evidence: Sea level is rising, says Chris Piecuch, a physical oceanographer and sea-level scientist at WHOI. Not only that, it’s rising faster over time. Scientists use computer models to predict how it will change in the future. But "I look more to the past," Piecuch says. "What’s happened over the past few decades or the past few centuries." By studying tiny microfossils buried in salt marsh sediment, he can track sea level back thousands of years. For at least the past 3,000 years, those levels remained fairly constant or increased only slightly. That is, right up until the Industrial Revolution. More recent instrumental data show that’s no longer the case. Scientists have been tracking sea level along coastlines using tidal gauges for more than a century. And since the 1990s, satellite measurements have given them an even more complete view of sea level over the global ocean. Those data unequivocally show a rise in sea level. Averaged over the entire ocean, the increases are small—just three millimeters per year, or about the width of two grains of rice laid side by side. But those millimeters add up, with sea level rising more than seven centimeters (a little more than three inches) in just 25 years. What’s more, Piecuch says, "it’s not just rising, it’s accelerating. It’s rising faster every year."