Sacred Headwaters #19: Sea Level Rise
We know sea levels are rising because of climate change. But the exact details -- how much? how quickly? -- are much less clear than one might think.
Sacred Headwaters is a bi-weekly newsletter that aims to guide a co-learning process about the existential issues and planetary limitations facing humanity and about how we can reorient civilization in a way that will enable us to thrive for centuries to come. If you’re just joining us, consider checking out the first issue for some context and head over to our new table of contents to browse the whole library. The newsletters are not strictly sequential, but this exploration is meant to build on knowledge and understanding over time. Subscribe below if you haven’t already, and please share with friends, family, and colleagues who may be interested:
Table of Contents
Sacred Headwaters has a rudimentary table of contents. I hope that this will help readers to “catch up” more effectively, facilitate using this as a reference, and give a better picture of what this is about if you’re just joining us.
Issue #19: Sea Level Rise
We’ve read about a lot of things that aren’t ostensibly related to climate change over the last few months. I hope that I’ve made an effective case over the last few months that our efforts to mitigate climate change need to be grounded in efforts to transform the underlying structure of our global economic and social systems, and that climate change is just one of the many crises caused by these systems, but we haven’t looked in much detail at climate change itself since the first issue.
Over the next couple months, we’re going to explore some of the major drivers of the human impacts of climate change, starting with sea level rise. My hope is to both support a better understanding of the science involved in predicting and quantifying these climatic changes and to explore how our current systems are failing to account for them — in spite of scientific consensus. Part of the answer to that latter question, of course, has been explained in the issues about racial capitalism and environmental justice.
I live in a small town on the Pacific coast. We’re rapidly developing our downtown area, located at sea level (and at the confluence of three rivers), even in-filling the ocean in places to allow more development. We are doing this because we’re operating under provincial guidelines that tell us to plan for one meter of sea level rise by 2100, an estimate in line with the IPCC’s Special Report on the Ocean and Cryosphere in a Changing Climate.
But what if the IPCC is — as they often are — being overly conservative in their estimates?
There are a number of scientists who argue that the IPCC’s estimates are overly conservative and that sea level rise could significantly exceed one meter by 2100, sinking huge amounts of existing and yet-to-be-built infrastructure and causing mass migration away from coastal cities. It depends largely on ice sheet dynamics: will we lose the Greenland Ice Sheet? What about the West Antarctic Ice Shelf? Even NOAA, a US government agency, reported in 2017 that sea levels could reasonably rise as much as 1.3m by 2100 and that rapid Antarctic ice loss could cause up to 2.5m of rise by 2100. And of course, because Earth’s temperature has a delayed response to CO2 emissions and sea level has a delayed response to surface temperature, even if sea level rise doesn’t exceed one meter by 2100, it will continue beyond the end of this century, regardless of our actions today.
What would one meter of sea level rise mean for our civilization? For our coastal cities and for entire low-lying countries? What would three meters of sea level rise mean?
In this issue, we’re going to read about some of the uncertainties involved in modelling sea level rise and explore the impacts of moderate and extreme levels of sea level rise around the globe. My takeaways? Predicting sea level rise is governed by tremendous uncertainty, but even the lower bounds of that uncertainty have unconscionable impacts that will be felt overwhelmingly by the world’s already vulnerable, both geographically and due to economically-driven inability to adapt. The upper bounds are downright terrifying and would likely play a major role in the end of civilization as we know it.
Sea Level Rise and Implications for Low-Lying Islands, Coasts and Communities, Executive Summary (15 minutes)
This is the executive summary of Chapter 4 of the IPCC’s Special Report on the Ocean and Cryosphere in a Changing Climate referenced above. It’s a bit dry, as these things often are, but it gives a concise summary of the IPCC’s position on predicted sea level rise and an overview of humanity’s differential capacities for adaptation — and the limits of those capacities. There are a few really notable points. First and foremost, sea level will continue to rise for centuries, regardless of our actions today, and the trajectory of that rise is the subject of deep uncertainty, especially beyond the 21st century. Second, while rising seas will directly inundate some regions, the more significant issue is the rising frequency and impact of extreme sea level events, usually associated with storm surges and high tides. What are today 100-year flood events will be commonplace in 2100 in all emissions scenarios. Floods of this magnitude will happen annually in low-lying areas by 2050. Third and finally, we will reach technical limits to our ability to adapt to and mitigate sea level rise by 2100 — meaning, after that, regardless of how much money we have, we will no longer be able to protect our coastal population centers from the continued rise of the ocean. The authors also note that we are likely to hit economic limits to adaptation far earlier, and those economic limits vary widely based on regional wealth and population. In other words, the world’s poor are most vulnerable to the impacts of rising seas. The summary talks briefly about changing the paradigms with which we manage risk and uncertainty in order to plan appropriately for rising GLSR; you can read more about what they’re talking about in Issue #8: Systemic Risk and Resilience.
Coastal Risk Screening Tool (5 minutes)
This is an interactive tool that uses projected sea level rise and elevation models to predict what low-lying areas will be subject to annual floods by 2050. You can change the variable that’s being displayed (and the year you’re looking at) by clicking “Choose Map” in the top left. This visualization is built on top of a paper that used a new, highly accurate digital elevation model — CoastalDEM — to assess how much of the world would be below projected high tide lines in various emissions scenarios. No need to read the whole paper, but take a few minutes to play around with the risk screening tool. Look at your home if you live in a coastal area, or a coastal city you’ve recently visited. The authors of this paper found that, in a high emissions scenario, 630 million people will be living below annual flood levels by 2100.
A new paper in Scientific Reports (2020) assessed similar variables with a different methodology and found even more dire results (summarized in this New York Times article).
Note: there are obviously complexities involved in modelling flooding. The authors of the visual tool explain all the details of models have been applied to develop the tool — click the “Details and Limitations” button on the left to learn more.
“James Hansen’s Bombshell Climate Warning Is Now Part of the Scientific Canon” (10 minutes)
In 2015, James Hansen, the climate scientist who testified before Congress about climate change in 1988, released a paper arguing that the major ice sheets of the world are likely to suffer nonlinear and rapid degradation that could cause, among a whole host of other terrifying developments, global sea level rise of multiple meters in a matter of decades. This short piece by Eric Holthaus summarizes the paper’s findings and some of the critiques issued by other scientists at the time. It also includes a link to a 15-minute video in which Dr. Hansen explains the dynamics involved in and resulting from rapid ice melt. Many climate scientists have expressed skepticism of Hansen’s high-end estimates and short timelines, but there is general agreement that ice sheet collapse will be non-linear and that we currently have a great deal of uncertainty about how — and how fast — it will occur.
Rapid collapse of Antarctic glaciers could flood coastal cities by the end of this century (15 minutes)
Hansen’s 2015 paper used fairly crude modelling of ice sheet degradation, estimating the rates of acceleration of ice melt based on paleoclimate data and recent ice loss. Since then, other studies have come out arguing that specific mechanisms of rapid ice loss are likely to occur, particularly in high emissions scenarios. This is another piece by Eric Holthaus and it looks at a number of studies focusing on two glaciers in Antarctica, the Thwaites Glacier and Pine Island. The papers argue that these ice sheets are at risk of marine ice-sheet instability, meaning, basically, that because they extend out over the ocean, we could reach a temperature threshold at which they will rapidly and irreversibly collapse. The potential timeline and degree of sea level rise that would result from this are uncertain, but these authors suggest that it is not out of the question that we could see rapid sea level rise within 20-50 years, and that six feet of rise may be more likely than the IPCC-forecast one meter by 2100. The West Antarctic Ice Sheet could contribute 11 feet of sea level rise if emissions are not reduced.
There’s a neat multi-part series specifically on the Thwaites Glacier (2019). We’ll likely learn much more about the glacial dynamics in West Antarctica in the next year or two: researchers are using a submarine to study ocean currents and ocean floor-ice interactions in the area.
On a related note, in the last six months, studies have shown that the Greenland Ice Sheet is beyond its “point of no return” and that we are seeing record-setting, model-exceeding, and accelerating rates of ice loss.
“Rising seas give island nation a stark choice: relocate or elevate” (10 minutes)
Tony de Brum, foreign minister of the Marshall Islands, has called the impacts of climate change on his nation genocide. The Marshall Islands is facing a very near-term crisis. While the rest of the world suffers from gradually rising seas and increasing flooding from extreme sea level events, the island nation may literally be underwater within decades, even under conservative estimates of climate change. This short National Geographic essay looks at the impacts of climate change on the Marshall Islands and on the options they are considering to deal with it: retreat by abandoning their nation altogether, or try to build new islands by dredging sensitive coastal habitat for material? They have no good choices.
Book Recommendation: Sea Level Rise: a Slow Tsunami on America’s Shores, Orrin Pilkey and Keith Pilkey
In many places around the world, coastal development is continuing on as though there were no consensus predictions about sea level rise. It’s almost to the point of caricature in places like Florida where they repeatedly rebuild in the same locations, flood after flood, and their politicians double down, denying climate change along the way. In this book, the authors lay out the impacts that rising seas will have on the coastal infrastructure of the United States and examine our options for dealing with it, concluding that, in most areas, retreat is the best approach to adaptation.
Looking to catch up on previous newsletters? Head to the new Sacred Headwaters Table of Contents to browse what is developing into what feels like a curriculum.
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