Sea levels are going to rise
The amount of carbon dioxide in the Earth’s atmosphere directly and indirectly determines the sea level. The more CO2 the higher the sea level. The details matter, the mechanism is complex, and as CO2 levels change, it takes an unknown amount of time for the sea level to catch up.
The present day level of CO2 is just over 400ppm (parts per million). For thousands of years prior to humans having a large effect on this number, the level of atmospheric CO2 was closer to 250. Human release of CO2 into the atmosphere by the burning of fossil fuel, and other human activities, are responsible for this difference. We expect the atmospheric concentration of CO2 to rise considerably by the end of the century. It is remotely possible that by 2100, CO2 will be about where it is now, but only if a significant effort is made to curtail its release. If nothing is done about the release of CO2 by human burning, the number will exceed 1000ppm by 2100. Reasonable estimates assuming the most likely level of effort to change the energy system put CO2 at somewhere around 600 to 700ppm by the end of the century.
So, it is reasonable to ask the question, what is the ultimate sea level likely to be with atmospheric concentrations of CO2 between 500 and 700ppm?
How long will sea level rise take?
Once the CO2 is in the atmosphere, it stays there for a very long time. So, if we curtail emissions and manage to keep the atmospheric CO2 between 500 and 700, that number will not drop for centuries. So, again, we have to expect sea levels to rise to whatever level is “normal” for an atmospheric concentration of CO2 between 500 and 700ppm. That is a conservative and perhaps even hopeful estimate.
A fair amount of research (but not nearly enough) has been produced over the last two or three years with the aim of estimating how fast and to what degree the major glaciers of the earth (in Greenland and Antarctic) will melt with global warming. In the long view, all of this research is irrelevant. The simple fact is that with higher CO2 levels, a lot of that ice will ultimately melt, and sea levels will ultimately go up. But in the short and medium term, that research is some of the most important research being done in climate change today, because it will lead to an understanding of the time frame for this rise in sea level.
None of the research I have seen satisfactorily estimate this rate, but with each new research project, we have a better idea of the process of deterioration of major glaciers. As this research progresses, the glaciers themselves are actually deteriorating, but they are only beginning to do so. As the research advances, we will get a better theoretical model for glacial deterioration. As the glaciers deteriorate we will have increasing opportunity to calibrate and test the models. I expect that in a few years from now (ten or twenty?) there will be active competition in the research world between theoretically based models and empirical observations to provide rate estimates for sea level rise. But at present we have mainly theory (the observational data is important but insufficient) and the theory is too vague.
A new paper came out this week that explores the process of deterioration of a major part of the Antarctic glacial mass. I’ll summarize this research below, but the main point of this post is to put all of this recent research in the context outlined in the first few paragraphs above. How much sea level rise can we ultimately expect, even if we have no good idea of when it will happen?
It may not matter how fast sea level rises
Uncertainty about the time frame for glacial melt is important for all sorts of practical reasons, but an interesting aspect of human culture and economy obviates that uncertainty, and does so rather ironically. In our economic system, we value things in many different ways. There are things that have great value in part because they are fleeting, rare, or ephemeral. People pay a lot for a great meal that is gone in 20 minutes, a random act of erotic pleasure, two minutes of terror on a carnival ride, or a small pile of white powder.
But we also pay good money for things because of their long term value. A classic problem in economics asks why a man (it’s always a man) in, say, Egypt, is willing to plant and tend hundreds of date tree saplings, knowing full well that the first fruit will not be provided until long after his own death. The reason, of course, is that his son will inherit these trees. Of course, his son is not likely to gain much from these trees because they will still be young and small. So the value of this grove of trees to his son is based mostly on the value to the son’s son. And so on.
This is how we place value on real estate. The main reason that a home you might consider buying today is of a certain value is that you can sell it for a similar or greater value in the future. The fact that short term fluctuations may destroy a good part of that value over the next decade does not obviate the longer term value of the property.
Some of the most valuable property in the US and in many other countries is within spitting distance of the ocean. The ocean itself adds this extra value either as commercial or industrial space, or as high-end domestic or tourist space.
If sea level rise sufficient to destroy that property was imminent, so the property would be destroyed this year, then the value of that property would be zero. But considering that the value of the property is always based in large part on the future sale value, then sea level rise sufficient to destroy it, but that won’t happen for a century, is sufficient to destroy that long term component. If you acquire property today that will eventually be flooded by the sea, you might think you own it. But really, you are renting it. When the sea rises up and inundates the lot, the lease is up.
So, in a way, it does not matter how long it will take the sea to rise, say, 10 meters. Any property that would be destroyed with sea level rise is, right now, worth less than a market ignorant of this inevitability would price it.
Why is it hard to estimate the rate of sea level rise?
Most of the ice in Antarctica is sitting on the interior of the continent, well away from the sea. But much of this ice is held in large catchments, or valleys, that have outlets to the sea. Those outlets are plugged with huge masses of ice, and that ice is, in turn, held in place by grounding lines, where part of the ice sits tenuously on the bedrock below sea level.
Behind the groundling lines, upstream, are valleys of various depths, but deeper than the point of grounding itself. It is thought that if the ice sitting on the grounding line falls apart, the plug of ice will deteriorate fairly quickly until a new grounding line, perhaps many kilometers upstream, is established. But that grounding line may be subject to deterioration as well, and eventually, the outlet valley that connects the interior catchment to the sea becomes open water, and the ice in that catchment can also deteriorate, and fall into the sea mainly in the form of ice bergs regularly calved off the glacier, like we see today in Greenland.
The main cause of global warming induced melting of the ice near the groundling line is warm water. The surface of the Antarctic glaciers does not melt very much from warm air, because the air over the southern continent is rarely above freezing. However, with global warming, we expect air temperatures to go above freezing more commonly. This would contribute to thinning of the ice over the grounding lines, and thus, more rapid breakdown of the plug holding most of the ice in place.
It is thought that when a grounding line fails, and the plug of ice begins to move into the ocean, steep cliffs are formed alongside the deteriorating ice. This would cause the ice behind the cliffs to destabilize, causing ice bergs to form at a very high rate. Also, the interior ice, in the large catchments, is generally thought to be unstable, so when Antarctic glaciers reach a certain point of deterioration, those glacial masses may deteriorate fairly quickly.
Each of these steps in glacial deterioration is very difficult to model or predict, as these phenomena have never been directly observed and the process involves so many difficult to measure mechanical and catastrophic events.
Upstream from the grounding line, though the horizontally flowing glacial masses in the plug, and up into the catchments, the sub-ice topography is complex and will likely control, by speeding up or slowing down, glacial deterioration. It is thought that many of the glacial masses that make up Antarctica’s ice have melted and refrozen numerous times, and glacial ice has moved towards the sea again and again, over the last several million years. As glacial ice moves along it carves out valleys or deposits sediments in a complex pattern, which then determines subsequent patterns of ice formation or deterioration. It is reasonable to assume that each time the glaciers melt and reform, the terrain under the ice becomes, on average, more efficient in allowing the movement of ice towards the sea. Thus, any estimate of the rate of glacial movement and deterioration based on past events is probably something of an underestimate of future events.
This has all happened before
We know that the world’s glaciers have melted and reformed numerous times from several sources of evidence, and that this has been the major control of global sea level, as water alternates between being trapped in glacial ice and being in the oceans.
We know that global sea levels have gone up and down numerous times, because we see direct evidence of ancient shorelines above current shorelines, and we have direct evidence that vast areas of the sea have been exposed when glaciers were at maximum size.
We can also track glacial growth and melting by using oxygen isotopes that differ in mass. Glaciers tend to be made of water that contains a relatively high fraction of light oxygen, while the ocean water tends to have relatively more heavy oxygen. This is because water molecules with heavy oxygen are slightly less likely to evaporate, so precipitation tends to be be light. Glaciers are ultimately made of precipitation. There are organisms that live in the sea that incorporate oxygen from sea water into their structures, which are then preserved, and can be recovered from drilling in the deep sea. By measuring the relative amount of heavy vs. light oxygen in these fossils, controlling for depth in the sea cores, and dating the cores at various depths, we can generate a “delta–18” (short for “Difference between Oxygen–18 and Oxygen–16”) curve. This is an indirect but very accurate measure of how much of the world’s free water is stuck in glaciers at any given moment in time.
The Delta–18 curve for Earth for the last ca 800,000 years looks like this:
That curve is made from deep sea curves, and unfortunately, the deep sea curves don’t go back far enough in time to get a good idea of glacial change, at this level of detail, for enough time to really get a handle on the full history of glaciation. But by piecing together data from many sources, and careful use of dating techniques like Paleomagnetism, it is possible to get a long view of Earth history. The following graphic (from The Panerozoic Record of Global Sea-Level Change by Miller et al, Science 310(1293)) shows the general pattern.
The Earth was warmer many tens of millions of years ago (before the modern ecology, flora, and fauna evolved), fluctuating between warm and very warm over long periods of time. Then, in recent millions of years, things cooled down quite a bit. It is during this cooler period that the modern plants and animals became established, and that humans came on the scene.
Here’s what I want you to get out of this graphic. Look at the purple line. These are global sea levels after about 7 million years ago. Note that sea levels were often tens of meters higher than they are today (relative to the zero line on this graph).
Now have a look at this graph.
This is a very complicated graph and in order to understand all of the details you’ll have to carefully read the original paper. But I can give you a rough idea of what it all means.
Each of the four graphics is a different way that paleoclimatologists can look at the relationship between atmospheric CO2 and sea level, and compile a large number of data points. Think of each graphic as a metastudy of CO2 and sea level using four independent approaches and all of the data available through about 2012.
In each graph, note the dotted lines. The vertical dotted line is CO2 at 280ppm, taken as the pre-industrial value (though we know that is probably an overestimate since lots of CO2 had been released into the environment by human landuse and burning prior to the presumed beginning of the “pre-industrial” period). The horizontal line is the present day sea level.
Each of the little symbols on the graph is a different observation of CO2 and sea level from ancient contexts, using various techniques and with various paleoclimate data sets over many millions of years.
Note that at the point where the pre-industrial CO2 and the modern sea level intersect, there are many points above and below the line. This is partly error or uncertainty, and partly because of the time lag between CO2 reducing over time and subsequent growth of glaciers. It takes many thousands of years for these glaciers to grow (they melt much more quickly).
As we go from pre-industiral levels of CO2 through the values of interest here, getting up to 600 or more parts per million, past sea levels are generally higher than the present. In fact, at 400ppm, where we are now, sea levels are substantially higher than the present for almost all of the data points. This probably means the following, and this is one of the most important sentences in this post, so I’ll give it its own paragraph:
Present day carbon dioxide levels are associated with sea levels many meters above the present sea level; the current Earth’s atmosphere is incompatible with the current Earth’s glaciers, and those glaciers will therefore become much smaller, and the sea level much higher, even if we stop adding CO2 to the atmosphere this afternoon.
The other interesting thing about this graph is that above about 600ppm atmospheric CO2, the sea levels observed in the past are even higher, way way higher. These are time periods when there was virtually nil glacial ice on either pole, or elsewhere. This is what the Earth looks like when virtually all the ice is melted. This is the Earth that we are likely to be creating if we allow CO2 levels to approach 1000ppm, and the track we are on now virtually guarantees that by the end of the century.
One might assume that we would never let that happen, that we would solve this problem of where to get energy without buring fossil fuel before that time. But at this very moment there is about a 50–50 chance that the next president of the United States will be a man who believes that climate change is a hoax. In other words, it is distinctly possible that one of the largest industrial economies in the world, and a globally influential government, will ignore climate change and forestall the transition to clean energy until 2024.
Look at this graph. The upper line, “High Emissions Pathway (RCP 8.5)”
I now officially rename the “Trump Line.”
So, how high will the sea levels rise?
There really is little doubt that we are looking at several meters of sea level rise given our current CO2 levels. How many meters?
From the paper cited above: “…our results imply that acceptance of a long-term 2 degrees C warming [CO2 between 500 and 450 ppm] would mean acceptance of likely (68% confidence) long-term sea level rise by more than 9 m above the present…”
Personally, I think this is a low estimate, and the actual value may be more like 14. Or more. There is no doubt that we are going to add many tens of ppm of CO2 to the atmosphere over the next few decades even if we act quickly on changing our energy system, and the chances are good that we will be close to 600. This is at the threshold, based on the paleodata, between lots of glacial ice melting to produce 9, 15, or so levels of sea level rise, and nearly all of the glacial ice melting, to produce sea level rise of over 30 meters.
And, if we follow the Trump Line we’ll reach that level of CO2 well before the end of the century.
Again, the question emerges, how long will it take for sea level to rise in response to the added CO2? Than answer, again, is we don’t know, but in important ways, as noted above, it matters less than one might think.
We are probably going to be stupid about sea level rise
There is another aspect of this problem that is underscored by the most current research, and several other research projects. For the most part, the glaciers will not melt evenly and steadily. This is not a situation where we can measure how much ice melts off every decade, and extrapolate that into the future. What we now know about the big glaciers is that they will almost certainly deteriorate a little here and a little there, then suddenly and catastrophically break down, losing a huge amount of their ice to the sea, then for a period of time continue to fall apart at a lower but still accelerated rate, which will slow down after a while until some level of stability is reached. Then, that stability will remain threatened for a period of time until the next catastrophic collapse of that particular glacier.
Also, as noted in the research project I’ll report below, some of these catastrophic steps that happen later in the process may in some cases be the largest.
Here’s why this is important. Honestly, do you even believe that we have already added enough CO2 to the atmosphere to flood all of the planet’s major coastal cities, and major areas of cropland, and that this can’t be stopped? Isn’t that a bit extreme, alarmist, even crazy? Of course it seems that way, and even if you accept the science, a significant part of you will have a very hard time accepting this conclusion.
Those in charge of policy, the people who can actually do something about this, are not immune to this sort of cognitive dissonance. So, as long as the glaciers are only adding a foot a century instead of a foot a decade, the massive melting scenario will be on the back burner. Then, of course, one or two or more of these glaciers are going to lose their grounding lines within a few years of each other, and start to add huge amounts of water to the sea, and everyone will freak out and catastrophic coastal flooding will happen, and then the whole thing will slow down and more or less stop for a period of time, and once again, the prospect of sudden and major sea level rise will return to the back burner.
Then it will happen again.
New research on glacial collapse
OK, about that new research. Here is the abstract:
Climate variations cause ice sheets to retreat and advance, raising or lowering sea level by metres to decametres. The basic relationship is unambiguous, but the timing, magnitude and sources of sea-level change remain unclear; in particular, the contribution of the East Antarctic Ice Sheet (EAIS) is ill defined, restricting our appreciation of potential future change. Several lines of evidence suggest possible collapse of the Totten Glacier into interior basins during past warm periods, most notably the Pliocene epoch, … causing several metres of sea-level rise. However, the structure and long-term evolution of the ice sheet in this region have been understood insufficiently to constrain past ice-sheet extents. Here we show that deep ice-sheet erosion—enough to expose basement rocks—has occurred in two regions: the head of the Totten Glacier, within 150?kilometres of today’s grounding line; and deep within the Sabrina Subglacial Basin, 350–550?kilometres from this grounding line. Our results, based on ICECAP aerogeophysical data, demarcate the marginal zones of two distinct quasi-stable EAIS configurations, corresponding to the ‘modern-scale’ ice sheet (with a marginal zone near the present ice-sheet margin) and the retreated ice sheet (with the marginal zone located far inland). The transitional region of 200–250?kilometres in width is less eroded, suggesting shorter-lived exposure to eroding conditions during repeated retreat–advance events, which are probably driven by ocean-forced instabilities. Representative ice-sheet models indicate that the global sea-level increase resulting from retreat in this sector can be up to 0.9?metres in the modern-scale configuration, and exceeds 2?metres in the retreated configuration.
Chris Mooney has written up a detailed description of the research including information gleaned from interviews with the researchers, and you can read that here. In that writeup, Chris notes:
Scientists believe that Totten Glacier has collapsed, and ice has retreated deep into the inland Sabrina and Aurora subglacial basins, numerous times since the original formation of the Antarctic ice sheet over 30 million years ago. In particular, they believe one of these retreats could have happened during the middle Pliocene epoch, some 3 million years ago, when seas are believed to have been 10 or more meters higher (over 30 feet) than they are now.
“This paper presents solid evidence that there has been rapid retreat here in the past, in fact, throughout the history of the ice sheet,” Greenbaum says. “And because of that, we can say it’s likely to happen again in the future, and there will be substantial sea level implications if it happens again.”
And, from the original paper (refer to the graphic below):
The influence of Totten Glacier on past sea level is clearly notable, but for any particular warm period it is also highly uncertain, because the system is subject to progressive instability. Our results suggest that the first discriminant is the development of sufficient retreat to breach the A/B-boundary ridge. This causes an instability-driven transition from the modern-scale configuration to the retreated configuration. Under ongoing ice-sheet loss, the breaching of Highland B causes further retreat into the ASB. Each of these changes in state is associated with a substantial increase in both the absolute and the proportional contribution of this sector to global sea level.
This is a video by Peter Sinclair that dates to a bit earlier than this research was published, but covers the same issue:
Many of the interesting natural areas, like national parks or preserves, have a museum. In the museum there is often a geology exhibit, showing the changes in the landscape over long periods of time. Almost always, there was a period of time when the place you are standing, looking at the exhibit, was part of a “great inland sea.”
Let me introduce you to my little friend … the Great Inland Sea. Because it is coming back.