India, June 13 -- In 1751, Captain Henry Ellis of an English slave-trading ship lowered a bucket with a built-in thermometer while sailing 25degN in the north Atlantic Ocean. In those times, water temperatures at different sites and depths were captured by seafarers sailing across the globe.

The captain was startled by the findings. The deep water in the ocean was icy cold. "The cold increased regularly, in proportion to the depths, till it descended to 3,900 feet: from whence the mercury in the thermometer came up at 53 degrees (Fahrenheit); and tho' I afterwards sunk it to the depth of 5,346 feet, that is a mile and 66 feet, it came up no lower," he wrote in a letter.

This account, according to Stefan Rahmstorf of the Potsdam Institut...