Global climate change is warming oceans, melting polar ice and causing sea levels to rise around the world. In Oregon, scientists predict that in the next 80 years, waters will rise at least 3 feet, but that a rise of more than 6 feet cannot be ruled out. That level of increase would submerge small islands in the Columbia River and leave much of Sauvie Island underwater as well. The National Oceanic and Atmospheric Administration has released a new mapping tool that helps people visualize various levels of sea level rise around Oregon. Jonathan Allan is a coastal geologist with the Oregon Department of Geology and Mineral Industries. He joins us to discuss how sea level rise is already impacting Oregon.
Note: This transcript was computer generated and edited by a volunteer.
Dave Miller: We turn now to another recent map put out by NOAA, another way to see how climate change is affecting our lives. This map is focused on rising sea levels due to warming oceans and melting polar ice. Scientists predict that, in the next 80 years, globally, waters will rise at least three feet. A rise of more than six feet cannot be ruled out. That level of increase would submerge small islands in the Columbia River and leave much of Sauvie Island underwater as well. Jonathan Allan is a coastal geologist with DOGAMI, Oregon’s Department of Geology and Mineral Industries. He joins us now. Jonathan Allan, welcome to Think Out Loud.
Jonathan Allan: Thank you for having me.
Miller: Let’s just start with the big picture. What do you see as the most likely scenario in terms of sea level rise for the Oregon coast for the rest of this century?
Allan: The projections that NOAA has been producing are indicating that regionally along our coastline, sea level is expected to rise by a few feet certainly by the end of the century. But the degree of change actually will vary spatially along our coastline, as well as up in the Washington Coast, for a variety of reasons relating to regional tectonics and various other factors.
Miller: Well, let’s turn to the tectonics one. It’s really interesting, because I understand that on the Oregon Coast, unlike say in Florida, some of the sea level rise is going to be effectively erased by the rise of the plate that we’re all standing on right now, the North American tectonic plate. Which of these enormous forces, rising sea level or I guess in this case, rising land, is moving faster?
Allan: So currently on the Oregon coast, it actually varies depending on where you are. In a general sense, on the central to south Oregon coast, from about Coos Bay north to around Tillamook, that portion of the coastline is very slowly being transgressed by sea level rise, meaning it’s gradually flooding over the long term. And that means that the rate of sea level rise is exceeding the actual uplift of the land in that portion.
As you go south of about Coos Bay, that process reverses. And in the very southern part of the Oregon Coast, the rate of tectonic uplift is actually exceeding the local rate of sea level rise. But at some point in the not too distant future, those processes, at least on the south coast will actually cancel out. And so the effects of sea level rise will start to become more pervasive across a broader area of the coastline.
Miller: Do we know, or have a good scientifically educated guess, about what will happen specifically as a result of the Cascadia Subduction Zone earthquake, in terms of sea level?
Allan: That’s a really interesting and great question. Obviously we know from significant research that has been done in the region that past subduction events can instantly lower our coastline by about 2 to 3 feet. And it varies spatially along the coastline. So that’s equivalent to obviously raising sea level in that instant of time.
Miller: Wow, that that could be as much as 80 years of potential incremental sea level rise, in three minutes.
Allan: That’s correct. And so obviously, looking to the future, as you think about raising sea level along our coastline, and then you factor in the effects of a Cascadia-type event, then we’re really starting to talk about pretty significant changes associated with the combined effects of those processes.
Miller: When it comes to climate change modeling, we’ve all heard in the past about the possibility of different kinds of tipping points or inflection points, positive feedback loops where there is this one smallish thing, but it turns much bigger very quickly. Is that tied to sea level rise as well? Are there inflection points that modelers are paying a lot of attention to?
Allan: Yes. In terms of the effects of global sea level rise, there are two real main components. One is what we call a steric effect, which is associated with water temperatures. As water temperature warms, it expands. And that contributes to a rise in water levels. So that’s one component.
The second component is changes associated with glacial melting, both land based but also in the major areas such as Greenland and Antarctica. And those are two areas that would contribute the largest amounts to very significant changes in sea level, were they to fail in a catastrophic manner.And so there’s a lot of research that’s actually ongoing to try to better understand what’s actually happening in those areas under today’s conditions, and then what are the likely downstream effects associated with any form of acceleration of melting in those regions?
Miller: What happens when you combine sea level rise with more severe storms?
Allan: That’s a really excellent question. When we look at say a product like what NOAA has produced here with these sea level rise projections, where you can adjust the rate of increase in one foot increments and see the degree of flooding, what that shows you is almost like a bathtub type response. And it’s only considering one factor which is changes in water levels. But it’s ignoring the other components because they’re complex to demonstrate. And those other factors relate to changes in storminess, or events such as big flood events and things like that. What we’re really talking about is the joint probabilities of increasing water levels combined with the effects of extreme storms. Over time, we would expect to see as water levels rise along the Oregon Coast, what we’re effectively doing is if we hold our storm conditions and wave climate constant as we experience now, we’re simply raising the elevations of which those ocean waves can now reach the back of the beach. And so that actually will directly contribute towards increased erosion and flood risk and things like that.
And similar effects can obviously occur in our riverine environments where adjusting ocean water levels, and then we have large flood events taking place on top of those rising water levels, will contribute to increased flood risk as well.
Miller: How much is the Columbia River itself affected by rising sea level?
Allan: Well, that’s an interesting question. So discharge on the Columbia River is strongly controlled in order to mitigate flood risk and things like that. But at the same time, we have rising ocean water levels in our region here. And so if we assume that conditions in the upper portions are not going to change ‒ I mean, we’ve seen the effects of large riverine flood events such as what happened in the late 1990s ‒ one can expect to see similar large flood events in the future. And so combining those types of scenarios with rising water levels over the next 50 to 100 years, then we are starting to look at the potential for increased flooding in low lying areas.
And so what this NOAA sea level rise viewer allows you to do is start to see at least those areas that are susceptible to ocean flooding, in the absence of riverine flooding. But then that’s where other modelers can start to integrate the two and really start to better understand the sort of joint combinations of those processes.
Miller: In other words, even Oregonians who don’t live near the coast, which is obviously the majority of Oregonians, we could still be affected by sea level rise 80 miles away.
Allan: Yeah. A great example is if you use the sea level rise viewer and you zoom into the downtown Portland area, particularly in the area around Sauvie Island, you can play around with adjusting the various scenarios of water level rise under various conditions going out in the future. And then just think about, say, the 1996 events happening on top of those types of rises in water levels, and you can really start to better appreciate the potential for these flood problems in the future.
Miller: My understanding is that the data that NOAA used for the mapping tool that was put out recently, the data itself isn’t new. What is new about this map?
Allan: NOAA actually produces national level updates to the sea level rise projections on about a four year basis. And so the most recent update was done in 2022, prior to that it was 2017. And so we can expect to see another update in a few years time.
I think one of the really neat aspects about the sea level rise viewer is the inclusion of a variety of other components that may be of interest to resource managers or the public at large. And these look at things like the vulnerability of certain areas. It includes high tide flooding under today’s conditions. You can actually zoom into particular locales, and they have neat little animations where you can adjust different water level changes and visually see what those impacts might be at a particular location. And as well as I think another key component is incorporating uncertainties based on measurements of the ground elevations and things like that. They’ve really tried to bring in a lot more useful information into a product like this that I think, both now and looking to the future, they’ll enhance even further. It’s obviously going to be extremely useful for both resource managers, but the public as well at large.
Miller: How much are Oregon’s coastal communities preparing for these rising sea levels?
Allan: That’s another excellent question. I think this is one of those challenging problems because obviously sea level along our coastline is rising gradually, varies along our coastline. We’re already seeing the effects of large storm events happening in different parts of the coast. And those responses involve putting in engineering structures to protect coastal properties. Some communities have started to try to better understand what the future projections are likely to be. Our agency has done erosion hazard mapping for a large chunk of the Oregon coast where we try to factor in the effects of extreme storms. And those data can be used by coastal planners to think about where best to place property or where not to allow property to be developed.
Miller: Jonathan Allan, thanks very much.
Allan: Thank you.
Miller: Jonathan Allan is a costal geomorphologist with DOGAMI, that’s the Oregon Department of Geology and Mineral Industries.
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