Rising Sea Level - A Stealth Threat

by John Englander

Sea-level rise is in the news with increasing frequency. Yet, the longer-term threat is largely underestimated. The risks in terms of economic impact, emergency preparedness, and national security have profound strategic importance. The latest news from Greenland and Antarctica strongly suggests that there is no time to waste when it comes to preparing for this threat.

Extreme change caused by sea-level rise (SLR) has only begun to shift the shorelines. Following are nine key facts that are often overlooked or misunderstood.

Ability to Stop Sea-Level Rise Higher sea level is now unstoppable despite efforts like the recent climate negotiations in Paris (known as COP-21), which are commonly perceived to be a potential solution to sea-level rise (SLR). As explained in the blog post, Paris Climate Agreement – The Good, the Bad and the Ugly, the 196 countries only agreed to limit maximum global warming to 3.6°F (2.0°C) over pre-industrial rates, but could not even agree on a method to reach the goal. That level concedes an additional 2°F beyond the 1.5°F that has already happened. Even if the agreed target can be reached, basic physics and thermodynamics guarantee that vast additional amounts of land ice will melt, raising sea level much higher.

Despite these very worthwhile efforts to reduce greenhouse gas emissions and the various sustainability efforts, so much excess heat has already been stored in the oceans that the world is now committed to substantial SLR with no hope of avoidance. Nations have passed a tipping point. However, it is important to note that, if they do not reduce greenhouse gas emissions and slow the warming process, then ice-sheet melt and SLR would accelerate and be dramatically worse – potentially catastrophic – within this century.

Accuracy of Projections SLR could be much worse than most projections suggest. Nearly all the forecasts omit or minimize contributions from Antarctica for a reason that is misleading. Scientists are essentially asked to state how much SLR will occur by the year 2100, but must be able to document the number to roughly a two-thirds statistical confidence (one standard deviation). The question of how several miles of ice on Greenland and Antarctica will collapse cannot be answered precisely anymore than when the Yellowstone volcano will blow or the next major San Andreas earthquake will occur.

Uncertainty about the timing of an event does not diminish its danger. In the case of those two ice sheets disintegrating, measurements and other data present a very clear picture of increasing instability. December 2012 projections of SLR this century range from 3 to 6 feet, but always contain a statement that higher values cannot be ruled out. Furthermore, every few years, the upper end of the projection is generally raised. Scenario planning for SLR often uses an average of the various projections presented. The naiveté of such an approach becomes clear when compared to planning for familiar disasters like hurricanes or earthquakes, where scenarios are planned around extreme cases. The underestimate is even worse since the assumed “worst case” is not at all the worst case.

Perception of Flooding vs. Sea-Level Rise Flooding from storms, heavy rainfall, and extreme tides is often confused with SLR. Although it is true that rising sea level would raise or amplify each of those short-term duration events, there are fundamental differences. Higher sea level is global and is essentially permanent, as it is almost certain to persist for more than a thousand years.

Presentation of Metrics & Variations Global average sea level – the often-cited metric – misses a vast range of regional variations due to ground subsidence and changing ocean currents. As a global average, over the past century, sea level is approximately 8 inches higher. In New Orleans, Louisiana, however, the rise has been over 45 inches, and, in Norfolk, Virginia, 30 inches, with the difference mostly being land subsidence. Rising sea level presents different problems in different places. For example, what works in Manhattan, New York, would not work in Miami, Florida, due to the porous limestone that makes sea walls ineffective.

Threats to Non-Coastal Areas Unlike the damage from storm waves that are somewhat limited to the coastline, SLR extends through marshes and wetlands and can push hundreds of miles up tidal rivers, greatly expanding the vulnerability zone. For example, Sacramento, California, is on a tidal river and is extremely vulnerable to SLR though it is over 80 miles from the coast.

Consideration of Direct & Indirect Vulnerabilities Wider community and peripheral vulnerability needs to be considered as well. For example, perhaps a building has adequate elevation and design to maintain functional use when sea level is three feet higher. However, the access roads, utilities, or distant zone of vulnerability could affect the building indirectly or even create a virtual “island” due to submerged areas in the surrounding region. Rising sea level needs to be considered at the level of a particular asset, the various infrastructure layers, and the regional or even international level.

Effects on Critical Infrastructure Problems are not just limited to flooding. For example, sustained higher sea level would change the critical clearance heights for vessels getting under bridges, where tolerances are now sometimes measured in inches. It would also mean groundwater penetration into landfills, fresh water aquifers, toxic waste sites, and cemeteries, posing new situations for public health and safety.

Development of Realistic Projections Most design specifications do not take into account a realistic range of SLR over the planned or true lifetime of a project. This includes a vast range of work: road elevations, drainage contours, bridge heights, tunnel entrances, water and wastewater infrastructure, nuclear power plants, refineries, ports, etc. Design life for projects is often 20-30 years. Adding the lead-time for project approval and construction can add another decade – thus getting into the mid-century.

Although design life and financing may only look to mid-century, the reality is that major buildings and infrastructure often are in use more than a century after construction. The latest sea-level projections from the U.S. National Climate Assessment exceed six feet by the end of this century. This presents a challenge because communities cannot wait until the collapse rate of Antarctica becomes unambiguous before raising or relocating all coastal assets and infrastructure.

Hope of Technology “Future technology” is often cited as the solution to the problem of SLR, yet sober evaluation shows that to be little more than wishful thinking. Although innovation and new technologies could certainly play a part in SLR adaptation measures, engineers must understand the limitations when protecting vast assets and landmasses – urban as well as rural. Technology in terms of electronics like smartphones is its own category and does not directly relate to stopping SLR. Technological advances will likely lead to the creation of power from non-greenhouse gas energy sources and continued advances in materials and design. However, there is no way to stop ice from melting at 32°F or to stop sea level from rising as the size of the ice masses on land decrease. The ocean cannot be “pushed” downward. It does not care about laws, regulations, or politics. The ocean will do what it will, like other forces of nature such as hurricanes, tornadoes, earthquakes, and avalanches.

Actionable Items The disaster preparedness community must now perform at least three actions:

  • Get informed and know the facts. Understand how SLR might affect specific areas of expertise. Expose the new reality to colleagues and professional organizations to expand scenario planning and discussion.

  • Assist audiences in assessing the vulnerabilities of future projects. For example, a “9-box matrix” can plot short-, medium-, and long-term time horizons against the realistic low, medium, and high scenarios for flooding from rising sea level, combined with the impacts from storms and extreme tides. Different locations and clients have different time horizons and risk tolerances. This tool allows for a full range of scenario planning and vulnerability assessment.

  • Seize the opportunity to be seen as a leader. SLR is a long-term trend that will cause tremendous disruption, but also tremendous economic growth and opportunities. As businesses and communities continue to realize the necessity of SLR adaptation, enormous projects can be undertaken to build resilient communities. Now is the time to be on the forefront of SLR adaptation planning, building, and design.

Communities are in the early stages of recognizing the revolutionary reality of sustained and accelerating sea-level rise. It is becoming clear that each community needs to help the international community prepare for this unprecedented era – thus rising with the tide.


John Englander is an oceanographer, consultant, and leading expert on sea level rise. His broad marine science background with degrees in geology and economics, and personal experience in Greenland and Antarctica allow him to see the big picture on sea level rise. He brings the diverse points of view of an industry scientist, entrepreneur, and chief executive officer (CEO). For over 30 years, he has been a leader in both the private sector and the nonprofit arena. The legendary Captain Jacques Cousteau tapped Englander to succeed him as CEO. Today, as the founder of the Rising Seas Group, Englander works with businesses and government agencies to understand the risks of sea level rise and the need for “intelligent adaptation.” He goes beyond the usual projections and explains the “uncertainties” that could yield considerably higher sea level as early as mid-century. His bestselling book, “High Tide on Main Street: Rising Sea Level and the Coming Coastal Crisis,” clearly explains the science of sea level rise, the impending devastating economic impacts and the opportunity to design for a more resilient future.  He is a sought after speaker. In recent weeks he has given keynote lectures at the U.S. Naval Academy and the American Planning Association. His blog and website are at: