For a strategy so quick and elegant, long-range acoustic thermometry--taking the temperature of entire oceans with pulses of sound--has been a long time coming. Expected to provide solid data on one environmental threat, global warming, the techniquehas run afoul of concerns that it could pose another: harm to marine mammals from the powerful sound (Science, 17 May 1991, p. 912and 1-5 April 1994, p. 339). But while a major experiment is on hold, smaller tests in the Arctic and Pacific oceans have been allowed to go ahead and are neat-ing up the field with evidence that measurable ocean warming is under way.
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