Fingerprinting the ocean

Which is more likely to cause flooding in Europe; the Greenland ice cap or the west Antarctic ice sheet? They are both currently melting. And we can measure how fast, but it’s only been a recent development we have satellites that can resolve this, so it’s hard to draw conclusions on future melt rates from that. We might want to look at the past. And glaciologists have ways to find clues on how big ice sheets have been in times gone by (like they show here), but that information is often patchy. Sea level itself provides clues too. There are ways of telling where water that runs into the oceans has come from.

If you have an ice sheet, and a part of that ice sheet melts, several processes take place. The ice sheet becomes lighter and smaller, causing the Earth’s crust to bounce back up like a lilo, and the ice also lessens its gravitational pull on the sea water around it. The whole sea would in effect flow away from the shrinking ice sheet. So strangely enough, the most sea level rise you would find would be on the other side of the globe. Near the ice sheet, relative sea level would only fall.

Modelled results of what happens if 1mm sea level equivalent melts from the Greenland Ice Sheet: the resultant sea level change ranges from <0mm (blue) to>1.2mm (dark orange). From: Mitrovica, Tamisiea, Davis and Milne, Nature 409, 2001

So what if the Greenland ice sheet melts? That would be ~6m overall sea level rise, so that would be felt everywhere, but the southern hemisphere would be hit hardest (apart from the northern hemisphere having many more big cities in low-lying coastal areas). For Europeans, it’s the west Antarctic ice sheet that’s the main threat.

So how can that feature be used? If you want to know where past sea level rises originate from, you need to make reconstructions at a wide range of latitudes. The spatial pattern of where the rise is highest to where it even may be negative will tell you where the water involved came from. Simply speaking, the hemisphere where you find the smallest rise is the culprit. This process is called "fingerprinting"; this term has a rather chemical ring to it, but sea level scientists use it in a more spatial way. And if you can then find out under what circumstances it is which ice sheet that reacts, you may get an idea of what will happen in our future. And that is information of which it is quite imaginable it will be ignored by the relevant authorities, but at least everyone with access to scientific literature will have an idea of where not to buy a house...

Big change for small Arctic creatures

Sometimes it’s important to study the obvious. Among almost all, except some right-wing Americans, it is known that we are experiencing a period of rapid climate change. And with climate change come biological changes. But it matters to find out what exactly is happening; to get an idea of the scale of the phenomenon, and of how various aspects of it interact. So even though everybody can guess that the Barents Sea is warming, and that that must influence whatever small critters are living at its bottom, I spent two years trying to figure out what the difference really was between, roughly, 20^th and 21^st century foraminifera in that basin.

Some of the foraminifera species we studied

How did that all come about? In the 90s, Morten Hald, Per Ivar Steinsund and Sergei Korsun had made an effort, collecting all available information on which foraminifera species lived where. And in the years 2005 and 2006, a vessel of the Norwegian Institute of Marine Research had gone and collected samples in the same area. My job was to analyse these samples for foraminifera, and compare my findings to the database of foraminifera assemblages that had been compiled. The paper is published in Global and Planetary Change, as 'Changes in distribution of calcareous benthic foraminifera in the central Barents Sea between the periods 1965-1992 and 2005-2006', by M.H. Saher, D. Klitgaard Kristensen, M. Hald, O. Pavlova, and L. Lindal Jørgensen, to be found here. 

We found changes indeed. At my sample sites, temperature had on average increased by almost 1°C. All the cold water species had lower abundance in the 21^st century than in the 20^th. Evident? Maybe. But yet another small piece in the whole picture of how exactly various species respond to climate change.

Our main goal had been finding out which species had changed in abundance and how, but just out of curiosity I also wanted to calculate how big the total change had been for each sample. I found an appropriate method for quantifying change, calculate a value for each sample, and had some mapping software produce a map of the results. When it came out I was surprised to see a clear pattern. A band of highest amplitude of change followed the general outline of the maximum ice edge in spring. I hadn’t expected that!

The main figure in the article (but changed in style as to not breach copyright), with the yellow circles indicating the amount of change between the 20th and 21st Century as found in the foraminifera assemblages.

The maximum ice edge is a place where many things come together. In the Barents Sea, inflowing Atlantic water mixes with polar water. Where these waters meet tends to be where the ice edge is. Atlantic water is too warm to freeze over. And the water covered in ice doesn’t receive much sunlight, so there isn’t much life that can eat the nutrients in the water; at the ide edge, the wind can stir them from underneath the ice. That makes the ice edge a very productive region. And now we found it is not only where life is abundant, but also where it changes in abundance.

So what are the implications of this? With the cold foraminifera species vanishing from the Barents Sea, they may soon vanish altogether. They can’t move much north from there. Will anybody miss them? They are not charismatic macrofauna, after all. But it would be a few more species gone, which are fascinating, if only you are willing to find out.

And if there was already such change happening in the pre-2007 years, it would have been very interesting to see what 2007, the epicyear of low sea ice, would have shown. That year is famous for its summer ice minimum; not its spring ice maximum. But that was low too. 

The extent of sea ice in March 2007; March is normally the month with the largest extent. The area has dropped steadily over the years (left) with a big dent in 2005-2007. After 2007 it has been rather stable. Data: Fetterer, F., K. Knowles, W. Meier, and M. Savoie. 2002, updated 2009. Sea Ice Index. Boulder, CO: National Snow and Ice Data Center. Digital media.

The research vessel did set out to collect samples in 2007. Unfortunately, the weather was too rough, and no samples were collected. The next year, the ship didn’t even go. So there is still much to find out at the bottom of the Barents Sea. I hope some time in the future, someone will go back there, collect samples, and then write a comparison with both the 20^th century database and this work. I am quite keen to see what’s going on there in the post-2007 years…

How high was sea level in the last interglacial?

Let me start with a disclaimer: I will not give a definitive answer to the above question. That being out of the way I can now freely discuss the difficulties of trying to answer a question like that.

It is, in a way, an interesting question: the last interglacial was only ~125.000 years ago, so the continents were all practically in the same location as they are now, and the oceans were equally deep. We know from ice cores and fossil plants and such things how high CO2 levels and CH4 levels in the atmosphere were. We know from ice cores, microfossils, and many other sources how warm it approximately was. So you could say that if you know how high sea level was back then, you know how high sea level is at these CO2 levels and these temperatures, and that might be useful. Additionally; if you can reproduce that in a climate model, you have reason to believe your model resolves sea level well, and may be able to predict it too. Unfortunately, it's not that simple. 

Picture of the 1953 flood

One thing is that we had already passed the CO2 levels of the last interglacial when the Mauna Loa observatory started measuring in the fifties. We may not yet have reached reached globally averaged temperatures comparable to those of 125.000 years ago, but it's hard to pinpoint that; every place on Earth has its own temperature history, and it's not easy to compare two periods that are so similar. And ice does not melt instantaneous. Just suppose we reach, this very day, the very temperatures we had in the last interglacial, the ice caps won’t have had time to adjust to that. And we don’t give them any; temperatures keep rising. We can only get an equilibrium when the situation remains stable for a while. That won’t happen in our lifetime!

So apart from the issues associated with a comparison, we still have this sea level issue to deal with. If you talk about “sea level” in a given time, without further specification, it almost automatically means “globally averaged sea level”. And the problem with that is that you can perhaps measure it today; satellites scan the entire Earth surface, and you can calculate the average of all their data. And sea level famously isn’t level; temperature differences, the rotation of the Earth, wind, gravitational pull of things such as ice sheets and so on, all make the sea surface rather bumpy. So you can’t measure past global average sea levels (further back than the satellite era), as it’s not possible to make a sea level reconstruction for every location on Earth covered by sea. So what can we measure? Local sea level, evidently.

There are many ways of reconstructing local sea level (such as this, this, this, this, and this), and every method, of course, has its own caveats. They also might not represent the same aspect of sea level; some might e.g. reflect low tide, while others are more representative for mean sea level. And tide ranges don't stay constant over time.

And if you have produced a local sea level reconstruction, you're not done; you also have to take into account that not only sea level in itself, but also the Earth’s crust might have gone up and down. Locations affected by earthquakes, volcanism, or (occasional) ice cover are prone to do a certain amount of moving vertically, and fast enough to pose a problem over the time scales discussed here. You can, of course, only use stable regions, but that leaves you with quite a small number of data points. An iconic paper by Robert Kopp and co-workers in Nature tried to extract a global average from a limited amount of data from the Last Interglacial. They, for instance, had no data points along the eastern and western shores of the Pacific; the only data from that ocean came from islands in the middle, and from its polar boundaries. They come up with an average of ~7m higher, but given the data scarcity it is hardly surprising they give rather large uncertainties. And these 7m, being a global average, of course are only a mathematical reality; at any specific location the value may be drastically different. 

The difficulty with reconstructing sea level also makes its prediction difficult.We only have good data coverage over the last few decades, and only moderate coverage over the last few centuries. If your sea level model manages to hindcast the patterns observed in that time interval, that doesn't necessarily mean it can resolve anything novel happening, like, say, the collapse of the West Antarctic Ice sheet. And that's exactly the sort of things we would like to get a handle on.

So if you headlines in the newspaper, on Twitter or wherever, that say something along the line of “sea level in period X (say, the last Interglacial) was #m higher/lower than today”, do realise it could mean all sorts of things. If one person for instance claims sea level was likely to be 8m higher than today in the Last Interglacial, and you read somewhere else it was 8m lower, it doesn’t mean one of them has to be wrong, as much as climate skeptics would like that to be the case. In this case it concerns one global average, and a local record from the Netherlands. And it's many, very many of such results, which may seem contradictory, that altogether will paint a comprehensive picture of past sea level. And in the long run, this will hopefully give us a solid grasp on future sea levels.

Conversion of a skeptic. Really?

The New York times let him write an op-ed. The Guardian blogged about him. The BBC had a piece about him on their news website. The Carbon Brief interviewed him. Twitter was buzzing with his name. Richard Muller was the talk of the day. Why; had he discovered something exceptional? Had he found the cure for cancer? Had he solved the hunger problem? No. He had found something out that had already been known for decades. So why all the excitement? I’m not so sure!

So what was the issue? Muller suspected there was something wrong with the current global average land temperature records. So he set out to investigate. Land temperatures are, of course, only a small part of the climate story, but he does have a point that most humans reside on land, and are therefore much more interested in land temperatures. And these are hardly independent of the ocean temperatures; the oceans have a much higher volume and heat capacity than the land (or rather; the atmosphere at a little bit above the surface, where land temperature is traditionally measured). But one can only do so much at any given time. And measuring temperatures is hampered by urbanisation and uneven distribution of measuring stations. So far no problem: it's always good if someone keeps a critical eye.

It took him and his co-workers a few years to trawl through the data. They’re done now; the accompanying manuscript has been submitted to JGR. His conclusions: actually, the records are fine. Temperatures are rising. And he goes further: humans are too blame. So far still so good. It had long been established, but there’s nothing wrong with corroboration.

Muller in action

Was that what all the buzz was about? No, it was about his conversion from climate skeptic to climate, well, scientist. Does it matter? Maybe! People like senator Inhofe have one person less to point at, saying that scientists have no consensus (like these people) and climate change is a hoax. And that’s good.

But does it mean Muller is a lighting example for climate science? No. His article is not yet published; it will be up to the editors of JGR whether he did a thorough enough job for his work to be published. If he does then we have another interesting article. But with Muller it seems not be about what he publishes, but what he says outside science. And that makes my hair stand up. Listen yourself to what he says here. My problems with these things are (in more or less chronological order):

1)    He sees a distinction between global warming and climate change. He only acknowledges the first. He acts as if these things are not related. But every rational person will see that atmospheric temperature is an aspect of climate, and that, for instance, temperature and ice volume are not independent. If you only look at land temperatures you’re missing most of the story. If you think climate change goes away when you disprove a rise in land temperature you’re not a very believable scientist. Just pointing out that some people attribute Hurricane Katrina to global warming, which indeed can’t be done, does not mean global warming is not part of the much wider process of (anthropogenic) climate change.

2)    He claims the US CO2 output is dropping. That’s not in the paper, that’s not a statement backed up by data. I struggled to find recent data on this. This blog gives a graph, and it indeed shows a decline, but the figures are provided by BP, and the report they came from  has a disclaimer that says "BP regrets it is unable to deal with enquiries about the data" so I won't take their word for it. I do hope Muller is right, but I would like him to point out where he got the data from. 

3)    His thoughts on the solution boil down to: change China! I’m not saying China does not pollute, or that it pollutes a lot, but it’s not helping if non-Chinese get all patronising and want to “help” China to develop clean technologies, while proclaiming that they themselves are not the problem and don’t have to cut down on their own pollution.

4)    He dismisses 90% of Al Gore’s Inconvenient Truth without getting into detail on what exactly is wrong with it. In the scientific community, this film/book is accepted as largely correct.

5)    He attributes global warming to humans, simply by fitting the temperature curve and the CO2 curve. And many of us have done such fitting exercises, but it's not the pinnacle of science. Muller, however, claims he has done a better job than anybody had before. That is blatantly untrue: lots of proper research (like this for instance) has been done on attributing climate change to various causes.

6)    He lashes out at Michael Mann, using false arguments. He for instance says Mann denies the existence of the Medieval Warm Period, while in reality, Mann is one of the main authors to discuss this feature (e.g. here). Do read Mike Mann’s Facebook page, by the way (it’s public); he has gone through the effort of dismissing all the false statements, with links to proof.

So what is my conclusion? I think Muller just likes the limelight. I would pay attention to what he manages to get published, as that will have withstood a critical eye. But I don’t believe a thing of what he says which is not backed up by solid evidence. A man like this might be more a Trojan Horse than anything else: pretend to be a bona fide scientist, and as soon as people believe that, fill their minds with rubbish. Watch out for Muller! And do to him what he did to the temperature records: first evaluate it properly, and only then decide if you believe it or not…

The Greenland story

It was all over the news, all over the world: 97% of the surface of the Greenland Ice Sheet melting! Quite a lot of sources, including 350.org,  de Volkskrant and het NOS journal got carried away, and announced, either on twitter or on national TV, that 97% of all Greenland ice was gone. They should have spent a second to ponder this: for instance, the offices of de Volkskrant would be flooded if that had indeed been the case. But 97% of the surface experiencing melt is spectacular enough in itself. Generally, no more than 50% undergoes melting in summer. 97% is really rare.

Some twitter sources also mentioned this event had been predicted. In an article, that attracted quite some attention, Jason Box of Ohio State University, and co-workers, stated they expected melt over 100% of the surface to occur in the near future. So what did they base that on, and were they really that precise?

The map showing decreased reflectivity over almost the whole of the ice cap, which gets the bulk of the attention.

Box et al. studied the reflectivity of the Greenland ice. Reflectivity, or albedo, is one of these things that stabilises ice sheets; it reflects sunlight back so effectively that the radiation can hardly make a start at melting any ice before it finds itself reflected back into space. But if high temperatures manage to get the melting process going, this lowers the reflectivity, and then your ice and snow are in peril. This self-reinforcing process, also known as positive feedback, might well herald your ice cap’s decline. What’s even worse is dirt blown on top of the snow; this may start melt at lower temperatures.

So what did Box and his fellow scholars do? They basically measured reflectivity and melt from a satellite, calibrated these results with observations from weather stations on the surface, and ran a climate model in order to get an idea of the sensitivity of the reflectivity to temperature. And what is so new about this research? Satellites have been measuring the albedo of Greenland for many years, and ground-truthing with weather stations has been done since early days too. But the results of Box et al. go all the way to the year 2011, bringing this research up to date. And their combination of observations and modelling could potentially give new insights in how the process works.

Observations of reflectivity

So what did Box and colleagues find? The reflectivity of the Greenland Ice Sheet is at a low point; 8% lower in 2011 than it was in 2000. And this is not an incident; they have observed a significant trend, though admittedly a short-term one. They further found a 26% increase in melt between 2000 and 2011. And to give you an idea of how much that is: if that rate would remain constant at 2011 level, the ice cap would be lost in roughly 6000 years. And the sensitivity of the reflectivity to temperature? That’s where it gets confusing. Over large areas of the ice sheet, reflectivity only goes up with higher temperatures. This can be explained by warm air bringing in more snowfall. But strangely enough, snowfall doesn’t always correlate with higher reflectivity in their data. And when you look at the sensitivity of the reflectivity to temperature, or in other words; by how much the albedo goes up or down with every degree temperature change, it becomes clear that their data is only statistically robust in the regions that are melting already.

The authors warn that they think summer melting will occur over the entire ice sheet in another decade, if the coming years will be like 2010 and 2011. But that is a big “if”. Box emphasizes only the decreased reflectivity in his own blog post, without being too specific about the lack of straightforward relation with actual melting. The big take home message of this paper might be that the processes governing ice melt are not yet sufficiently understood. And we want to understand it, if only to get an idea what we should do with our coastal defences. The amount of melt in 2011 measured already translates to more than a millimetre of globally averaged sea level rise. And that does not sound like much in itself, but it does when you realise it was only 1.7 mm/year on average for the 20^th Century in total; that includes for instance Antarctica, mountain glaciers, and thermal expansion.

So did they predict the ~100% melt?

Well. In a way they did. But what they really predicted was a shift to net melt over the area that nowadays experiences net snow accumulation, averaged over the whole summer. They did not mention short periods of 100% surface melt. However, you can’t get to net summer melt without, well, melting large areas of the surface once in a while. So people who say “they predicted this!” are exaggerating. But Box and colleagues are right in saying that this event greatly supports their conclusions. Given the uncertainties in their data, this was more a lucky guess than rock-hard data, yet I hope it will attract attention to the danger of Greenland melt. It’s not as if we who are alive today will ever see an ice-free Greenland, but we may well see a Greenland Ice Cap that raises average sea level by 2mm per year or more, and that is something we need to prepare for. Those who love Amsterdam, London, New York or one of these other iconic cities near sea level might wish Box luck in keeping up the good work…

What is a species? And why care?

What is a species? A nice rule of thumb is that a group of organisms that can produce fertile offspring together is a species. And as long as you are dealing with nicely large, long-living, accessible species like cats and horses that will do. But what if you are dealing with organisms whose reproduction has never been observed? And why would it matter?

It helps to define species, even if you can’t be too sure of whether you’re actually getting it right. If I say I saw a picture of a dragon, you will all have an idea of what I saw, even though nobody could possibly conclusively define a dragon. If people know what you mean a lot is won. The same holds in micropalaeontology.

Micropalaeontology is the study of microfossils; the preserved remains of micro-organisms. An example of a group of such microorganisms is foraminifera; unicellular organisms that live in the sea, and produce little shells. That shell is what can remain preserved when the organism dies: the microfossil. They tend to be 0.1 to 1 mm in size. Their use in environmental science is endless; they are widespread and abundant, and there are many different species with each their own environmental preferences. Their evolution is fairly well-studied as well; if you show a micropalaeontologist a handful of foraminifera, he or she can most likely tell you, after barely more than a glance, how old they are, and what environment they lived in. And even their little shells can be studied; they can hold a wealth of information.

An example of an assemblage of foraminifera; in this case form Myanmar/Burma. Picture: Psammophile. Source: Creative Commons.

But back to the question of subdividing them into species. Traditionally, species have been defined on the basis of shape. Later, when more information became available, environmental preferences were taken into account as well. The whole classification of species was episodically revised, based on new information; the result was an ever-changing system, where not everybody used the same version. But everybody knew that; as long as you knew what classification someone used you knew, more or less, what you were up to. But a certain level of subjectivity cannot be avoided. Not every specimen looks like a textbook figure. But in spite of its confusions and imperfections, the system worked.

And then DNA analysis was invented. Suddenly, it could be objectively determined if organisms belong to the same species or not. And it is done on foraminifera too. When there was a workshop on foraminifera taxonomy (species classification), the researchers working on foraminifera DNA decided to put the old system to the test. They provided the participants of the workshop with 40 pictures of foraminifera of a specific genus of which they had sampled the DNA: they therefore knew which of these belonged to the same species. And now they asked us to group them the old way, and tell us what name they would give these species.

These are specimens of Ammonia beccarii; a species that has sometimes been subdivided into various species, but of which DNA research has revealed that it is indeed only one. Photo: Hans Hillewaert. Source: Creative Commons.

The first thing that became apparent was that it wasn’t an easy job. Every group of experts struggled! And every group came up with slightly different results. And the names assigned to the species did not always match either. That is a measure of the mentioned flexibility in classification, and subjectivity. But then they were shown what the DNA had revealed.

Some results were as expected. Sometimes the old-fashioned method split a species into two different ones, or left a specimen out that looked odd, but that is all within expectation. But there were shocks too: some species turned out to contain specimens that look quite different, and that none of the participants would have considered to be the same species, if they would find them in their samples. That provided food for thought.

Foraminifera pictures taken with a Scanning Electron Microscope; the top left is classified as an Ammonia beccarii, like the specimens in the picture above. And according to the USGS, the top right is an Elphidium excavatum forma clavatum, but are they sure? This was one of the species that created some confusion in the "shape vs DNA" game... 

Does this mean we have to forget about micropalaeontology? No; as flawed as the discipline is, it still answers (and raises!) very relevant questions. And it helps to know how big the uncertainties are. Does this mean we have to now sample the DNA of all foraminifera we study? No; that would be too time- and money-consuming, and beside that; most of the specimens we study are long dead, and don’t contain DNA anymore. So what is the relevance of this work?

To give you an idea of how confusing it is: one of these pairs are two specimens of the same species, but the other pair is two different species. I'm not going to say which is which, but I think it illustrates similarity isn't enough to decide. 

One of the things DNA research can do is tell the micropalaontological community which differences in shape are indicative of a different species, and which are just variation within a species. They could improve on their classifications that way. The research can also help in cases where a species seems to be able to adapt to very different environments; can they really, or are we dealing with several species that look the same? Knowing that would tell us something about the adaptability of marine species; quite useful knowledge in these times of rapid change. Various experts probably already have a long list of further questions they would like to see answered, and the process of answering will create a multitude of new questions. It’s even possible we’ll see new species evolve into existence right under our eyes…

North Carolina and the sea - an update

Is North Carolina asking citizens to think for themselves? Regulations, put in place with the best intentions, often turn against their purpose. Think of regulations that limit the height of the ladders window cleaners are allowed to use in their work; the idea behind them is increasing the safety of those who clean windows. But it results in window cleaners having to resort to scaffolding or boom lifts more often; this makes their services much more expensive. With the result that people will try to clean their own windows. Without the experience that comes with the profession. This law is reported to only have resulted in an increase in window cleaning accidents… And boom lifts aren’t fail-proof either; I found seven cases of death and 19 of injury due to boom lift in the Netherlands since 2003.

Source: Aubrey Dale, Creative Commons

So well-meant laws often have a reverse effect. But could it work the other way? As I wrote in a blog post in early June; North Carolina was considering making it unlawful to base coastal protection policies on up-to-date sea level change research. This law didn’t make it; the House of Representatives have voted for its revision. The new version, which will have to get an OK from the governor before it becomes a law, contains the clause that the Coastal Resources Commission shall direct its Science Panel to actually study scientific literature, and come up with recommendations only after that. They have until December 2015 to write the report. So the threat of North Carolina making it unlawful to be informed about sea level change is gone. On the long term, that is. The new version also contains a clause that says, and I quote, “The Coastal Resources Commission and the Division of Coastal Management of the Department of Environment and Natural Resources shall not define rates of sea-level change for regulatory purposes prior to July 1, 2016.”

An example of coastal erosion from California

Science (the magazine) considers this bad news; those who wish to know if it’s wise to build a new house somewhere on the coast get no guidelines from their state for the next four years. But it also means they are allowed to think for themselves. If policy makers are forced to give out meaningless guidelines, it may well go unnoticed by the consumer of these guidelines that these are completely detached from reality. But when the state publicly announces silence on the topic, people will be quite aware they have to find out for themselves. And not everybody will be pleased that they pay their tax, but still have to spend time on making their own guidelines; and some people will undoubtedly find incomplete or inaccurate information in their search, but altogether I think it’s a much better situation than one in which it is downright illegal to do the sensible thing. So this revised law is a watered-down version of a law aimed at keeping the people ignorant; this version may serve to make them better informed that they were before!