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This is the NOAA Ocean podcast, I'm Troy Kitch. It's impossible to miss the impacts of sea level rise in many coastal places around the nation. Take Charleston, South Carolina. In 2020, this coastal city experienced a record 14 days of sunny day flooding... that's what many people call these type of days when there are no storms, no rain, no strong coastal wind, nothing special, but low-lying areas along the coast are flooding. This type of minor coastal flooding is so common in all around the world that you could say it's become the 'new normal'... that's how things are today. But what about 10, 20, 30 years from now? What can we expect in the coming decades for places like Charleston or for the coastal place where you live?

In this episode, we're going to talk about a report released in 2022 that provides some startling insights on what the future holds. It's called the Sea Level Rise Technical Report and it provides sea level rise projections for all U.S. states and territories out to the year 2150.

Here are two things from the report you need to know up front: over the next 30 years, we can expect the same amount of sea level rise that we experienced over the past 100 years, so sea level rise is accelerating. And for coastal flooding, we can expect more of that, with an increase in frequency of flooding events that cause damage. But that's not all. So to dig deeper into the report, we have two members of the Federal Sea Level Rise Task Force joining us: Mark Osler, NOAA's Senior Advisor for Coastal Inundation and Resilience, and William Sweet, an oceanographer and scientist with the National Ocean Service who is an expert in sea level rise and is the lead author of the new report.

HOST: Mark, let’s start with you. This report is a product of the Federal Sea Level Rise Task Force. Can you provide us some context about the task force and how the report fits into the big picture?

MARK OSLER: This is a cross-agency science team that was convened by the White House in 2015 in recognition of the need and increasing demand for authoritative, consistent, and accessible science around sea level rise and the associated hazards that sea level rise brings to our coast. There are many different parts of the federal government at work on issues of sea level rise that this task force brought together to help coordinate and develop the necessary science through sustained coordination and participation of key agencies. All of this towards the goal of incorporating sea level rise information into agency-based tools that are user-friendly; things like maps and visualizations and analysis tools that can actually help decision-makers on the ground, whether it's an engineer or a planner or a state hazard mitigation officer, to help get the science refined and in a useable format to support decision-making.

HOST: So the task force pulls together all we know about sea level rise and boils it down to make it easy to understand?

MARK OSLER: Sea level rise science is advanced through publications and scientific journals and research documents. It takes a high degree of expertise to actually distill all that research down into an aggregate statement on most likely outcomes, something authoritative where the government says this is actually our best understanding of how this process of sea level rise is changing. So at its highest level the groups purpose is to do that: to be a group that can digest with their own expertise all of the state of the science, all the cutting edge research, and say OK well what does this mean today in terms of the future conditions at our coast per sea level rise under different scenarios.

HOST: The last sea level rise technical report came out in 2017. So, William, there's generally an updated report every five years or so?

WILLIAM SWEET: About a five-year interval which largely reflects the updates in science and observations and models, pulling from the very best on the international scale usually following as best possible the cadence of the International Governmental Panel on Climate Change's release of their report. So we put it out on about a four- to five-year cycle to capture new information — the data, the science, and the models — and translate that for the needs of the United States.

So what are the projections for sea levels in the U.S. for the coming decades?

WILLIAM SWEET: The United States Sea Level Rise Task Force is projecting that sea levels along United States coastline will rise somewhere between 10 and 126 inches in the next 30 years or by 2050, relative to those today. The basis for this are the models themselves, which come from the Sixth Assessment of the International Governmental Panel on Climate Change, as well as the regional sets of observation that we have along the United States coastline. Together, the two of them both point to a rise along the coastline.

HOST: As I was reading through the report, it's very clear that the rise along the coastline won't be the same everywhere. It’s not like water rising in a bathtub. There are different rates of sea level rise from place to place. Why is that?

WILLIAM SWEET: There's three particular reasons. One, it's really about what does that change doing relative to land, so the relative sea level component. How is land changing? Is it sinking or is it rebounding like it is in Alaska. Over most the lower 48 states, land is sinking to some degree for both natural and unnatural reasons. There's two other reasons why the ocean is not rising like it would in a bathtub. Changes in ocean circulation: the Gulf Stream, for instance, it fluctuates in speed and when it does, it causes sea levels to vary along the U.S. coastline. All models suggest that the Gulf Stream system will slow down in a warming world and, if so, it's going to cause more or less permanent changes along the East Coast, higher than global [sea level]. The other factor is where ice melts matters. Where we have these tremendous amounts of ice locked up on land, for instance in Greenland and Antarctica. And when these large ice sheets lose mass it affects the gravity and rotation of the actual earth itself. So typically what has happened through time and what is projected to happen is Greenland and Antartica, they lose ice mass that contributes to global rise — the water near the sources will actually decrease some as the gravitational tug decreases. But far away from these sources of ice, you'll have additional amounts of rise. So it's the summation of those three factors: changes in land height, changes in circulation, and changes in response to melting land-based ice, which will cause the ocean to rise at different rates.

HOST: But, overall, we can expect more coastal flooding — more damaging coastal flooding — on average in the future.

WILLIAM SWEET: What we find is that the frequency of minor flooding is likely to be exceeded by that of moderate flooding in 30 years. And so what this means is moderate flooding that today is typically associated with damaging amounts of water levels in the streets, affecting businesses, or personal property — you know, there have been instances just recently where we've had not too big of storms causing very big damages around the country, of water levels that are just exceeding hurricane height storm surges that occurred 30, 40, 50 years ago. We are able to project that if adaptive measures aren't taken — risk reduction — our current footprint is going to be at greater risk.

HOST: Mark, one thing that is striking about this report is how specific it is.

MARK OSLER: We're specifically telling you, with a fair degree of certainty, this is how it will change in detail, by location. And so We are able to look at those statements of future conditions and plan and adapt. The hope is that this information is indeed sobering, but is also empowering and becomes the basis for action. That it is not a poorly defined statement that the future may be less nice than the present. This report is telling you: this is where the coastal water levels will be, on average. This is how the extremes are changing. And so, you can take that to the bank for the next coming decades, which is critical for financial planning, urban planning, all sorts of insurance and risk transfer implications can rely on this data in a way that is much more specific that we are able to produce for many other aspects of our changing climate.

HOST: William, we've talked about increases in minor and moderate flooding due to sea level rise. Can you talk about the differences between minor, moderate, and major coastal flooding?

WILLIAM SWEET: The coastal flooding that we've been monitoring due to increases of sea level rise — we're calling this high tide flooding — are becoming much more common now than they used to be. And so we have elevations on land that the Weather Service in partnership with local emergency managers have established through years of impact monitoring, and they have made these elevation thresholds for three severity levels: minor, moderate, and major. Minor flooding typically is mostly disruptive, causes a delay or a deviation in your path to work, whether you're walking or driving. But moderate or major flooding more often causes damaging impacts, or can be destructive. And when these are likely to occur, the Weather Service issues coastal flood warnings for a significant risk to property and life. As more people move to the coast and sea levels continue to rise, that risk is really growing and it's growing rapidly.

HOST: I'd like to talk about this risk in coming years. We're now in the midst of accelerating sea level rise around the world and the report points to what we can expect in the next three decades. But what can we expect beyond that?

WILLIAM SWEET: Over the last several years, we have witnessed the impacts of sea level rise occurring now. Flooding of streets when it's sunny outside. More times than not, there's no localized storm and there's water coming out of stormwater systems, onto the streets, getting up towards people's property, getting up towards people's businesses. And that's sea level rise, plain and simple. So I think the sense of urgency is pretty much there. Folks know what sea level rise looks like. It's the increase frequency of these kind of events that used to be in response to a big storm and it made sense. You were flooding because there was a storm. But now, we are flooding more often than not when there's no storm in sight. And so what this report does, is it says there is to be more of that. That is to be expected. And by how much are these flood frequencies likely to change is largely due to the amount of sea level rise that occurs. And that amount of future sea level rise is very much related to the amount of future emissions that we pump into the atmosphere. Not so much the next 30 years, that's pretty much baked in to the system at this point, and so that's why we have very good guidance as to what we expect to happen in the next 30 years. But beyond that, it's collectively in our hands as to how much sea levels are potentially going to rise. More emissions equals more heating, equals more ice melt, equals more thermal expansion, equals higher sea levels, equals more flooding. And that we are trying to put in context for the United States as to what to expect now, a few decades from now, and potentially what could happen by the end of the century and beyond.

HOST: Does this report provide data for all coastal areas of the United States?

WILLIAM SWEET: This new report provides scenarios for every region of the U.S. What we've been able to do is downscale the climate models — information extracted from them — at a one degree resolution along all United States coastlines. We have almost done the same thing with the variability part, the extreme water levels, as we're calling them: the effects of high tides, typical storms, or when the wind is blowing whether from a hurricane or a 20 knot wind that people go sailing in. We are able to provide those two sets of information at almost every coastline along the United States, so that whether you're a big city, a small city, or somewhere in between, you'll have the information that is based upon the best science and the latest observations to plan and prepare for what the future may hold.

HOST: So the report covers sea level rise scenarios for all locations and covers most locations for scenarios that involve variability, when there are storms or winds or extra high tides. When reading through the report, it jumped out at me how much more of the U.S. is covered in this report compared to the technical report that came out around five years ago. Mark, why is there now an effort to cover ultimately all of the U.S. coastline?

MARK OSLER: So understanding why we have gaps in our current coverage, to me it helps to understand why is the federal government in the business of measuring coastal water levels at all, and why have we been doing this, in some cases, for over a hundred years. And the answer to that, briefly, is to support safe marine transportation, navigation, and commerce at our coasts and into our inland waterways. That's the original reason. What we have is sort of a natural clustering of scientific focus on the population centers of the United States. And that's right and proper. We don't have large port systems in rural areas, so we typically have not needed to have as rich a data set in those areas. Climate change is turning that paradigm on its head. Where we understand that our ability to measure, model, and predict how our environment is changing is relevant to every community, every citizen of the country, no matter whether they live in an urban area or a rural area, whether it's an East Coast or West Coast state, whether it's a U.S. territory or in Alaska or anywhere else. And so, for the sea level rise data, we have the same effect. If you were to do a close survey of where sea level rise projections have been available in the past, they are typically focused on the U.S. population centers. And efforts to interpret and expand our ability to make skillful statements are on sea level rise are in areas outside of those population centers. This report, and the advances of science that this report represents, really makes good on a promise to deliver climate change information to every part of the United States, including the territories, in a way that really hadn't been possible before and really hadn't been a focus in the same way that it is today.

HOST: William, I'll leave the last word with you. You've been working on this report for years. What's the one thing you'd like us to take away from it?

WILLIAM SWEET: I've grown up near the water for a large part of my life, and I currently live near the water and I see the changes firsthand. So it's real. I'm not just a scientist, I'm a citizen of a coastal community. What the data is telling us is that sea levels are rising, and we're starting to flood more often, and that is the pattern — and the tell-tales are all pointing to more — and I want us to be ready. I want my kids to live in an area that is still on the water, that still enjoys the benefits of being on the water, and the joys that come with it, and I want it to be accessible to them and others. And we just need to recognize that that change is at hand and that we need to plan and prepare for the future.

HOST: That was Mark Osler, NOAA's Senior Advisor for Coastal Inundation and Resilience, and William Sweet, NOAA oceanographer and scientist, and lead author of the new report. Check our show notes for links to the full technical report and an overview we've prepared to walk you through the key takeaways from the report. You've been listening to the NOAA Ocean Podcast, and we'll return next month.