A new review analyzing three decades of research on the historic effects of melting polar ice sheets found that global sea levels have risen at least six meters, or about 20 feet, above present levels on multiple occasions over the past three million years. What is most concerning, scientists say, is that amount of melting was caused by an increase of only 1-2 degrees (Celsius) in global mean temperatures.

A new review analyzing three decades of research on the historic effects of melting polar ice sheets found that global sea levels have risen at least six meters, or about 20 feet, above present levels on multiple occasions over the past three million years.

What is most concerning, scientists say, is that amount of melting was caused by an increase of only 1-2 degrees (Celsius) in global mean temperatures.

Results of the study are being published this week in the journal Science.

“Studies have shown that both the Greenland and Antarctic ice sheets contributed significantly to this sea level rise above modern levels,” said Anders Carlson, an Oregon State University glacial geologist and paleoclimatologist, and co-author on the study. “Modern atmospheric carbon dioxide levels are today equivalent to those about three million years ago, when sea level was at least six meters higher because the ice sheets were greatly reduced.

“It takes time for the warming to whittle down the ice sheets,” added Carlson, who is in OSU’s College of Earth, Ocean and Atmospheric Sciences, “but it doesn’t take forever. There is evidence that we are likely seeing that transformation begin to take place now.”

Co-author Peter Clark, an OSU paleoclimatologist, said that because current carbon dioxide, or CO2, levels are as high as they were 3 million years ago, “we are already committed to a certain amount of sea level rise.”

“The ominous aspect to this is that CO2 levels are continuing to rise, so we are entering uncharted territory,” Clark said. “What is not as certain is the time frame, which is less well-constrained. We could be talking many centuries to a few millennia to see the full impact of melting ice sheets.”

The review, which was led by Andrea Dutton of the University of Florida, summarized more than 30 years of research on past changes in ice sheets and sea level. It shows that changes in Earth’s climate and sea level are closely linked, with only small amounts of warming needed to have a significant effect on seal levels. Those impacts can be significant.

Six meters (or about 20 feet) of sea level rise does not sound like a lot. However, coastal cities worldwide have experienced enormous growth in population and infrastructure over the past couple of centuries – and a global mean sea level rise of 10 to 20 feet could be catastrophic to the hundreds of millions of people living in these coastal zones.

Continue reading at Oregon State University.

Ocean image via Shutterstock.