About once a day, someone tells me that human caused climate change is not real because this or that thing in the latest report by the Intergovernmental Panel on Climate Change (IPCC) contradicts something I, or some other scientists or science writer, has said.
I’ve noticed an uptick in references to the IPCC report by those intent on denying the reality of climate change. This even happened at recent congressional hearings, where “expert witnesses” made similar claims.
How can that be? How can the flagship scientific report on climate change, the objective source of information about the science of climate change, be used so frequently to argue that scientists have climate change all wrong?
Obviously, one way this can happen is if the information is cherry picked or misrepresented. That, certainly, happens and is almost always part of the recipe. But there is another only barely less obvious reason, and this is a reason that becomes more and more relevant every passing year. What is it? Hold on a sec, first a bit of context.
As a scientists and writer-about-science I often have access to temporarily secret information. Also, I make it a point to keep track of opinions held by trusted experts in the field, as they change and adapt to new findings. This secret information is, of course, peer reviewed research that isn’t published yet, and is under embargo.
To be embargoed means to be held in secret, but distributed to a small number of trusted individuals or agencies (often news outlets and science writers), with an “embargo date and time” after which the information is no longer secret. There are a few reasons this is done. One is that many scientific outlets rely on the splash factor to get readership, and having a paper that changes how we think about the world be released at a particular planned moment helps with that. Related is the idea that publishers, research institutions, and the scientists themselves want the paper published alongside other products to help the press and the public understand the material better, such as a press release, selected graphics, maybe a nice video. This all requires production time and effort, and it is pretty much wasted effort if it does not become publicly available at the same exact moment the paper becomes available.
A few papers exist as early drafts long before publication, and those are passed around for the purpose of getting some preliminary feedback, and to get the conversation about the topic going among experts. That is less common because many journals don’t like it, and how often this happens depends on the field of study. Indeed, there are entire “journals” that started as and still serve as semi-formalized outlets for early drafts of appers, academic theses, or reports are routinely published, sometimes years before a final peer reviewed product comes out, representing for example that year’s output from a long term grant. (NBER and BAR come to mind as examples of this.)
Authors and publishers send me embargoed papers they think I might want, or more commonly, ask me if I’d like to have a copy of an embargoed paper, giving me a chance to say yes. Often, I know of a subset of scientists who also have the paper (typically, the co-authors) and I can ask them questions about the paper before hand. Most outlets will provide a science writer with this sort of contact information. This is how all those fully formed news reports come out in the media the moment a paper is released. Days or even weeks of work has already happened, quietly and in secret, before the paper’s release.
Other research is available in other ways. I have colleagues who are always working on certain things, and they’ll say things like, “well, we don’t have it finalized yet, but this thing you said is probably wrong because X turns out to be larger than Y, even though we previously thought the opposite … we’ve got a paper coming out probably next summer on this…” or words to that effect.
All this is, of course, why I write the blog posts and you read them. You could do this too; You could have foreknowledge of the developments on the leading edge of a particular scientific field as well. You just have to become a credible quasi-journalistic outlet (I am not now nor have I ever been a journalist) and develop a pertinent Rolodex, and gain the trust of everybody. Takes a few years.
I mention all this because it makes this happen now and then: I have a concept of some aspect of climate change research that is not yet generally understood outside a limited range of experts. Then, of course, the dissemination of information catches up and everybody knows the same thing, and the revised, updated view of that bit of science is now added to general knowledge. Close behind, perhaps, follows a shift in, or refinement of, consensus. This is how science works large scale.
The scientific understanding of an active area of research is dynamic and requires currency. Six months old is old. A year or two old is ancient.
I’ll give you three examples.
A while back the generally understood consensus of sea level rise was that sea levels were going up at a certain relatively low rate, on average. However, that estimate was faulty because of a lack of integration of a full understanding of how water moves between fresh water reservoirs and the sea, and certain really cool research on ocean warming, gravitational effects, etc. had not yet been published. Also, some time was missing; there had been a couple of strange quirky sea level related events that turned out to be outliers, so data sets needed to be full updated, and a couple of years added over the passage of time. For this reason, what was generally known at one point in time was different from what came to be understood a few years later. People in my position saw it coming, people who were not tracking the literature held the old and incorrect view.
Second and related example: There was a set of estimates for how fast glaciers in polar regions (Greenland and Antarctica) would melt with global warming, and how much this process would contribute to sea level rise. However, there was some new research coming to bear on the issue that was starting to change that. Glaciers don’t just melt, but they also structurally fall apart, big chunks ending up in the sea and melting there. Some increase in understanding how that happens emerged. The upper limit of how fast that could probably happen, in the general publicly available knowledge base, was modest. But over a fairly short period of time, a previously highly speculative and closely held thought that the upper limit on how much ice could deteriorate was higher, and a similarly unexpressed thought that the lower limit on how soon that might start to happen, began to make its way into the more public discussion. This is still very much an area of uncertainty and very active research. Look for big changes and many surprises over the next 24 months. But today, the best informed experts have a very different view of what might happen, and what is likely to happen, than widely held a few years ago, because of this shift. Polar glaciers will likely fall apart and contribute to sea level rise more and sooner than the best guesses would have suggested five years ago.
A third example just went through a major change. A few years ago it was generally thought, and often repeated, that it was difficult to attribute human caused climate change as a reason behind any particular bad weather event. That has shifted dramatically over time. A set of studies a few years back failed to find any clear association in a majority of weather events. A year later, a similar number of studies, of new weather events, either attributed the events to climate change or resulted in “we can’t say one way or another.” The most recent papers are generally showing a likely connection. Meanwhile, certain research linking certain climate phenomena to a large set of bad weather events was developing. Note that the previous studies were conducted mainly ignoring this new and emerging research. I was a little like saying “We don’t know why so many more people are falling on the subway tracks these days” while ignoring a growing set of observations of bad people showing up at the subway stations and pushing people off the tracks on purpose. In the absence of consideration of this nefarious and willful behavior, one could not say that the increase in untoward events was anything other than a random uptick in numbers. Seeing and acknowledging an actual cause makes it impossible to not link the cause and effect.
This happened, as noted, slowly and in the background in the literature, and suddenly, just a few days ago, a crowing paper took that likely cause of severe weather, ran it in highly sophisticated and reliable models, and demonstrated that this is a thing. Humans release fossil carbon in greenhouse gasses (and do some other bad things), certain things about our climate system change unambiguously because of this, this causes an important but heretofore not fully understand change, which then causes additional droughts and floods across the globe.
Five years ago, that would have been regarded as speculation, worthy of consideration but nothing that could nail down our understanding of the greenhouse gas – severe weather link. Today, the link is sufficiently established to regard it as scientific fact rapidly becoming consensus, though there will certainly be a bit more fighting about it, and much refinement of the theory and data.
All of these examples can be rephrased in relation to the last IPCC report.
The most recent IPCC report was published nominally in 2014. It was restricted to existing peer reviewed literature, thus not including the pre-embargoed material (though there was an effort by many scientists to get stuff out in time to be employed in that process). The report took time to produce. The physical science basis part of the report, on which the rest is based, actually dates to 2013 nominally, though it includes some 2014 material.
It is now April 2017. A claim that “The IPCC Report said bla bla bla therefore you are wrong” is the same as “in or before 2013, at least 4 years ago, the best we knew was bla bla bla therefore your are wrong.
Let’s return to the sea level rise example and consider the thinking of how fast and how much glacial melting, and other factors, would cause sea levels to rise in the future.
There were several studies used in the IPCC report, mostly dating to or before 2011. I would regard the science in the IPCC report to reflect the thinking primarily of the first decade of the 21st century on this subject. The last 2 years, or even one year, of research on sea level rise contrasts remarkably with that early work, suggesting a faster rise and more of it. That is just what is published. I don’t happen to know of any new work coming out shortly, but I can promise you that the summaries, the estimates, and the graphics that would be produced by an IPCC-like agency working on a summary of the physical science of sea level rise as it stands right now would be significantly different than what the last such report by the actual IPCC provided in 2014.
Two IPCC reports back, it was estimated that global sea level could rise between 18 and 59 cm by 2100. The subsequent report, the most current one, estimated that sea levels can rise between 29 and 82 cm by 2100. A recent and well regarded paper, dating to early in 2016, and using the best available information and methodology, estimates that the global sea level could rise by more than a meter by 2100 from just the melting of Antarctic, not counting Greenland.
Longer term sea level rise estimates have also risen, with a key paper published in 2013 suggesting that we may be in for as much as two meters over the next few centuries, and the aforementioned most recent report suggesting “more than 15 metres by 2500.”
(I hasten to add that an estimate of between 8 and 15 meters has been on the table for a long time, coming from palaeoclimatologists, who have always seen higher levels because in the past, similar conditions today produced such high levels, indicating that current levels are actually unusually low.)
Climate science is progressing very rapidly, especially in some areas. There are things we know now, or that we feel fairly comfortable asserting as pretty likely, that one year ago, and certainly four years ago, were fairly uncertain or in some cases inconceivable.
Citing the most recent IPCC report about a climate change relate issues tells me two things:
1) You don’t read the literature or talk to climate scientists; and
2) You are not especially interested in an honest conversation about this important scientific and policy issue.
The recent work on sea level mentioned above is here, the IPCC report is here, and a summary of the IPCC and other sources is here.
This is the fourth-largest number on record going back to 1990, said insurance broker Aon Benfield in their Annual Global Climate and Catastrophe Report issued January 17 (updated January 23 to include a 31st billion-dollar disaster, the Gatlinburg, Tennessee fire.) The average from 1990 – 2016 was 22 billion-dollar weather disasters; the highest number since 1990 was 41, in 2013.
The number of devastating floods that trigger insurance payouts has more than doubled in Europe since 1980, according to new research by Munich Re, the world’s largest reinsurance company.
The firm’s latest data shows there were 30 flood events requiring insurance payouts in Europe last year – up from just 12 in 1980 – and the trend is set to accelerate as warming temperatures drive up atmospheric moisture levels.
Globally, 2016 saw 384 flood disasters, compared with 58 in 1980, although the greater proportional increase probably reflects poorer flood protections and lower building standards in the developing world
As I’m sure you’ve heard, he year 2016 was the hottest year on record, and 2017 is also going to be hot. (I personally doubt 2017 will be hotter, but then again, I was thinking that 2016 might not break the 2015 record.)
Mark Bgoslough as an interesting piece here on how global temperature records are made, analyses, and reported. I recommend reading that. Here, I want to use a graphic he made for that item to point something outI’ve added the green lines. I’ll just leave it here without comment.
People in the northeastern US should be about 50% more concerned about global warming than everyone else, because new research suggests that this region will warm about 50% faster than the globe in coming years.
The fastest warming region in the contiguous US is the Northeast, which is projected to warm by 3°C when global warming reaches 2°C. The signal-to-noise ratio calculations indicate that the regional warming estimates remain outside the envelope of uncertainty throughout the twenty-first century, making them potentially useful to planners. The regional precipitation projections for global warming of 1.5°C and 2°C are uncertain, but the eastern US is projected to experience wetter winters and the Great Plains and the Northwest US are projected to experience drier summers in the future.
Regardless of the so-called temperature target, what this study shows is that even if we do keep the globe as a whole to a 2°C temperature increase, some regions, like the Northeast United States will far exceed this threshold. So, what is “safe” for the world is unsafe for certain regions.
A recent poll tells us that 90% of rural Australians are concerned about the impacts of climate change. Most were concerned about drought and flooding. Fewer than half this coal fire power stations should be phased out.
I think that if you did a similar poll in the US, you would find that most rural Americans don’t are about climate change, and even fewer think coal should be phased out. Since all rural people, Australians or Americans and everyone else, have already been affected to at least some degree by climate change, and since the science strongly suggests that things will get much worse for them in the future, all of these folks should be concerned and all of them should be for doing something about it. The good news is that the cognitive dissonance we see in the Australia between climate change and concern may be a harbinger for future changes in American attitudes. Australia has probably been affected by severe weather caused or enhanced by climate change to a much larger degree than has Rural America. In short, I expect disdain for coal to catch up to concern about climate change in Oz, while in America, eventually, people will get more and more on board with both.
A question on everyone’s mind: “Is the California Drought over and what does this mean?”
It looks over. Reservoirs are filling, snow is piling up in the mountains, everything is wet.
However, there are several things still to consider. For one, the recharging of water supplies is not complete, and if near-zero-rain conditions return right away, the drought will slowly return. This is of course always a concern, but right now we have a slightly different question to ask for California. Is it the case that the conditions that led to the California drought are the “new normal” (a phrase I’m not really happy with) I the sense that from now on, there will be less snow pack, less rainfall, etc. In other words, is it the case that the future of California is generally much dryer all the time with the occasional drenching rainy season, because of climate change?
We don’t know yet, but there is one fairly obvious area of concern: Snow pack. Snow pack plays a role in watering California. Snow pack forms during the rainy winter, and slowly melts thereafter. If that precipitation wasn’t temporarily stored up as snow, the winter rains would be more flooding, and there would be less water retained in the system for the rest of the year. Increasing warmth, due to global warming, has caused more of the precipitation that falls in the mountains to be rain rather than snow, and it has caused the snow to melt more quickly.
Warmer temperatures also mean more evaporation, so getting everything all wet and squishy for a few months during the Winter may mean less a few months later when a warm and dry atmosphere starts to drunk the moisture out of the ground and off the reservoir’s surfaces at an accelerated rate.
I have been noting for years (well, for a couple of years) that the best available paleo data suggest that the current levels of CO2 and/or temperature, protracted over a reasonable amount of time, should be associated with sea levels of about 8 meters. In other words, if you are worried about sea level rise, and you should be, the amount of sea level rise that we are currently locked into is enough to inundate much of Southeast Asia’s rice growing land, large parts of various US states such as Louisiana and Florida, and to cause retreat from many of the world’s most densely settled cities.
Over recent months the interface between the scientific research and journalism has started to squeeze out the occasional example of this startling fact, one we’ve known for years but have been afraid to say about else we be considered non reputable. From the Independent:
The last time ocean temperatures were this warm, sea levels were up to nine metres higher than they are today, according to the findings of a new study, which were described as “extremely worrying” by one expert.
The researchers took samples of sediment from 83 different sites around the world, and these “natural thermometers” enabled them to work out what the sea surface temperature had been more than 125,000 years ago.
How long will this take? Nobody knows. This depends on how fast the major glaciers melt.
Carlos Gimenez, mayor of Miami, is already rolling up his pants:
“Let’s be clear, sea-level rise is a very serious concern for Miami-Dade County and all of South Florida,” Mayor Carlos Gimenez told the crowd Wednesday morning at the South Miami-Dade Cultural Arts Center during his annual State of the County address. “It’s not a theory. It’s a fact. We live it every day.”
The British Antarctic Survey is abandoning its Halley Base, in Antarctic, because the ice shelf on which it is located had developed a huge crack, so it is no longer safe to be there. They’l be out by the end of March. The crack is known as the “Halloween Crack.” Here’s a short video:
In the Arctic, sea ice growth so far this year is below any previously observed year. From the National Snoe and Ice Data Center:
Along the coast lies Kutubdia, an island in the Bay of Bengal where lush green rice fields give way to acres and acres of flat fields. Consisting of small rectangles of varying hues of brown, they are salt fields. The encroachment of saline water from rising tides has made rice farming impossible.
They now “farm” salt. That is not euphemism for farming in salty conditions. They take salt out of the water. That is not a business that will have a lot of future when everybody else along the coasts of low lying countries are doing it as well.
At the end of 2015, it looked like the negative effects of climate change were accelerating. That turned out to be true, and acceleration of the effects continues. This is probably not a good time to official deny the reality and importance of climate change, but that seems to be what we are doing in the United States.
When the sea levels rose following the last major glaciation, most rapidly between around 18,000 and 10,000 years ago, somewhat less rapidly until about 6,000 years ago, a lot of interesting things happened.
I used to live, and do archaeology in, New England (the one in the US). It was always fun to contemplate George’s Bank. George’s Bank is a high place out in the ocean, not far from Boston. If you’ve ever been whale watching off P-town, you were probably out on George’s Bank, where the baleen whales forage and frolic, and are easily found during the right season. This is also a great fishing ground.
But prior to the melting of the glaciers and the rising of the seas, George’s Bank was an island, and initially, a rather large one. It is almost certainly true that at the time Clovis Period native Americans were in the area, George’s bank was readily accessible by modest water craft, and very likely colonized by them. But, over time, the island would have become smaller and smaller, and eventually, inundated. Anyone who lived there would have to move. A similar story happened all along the East Coast of the US. In m view, this is one of the most under-studied and under-appreciated “events” in North American prehistory, and likely relates to numerous observations in coastal prehistoric archaeology. But, perhaps owing to the deeply seated (seemingly hard wired and primordial) belief that the sea does not change even when we know it does change, this has not been developed sufficiently as an academic topic. Someone please do so.
Anyway, that’s an interesting story, and versions of this happened all over world for thousands of years at the close of the last glacial. And, starting about now (geologically speaking), some version or another of this story will be happening for the next several centuries or so, as sea levels begin once again to rise rapidly, because we are polluting the earth.
Entire island nations will disappear, and entire ecological systems will vanish. But first, the canaries have to die.
And the first canary, that we know of, is Melomys rubicola, aka the Braqmble Cay Melomys. Bramble Cay is a very tiny atoll that is part of the Great Barrier Reef, and it has been inundated by human caused sea level rise. The Brable Cay Melomys is a rodent that lived only there. Lived.
Michelle Innis, writing in the New York Times, quotes the local expert:
“The key factor responsible for the death of the Bramble Cay melomys is almost certainly high tides and surging seawater, which has traveled inland across the island,” Luke Leung, a scientist from the University of Queensland who was an author of a report on the species’ apparent disappearance, said by telephone. “The seawater has destroyed the animal’s habitat and food source.”
“This is the first documented extinction of a mammal because of climate change,” he said.
Go read Michelle’s report, HERE, it is quite unsettling. Then imagine similar scenarios of permanent disappearance. Times a thousand. No, times a million. You won’t be able to keep track.
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.
Human caused greenhouse gas pollution has locked us into a situation where the global sea level will rise, at an unknown rate, high enough to inundate most major coastal cities and vast areas of agricultural land in low lying countries, and wipe out thousands of islands. Entire countries (small, low lying ones, and pacific ocean nations) will either disappear entirely or be made very small. Even as we head towards a likely limit in global food production in relation to increasing demand, large productive agricultural areas will be destroyed. As far as I can tell, there is nothing to stop this from happening, though reducing our greenhouse gas pollution to zero over the next several decades may prevent the global ocean from rising to its absolutely maximum amount.
So sea level rise is important.
The surface of the Earth comes in two forms: Ocean bottom and continent. They are totally different geologically, with the ocean bottom consisting of relatively heavy basaltic rock formed at the margins between spreading plates, and continents of lighter rock, generally formed from below.
The global ocean sits mainly on the oceanic plates, but at its edges (except in a very few special locations), it rests against those continents. Over time the sea rises and falls. When the sea is at its lowest point, with a good amount of its volume reduced because it is trapped in glacial ice, most of the continents are exposed. When the sea is at its highest point, vast areas of the continental margins are inundated. At present, the ocean is pretty high, covering much of the continental margin that it ever covers, but there is room to grow, with large areas of the coastline subject to future inundation.
Rising surface temperatures caused directly or indirectly by human release of greenhouse gas pollution melt glaciers and warm the ocean, both of which are causing the global sea level to rise. This is a long and complicated process. We add greenhouse gas, mainly CO2, to the atmosphere, and this causes warming, enhanced by various positive feedbacks that either cause an increase of additional greenhouse gases such as water vapor, methane, and more CO2, or reduce the ability of certain natural systems to absorb these gasses. The greenhouse gas causes warming, which causes more greenhouse gas, which causes more warming. Meanwhile, most of this extra heat is actually trapped in the ocean where it only contributes a little to melting glaciers, but does contribute to expanding the volume of the ocean. The ultimate amount of heating, and the ultimate amount of sea level rise, takes a long time to be realized, and the rate of this change is only roughly estimated.
What we have already done to the atmosphere will cause sea level rise to continue for a very long time, possibly many centuries, possibly thousands of years. We have increased the amount of CO2 in the atmosphere from the mid 200s parts per million (ppm) to 400ppm, and we expect that increase to continue for decades. Evidence from the past, through the science of paleoclimatology, tells us that when the atmosphere holds between 400ppm and 500ppm of CO2, the global sea level is many meters above the present level.
Understanding sea level change is therefore critically important to understanding the impacts of climate change. We can measure current sea level rise and assume that steady increase over time (even if it is a bit variable) is mostly caused by global warming, heating the ocean and melting glacial ice. But there are problems with these measurements and associated estimates. Recent research has shown that Antarctic, which holds most of the world’s ice, is or could or will contribute a very large amount of water to the sea. But, other recent studies show that some of the expected reduction in glacial size might not be happening at the rate previously estimated. At the moment, sea level is rising at a certain rate, and some research explains a good amount of that increase from melting ice, but other research takes that melting ice out of the equation and leaves that portion of the sea level rise unexplained, for now.
Past sea level change (up or down), prior to the industrial revolution when we started releasing all this greenhouse gas pollution, should give us a baseline against which to assess modern day measurements, and is an essential part of the process of understanding this critically important system. But it is difficult to measure sea level, at present or in the past. We can measure the current position of the sea at a given part of the continental margin by just going there and measuring it. Sea level over recent decades, going back in some places a few centuries, can be estimated using tide gage records. We can sink cores (or trenches) in relatively protected areas (such as behind barrier islands) and find organic material that would have been formed just below the surface of the sea, measure its elevation and date it, to give an estimate of sea level in the past. We can put the tide gage data and the coring data together and get a rough estimate of sea level change.
But that estimate is not just rough, but almost useless, without a lot of careful further study. As the organic material representing older sea levels is buried by later organic material or other sediment, it tends to be compressed and lower in elevation. The study of this process is many decades old, and this can be adjusted for, but it is complicated. The actual sea level at a given point along the coast depends partly on how big the ocean is at the moment (obviously) but also on the position and strength of major currents. At present, and many times in the past, the North Atlantic ocean is bunched up way out at sea because of the movement of currents. This lowers the sea level along the coast in many areas. But if these currents either move or change in their strength, this effect changes, and the coastal sea level goes up or down independently of the global sea level.
Wherever there were large glaciers, the land has been pushed down by the weight of the ice. After the glaciers melt away, the land rebounds. Where this happens along the coast, estimating global sea level from local sea level becomes quite complicated. Meanwhile at the outer edge of the glacial mass, the land is actually pushed up to compensate for the depression caused by the massive glaciers. This is called “forebuldge.” Forebuldge makes the sea level look lower than it should, until the forebuldge reduces and flattens out. Indeed, the rebound effects of enormous glaciers in Canada are still happening, changing the position of the shoreline of Hudson’s Bay fast enough that cabins built on the shore a century ago are now a long walk from the sea.
This is all manageable, and people have been working on collecting these data and figuring out how to use it since the 1960s. But now, this week, what may be the first research project to put most of these data together to provide a pretty good estimate of sea level variation over the last 3,000 years, has been published.
The key result from this paper is the graph at the top of this post.
We present the first, to our knowledge, estimate of global sea-level (GSL) change over the last ?3,000 years that is based upon statistical synthesis of a global database of regional sea-level reconstructions. GSL varied by ?±8 cm over the pre-Industrial Common Era, with a notable decline over 1000–1400 CE coinciding with ?0.2 °C of global cooling. The 20th century rise was extremely likely faster than during any of the 27 previous centuries. Semiempirical modeling indicates that, without global warming, GSL in the 20th century very likely would have risen by between ?3 cm and +7 cm, rather than the ?14 cm observed. Semiempirical 21st century projections largely reconcile differences between Intergovernmental Panel on Climate Change projections and semiempirical models.
So now we have a much better idea of the nature of global sea level rise for a couple thousand years prior to human greenhouse gas pollution, and we have a firm demonstration of the effects of this pollution on sea level over the last century or so.
Of this, Rahmstorf says, “The fact that the rise in the 20th century is so large is a logical physical consequence of man-made global warming. This is melting continental ice and thus adds extra water to the oceans. In addition, as the sea water warms up it expands.”
How much will sea level rise by the end of the century?
In his post, Rahmstorf brings in a second study on sea level rise, also just published (see the RC post for more details). That research attempts to estimate the amount of sea level rise expectd by 2100. There are four separate studies, each using three different (RCP) assumptions about future human caused climate change, and each combination of study and model provides a range. In centimeters, the lowest numbers are around 25 (close to the amount that has already happened over the last century) and the highest numbers are around 130-150 (so, up to about five feet).
Rahmstorf appears to agree with my thinking on this, which is that these estimates don’t account for catastrophic deterioration of ice sheets and subsequent increase in melting, if such a thing results from what appears to be increasing instability of some of those glacial features. For example, huge parts of the Antarctic ice sheet are in the form of vast glacial rivers pinned in place by a precarious “grounding” of ice on rock near the mouth of those rivers.
If that grounding falls apart, the entire river can start to march to the sea very quickly, establishing a new grounding line upstream. It is possible that such a new grounding line is way upstream. As all that ice falls into the sea, it would likely expose high vertical cliff that would then start producing ice bergs at a very high rate for many years. There may be other features currently deep under the ice that would be exposed, such as pre-melted water near warm spots. In other words, the drainage of meltwater will not be made less efficient by such a collapse, but rather, more efficient, regionally and for a certain period of time. The point is, the impact on the rate of glacial melt of such events is pretty much unknown and very difficult to estimate.
Rahmstorf notes, “The projections on the basis of very different data and models thus yield very similar results, which speaks for their robustness. With one important caveat, however: the possibility of ice sheet instability, which for many years has been hanging like a shadow over all sea-level projections. While we have a pretty good handle on melting at the surface of the ice, the physics of the sliding of ice into the ocean is not fully understood and may still bring surprises. I consider it possible that in this way the two big ice sheets may contribute more sea-level rise by 2100 than suggested by the upper end of the ranges estimated by Mengel et al. for the solid ice discharge, which is 15 cm from Greenland and 19 cm from Antarctica. (The biggest contributions to their 131 cm upper end are 52 cm from Greenland surface melt and 45 cm from thermal expansion of ocean water.)”
He backs this up by reference to other recent studies showing that ice sheets have in the past broken up at surprisingly high rates.
One and a half meters, or five feet, of sea level rise within the lifetime of those born today is possible. Half of that is extremely likely. Double that may even be a possibility. This is expected to continue for centuries, even millennia, or until all the ice melts, whichever comes first.
How many things in your life originate from some thing that happened in the past? The invention of agriculture (that happened many times from about 10,000 to 4,000 years ago), the invention of writing (again, multiple times, thousands of years ago), the modern western system of government and law (depending on where you live, the Magna Carta, the US Constitution) hundreds of years ago. If you are religious, it is likely that your religion’s roots are thousands of years old. The establishment of property rights, water rights, all of that.
If human civilization exists, with some continuity with the present, 1,000 years from now, such a list will include the release of fossil carbon in the form of greenhouse gasses by the people of the 19th, 20th, and 21st centuries. That was the event that caused the sea to rise and engulf so much of the fertile land, causing a major (if possibly slow moving) exodus of most of the settled people of the world. In a thousand years, after we’ve either stopped using fossil fuel, or didn’t but just used it all up, people will still be measuring for the rise of the sea that we are causing right now.
There is a new study by a French/English team looking at the rate at which Antarctic glaciers might contribute to sea level rise, due to global warming, between now and 2100 and 2200 AD.
The study produces several estimates, but suggests that glaciers in Antartica might contribute as much as 30 cm by 2100 and 72 cm by 2200. That is a large amount of sea level rise, but it is actually less than other studies that rely more on paleoclimate evidence have suggested. I personally have something of a bias towards paleo evidence; Good paleo evidence is evidence of what actually happened, suggesting that contradictory results form modeling that does not make direct use of paleo data is suspect.
The new study, by Catherine Ritz, Tamsin Edwards, Gaël Durand, Antony Payne, Vincent Peyaud, and Richard Hindmarsh came out today in Nature, and is called “Potential sea-level rise from Antarctic ice sheet instability constrained by observations.”
The results of this paper raise key IPCC estimates of sea level rise by a tiny bit, which is conservative, as the IPCC estimates are probably low (again, coming from my paleo perspective).
This study looks specifically at marine-ice-sheet instability (MISI). This is the very difficult problem of how ice sheets that are grounded on bedrock sitting below sea level deteriorate. The full-on collapse of such ice sheets has not been directly observed, and it is a very difficult process to model. I liken it to trying to solve the following problem.
An engineer, a theoretical physicist, and a paleoclimatologist are at a wedding. There is a ice large sculpture of a swan on a flat topped table, for decoration. The three start a betting pool on how long it will take for the entire swan, which has already started to melt, to end up on the floor.
The engineer notices some of the meltwater dribbling off the back of the table. She places a set of beer mugs under the streams of water, and records how long it takes for a measured amount of liquid to accumulate. She uses this to generate a graph showing melting over time, estimating the volume of the swan by looking it up in his manual on Ice Sculpture Specifications, and suggests that it will take eleven hours.
The theoretical physicist estimates the volume of ice by assuming a spherical swan, measures the air temperature, and calculates the rate of conversion from ice to water using thermodynamics. He comes up with a different estimate, because the engineer forgot to account for density differences in ice vs water. He estimates that the swan will be entirely the floor in eight and a half hours.
The paleoclimatologist disagrees, and says, “It will take between one and three hours for that swan to be on the floor.”
“Why do you think that, you are clearly an idiot, and I am clearly a physicist, so I must be right!” says the theoretical physicist.
Just as the paleoclimatologist is about to answer, the already melting neck of the swan breaks, and the upper part of the neck and head fall backwards, knocking off one of the large wings. All of those pieces slide off the table and crash on the floor. Off balance, the swan now tips abruptly to one side which causes the second wing to fall off, hitting the main body and pushing it towards the edge of the table. The swan ice sculpture then slid with increasing speed towards the edge of the table, then went over the side, leaving nothing but a large wet spot on the table.
“Because,” the paleoclimatologist says. “Last wedding I went to, that happened.”
I think you get the point.
Ritz, Edwards, et al. try to address the problem by using what they claim to be a better approach to modeling of ice sheet disintegration. From the abstract:
…Physically plausible projections are challenging: numerical models with sufficient spatial resolution to simulate grounding-line processes have been too computationally expensive to generate large ensembles for uncertainty assessment, and lower-resolution model projections rely on parameterizations that are only loosely constrained by present day changes. …Our process- based, statistical approach gives skewed and complex probability distributions … The dependence of sliding on basal friction is a key unknown: nonlinear relationships favour higher contributions. Results are conditional on assessments of MISI risk on the basis of projected triggers under the climate scenario A1B…, although sensitivity to these is limited by theoretical and topographical constraints on the rate and extent of ice loss. We find that contributions are restricted by a combination of these constraints, calibration with success in simulating observed ASE losses, and low assessed risk in some basins.
Nonlinear relationships. That is the swan’s head falling off.
Like another recent paper on Antarctic ice sheets, other studies as well as the paleorecord conflict with the present study enough that this study has to be reviewed carefully before we can assess its contribution to understanding Antarctic ice sheet melting. It may be right, and that would be good news in comparison to some of the higher estimates. However, ice sheet deterioration is very complex, and it is possible that this modeling effort does not account for enough of the important variables, and may not be detailed enough to be reliable. The authors note some of these problems.
It will be interesting to see how other scientists working on this problem respond. I’ll keep you posted.
A recent study that is getting a lot of press suggests that the massive ice sheets of Antarctica are on average growing rather than shrinking, and thus, not contributing to sea level rise. (The authors of the study warn that this will reverse in the near future with global warming.) However, there is reason to believe that these conclusions are incorrect.
Antarctica is the sleeping giant of climate change. Human activity, mainly the release of greenhouse gasses from burning fossil fuels, has been changing the climate rather dramatically for the last few decades, and the consequences of this change are mostly negative. Failed agricultural systems have led to failed states and regional political instability. Dramatic changes in weather patterns, including droughts in Australia and California, a series of unprecedented tropical storms over the last several years, major flooding (if anyone from Texas is reading this, nice to know you have internet access in your tree), all have a global warming contribution, because weather is climate and climate is changed and changing. But sea level rise, while mostly a thing of the future rather than the present, may have the biggest effect of all, at least on land. As we warm the planet, the polar ice sheets will contribute much of their ice to the sea, and based on what we know of the past, direct measurements over the last 20 years or so, and from models of the medium term future, this could mean an increase in sea level of several meters. The best available science currently suggests that by the end of the century average sea levels could be about a meter higher than they are now. It would not be unreasonable to regard that as a conservative estimate.
I’d like to take a moment and point out an important aspect of the sea which people, especially those that don’t live on the sea, forget. The average altitude of the sea at a particular point along the shore is not the part you have to worry about. Well, that is important, but it is not the part that bites. Consider the cobra snake. A cape cobra can strike at a distance well over half its own body length. So if you are standing ten feet away from a fifteen foot long cobra, the snake might seem a safe distance away, but you are actually within its striking range. One could say that the sea has two overlapping but distinct distances at which it strikes. One is the normal storm range. If you raise the sea along a beach in Cape Cod by six inches, nothing interesting happens most days. But the dozen or so medium size storms that will occur over a year (especially in winter when the storms come in from the Atlantic) will convert that foot of elevation into several horizontal feet of beach erosion, in a very short amount of time. The second is what happens when more serious storms, like tropical cyclones or their extratropical spawn, come along. New York City was built and reinforced from the sea, over time, mainly when the Atlantic was about a foot lower than it is now. A couple of years ago, when Super Storm Sandy came along, the storm gathered up that extra foot of sea level and turned it into an extra large storm surge sufficient to flood the subway system in lower Manhattan. Long before the sea in that area rises another three feet, there will be the occasional storm surge that will be even more severe.
Since a large percentage of the world’s population, a large percentage of the world’s agricultural activity, and an even larger percentage (probably) of the world’s real estate value will become subject to flooding, sometimes severe, and eventually be replaced by the rising sea over the next century and beyond, sea level rise is a very important phenomenon.
You have probably already heard about the study, “Mass gains of the Antarctic ice sheet exceed losses” by H. Jay Zwally and others (see citation and abstract below), that came out a couple of weeks ago telling us that the contribution to sea level rise by the Antarctic is currently zero or negative. Or at least, that is how many press outlets are reporting the story.
There are two problems with this study that you need to know about. First, the study examines a data set that ends in 2008. The second problem is that there are indicators that the study is simply wrong, even though it likely has significant merits.
The fact that the study being reported uses older data could explain why it conflicts with everything else the science is telling us. Michael Mann, quoted in The Guardian, notes, “…the claims are based on seven-year-old data, and so cannot address the finding that Antarctic ice loss has accelerated in more recent years.” To this I’ll add that it is somewhat annoying that those reporting the story, including, oddly, the authors of the study, are using forms of the word “current” to describe the result. These results are old, out dated, and while potentially valuable, a data set ending in 2008, when speaking of a rapidly changing system, is not current.
Average global sea level is a measurable verifiable established fact, and the contribution of major ice sheets to this has been measured and found to be important. If the study is correct, and Antarctica was not contributing to sea level rise during that period prior to 2008, then something is terribly wrong. There is simply not enough wiggle room in the other sources of sea level rise to account for the missing volume of water. One could argue that a beautiful hypothesis (positive mass balance in Antarctic ice) has been killed by an ugly fact (actual observed sea level rise). But Zwally’s study does not present a mere hypothesis, but rather, is based on detailed observations incorporated into a set of carefully done calculations.
So, perhaps the observations are wrong. There may be two reasons the observations (and the calculations derived from them) are wrong. One is simply that the satellite data they use are inherently less accurate than needed. The measurements are of a very small change over time over a very large area. If the satellite method is just a little off, this could cause a problem. (By the way, the data end in 2008 because the instrumentation on the satellite stopped working then.) This study’s main contribution may, in the end, to be to point out a problem with the instrumentation prior to that time. This doesn’t seem that likely for the simple reason that the whole point of putting fancy instruments in a bird is to get super accurate information.
The second possible reason seems more likely. Part of the process of determining that Antarctica has a positive mass balance (more ice over time rather than less) involves assumptions (and some measurements) about the response of the bedrock underneath the very thick ice sheets. If that is wrong, then that is a problem.
Since the sea level has in fact been going up, and there is no easy way to account for that than a certain contribution to Antarctica, and all the other science shows an increasingly melting Antarctic, and the study uses older data, then I’m afraid I have bad news. Sea level is still going up, Antarctica is still contributing to it, and the amount of this contribution is still, as the science has been suggesting for several years no, only going to increase.
The following resources will be of interest to anyone following this story.
Goldberg, Suzanne. 2014. Western Antarctic ice sheet collapse has already begun, scientists warn. (The Guardian)
Lewis, Renee. 2014. West Antarctic ice melt is now ‘unstoppable,” NASA report says. (Al Jazeera report)
Lewis, Renee. 2015 Experts dispute NASA study showing Antarctic ice gain. (Al Jazeera report)
Plait, Phil. 2015. Is Antarctica Gaining or Losing Ice? Hit: Losing. (Slate)
Sea Level Rise Research Group. 2015 global mean sea level time series. (data site)
Sinclair, Peter. 2015. Keeping it simple on sea level rise. (Blog post)
Sou. 2015. Antarctic ice – growing or shrinking? NASA vs Princeton and Leeds etc. (Hot Whopper)
Zwally, H. Jay, 2; Li, Jun; Robbins, John W.; Saba, Jack L.; Yi, Donghui; Brenner, Anita C. 2015. Mass gains of the Antarctic ice sheet exceed losses. Journal of Glaciology, International Glaciological Society.
Mass changes of the Antarctic ice sheet impact sea-level rise as climate changes, but recent rates have been uncertain. Ice, Cloud and land Elevation Satellite (ICESat) data (2003–08) show mass gains from snow accumulation exceeded discharge losses by 82?±?25?Gt?a–1, reducing global sea-level rise by 0.23?mm?a–1. European Remote-sensing Satellite (ERS) data (1992–2001) give a similar gain of 112?±?61?Gt?a–1. Gains of 136?Gt?a–1 in East Antarctica (EA) and 72?Gt?a–1 in four drainage systems (WA2) in West Antarctic (WA) exceed losses of 97?Gt?a–1 from three coastal drainage systems (WA1) and 29?Gt?a–1 from the Antarctic Peninsula (AP). EA dynamic thickening of 147?Gt?a–1 is a continuing response to increased accumulation (>50%) since the early Holocene. Recent accumulation loss of 11?Gt?a–1 in EA indicates thickening is not from contemporaneous snowfall increases. Similarly, the WA2 gain is mainly (60?Gt?a–1) dynamic thickening. In WA1 and the AP, increased losses of 66?±?16?Gt?a–1 from increased dynamic thinning from accelerating glaciers are 50% offset by greater WA snowfall. The decadal increase in dynamic thinning in WA1 and the AP is approximately one-third of the long-term dynamic thickening in EA and WA2, which should buffer additional dynamic thinning for decades.
I don’t care that the director or CEO of an advocacy organization concerned with poverty is an active academic. Indeed, my view of active academics is that many are largely incompetent in areas of life other than their specialized field. If that. So really, if you told me there is this great advocacy organization out there run by a well established active academic I’d figure you had that wrong, or I’d worry a little about the organization. On the other hand, everyone should care that university positions be given to active academics with credentials. So, when the University of Western Australia got paid off (apparently) to give Bjørn Lomborg a faculty position everyone looked at the UWA and said, “WUT?”
That was a situation up with which the members of that university community would not put, to coin a phrase, and the public outcry put a quick end to it. This is appropriate, because according to a new post by Stefan Rahmstorf at RealClimate, “… apart from one paper in 1996, Lomborg has never published anything in any field of science that was interesting or useful to other scientists, or even just worth the bother of contradicting in the scientific literature.”
I’ve talked about Lomborg here before. Here I noted,
There is currently a twitter argument happening, along with a bit of a blogging swarm, over a chimera of a remark made by John Stossle and Bjorn Lomborg. They made the claim that a million electric cars would have no benefit with resect to Carbon emissions. The crux of the argument is that there is a Carbon cost to manufacturing and running electric cars. When we manufacture anything, we emit Carbon, and when we make electricity to run the cars, we emit Carbon, etc. etc.
Lomborg is wrong, wrong, wrong, wrong, wrong. But here I want to focus on one aspect of why he is wrong that applies generally to this sort of topic….
Stefan’s post looks in detail at two things (and in less detail at many other things). First, is the question of whether or not Lomborg is an actual practicing academic with a good publication record and all that. He is not. Stefan’s analysis is clear.
Second, is a more detailed look at Lomborg, sea level rise, Bangladesh, and all that. This is especially interesting because Stefan is one of the world’s leading experts on sea level rise. He has two peer reviewed papers on the “top ten most cited” on the Web of Science (which has well ove 40,000 sea level rise related papers), which are heavily cited. Stefan’s post is a must-read because of Stefan’s overview of sea level rise, aside from the stuff about Lomborg. Go read it.
So go read the post, learn about Bjørn Lomborg’s academic qualifications, how wrong he has been about sea level rise, and some other good stuff.
I suspect we are not going to see much more about Bjørn going forward.
Ultimately sea levels will rise several feet, given the present levels of CO2 in the atmosphere. We already knew this by examining paleo data, and finding periods in the past with similar surface temperatures and/or similar atmospheric CO2 levels as today.
I put a graphic from a paper by Gavin Foster and Eelco Rohling at the top of the post. It does a good job of summarizing the paleo data.
If we keep pumping CO2 into the atmosphere at current, or even somewhat reduced, levels for a few more decades, the ultimate increase in sea levels will be significant. Find the 400–500 ppm CO2 range on the map and notice that the average sea level rise in times past, indicated by the horizontal orange-reddish line, is 14 meters.
Let me rephrase that to make it clear. We have already caused something like 14 meters of sea level rise. Like the horrifically sad words uttered by a movie or TV character who has received a fatal wound and turns to the killer, uttering “You’ve killed me” (then they die), we’ve done this. It is just going to take some time to play out. But it will play out.
A conservative estimate is that likely sea levels will rise 8 meters or more, quite possibly considerably more. But generally, people who talk about sea level tend to suggest that this will take centuries. Part of the reason for that is that it takes a long(ish) time for the added CO2 to heat up the surface, then it takes a while for that heat to melt the ice sheets. However, there is no firm reason to put a time frame on this melting.
A new paper that is making a great deal of news, and that is still in peer review, suggests that the time frame may be shorter than man have suggested. We may see several meters of sea level rise during the lifetime of most people living today.
What is not known
We don’t really how long this will take. Looking at the paleo record, we are lucky to get two data points showing different ancient sea levels that are less than a thousand years apart. There are a few moments during the end of the last glaciation where we have data points several centuries apart during which sea levels went up several meters. We don’t have a good estimate for the maximum rate at which polar ice caps and other ice can melt.
The current situation is, notably, very different from those periods of rapid sea level rise. The amount of CO2 in the atmosphere is approximately double the Pleistocene average, and the rate at which CO2 levels and temperatures have gone up has not been seen in tens of millions of years. Whatever rate of sea level rise over the last several tens of thousands of years must be regarded as a minimum, perhaps a very low minimum.
What is new
The new paper argues for more sea level rise, ultimately, than many others have suggested, but it is still within the range of what we had already guessed from the paleo record. Most current research on the rate of glacial melting show relatively slow levels compared to what the new paper suggests. In particular, the new paper suggests that this is wrong, and that we may see three meters of sea level rise over the next fifty years.
The paper is very complex and covers a lot of ground that I will not attempt to address here. The tl;dr is that the researchers model the current melting of ice, and finds that the rate is accelerating over time. This means that current rates are a gross underestimate of the rate of sea level rise.
Mann talks about some of the effects of sea level rise, including global effects. We are already seeing food prices being affected now and then by climate catastrophes. Consider the fact that much of the rice grown in southeast Asia is grown on land that will be inundated by this sea level rise. This applies to the US as well. This combined with increased drought in places that are not flooding, and social unrest such as occurred in Syria when crops fail – causing further agriculture in those areas to simply stop happening – will cause a major food crisis in the near future. Our children and grandchildren will be hungry, at war, living in a post-civilization world. That is the world those who deny climate science and stand in the way of taking action are causing.
Here is the abstract of the paper:
There is evidence of ice melt, sea level rise to +5–9 meters, and extreme storms in the prior interglacial period that was less than 1°C warmer than today. Human-made climate forcing is stronger and more rapid than paleo forcings, but much can be learned by combining insights from paleoclimate, climate modeling, and on-going observations. We argue that ice sheets in contact with the ocean are vulnerable to non-linear disintegration in response to ocean warming, and we posit that ice sheet mass loss can be approximated by a doubling time up to sea level rise of at least several meters. Doubling times of 10, 20 or 40 years yield sea level rise of several meters in 50, 100 or 200 years. Paleoclimate data reveal that subsurface ocean warming causes ice shelf melt and ice sheet discharge. Our climate model exposes amplifying feedbacks in the Southern Ocean that slow Antarctic bottom water formation and increase ocean temperature near ice shelf grounding lines, while cooling the surface ocean and increasing sea ice cover and water column stability. Ocean surface cooling, in the North Atlantic as well as the Southern Ocean, increases tropospheric horizontal temperature gradients, eddy kinetic energy and baroclinicity, which drive more powerful storms. We focus attention on the Southern Ocean’s role in affecting atmospheric CO2 amount, which in turn is a tight control knob on global climate. The millennial (500–2000 year) time scale of deep ocean ventilation affects the time scale for natural CO2 change, thus the time scale for paleo global climate, ice sheet and sea level changes. This millennial carbon cycle time scale should not be misinterpreted as the ice sheet time scale for response to a rapid human-made climate forcing. Recent ice sheet melt rates have a doubling time near the lower end of the 10–40 year range. We conclude that 2°C global warming above the preindustrial level, which would spur more ice shelf melt, is highly dangerous. Earth’s energy imbalance, which must be eliminated to stabilize climate, provides a crucial metric.
A large portion of the glacial mass in Antarctic, previously thought to be relatively stable, is now understood to be destablizing. This is new research just out in Science. The abstract is pretty clear:
Growing evidence has demonstrated the importance of ice shelf buttressing on the inland grounded ice, especially if it is resting on bedrock below sea level. Much of the Southern Antarctic Peninsula satisfies this condition and also possesses a bed slope that deepens inland. Such ice sheet geometry is potentially unstable. We use satellite altimetry and gravity observations to show that a major portion of the region has, since 2009, destabilized. Ice mass loss of the marine-terminating glaciers has rapidly accelerated from close to balance in the 2000s to a sustained rate of –56 ± 8 gigatons per year, constituting a major fraction of Antarctica’s contribution to rising sea level. The widespread, simultaneous nature of the acceleration, in the absence of a persistent atmospheric forcing, points to an oceanic driving mechanism.
The paper is “Dynamic thinning of glaciers on the Southern Antarctic Peninsula” by B. Wouters, A. Martin-Español, V. Helm, T. Flament, J. M. van Wessem, S. R. M. Ligtenberg, M. R. van den Broeke, J. L. Bamber.
Here is a simulation of grounding line retreat in action from NASA:
Karl Mathiesen at the Guardian has a writeup on the research here.
The sheet’s thickness has remained stable since satellite observations began in 1992. But Professor Jonathan Bamber of Bristol university, who co-authored the study, said that around 2009 it very suddenly began to thin by an average of 42cm each year. Some areas had fallen by up to 4m.
“It hasn’t been going up, it hasn’t been going down – until 2009. Then it just seemed to pass some kind of critical threshold and went over a cliff and it’s been losing mass at a pretty much constant, rather large, rate,” said Bamber.
The estimate of ice loss by this research might be overestimated, according to Andrew Shepherd, who notes that some of the thinning of the glacier could be due to changes in snowfall amounts on tip, rather than melting from the bottom. It will be interesting to see how this works out.
Caption for the figure at the top of the post:
Fig. 2 Mass variations for the sum of basins 23 and 24, as observed by GRACE and modeled by RACMO2.3.
Basins 23 and 24 are defined in (21, 22). The faint blue dots are the monthly GRACE anomalies with 1? error bars (20), and the thick blue line shows the anomalies with a 7-month running average applied so as to reduce noise. Cumulative SMB anomalies from RACMO2.3 are shown in red, with the light red area indicating the 1? spread in an ensemble obtained by varying the baseline period (20). The dashed light blue line shows the estimated dynamic mass loss (GRACE minus SMB). The vertical dashed lines indicate January 2003, December 2009, and July 2010, the start and ending of the different altimetry observations. (Inset) The GRACE time series for the individual basins 23 (blue) and 24 (red), before (full lines) and after (dashed lines) applying the SMB correction.
I recently noted that there are reasons to think that the effects of human caused climate change are coming on faster than previously expected. Since I wrote that (in late January) even more evidence has come along, so I thought it was time for an update.
First a bit of perspective. Scientists have known for a very long time that the proportion of greenhouse gasses in the Earth’s atmosphere controls (along with other factors) overall surface and upper ocean heat balance. In particular, is has been understood that the release of fossil Carbon (in coal and petroleum) as CO2 would likely warm the Earth and change climate. The basic physics to understand and predict this have been in place for much longer than the vast majority of global warming that has actually happened. Unfortunately, a number of factors have slowed down the policy response, and the acceptance of this basic science by non scientists.
A very small factor, often cited by climate contrarians, is the consideration mainly during the 1960s and 1970s, that the Earth goes through major climate swings including the onset of ice ages, so we have to worry about both cooling and warming. This possibility was obviated around the time it was being discussed, though people then may not have fully realized it at the time, because as atmospheric CO2 concentrations increased beyond about 300ppm, from the pre-industrial average of around 250–280ppm (it is now at 400ppm), the possibility of a new Ice Age diminished to about zero. Another factor mitigating against urgency is the fact that the Earth’s surface temperatures have undergone a handful of “pauses” as the surface temperature has marched generally upwards. I’m not talking about the “Faux Pause” said to have happened during the last two decades, but earlier pauses, including one around the 1940s that was probably just a natural down swing that happened when there was not enough warming to swamp it. A second pause, shorter, happened after the eruption of Mount Pinatubo, in 1991.
Prior to recent anthropogenic global warming, the Earth’s surface temperature has squiggled up and down do to natural variability. Some of these squiggles were, at least reionally large enough to get names, such as the “Medieval Warm Period” (properly called the “Medieval Climate Anomaly”) and the “Little Ice Age.” When the planet’s temperature started going distinctly up at the beginning of the 20th century, these natural ups and downs, some larger and some smaller, caused by a number of different factors, eventually became imposed on a stronger upward signal. So, when we have a “downward” swing caused by natural variation, it is manifest not so much as a true downturn in surface temperatures, but rather, less of an upward swing. Since about a year and a half ago, we have seen very steady warming suggesting that a recent attenuation in how much temperatures go up is reversing. Most informed climate scientists expect 2015 and even 2016 to be years with many very warm months globally. So, the second factor (the first being the concern over the ice age as possibly) is natural variation in the Earth’s surface temperature. To reiterate, early natural swings in the surface temperature may have legitimately caused some scientists to wonder about how much greenhouse gas pollution changes things, but later natural variations have not; Scientists know that this natural variation is superimposed on an impressive long term upward increase in temperature of the Earth’s surface and the upper ocean. Which brings us to the third major factor delaying both non-scientists’ acceptance of the realities of global warming, and dangerous policy inaction: Denialism.
The recent relative attenuation of increase in surface temperatures, likely soon to be over, was not thought of by scientists as disproving climate models or suggesting a stoppage of warming. But it was claimed by those denying the science as evidence that global warming is not real and that the climate scientists have it all wrong. That is only one form of denialism, which also includes the idea that yes, warming is happening, but does not matter, or yes, it matters, but we can’t do anything about it, or yes, we could do something about it, but the Chinese will not act (there is little evidence of that by the way, they are acting) so we’re screwed anyway. Etc.
The slowdown in global warming is not real, but a decades-long slowdown in addressing global warming at the individual, corporate or business, and governmental levels is very real, and very meaningful. There is no doubt that had we started to act aggressively, say, back in the 1980s when any major hurdles for overall understanding of the reality of global warming were overcome, that we would be way ahead of where we are now in the effort to keep the Carbon in the ground by using clean energy. The precipitous drop we’ve seen in photovoltaic costs, increases in battery efficiency and drop in cost, the deployment of wind turbines, and so on, would have had a different history than they have in fact had, and almost certainly all of this would have occurred faster. Over the last 30 or 40 years we have spent considerable effort building new sources of energy, most of which have used fossil Carbon. If even half of that effort was spent on increasing efficiency and developing non fossil Carbon sources, we would not have reached an atmospheric concentration of CO2 of 400ppm in 2015. The effects of greenhouse gas pollution would be less today and we would not be heading so quickly towards certain disaster. Shame on the denialists for causing this to happen.
I should mention a fourth cause of inappropriate rejection of the science of climate change. This is actually an indirect effect of climate change itself. You all know about the Inhofe Snowball. A US Senator actually carried a snowball into the senate chamber, a snowball he said he made outside where there has been an atypical snowfall in Washington DC, and held it aloft as evidence that the scientists had it all wrong, and that global warming is a hoax. Over the last few years, we have seen a climatological pattern in the US which has kept winter snows away from the mountains of California, contributing significantly to a major drought there. The same climatological phenomenon has brought unusual winter storms to states along the Eastern Seaboard that usually get less snow (such as major snow storms in Atlanta two winters ago) and persistent unseasonal cold to the northeastern part of the US. This change in pattern is due to a shift in the behavior of the Polar jet stream, which in turn is almost certainly caused by anomalous very warm water in parts of the Pacific and the extreme amplification of anomalous warm conditions in the Arctic, relative to the rest of the planet. (The jury is still out as to the exact process, but no serious climate scientists working on this scientific problem, as far as I know, doubts it is an effect of greenhouse gas pollution). This blob of cold air resting over the seat of power of one of the more influential governments in the world fuels the absurd but apparently effective anti-science pro-fossil fuel activism among so many of our current elected officials.
Climate Sensitivity Is Not Low
The concept of “Climate Sensitivity” is embodied in two formulations that each address the same basic question: given an increase in CO2 in the atmosphere, how much will the Earth’s surface and upper ocean temperatures increase? The issue is more complex than I’ll address here, but here is the simple version. Often, “Climate sensitivity” is the amount of warming that will result from a doubling of atmospheric CO2 from pre-industrial levels. That increase in temperature would take a while to happen because of the way climate works. On a different planet, equilibrium would be reached faster or slower. Historically, the range of climate sensitivity values has run from as low as about 1.5 degrees C up to 6 degrees C.
The difficulty in estimating climate sensitivity is in the feedbacks, such as ice melt, changes in water vapor, etc. For the most part, feedbacks will increase temperature. Without feedbacks, climate sensitivity would be about 1.2 degrees C, but the feedbacks are strong, the climate system is complex, and the math is a bit higher level.
As time goes by, our understanding of climate sensitivity has become more refined, and it is probably true that most climate scientists who study this would settle on 3 degrees C as the best estimate, but with wide range around that. The lower end of the range, however, is not as great as the larger end of the range, and the upper end of the range probably has what is called a “fat tail.” This would mean that while 3 degrees C is the best guess, the probability of it being way higher, like 4 or 5, is perhaps one in ten. (This all depends on which model or scientist you query.) The point here is that while it might be 3, there is a non-trivial chance (one in ten is not small for an extreme event) that it would be a value that would be really bad for us.
There have been a few recent studies using what’s called an “energy balance model” approach, combining simple climate models with recent observational data, concluding that climate sensitivity is on the low end of IPCC estimates. However, subsequent research has identified some potentially serious flaws in this approach.
These types of studies have nevertheless been the focus of disproportionate attention. For example, in recent testimony before the US House of Representatives Committee on Science, Space and Technology, contrarian climate scientist Judith Curry said,
Recent data and research supports the importance of natural climate variability and calls into question the conclusion that humans are the dominant cause of recent climate change: … Reduced estimates of the sensitivity of climate to carbon dioxide
Curry referenced just one paper (using the energy balance model approach) to support that argument – the very definition of single study syndrome …
…As Andrew Dessler told me,
There certainly is some evidence that climate sensitivity may be below 2°C. But if you look at all of the evidence, it’s hard to reconcile with such a low climate sensitivity. I think our best estimate is still around 3°C for doubled CO2.
So there is not new information suggesting a higher climate sensitivity, or a quicker realization of it, but there is a continuation of the consensus that the value is not low, despite efforts by so called luke-warmists or denialists to throw cold water on this hot topic.
Important Carbon Sink May Be Limited.
A study just out in Nature Geoscience suggests that one of the possible factors that may mitigate against global warming, the terrestrial sink, is limited in its ability to do so. The idea here is that as CO2 increases some biological activities at the Earth’s Surface increase and store some of the carbon in solid form as biomass. Essentially, the CO2 acts as plant fertilizer, and some of that Carbon is trapped in the detritus of that system, or in living tissue. This recent study suggests that this sink is smaller than previously suspected.
Terrestrial carbon storage is dependent on the availability of nitrogen for plant growth… Widespread phosphorus limitation in terrestrial ecosystems may also strongly regulate the global carbon cycle… Here we use global state-of-the-art coupled carbon–climate model projections of terrestrial net primary productivity and carbon storage from 1860–2100; estimates of annual new nutrient inputs from deposition, nitrogen fixation, and weathering; and estimates of carbon allocation and stoichiometry to evaluate how simulated CO2 fertilization effects could be constrained by nutrient availability. We find that the nutrients required for the projected increases in net primary productivity greatly exceed estimated nutrient supply rates, suggesting that projected productivity increases may be unrealistically high. … We conclude that potential effects of nutrient limitation must be considered in estimates of the terrestrial carbon sink strength through the twenty-first century.
We have good reason to be concerned about the potential for nasty climate feedbacks from thawing permafrost in the Arctic….research bring good news or bad? [From recent work on this topic we may conclude that] although the permafrost feedback is unlikely to cause abrupt climate change in the near future, the feedback is going to make climate change worse over the second half of this century and beyond. The emissions quantities are still uncertain, but the central estimate would be like adding an additional country with the unmitigated emissions the current size of the United States’ for at least the rest of the century. This will not cause a climate catastrophe by itself, but it will make preventing dangerous climate change that much more difficult. As if it wasn’t hard enough already.
disasters were happening long before humans started pumping heat-trapping greenhouse gases into the atmosphere, but global warming has tipped the odds in their favor. A devastating heat wave like the one that killed 35,000 people in Europe in 2003, for example, is now more than 10 times more likely than it used to be…. But that’s just a single event in a single place, which doesn’t say much about the world as a whole. A new analysis in Nature Climate Change, however, takes a much broader view. About 18 percent of heavy precipitation events worldwide and 75 percent of hot temperature extremes — defined as events that come only once in every thousand days, on average — can already be attributed to human activity, says the study. And as the world continues to warm, the frequency of those events is expected to double by 2100.
Antarctica is pretty much covered with glaciers. Glaciers are dynamic entities that, unless they are in full melt, tend to grow near their thickest parts (that’s why those are the thickest parts) and mush outwards towards the edges, where the liminal areas either melt (usually seasonally) in situ or drop off into the sea.
Antarctic’s glaciers are surrounded by a number of floating ice shelves. The ice shelves are really the distal reaches of the moving glaciers floating over the ocean. This is one of the places, probably the place at present, where melting accelerated by human caused greenhouse gas pollution occurs. The ice shelves are fixed in place along their margins (they typically cover linear fjord like valleys) and at a grounding point underneath the shelf some distance form the ice margin but under sea level.
The collapse or disintegration of an ice shelf is thought to lead to the more rapid movement of the corresponding glacial mass towards the sea, and increased melting. This is the big problem right now with estimating the rate of glacial melting in the Antarctic. This is not a steady and regular process, as rapid disintegration of an ice shelf is possible. Most likely, Antarctic glacial melting over the coming decades will involve occasional catastrophic of an ice shelf followed by more rapid glacial melting at that point.
The floating ice shelves surrounding the Antarctic Ice Sheet restrain the grounded ice-sheet flow. Thinning of an ice shelf reduces this effect, leading to an increase in ice discharge to the ocean. Using eighteen years of continuous satellite radar altimeter observations we have computed decadal-scale changes in ice-shelf thickness around the Antarctic continent. Overall, average ice-shelf volume change accelerated from negligible loss at 25 ± 64 km3 per year for 1994-2003 to rapid loss of 310 ± 74 km3 per year for 2003-2012. West Antarctic losses increased by 70% in the last decade, and earlier volume gain by East Antarctic ice shelves ceased. In the Amundsen and Bellingshausen regions, some ice shelves have lost up to 18% of their thickness in less than two decades.
This is one of many reasons that even the most extreme of the IPCC estimates of ice loss (generally) and its contribution to sea level rise have to be seen as a lower limit. This is a substantial change, and it is very recent. It isn’t just that the ice sheets have gotten thinner, but also, that the rate of melting at these margins is increasing.
Caption to figure: Fig. 1 Eighteen years of change in thickness and volume of Antarctic ice shelves.
Rates of thickness change (m/decade) are color-coded from -25 (thinning) to +10 (thickening). Circles represent percentage of thickness lost (red) or gained (blue) in 18 years. Only significant values at the 95% confidence level are plotted (see Table S1). Lower left corner shows time series and polynomial fit of average volume change (km3) from 1994 to 2012 for the West (in red) and East (in blue) Antarctic ice shelves. Black curve is polynomial fit for All Antarctic ice shelves. We divided Antarctica into eight regions (Fig. 3), which are labeled and delimited by line segments in black. Ice-shelf perimeters are shown as a thin black line. The central circle demarcates the area not surveyed by the satellites (south of 81.5°S). Original data were interpolated for mapping purposes (see Table S1 for percentage area surveyed of each ice shelf). Background is the Landsat Image Mosaic of Antarctica (LIMA).