MEASURING the temperature of something as stratified as the ocean has never been easy. Before the 1980s, ships automatically recorded the temperature of water flowing through their ports, but the great depth variance of these ports and the dearth of data outside major shipping routes made the figures incomplete and unreliable.

MEASURING the temperature of something as stratified as the ocean has never been easy. Before the 1980s, ships automatically recorded the temperature of water flowing through their ports, but the great depth variance of these ports and the dearth of data outside major shipping routes made the figures incomplete and unreliable.