Warming Stripes

Microclimatev01.00 credits/fixed

Responsible:Niccolò Calandri

Warming Stripes

Overview

Warming Stripes show the temperature anomaly relative to the average of the first 20 years of available data. Each stripe represents one year: colours range from blue (years cooler than the average) to red (years warmer than the average), making the warming trend immediately visible over time.

This visualisation was conceived by Prof. Ed Hawkins of the University of Reading (UK) in 2018 as a science communication tool for climate change, capable of conveying the global warming trend in an immediate and intuitive way without requiring technical expertise. Warming Stripes are today one of the most recognisable symbols of international climate communication.

Calculation Methodology

The calculation is based on two data sources:

Horizon	Source	Detail
Historical (1940 – present)	Open-Meteo Historical Weather	ERA5-Land reanalysis, ~10 km
Future projections	Climate Data Store CMIP6	CMIP6 climate models, SSP scenarios

The calculation process follows these steps:

Extract the annual mean temperature for each year in the historical series
Calculate the reference mean over the first 20 years of available data
Calculate the annual anomaly = temperature year X − reference mean
Colour each stripe on the blue-white-red scale proportional to the anomaly

Unit: degrees Celsius (°C, anomaly relative to the first 20-year mean)

Data Sources

Code	Name	Provider	Resolution	Availability
`WRD_OPNMT_99`	Open-Meteo Historical Weather	Open-Meteo (ERA5-Land)	~10 km	1940 — present
`WRD_CDSXX_99`	Climate Data Store CMIP6	Copernicus / ECMWF	variable	future projections (SSP)

Quality Range and Levels

This KPI is a graphical visualisation of thermal anomalies and does not include an A–E quality level classification. The value is not an environmental performance indicator with fixed thresholds, but a visual representation of the local climate signal. Interpretation is based directly on the colouring: a progression towards red indicates a warming trend, while blue indicates years that were relatively cooler than the reference mean.

Technical Notes

The reference mean is calculated over the first 20 years of available data (not over the fixed 1961–1990 period)
The colour scale is normalised to the anomaly range of the site-specific series
For future projections, the stripes continue with the selected SSP values
Ed Hawkins's original concept (2018) uses the 1971–2000 mean as the baseline

References

Hawkins, E. (2018). "Warming Stripes". University of Reading. Available at: https://showyourstripes.info
IPCC (2021). "Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report (AR6)". Cambridge University Press.
Hersbach, H. et al. (2020). "The ERA5 global reanalysis". Quarterly Journal of the Royal Meteorological Society, 146(730), 1999–2049.

Data Sources & References

Sources

WRD_OPNMT_99WRD_CDSXX_99

Methodology

Annual temperature anomalies calculated against the mean of the first 20 years of data. Historical source: Open-Meteo Historical Weather (ERA5-Land reanalysis, ~10 km, 1940–present). Projection source: Climate Data Store CMIP6 (SSP scenarios). Colouring: blue = below average, white = near average, red = above average. Visualisation conceptualised by Ed Hawkins (University of Reading, 2018).