Through decades of research, it has become clear that human civilization, roughly 6,000 years old, developed during an unusually stable period for global sea levels. But over longer spans, coastlines have been much more dynamic.
During ice ages, caused by wobbles in the Earth’s orbit, sea levels dropped more than 400 feet as ice piled up on land. But during periods slightly warmer than today, the sea may have risen 70 or more feet above the current level.
Dr. Dutton and other leading scientists are focused on the last sea-level high point, which occurred between the last two ice ages, about 125,000 years ago.
After years of surveying ancient shorelines around the world, scientists determined that the sea level rose by something like 20 to 30 feet in that era, compared with today. But how long did it take to make that jump? That is the question Dr. Dutton, using improved research techniques, wants to answer.
Large parts of the Florida Keys are simply ancient coral reefs that grew during the period of high seas, and were exposed when the levels fell. Trees, roads and houses now sit atop the old reefs. By recovering samples, Dr. Dutton hopes to date a sequence of corals as they grew along with the rising sea, potentially revealing the rate at which the water rose.
The research, likely to take years, may supply a figure for how quickly the ocean was able to rise under past conditions, but not necessarily a maximum rate for the coming decades. The release of greenhouse gases from human activity is causing the planet to warm rapidly, perhaps faster than at any other time in the Earth’s history. The ice sheets in both Greenland and West Antarctica are beginning to melt into the sea at an accelerating pace.
Scientists had long hoped that any disintegration of the ice sheets would take thousands of years, but recent research suggests the breakup of West Antarctica could occur much faster. In the worst-case scenario, this research suggests, the rate of sea-level rise could reach a foot per decade by the 22nd century, about 10 times faster than today.
In 2013, scientists reached a consensus that three feet was the highest plausible rise by the year 2100. But now some of them are starting to say that six or seven feet may be possible. A rise that large over a span of decades would be an unparalleled national catastrophe, driving millions of people from their homes and most likely requiring the abandonment of entire cities.
In essence, by revealing how sensitive the ice sheets have been to past warming, Dr. Dutton’s research may answer the question of whether such a rapid jump is possible.
Along those parts of the United States coast that are sinking at a brisk clip, including southern Louisiana and the entire Chesapeake Bay region, including Norfolk, the situation will be worse than average. On the Pacific Coast, a climate pattern that had pushed billions of gallons of water toward Asia is now ending, so that in coming decades the sea is likely to rise quickly off states like Oregon and California.
Along the East Coast, scientists with the National Oceanic and Atmospheric Administration say that many communities have already, or will soon, pass a threshold where sunny-day flooding starts to happen much more often.