Mapped: How ‘proxy’ data reveals the climate of the Earth’s distant past by Carbon Brief

At any one moment in time, thousands of measurements are being taken of the world’s weather. Across land, sea and sky, data is being gathered manually and automatically using a range of technologies, from the humble thermometer to the latest multi million-pound satellite.

Put together over many years, these measurements provide a record of the Earth’s climate and how it is changing.

But even the world’s longest climate archive only goes back to 1659. This is a mere snapshot in time considering the hundreds of thousands of years that humans have roamed the planet.

Fortunately, the Earth has long been keeping its own records, and this “proxy data” has been used by scientists to build a record of the Earth’s climate going back thousands of years.

But while even relatively well-known proxies – such as ice cores and tree rings – are frequently mentioned in reporting around climate science, much of the understanding of what they capture and how scientists use them is assumed.

To rectify this, Carbon Brief decided to write the definitive reference piece on proxy data. Drawing on interviews with a range of scientists from around the world, our article unpacks the different types of proxies, how the data is used in climate science and its limitations.

A key feature of the article is a custom-built interactive map of proxy data records from around the world. The archive of data – held by the US National Oceanic and Atmospheric Administration (NOAA) – contains more than 10,000 datasets. However, NOAA’s own map of the data was slow and largely unusable. It gave Carbon Brief permission to design and create a new version.

The map – built with Mapbox GL JS – balances the need to be user-friendly while also forming an effective resource tool. The interactive nature of the map means the reader is prompted to explore where the proxy data is located, filter by type, and obtain further information through the map dashboard and external references to the NOAA dataset. The piece is responsive and shows a snapshot of the data for readers on mobile.

The piece is built within a custom template, and includes data visualisations, animation and scroll-triggered transitions. We also produced an original set of 18 illustrations of the various proxy types, in order to assist the reader in understanding what some of them are.

The piece was well-received, with many within the science community saying it is a valuable resource, and teachers and professors informing us they were using it as an example in their teaching.