Rapid sea rise - 14,650 years ago

Global warming is driving the rising of the seas at rates thought impossible until now.

The rapid rise of global temperature over the last century is almost certainly unprecedented in recent Earth history, but our current rate of sea level rise has stiffer competition. About 14,650 years ago, as the thawing of the last ice began to hit its stride, sea level made a remarkable jump of 12 meters or more—and did so in less than 400 years. It's an event known to scientists as Meltwater Pulse 1A.

Said event happened here.

Northern Eurasian ice sheet extent at 90,000 years ago with ice-dammed lakes and

rerouting of drainage. Also the Quaternary glaciation limit is shown.

Fast forward to 14, 650 years ago and one sees this.

Previous extent of ice sheet with ages labeled in thousands of years.

Back to the ice sheets. During the last glacial period, an ice sheet once stretched across Scandinavia and the Barents Sea. The record of its shrinking is based on carbon dating of seafloor sediment cores, pinpointing times that ice retreated and life returned to a location. The reconstructions have indicated that the ice here had basically melted before the start of Meltwater Pulse 1A, giving it a clear alibi. But the carbon-dated ages assumed that the deep ocean carbon-14 delay in that region was constant over time, matching the modern pattern.

With that done, the reconstructed timing of Eurasian Ice Sheet melt shifts. Rather than showing that the local ice melted before Meltwater Pulse 1A even started, they see a major loss of ice during this event. Previous reconstructions gave the Eurasian Ice Sheet credit for perhaps one meter of the 12 or more meters of sea level rise that occurred then. This study pushes that contribution up to about five meters—plus another meter or so in the century following.

Endgame.

That question about the past is of interest to our future. The portion of the Eurasian Ice Sheet in question straddled topographic lows in contact with the ocean, making it vulnerable to rapid collapse. The same is true of the West Antarctic Ice Sheet today—the biggest wildcard for future sea level rise. Every ice sheet is different and the local details matter, but an equally rapid collapse of ice in Antarctica would be a worst-case scenario.

Rapid sea rise indeed.