Sea levels are rising faster than they have in 2,800 years. The culprit is man-made global warming according to a study in the Proceedings of the National Academy of Sciences published in February. Professor Bob Knopp, a climate scientist at Rutgers University, led the research with nine colleagues from various U.S. and global universities.
The scientists went around the world into two dozen locations to chart out past sea levels and rates of rise and fall. They looked at salt marshes and other coastal locations and used indicators to figure out what the sea level was at different times. Mangroves, coral, sediments, single cell organisms sensitive to salinity and other indicators in cores were used. They were able to check their figures by easy markers such as the rise of lead with the start of the industrial age and isotopes only seen in the atomic age.
Research indicated that until the 1880s and the world’s industrialization, the fastest seas rose was about 1 to 1.5 inches (3 to 4 centimeters) a century. Global sea level really didn’t get much higher or lower than 3 inches above or below the 2,000 year average. They found that seas rose about 5.5 inches or 14 centimeters from 1900 to 2000, for a rate of 1.4 millimeters per year. NASA says the current rate is 3.4 millimeters per year, which indicates an acceleration. The study blames the rise of global warming and says if humans had not been warming the planet there is very little chance that seas would have risen so much during the century. Instead of a 14 centimeter rise we would have had somewhere between a 3 centimeter fall and a 7 centimeter rise.
This study also forecasts that no matter how much carbon dioxide we emit, 21st century sea level rise will be much higher than what was seen in the 1900’s. If greenhouse gas pollution continues at the current pace the study projects increases of about 22 to 52 inches (57 to 131 centimeters). If however, countries fulfill the recent Paris climate accord and limits further warming to another 2 degrees Fahrenheit, sea level rise would be in the 11 to 22 inch range (28 to 56 centimeters).
While Kopp feels the major contributors to sea level rise in the 20th century were the melting of mountain glaciers and the natural expansion of ocean water as it warms he thinks in the 21st century that the huge ice sheets of Greenland and Antarctica will play a larger role in potential sea level rise.
Photo Courtesy of Mary Hollinger, NODC biologist, NOAA