We know the exact rate at which seawater expands with temperature, and the expected increase in sea level calculated from the observed increase in temperature matches the observed rate of increase of sea level.

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The inspection was expected to last three to four hours, with an increase in temperature of less than 1C, Tepco officials said.

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Dr Chris Huntingford, of the Centre for Ecology and Hydrology, said the temperature increase was "in agreement with simulations by many independent climate centres around the world".

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