Sea Levels and Flooding Risks on the Rise

By Irene Boland Nielson

Third in a five-part series on climate change issues.

Some 23 million Americans live near the coast at an elevation of less than 10 meters above sea level. Here in New York and New Jersey, recent storms like Superstorm Sandy drew attention to exposure to coastal flooding and many people are looking for maps to understand current and future flooding risks.

For current flood risk, FEMA maps are a good source of information. FEMA updates flood maps county by county using updated mapping technology and historic meteorological data. Check the website to view the current FEMA flood map.

Due to climate change, future risk is not the same as current risk. As seas rise and expand more coastal areas will be exposed to flooding and flooding risk will increase.

Climate scientists model the three main drivers of sea level rise. First, higher global temperatures lead to the expansion of the oceans because water expands when warmer. Second, land based ice which melts and adds surface water in quantities great enough to raise the ocean, (remember that floating ice does not add volume to the ocean when it melts). Third, and independent of climate change, continents are either rising or sinking due to geologic processes (rebounding from the last ice age) or human practices such as groundwater extraction or diversion of sediment rich waters in river deltas (think New Orleans). NOAA Sea Level Rise Vieweris a good source of information about sea level rise projections. You can move the slider bar to visualize sea level rise at different levels ranging from 0ft to 6ft and see historic records from tide gauges.

The National Climate Assessment released in June of this year projects sea level rise of 1 to 4 feet by 2100. We don’t know how much greenhouse gases will be released over the next century but we do know from the International Meteorological Organization that last year, global emissions increased at the fastest rate in 30 years.

Sea level rise is just one of many impacts of climate change, but unlike some climate change impacts that may vary in direction of change, sea level rise is only increasing. Projections examine not if but when the higher sea elevations will be reached. This is because the emissions already in the atmosphere will continue to expand the worlds’ oceans for centuries to come. Hopefully now you can dive into public information resources to understand why today’s coastal flooding risk is changing in the future.

Tags: sea level rise, climate change, flood zones, FEMA flood maps, evacuation zones, coastal flooding, flood, flood risk

About the Author: Irene Boland Nielson is the Climate Change Coordinator for the New York City based office of the U.S. EPA. She joined the EPA as a Presidential Management Fellow and has worked on a range of issues, including the Agency’s Strategic Plan, a memorandum of agreement with Department of Defense for a sustainable Guam, and the EPA Climate Adaptation Plan. Currently, she co-chairs the EPA Region 2 Climate Change Workgroup, administers Climate Showcase Community grants and works to promote sustainability in communities.

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