Researchers used data from a ship called the HMS Challenger that sailed the world's oceans from 1872 to 1876 along a 69,000 nautical-mile track in the Atlantic, Indian and Pacific oceans. The ship had a 200 person crew and took 300 ocean-temperature profiles at several depths with pressure-protected thermometers.
Data from the Challenger temperatures was compared to the modern-day Argo project. The result of the comparison was a 1.1 degree Fahrenheit (0.59 Celsius) temperature increase at the surface of the ocean over the last 135 years."
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