Rising Sea Levels
As the polar icecaps melt from global climate change, the sea level rises. The encroaching sea swallows coastal areas and decreases the total amount of land on the earth remaining above water. Some causes of beach erosion deposit the sand in another area, so as one beach shrinks another grows. The beach lost to rising sea levels, nonetheless, can not be regained. Coastal erosion due to changing sea levels is expected to continue.
Harsh Storms
Storms reaching the coast naturally erode a beach. Sometimes the sand is pulled further into the sea, while other times it is simply redistributed to another beach. Beach erosion due to storms has increased in recent history as the magnitude and frequency of storms have been augmented by climate change. The wind provides the energy to dislodge the sand, either directly or through the action of waves. Because of storms, beaches are considered temporary features that are dynamic, changing in size and redistributing themselves.
Damming of Waterways
Mankind has also significantly contributed to the erosion of coastal areas. Sand that is naturally lost to the ocean by storms is typically replenished by freshwater flowing from inland and carrying with it sediments. The moving water loses energy as it flows into the ocean, depositing the material it is carrying and supplying new sand for the beach. When these waterways are dammed, however, this supply of sand is lost. Eventually, the coast loses more sand than it gains, resulting in beach loss.
Man-Made Coastal Structures
The efforts of man to stop beach erosion usually do more harm to the coast than the intended benefits. Seawalls increase the rate of erosion, as the water that comes in contact with them reflect off the structures with greater energy than a wave would have, carrying more sand away with it. Groins and jetties are often successful in gathering sand for local beaches, but tend to starve other beaches downstream of the longshore drift, or movement of sand and gravel by natural tidal movement.