According to a study published in the Proceedings of the National Academy of Sciences (PNAS), sea level is rising faster than at any time in the past 2000 years and that this sea level rise has been linked to human-caused climate change.
The report, produced by a team of scientists funded by the National Science Foundation (NSF), tracked sea level changes over the past 2200 years. The research team found that sea level was mostly constant from a 1200 year period encompassing 200 BC to 1000 AD. Then, a climate warming known as the Medieval Climate Anomaly took hold from 1000 to 1400. The result was that seas rose by about a half millimeter per year during that 400 year time. Then, from about 1400 to 1900, a cool period called the Little Ice Age stabilized sea levels once again.
The report found that from 1900 onward, climate warming linked to human increases in greenhouse gases resulted in an average rise of sea level of 2 millimeters per year.
“Having a detailed picture of rates of sea level change over the past two millennia provides an important context for understanding current and potential future changes,” says Paul Cutler, program director at NSF’s Division of Earth Sciences.
“It’s especially valuable for anticipating the evolution of coastal systems,” he says, “in which more than half the world’s population now lives.”
Adds Kemp, A Yale University researcher and member of the sea level study team, “Scenarios of future rise are dependent on understanding the response of sea level to climate changes. Accurate estimates of past sea-level variability provide a context for such projections.”
Current projections for sea level rise this century are much higher than what the NSF research team observed for the past 100 year period. In fact, sea level has been rising at a rate of 3 millimeters per year since 1993 and some researchers expect that rate to rapidly increase. Current IPCC projections are for seas to rise between .6 and 1.5 feet by 2100.
However, IPCC research does not include melt water from glaciers in Greenland or Antarctica. Previous studies had indicated that these glaciers would be slow to respond to increased temperatures. But recent satellite observations show that a total of 300 cubic kilometers of ice is melting from both Greenland and Antarctica each year. If you combine estimates from new research that includes thermal ocean expansion, continental glacier melt, and Greenland and Antarctic melt, estimates climb drastically to a range of 1 to 2 meters (3.3 to 6.6 feet) with the possibility of much greater melt.
The NSF study provided an important baseline measurement of the impact of recent temperature changes on sea level and established a clear correllary between rising temperature and rising sea level.