As the atmosphere warms, heat is transferred to the oceans, which causes water expansion and rising sea levels. Today, Earth’s oceans are warmer than they have been in 100,000 years, according to research published in Science in January.
Scientists discovered this by using sediment cores from around the world to reconstruct sea surface temperatures from the last interglacial period, which started roughly 129,000 years ago. At that time, temperatures were similar to those from before the Industrial Revolution. The study also showed that 4,000 years later — so, 125,000 years ago — sea surface temperatures had warmed up to nearly match today’s readings. That means that, during the interglacial period, it took the planet millennia for a temperature increase that humans managed in just centuries. Alarmingly, sea levels back then were at least 20 feet higher than today’s.
The study is just one of a growing number that look at how the Antarctic Ice Sheet behaved in the past and suggest sea level rise could be higher — and come sooner — than scientists expected even a few years ago. Dozens of feet of sea level rise could take millennia, but the latest estimates suggest as much as 8 feet by the end of the century on the extreme end of projections. That timeline is still one of the biggest unknowns.