Dr. Gary Griggs: Rising seas threaten U.S. coastlines and cities

April 6, 2023

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Climate change is causing sea levels to rise, posing a catastrophic threat to people, private development, public infrastructure, and the economy.

On Thursday, April 6, 2023, SciLine interviewed: Dr. Gary Griggs, a distinguished professor of earth and planetary sciences at the University of California, Santa Cruz. He discussed topics including: which U.S. cities and infrastructure are most vulnerable to future sea-level rise; the hazards of short-term sea-level rise (including king tides, El Niño events, and large waves at times of high tides), long-term global sea-level rise, and coastal impacts of storms; what cities or communities need to consider before building seawalls, revetments or other barriers to protect them from sea-level rise and storm waves; other ways that humans can adapt to the reality of rising seas, such as managed relocation, realignment, or retreat; and what can be done to slow sea-level rise.

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Introduction

[0:00:20]

GARY GRIGGS: I’m Gary Griggs, and I’m a professor of earth sciences at the University of California, Santa Cruz. And I study coasts, which include beaches and sand, coastal erosion, coastal protection, and sea level rise and how that’s affecting us and what our options are for responding or adapting to that.

Interview with SciLine

What is sea-level rise, and what is causing it?

[0:00:47]

GARY GRIGGS: Sea-level rise just refers to the level of the oceans. And that changes as the planet warms. So, as the Earth gets warmer, two things happen: Sea water expands, and ice melts. And if we were to melt the remaining ice on the planet—which is in continental glaciers, in Greenland, and in Antarctica—we could raise sea level about 216 feet, plus or minus a few inches. That would impact probably several billion people around the planet. Right now there’s 635 million people living within 30 feet of sea level. No scientist thinks that’s going to happen in this century or the next, but we don’t need it all to melt to create major problems for coastlines around the world. Even three to five feet of sea-level rise is going to create some amazing, should say, incredible damage to coastal cities and coastal populations.

Which U.S. cities and infrastructure are most vulnerable to future sea-level rise?

[0:01:59]

GARY GRIGGS: Well, there are dozens of cities along the coast of the U.S. that are vulnerable to sea-level rise. Most of those are along the Atlantic coast and the Gulf States coast, because they’re very low lying very low relief. And that includes Washington, D.C., Annapolis, Atlantic City, Miami, Baltimore, Philadelphia, Charleston, Ocean City, Boston to name a few. And they are already experiencing what we call sunny day flooding. Even during calm days, sea level is now moving into those cities. And as sea level continues to rise, it will occur more often, lasts longer, and extend further inland. On the West Coast, we have a different geology, so that most of our cities are higher—not all of them. So, we will not experience those same effects as soon. In the long run, we will.

Do seawalls, revetments, or other barriers work to protect cities from sea-level rise and storm waves?

[0:03:00]

GARY GRIGGS: We’ve sea walls and rock revetements for decades to protect coastal communities, both private property and public infrastructure. And some of these, well engineered, well built, have lasted for ninety years, and some haven’t lasted for 90 days, depending on how they’re built and where they’re built. If we look around, we find that there are some impacts to those sea walls and resentments. Among the most important is what we call passive erosion. So, on a shoreline that’s natural, that’s unprotected, as sea level rises, the coastline and the beach will just continue to move inland. But once we put a solid barrier there—a seawall—and sea level continues to rise, we will flood or drown that beach. So, we’re not going to have a beach in the future. We’re going to be protecting private property at the expense of a public beach. And all protection ends somewhere—whether it’s a dam or a levee or a sea wall—at some point, it will be overtopped, or we will get a worse condition than we had planned for. So, these are—they can provide short- to intermediate-term protection, but at some point they’re going to be overtopped. And I think we should think about these as essentially short-term, very large band aids.

For cities considering barriers to protect against sea-level rise, what should be part of their decision-making process?

[0:04:31]

GARY GRIGGS: We have now—or the Corps of Engineers has now proposed a number of very large walls around some East Coast, Gulf Coast cities including Charleston, Miami, Galveston—even New York, New York and New Jersey. These are very expensive, we’re talking about billions of dollars: $50,000 to over $1 million per linear foot. So, I think cities need to ask: How long will these be effective? Who’s going to pay for them? What are their impacts? And who or which neighborhoods are protected, and which get left out, which raises a really important question about social equity.

Other than trying to physically hold the water back from existing cities and infrastructure, what are the other ways that humans can adapt to the reality of rising seas?

[0:05:21]

GARY GRIGGS: Responses to rising seas are really pretty limited. Doing nothing or denial isn’t going to work for long. We spent a huge amount of money along the Atlantic and the Gulf coasts nourishing beaches or adding more sand—something like $12.4 billion in adjusted costs, which has added about 1.4 billion cubic yards of sand. And that’s a hard volume to imagine, but it’s about 140 million dump truck loads. It’s proven to be a short term solution. And almost every place we’ve done it, it requires repeat nourishment. There are some places in Florida where we’ve nourished the same beach 18 times, which says something about how long it survives. It’s important to keep in mind that over the long run, there is nothing we can do to hold back the Atlantic Ocean or the Pacific Ocean. While it’s not at all popular, at some future time, we’re going to have to move inland, and we’re going to have to relocate away from the shoreline. Whether we call this managed retreat or unmanaged retreat, it will eventually occur. And there are a number of places where that’s already happening. It’s happening on places on the California coast, publicly. Well, Rodanthe in North Carolina is a place where there’s been a lot of publicity recently, Hawaii. So remember, we have 216 feet of potential sea-level rise to deal with, so we cannot hold back the oceans forever.

How does sea-level rise worsen the impacts of extreme events like storms?

[0:06:59]

GARY GRIGGS: I think it’s important to keep in mind that while sea-level rise is an important process that’s going to go on for centuries—and it’s rising now at an accelerating rate. Over the short term, probably at least till mid-century, it’s going to be these short term events—short term extreme events that are going to cause the most damage. Thinking about hurricanes like Katrina, and Sandy and Harvey, and Ian, and on the West Coast, El Niños and large waves arriving at times of high tides that we saw on January of this year—these are going to be more damaging over the short term, but they’re going to be riding on top of sea-level rise. So, the higher sea level rises, the further these extreme events will extend inland, and the deeper the water will be.

How does sea-level rise vary in different places?

[0:08:03]

GARY GRIGGS: The rate of sea-level rise is not the same everywhere. While sea level is rising for the global oceans, because of land motion, it’s going to be different in different locations. So, in New Orleans, for example, or Venice, the land is actually sinking. So, sea level is rising relative to the land three or four times faster than the global sea level. And then there’s places like Alaska or Scandinavia, or even parts of Northern California, where the land is rising. So, sea level is rising much more slowly. In fact, it may even be a negative rate because the land is rising faster than sea level is.

What can be done to slow sea-level rise?

[0:08:54]

GARY GRIGGS: There’s really only one thing we can do that’s going to have a big difference over the long term. As long as the planet continues to warm, we’re going to melt ice and expand ocean water. So, the more fossil fuels we burn—coal, oil and gas—the more greenhouse gases, particularly carbon dioxide, we put into the atmosphere, which is going to warm the planet and increase sea level. So, the only way we can slow this down and eventually stop it is to do everything we can as fast as we can to reduce and then eliminate our dependence on fossil fuels and move to renewables. So, today in the U.S., about 77% of all of our total energy is provided by oil, gas and coal. Although good news: Last year, for the first time, in terms of generating electricity, renewables provided more than coal. So, we’re making progress. We still have a long ways to go, but we’re making progress. This is what I call aggressive incrementalism. We just need to be even more aggressive.

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