Saturday, February 08, 2020

Old Weather & Shrinking Arctic Sea Ice

Visualizing the shrinking sea ice extent in the Arctic has become a very powerful method of demonstrating the effect of global heating on planet Earth. For example the National Snow and Ice Data Center's interactive animated map, Sea Monthly Mean Sea Ice Concentration Anomalies, uses satellite data to show how the extent of sea ice in the Arctic has shrunk since 1979.

One problem with using satellite data to measure sea ice loss is that we can't go back past the later half of the 20th Century using images captured from space. One possible alternative source of the extent of Arctic sea ice in the 19th Century is the data in historical ships' logs. In the 19th and early 20th centuries ship logs would record weather observations, noting such variables as barometric pressure, temperature and the ice conditions encountered during voyages.

In Weather Time Machine Reuters explores how the citizen science project Old Weather is digitizing these ship logs to create an invaluable record of historical weather conditions around the world. In particular Reuters examines the ship logs of the USS Jeanette.

In 1879 the Jeannette set off from the United States in an attempt to reach the North Pole. During its voyage to the North Pole weather conditions were entered into the ship's log every hour. Alongside Jeanette’s speed and course, the temperature, weather, wind conditions, cloud types and barometric pressure were all recorded. As the Jeannette sailed north it became trapped in ice. The ship eventually managed to get free but spent the next 21 months drifting in the sea ice of the Arctic. The ship was finally crushed by the ice on June 13, 1881. The entire crew survived the sinking, but many of the crew died before reaching safety.

Reuters observes how the data from the ship's log shows how the sea ice extent encountered by the Jeanette was far larger than it is today and helps to reveal how "conditions have changed in nearly a century and a half".

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