SEA LEVEL RISE SPEEDING UP

Climate scientists have been concerned about the risks from rising sea levels for nearly 50 years.

That a warming climate will raise sea levels makes intuitive sense--water, including all the water in the world's oceans, expands as it warms, and melt water from glaciers, ice sheets and the Antarcitc ice cap will of course end up in the oceans.

Although the pace of sea level rise seems small, on the order of a millimeter per year, its impact is multiplied by higher tides, stronger storm surges, sea-level-rise hotspots, and by the fact that 634 million people, close to ten percent of the world's population, live in low-lying coastal areas. The US is among the top ten countries with large numbers of people at risk from sea-level rise.

Pinning down the rate of sea level rise has proved to be challenging (see "Sea level measurement" at this URL). Now, however, a team of researchers has used sophisticated statistical techniques to deal systematically with the sources of uncertainty in different sea level data sets. "This likely is the first time a group of statisticians have had really close examination of sea level data," says Andrew Parnell, at University College Dublin.

Their approach allowed them to trace sea level changes over the past 2000 years, with increasing accuracy as more, and more accurate, data have become available in recent decades.

The group found that from 1 AD through 1800 AD, global sea levels rose by much less than one millimeter per year. They began to rise more rapidly at the start of the Industrial Revolution, and are currently not just rising, but rising faster and faster. They estimate that globally the rate is now 1.7 millimeter per year.

"Some people argue that sea levels are not rising," says Parnell. "We are showing them that sea levels are not only rising, but accelerating.

In terms of potential impacts, the East Coast of the US is at particularly high risk. It happens to be one of the sea level rise hotspots. For example, sea level near New York City is rising by 3 millimeters per year, putting more than $25 billion of infrastructure at risk.

New Orleans after Hurricane Katrina

September 11, 2005

Source: NOAA

Author: Lieut. Commander Mark Moran, NOAA Corps, NMAO/AOC

Parnell and his colleagues presented their new findings at the 2017 Joint Statistical Meetings, in Baltimore, Maryland.