by R. L.
According to newer, more precise measurements,the global average sea level rose three millimeters in each of the past two years. If this trend continues, it could provide strong evidence of global warming.
The measurements come from the Topex/Poseidon satellite, a joint venture between the United States and France that was launched in 1992. Topex measures sea level with a radar altimeter, a device that repeatedly bounces radar beams off the planet's surface and then calculates how long they take to return to the satellite.
Before Topex, climatographers had to rely on coastal tide gauges to measure sea level. Although these gauges have been recording rises of one to two millimeters per year, these results were regarded as uncertain because there are few gauges and because they are attached to piers, which can shift over time. Now researchers have a more definitive measuring tool.
The Topex results are consistent with computer simulations of global warming, which call for sea levels to increase two to seven millimeters per year. It's probably too soon to reach firm conclusions, however. The high sea levels, for example, may merely be a phenomenon caused by El Niño, an anomalous ocean current in the Pacific. [See "El Niño: The Weathermaker."] Only several more years of measurements will tell for sure.
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