The measurements, by the first comprehensive study of the expansion of the oceans, will increase concern that global warming is beginning to take place - and add further urgency to calls from low-lying island and coastal nations for cuts in the pollution that causes it.
The calls will come to a head next month when a hundred nations meet in Berlin to decide whether to tighten up the international treaty on climate change agreed at the 1992 Earth Summit.
Scientists have long predicted that sea levels will rise as the world heats up. By their best estimates, the waters have been rising by about one and a half millimetres a year over past decades. But preliminary readings by the Topex/Poseidon satellite suggest that the seas have been swelling by three millimetres over the past two years.
The old estimates are based on readings from 1,300 coastal measuring stations round the world. The stations are heavily concentrated in northern Europe, North America and Japan - only a third of them have been going long enough to show accurate trends - and their readings are confused because the land to which they are anchored often rises or falls because of geological processes or abstraction of ground water.
The satellite, by contrast, has taken half a million readings, every day, from all over all the world's seas and oceans, producing much more precise results.
Dr Steven Nerem, of NASA, says that the measurements have "the precision we need to measure detailed sea level and climate changes". But, he stressed, it is too early to come to any final conclusions.
He added that if the same rises were found over the next few years, it would show that global warming had started. This would have serious consequences. Even under the old estimates, five island nations - the Maldives, Tuvalu, Tokelau, the Marshall Islands and Kiribati - are expected to disappear altogether under water over the next century.Reuse content