Rising Sea Levels
Effects of climate change on oceans provides information on the various effects that global warming has on
oceans. Global warming can affect sea levels, coastlines, ocean acidification, ocean currents, seawater, sea surface
temperatures, tides, the sea floor, weather, and trigger several changes in ocean biogeochemistry; all of these affect
the functioning of a society.
There are a number of factors affecting rising sea levels, including the thermal expansion of seawater, the
melting of glaciers and ice sheets on land, and possibly human changes to groundwater storage.
The consensus of many studies of coastal tide gauge records is that during the past century sea level has risen
worldwide at an average rate of 1–2 mm/yr reflecting a net flux of heat into the surface of the land and oceans.
Corresponding studies based on satellite altimetry shows that this rate has increased to closer to 3 mm/yr during the
more completely monitored past 20 years. A recent review of the literature suggests that 30% of the sea level rise
since 1993 is due to thermal expansion and 55% due to continental ice melt, both resulting from warming global
temperatures. In another study, results estimate the heat content of the ocean in the upper 700 meters has increased
significantly from 1955–2010. It has to be reminded that in this context the usage of the word heat is extremely
improper, as heat cannot be stored in a body but only exchanged between bodies. Observations of the changes in
"heat content" of the ocean are important for providing realistic estimates of how the ocean is changing with global
warming. An even more recent study of the contributions to global sea level due to melting of the two large ice
sheets based on satellite measurements of gravity fluctuations suggests that the melting of these alone are causing
global sea level to about 1 mm/yr. In a recent modeling study, scientists used an earth system model to study several
variables of the ocean, one of which was the "heat content" of the oceans over the past several hundred years. The
earth system model incorporated the atmosphere, land surface processes, and other earth components to make it more
realistic and similar to observations. Results of their model simulation showed that since 1500, the ocean "heat
content" of the upper 500 m has increased.
The connection between sea level rise and ocean thermal expansion follows from Charles's law which simply
states that the volume of a given mass is proportional to its temperature. This contribution to sea level is monitored
by oceanographers using a succession of temperature measuring profiling instruments, which is then compiled at
national data centers such as the United States National Oceanographic Data Center. The International Panel on
Climate Change Fifth Assessment Report estimates that the upper ocean has warmed by 0.09 to 0.13 degrees C per
decade over the past 40 years. Other processes important in influencing global sea level include changes to
groundwater storage including dams and reservoirs.
Global warming also has an enormous impact with respect to melting glaciers and ice sheets. Higher global
temperatures melt glaciers such as the one in Greenland, which flow into the oceans, adding to the amount of
seawater. A large rise in global sea levels poses many threats. According to the U.S. Environmental Protection
Agency, “such a rise would inundate coastal wetlands and lowlands, erode beaches, increase the risk of flooding, and
increase the salinity of estuaries, aquifers, and wetlands.” The seasonal cycles are closely linked with the seasonal
changes in sea ice and sea surface temperatures. The timing and amplitude of the seasonal cycle has been altered by
global warming.