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Rising Sea Levels

Already, the average global sea level has risen by 8 inches in the past century. And, by the end of this century, average global sea level could rise an additional three feet, or more. The consequences include worsening coastal erosion, habitat destruction, and saltwater encroachment into freshwater environments, among others.

Why Is Sea Level Rising?

Climate change accelerates sea level rise in two ways:

  1. Rising temperatures are melting land-based glaciers and icepacks. This melt-water eventually makes its way to the oceans, where it contributes to sea level rise.
  2. Water expands as it warms. Even if no glaciers were melting, sea level would still rise due to increasing water temperatures.

Melting glaciers and warming water contribute relatively equally to sea level rise. Additional factors may accelerate or slow regional sea level rise. For example, the subsidence of coastal land along the Chesapeake Bay — due partially to groundwater extraction — is accelerating the relative rate of sea level rise in the region.

What are the Consequences of Sea Level Rise?

The environmental and economic impacts of sea level rise are potentially devastating. In the United States, a sea level rise of 3-4 feet could drown 25-80% of coastal wetlands, depending upon the ability of the wetland species to adapt to deeper water and/or to migrate inland. The rising waters could also inundate 5,000-10,000 square miles of currently dry land. One recent study suggests that the impacts of sea level rise — erosion and dry-land inundation, for example — could threaten 9% of the land within 180 U.S. cities by 2100.

The impacts of sea level rise include:

  • Loss of coastal habitats, including wetlands, mangroves and beaches.
  • Loss of currently dry land to advancing seas.
  • Stronger, deeper and more destructive storm surges.
  • Worsening coastal erosion.
  • Disruption and destruction of shorebird and sea turtle nests.
  • Population declines in fishes, shellfish and other species that rely on coastal wetlands for at least part of their lives.
  • Population declines in migratory birds — including waterfowl — that rely on coastal habitats during seasonal migrations.

Sea level rise may also compound other climate change impacts, such as:

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