Sea Ice Extent
Data on the extent of the sea ice in the arctic and antarctic going back to the 19th century is publicly available from NSIDC, moving from information interpolated from ships logs to modern data from satellite imaging (there's an interesting article about how it was done here).
Dave went to a Cambridge Museums Climate Hack in early 2018 and was part of a team working with the Scott Polar Museum. Their initial, hacked exhibit projected the sea ice extent onto the painted domes in their entrance hall, but when they asked to commission a permanent exhibit that wasn't a long term option (they're protected, and the projector would have faded them over time), so instead we built a stand-alone exhibit with a top which rotated to change the year, and a more normal (although still distinctly custom) 12 position rotary switch to select the month.
This was a collaboration with another Climate Hack participant, David Winterbottom, who wrote the software.
We've since built a second version for the Deutches Schifffahtrtsmuseum in Bremmerhaven, this time with much simpler hardware which we supplied as a kit - the month and year are both adjusted via rotary switches with software controlled end stops and the images displayed on a computer monitor - for the client is to install themselves.