The climate stripe code, which adds a stripe for the average temperature in De Bilt each year, starts at 1901. This marks the beginning of our official measurements. However, what was the temperature on Earth before that? Direct measurements date back only a few hundred years. Historical temperatures have been derived from sources such as tree rings. Evidence shows that Earths temperature has risen significantly in the past century, with 2024 likely being the warmest year since the year 1.
Temperature Reconstruction
Nature holds various clues regarding past temperatures, including tree rings, sediment composition in lakes and oceans, and the formation of stalagmites and stalactites in caves, among other data sources. A major international project PAGES2k has combined all global information to reconstruct the average world temperature since year one.
Climate Stripe Code
One way to visualize this climate data is through the climate stripe code, conceived by climate scientist Ed Hawkins. For the Netherlands, the KNMI releases an annual climate stripe code.
In Figure 1, you see the climate stripe code for the world since year one. Each year is assigned a color based on its temperature, benchmarked against the average temperatures from 1850 to 1900, the dawn of the industrial revolution. Years colder than this period are colored blue, while warmer years are red. From 1900 onwards, temperatures are based on global thermometer measurements taken over time. Notably, the climate stripes have grown significantly redder over the past century.