But now a new study shows the seas are actually rising three times faster as they were in the 1990s.
Using a new satellite technique, the study in the scientific journal Proceedings of the National Academy of Sciences estimates that before 1990, the ocean was rising at a rate of roughly 1.1 millimeter per year. From 1990 to 2012, however, that rate spiked to 3.1 millimeters per year. Though that rate might still seem small, even a rise of a few millimeters worldwide can lead to increased flooding events or more deadly storm surges at an alarming pace.
Importantly, the study's authors claim the new data — first reported by the Washington Post — shows that scientists had previously underestimated how fast the oceans were rising before 1990, before widespread satellite data was available.
The researchers, who all work in Europe, say their new report further confirms that the effects of human-made climate change are set to increase in the immediate future: the same conclusion in the Intergovernmental Panel on Climate Change's Fifth Assessment Report, a landmark United Nations document.
There is deep disagreement over the exact rate at which sea levels rose during the past century, because uniform satellite data on ocean levels didn't come into widespread use until the 1990s. Before that, the study says, researchers were forced to use information gathered from various gauges located around the globe, which for decades has led to imprecise projections.
Previous sea-level-rise estimates had not accurately accounted for additional melting in Greenland and Antarctica. (The seas also rise due to global temperature spikes. As the ocean heats, its water molecules expand.)
The study cedes that climate scientists don't all agree on the rate at which the ocean has risen over the past decade, as well as how fast the seas might rise in the future. (It's important to note that virtually all climate scientists agree that the oceans are rising and that human-made greenhouse gases are to blame.)
But scientists across the world have warned that the oceans are rising even faster than previously thought.
This past January, the National Oceanic and Atmospheric Administration (NOAA) updated its "extreme" sea-level-rise scenario to warn that, by 2100, the oceans could rise by 8.2 feet. That's more than a half-yard more than previous estimates.
Likewise, a group of researchers in March published a report in the journal Nature warning that oceans could rise by more than six feet by 2100 thanks to rapid ice thaws in Antarctica. By 2500, that study warned, the oceans could rise by 49 feet.
In Miami's case, the warnings are troubling: Even a foot of sea-level rise would decimate virtually all of South Florida by 2100 because the state is pancake-flat and barely contains any hills, let alone any major mountain ranges. The state also sits on top of a huge lump of porous limestone, which means that, as the seas rise, water quite literally bubbles up from the ground.
Miscalculations in sea-level rates can lead to catastrophe across the board. Florida Power & Light, for example, is petitioning to build two new nuclear reactors at Turkey Point in South Miami-Dade, but some environmentalists say they're worried that rising seas could flood the reactors. Sea-level rise also makes hurricanes worse: With every added millimeter, the storm surge from a massive hurricane can do that much more damage to the Miami area.
The ocean is also poised to make Miami unlivable: Just a foot of ocean rise would almost certainly lead to flooding that turns the Magic City into an unwitting version of Venice. If you thought traffic was bad here before, just wait until the roads no longer exist.