Article

A semi-empirical approach to projecting future sea-level rise

Potsdam Institute for Climate Impact Research, 14473 Potsdam, Germany.
Science (Impact Factor: 31.48). 02/2007; 315(5810):368-70. DOI: 10.1126/science.1135456
Source: PubMed

ABSTRACT A semi-empirical relation is presented that connects global sea-level rise to global mean surface temperature. It is proposed that, for time scales relevant to anthropogenic warming, the rate of sea-level rise is roughly proportional to the magnitude of warming above the temperatures of the pre-Industrial Age. This holds to good approximation for temperature and sea-level changes during the 20th century, with a proportionality constant of 3.4 millimeters/year per degrees C. When applied to future warming scenarios of the Intergovernmental Panel on Climate Change, this relationship results in a projected sea-level rise in 2100 of 0.5 to 1.4 meters above the 1990 level.

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Although almost 74 percent of salt marsh habitat is protected in the CHNEP, habitat continues to be lost to human-induced impacts including development, alterations of hydrology, and pollution. Salt marshes in Charlotte Harbor Estuary have been directly destroyed or impacted from construction activities for residential and commercial purposes including construction for seawalls, drainage ditches for agriculture and mosquito control, boat facilities, and navigation channels. Man-made hydrological alterations have reduced the amount of freshwater flow from some rivers (e.g., Peace, Myakka), while artificially increasing the flow through others (e.g., Caloosahatchee). The primary focus of this project is the extent and nature of salt marshes and the adaptation of salt marshes to climate change. This report includes the results of a new study to inventory and determine the areal extent of salt marsh types throughout the Charlotte Harbor National Estuary Program (CHNEP) study area; determine the vulnerability of those marshes to climate change; identify the need and opportunities for avoidance, minimization, mitigation, and adaptation (AMMA) to climate change, and recommend strategies to implement alternate AMMA. This report is designed for local for use by governments, stakeholder groups and the public at large in developing coastal and land use planning, and avoidance, minimization, mitigation and adaptation of climate change impacts to salt marshes throughout the CHNEP study area. This is the first salt marsh mapping in the CHNEP that includes a mapping of the salt marshes by type. There are 12 different types of salt marsh in the CHNEP. Seventy percent of the salt marshes of the CHNEP are high marsh and 30% of the salt marshes are fringing marsh. The fringing marsh is found on major rivers and tributaries.The salt marshes are moving landward where there is opportunity to do so. The current pace of sea level rise appears to be at pace that allows marsh migration on mainland shores. In contrast, in other locations salt marshes are drowning where there is no location to move to such as the center of islands in Pine Island Sound. Elsewhere areas of former salt marsh have been replaced by: deeper water salt marsh types, mangrove forest, or open water. Leather fern marshes have been significantly impacted by freeze events associated with recent extremes in winter climate. Recovery appears to be occurring very slowly. Barriers to the movement of salt marshes have already contributed to the disappearance of salt marshes from areas of former shoreline extents. These barriers include the standard model example of sea walls, and bulkheads, but also include spreader canals, road beds, rip rap revetments, borrow pits, stormwater treatment beam barriers, and even golf course bunkers. The best solution to maintain salt marsh habitats in the CHNEP is planned relocation and adaptations allowing the salt marshes to maintain themselves at the elevations of sea level that occur through time. There are adaptations that can be undertaken to assist in salt marsh migration and in some locations this has been occurring. These adaptations include; 1) Maintaining the existing marsh migration corridors that have been established on Cape Haze, the Eastern Charlotte Harbor shoreline, and Estero Bay Preserve State park and identify the highest priority marsh migration corridors so that they can protect these areas from future development. 2) Acquisition/Protection of inland/landward buffer zones to provide an opportunity for salt marsh habitats and wildlife to migrate inland. 3) Support the restoration of existing salt marshes by removal of exotic vegetation, backfilling ditches, removal of barriers to tidal connection, and degradation of exotic dominated uplands to make the salt marsh more resilient and capable of self-sustaining substrate building and migration. 4) Stop shoreline hardening including seawalls, bulkheads, rip-rap, and "living shorelines" backed by rip-rap. Use natural shoreline vegetation for shoreline stabilization instead 5) Re-engineer existing vertical shoreline infrastructure to a sloped soil based shoreline with GeoWeb or other permeable stabilization. 6) Restore impaired water flows to enhance sediment supply for salt marsh deposition. 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It is necessary to refine the CHNEP salt marsh environmental indicators and targets related to quantities and qualities, as appropriate, to the future distribution of salt marshes in a world with higher sea levels and a changed climate. It is possible utilizing the tools developed in this study to do so provide the CHNEP conference proceeds to this decision.

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