (default: SSP5-8.5) are appended as additional stripes up to 2050.

Data are sourced from ERA5-Land reanalysis (via Open-Meteo) at approximately 10 km resolution for historical years, and from CMIP6 SSP projections (via Copernicus CDS) for future years.

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What You See on the Platform

Assessment > Microclimate > "Warming Stripes" (Slider Card)

Slider Card. A horizontal bar of colored vertical stripes, one per year, rendered as a row of flex-width elements inside a rounded container with a past/future toggle.

Purpose: To give an immediate visual sense of whether the site's local climate has been warming or cooling over the past ~80 years and into future projections, without requiring any numerical reading.

Description: The chart occupies a card in the Microclimate assessment section. At the top-left of the card, the title "Warming Stripes" is shown with a flame icon. A Past / Future toggle controls which data is displayed: Past (default) shows historical data from ~1940 to the present; Future appends SSP projection stripes to 2050. When Future is selected, a scenario selector appears (SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP5-8.5 — default SSP5-8.5) and future stripes animate in with a wave effect. Below the stripe bar, a year axis shows labels at the first year, every 30 years, and the last year. A tooltip modal (accessible via the info icon) shows the full color gradient and the labels "Colder" (left) and "Warmer" (right). Clicking any individual stripe shows a small tooltip with the year, absolute temperature in °C, and the anomaly value with its sign.

Temperature Anomaly
−1.5 °C
+4.5 °C
Colder than baselineWarmer than baseline

How it's calculated: For each year displayed, the anomaly = annual mean temperature − mean of the first 20 years of the site's historical series. The color is selected from the 15-stop fixed gradient (range −1.5 °C to +4.5 °C). Historical data uses ERA5-Land reanalysis via Open-Meteo; future data uses CMIP6 SSP projections via Copernicus CDS.

Legend: The stripe color encodes the annual temperature anomaly relative to the site baseline. The scale is fixed:

Interpretation example:

If the stripes show a predominantly blue band from 1941 to the 1980s, a transition through white in the 1990s, and an increasingly red band from 2000 to the present, the site has experienced a clear local warming trend of approximately +1–2 °C above its historical baseline — consistent with the broader regional signal of accelerating climate change.

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