Understanding how the earth's temperature has changed in the past is crucial to understanding the climate change we're experiencing now.
Reliable tracking of the temperature began in the Midlands, where a measurement has been taken and recorded every month since 1659. But the temperature in one country doesn't give a good picture of what's happening in the rest of the world, and accurate figures for the global average temperature go back only as far as the mid-19th century.
For periods earlier than that, scientists are forced to infer the world's temperature from so-called "proxy" data — clues hidden in ice cores, tree rings and other biological and geological sources.
The data provided below charts the world's changing temperature since 1850. The figures, which are maintained by the UK Met Office's Hadley Centre, describe the temperature "anomaly" (the difference) between the year in question and the reference period of 1961–1990.
For simplicity's sake, our spreadsheet only includes the "best estimate anomaly" for each year. If you'd like the full dataset, complete with 95% uncertainty ranges, you can find it online, with explanatory notes.
The data provided below is known by the somewhat unprepossessing name HadCRUT3. Similar datasets are maintained by other research bodies such as NASA's Goddard Institute for Space Studies and NOAA's National Climatic Data Center.
• Can you do something with this data?