The domino sea level effect

Some existing projections of global warming predict that by the year 2100, global sea levels will have risen by one meter due to polar ice cap melting and water expansion caused by rising temperatures. In a paper this week in Nature Geoscience, however, researchers determined that given our current levels of atmospheric carbon dioxide, our seas should actually be 25 meters higher than they are.

Twenty-five meters?! Even one meter of sea level rise could affect a tenth of the world’s current population. The fact is bitter but true, says lead author Eelco Rohling of the University of Southampton, UK. He and his team used data to create a model of fluctuations in sea level over the last five glacial cycles. Their data predicted that in our current world, sea levels should be 25 (plus or minus 5) meters higher at equilibrium than we’re seeing today. In addition, the model agrees with ice-core data from the Middle Pliocene epoch (3-3.5 million years ago) — when CO₂ levels were similar to what they are now — that show sea levels at about 25m higher than today.

Why, then, are our sea levels still so much lower? Rohling explains that the predictions in his model and the ice core data are for an Earth that is at equilibrium, when the climate has stopped changing and has had time to stabilize. Currently, he says, our Earth is still in the changing phases. Because the inputs to change in sea levels are slow (picture hundreds of thousands of miles of ice sheets melting into the sea), we haven’t yet begun to see really large changes.

Rohling says that even if we ceased all of our carbon emissions now, we’d still suffer the consequences of the swinging pendulum. He says in a statement:

“Even if we would curb all CO₂ emissions today, and stabilise at the modern level, then our natural relationship suggests that sea level would continue to rise to about 25 m above the present. That is, it would rise to a level similar to that measured for the Middle Pliocene.”

If Rohling is right, then we really do have a doomsday scenario on our hands; if he’s right, it’s just a matter of how long this stabilization will take to complete.

Rohling, E., Grant, K., Bolshaw, M., Roberts, A., Siddall, M., Hemleben, C., & Kucera, M. (2009). Antarctic temperature and global sea level closely coupled over the past five glacial cycles Nature Geoscience DOI: 10.1038/ngeo557