The winter of 2018 has seen some extreme cold. When the polar vortex froze the US east coast, some people took this as evidence that global warming is a myth. Something similar is now happening as the “Beast from the East” grips Europe. But analyzing hundreds of millions of weather records to look for all-time high and low temperatures tells a different story.

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Feel free to embed this map on your own site. Grab the embed code at the bottom of the post.

How we made it

The visualization was created from a single spreadsheet of data using the Flourish “Time map” template. The template takes data with columns for time, latitute, longitude (plus optionally category, size, name and more) and visualizes them over a three-dimensional map.

In this case, the spreadsheet consists of all-time min and max temperatures extracted from GHCN-Daily. This massive dataset, maintained by the US National Oceanic and Atmospheric Administration, consists of hundreds of millions of daily highs and lows recorded at more than 100,000 weather stations around the world, a few of which have records stretching right back to the 1700s.

Having downloaded the raw data, we analyzed it to pull out the highest and lowest temperatures ever recorded at each weather station. As you’d expect, the resulting spreadsheet had an equal number of highs and lows. We then filtered out just the last 20 years to see how highs compare to lows in recent decades. This revealed the strong trend towards hot records over cold ones, and also reduced the data sheet to around 40,000 rows, a small enough file to visualize even on a mobile phone.

Once the data was ready, making the map was quick and easy, requiring little more than choosing the right template, uploading the spreadsheet and changing the color scheme to blue and red to fit with the hot/cold topic. The final step was to load the visualization in the Flourish story editor to make the guided tour.

Embed the map in your own site

To embed the map in your site, go here and click the embed icon top-right to grab an embed code.

Alternatively you can embed a video version using Vimeo. Here’s how it looks: