Sea levels are rising so fast along the U.S. East and Gulf coasts that some places have seen a greater increase in the last 50 years than the global average over the past 130 years. (Examples include Atlantic City, NJ; Norfolk, VA; and Galveston, TX.)
Other tide stations, such as those at New York City and Washington, DC, have rates of sea level rise over these 50 years that approach the global rate over the 130-year period. (The 50-year rate of rise between 1963 and 2012 is drawn from the latest 50-year fit available as of this post and is compared with the global average sea level rise from 1880 to 2009.)
These and other tide stations are featured in our updated Sea Level Rise and Global Warming infographic. Those who are taking steps to prepare and protect their coastal communities are taking their local tide stations into account.
Updated graphic from the Sea Level Rise and Global Warming infographic, which features the latest 50-year trend (1963-2012) available at time of revision (April 2014) NOAA Data: [email protected] and updated annually at http://1.usa.gov/1mi4AHN.
Why is the rate of local sea level rise different from the global rate?
It turns out that figuring out the global mean sea level rise is notoriously difficult. This is due in part because all the factors that influence the elevation of the sea — such as variations in tidal cycles, local land movement, groundwater depletion, ocean currents, land ice changes, and so forth — have to be independently verified before local tide stations around the world, plus satellite data, can yield the mean sea level rise rate.
For example, Alaska terrain is rising much faster than global sea level rise and local sea levels there have been dropping as a result. Meanwhile, Louisiana is sinking, which contributes to large local sea level rise. It would be hard to figure out global sea level change with just those two tide stations. However, when you can compare stations around the world, and know the other factors influencing local sea elevations, one can figure out the global sea level rise rate. The most well known rate of global sea level rise published for 1880-2009 is around 8 inches (210 mm).
A note on the 50-year rate featured in the 2014 update to the infographic
With the “8 inches since 1880” global mean sea level rise as a “yardstick,” our original infographic used the linear mean sea level trend (tide station start year to 2006) to calculate sea level rise from 1880 to present. However, it was pointed out that the short record of some of the stations used provided limited confidence for extrapolating to 1880. Hence we switched to the 50-year trend for stations that had complete data over the entire 50-year period. Since NOAA updates these 50-year fits each year the full table provided by NOAA is preserved in the methodology and assumptions for the data supporting this infographic.
Given the projected increase in global sea level rise, the most recent 50-year mean sea level trends by NOAA is probably a minimum projection for the next half century.