War is not merely a political act, but also a real political instrument, a continuation of political commerce, a carrying out of the same by other means. All beyond this which is strictly peculiar to War relates merely to the peculiar nature of the means which it uses.
But most of all I’m reminded of Gary Kasparov’s declaration that the point of modern propaganda is not to make you believe something but it’s to make you believe nothing. (I paraphrase slightly). Much of the piece is about how the Russian propaganda operation as been so successful at engendering doubt about Ukraine and the state of relations between Russia and Ukraine.
I sometimes feel the invasion of Ukraine has really been a wake-up call for many of us because it’s just so undeniable. An actual event happening to real people that we know with a pretty clear narrative. The genius of Russian influence operations has always been to muddy the waters sufficiently that it was a little hard to trust anything that anyone said or wrote.
In this sense I’ve also found Timothy Snyder’s series on the making of modern Ukraine (which I’ve been listening to over the last few weeks) brilliant and helpful and interesting. The subject is fascinating, but it also because it becomes clear listening to a historian that, yes there can be different ways to interpret events, but the events themselves are real and we have a duty to try to learn the facts before judging them.
This is of course exactly how scientists should think, that we have to establish good observational data before trying to interpret it. We also need, inevitably to consider what are the uncertainties and likely range within that data. What is missing? What can’t we know? What is the most likely interpretation based on the things we can observe? How reliable are our measurements?
One of my favourite teachers at school who really helped to develop the way I think was very clear on how to do this. And he was not a scientist, he was a historian.
Ultimately, I was more interested in understanding the physical world and went on to study glaciers, ice sheets and the climate system at the poles. However, as I’ve been focusing more on sea level rise and how on earth we adapt to a changing climate it’s quite clear that going back to the social sciences will be important to understand human behaviour. And the murky way other actors seek to influence us as we adapt to climate change is also going to be important to understand. There has been undue influence from a “Merchants of Doubt” perspective for sure for many years when it comes to the causes of climate change and the effects. This is very clear in the mess of climate denial that the new Lord of Twitter has unleashed, it’s a little bit like returning to 2009.
Anyway, this is a bit incoherent maybe. But it’s a great piece for clarifying what we know now and maybe for working out what comes next in terms of Russian interference in democratic institutions. And from a climate scientist perspective it’s also another reason to try to avoid (if we can), becoming just another cultural battleground. This is also key: it’s not always about money, sometimes people really are being manipulated for other reasons:
“When people act in the interest of a foreign power, it is sometimes for money, it is sometimes because the foreign power knows something about them, it is sometimes for ideals, and it is sometimes for no conscious motive at all — what one thinks of as one’s own motives have been curated, manipulated, and directed. It seems quite possible — I raise it as a hypothesis that reasonable people would consider — that some mixture of these factors was at work at FBI New York in 2016.”
I was recently asked to comment on this interesting new paper by David Rounce and co-authors for AP by Seth Borenstein called “Global glacier change in the 21st century: Every increase in temperature matters”. You can read his resulting summary here . I’m posting here the slightly expanded and lightly edited response I sent to Seth in response to his (very good) questions.
The authors only look at the small glaciers and ice caps in this study, not the big polar ice sheets, though they do also cover small peripheral glaciers in Greenland and Antarctica that are not part of the main ice sheets. Of course, this means that sea level rise from all the other important processes like thermal expansion and ice sheet met also have to be taken into account on top of the numbers given here.
Their main findings were that at 1.5 °C above preindustrial, we can expect total glacial mass loss between 2015 and 2100 would be 26% with 90 mm of sea level rise and 49% of the small glaciers and ice caps lost globally. The paper only deals with these small glaciers and does not count the big ice sheets!
At 4°C, we’re looking at 41% mass loss with ~154 mm of sea level rise and 83% of glaciers lost. At 2.7 °C, where the world is now heading, 32% mass loss, 115 mm of sea level rise and 68% of glaciers lost.
I’m sad to say that the results aren’t exactly a surprise – the community has known for some time that the loss of glaciers is basically linear with temperature, so the title of the paper is really spot on, every tenth of a degree really does matter. This earlier paper by my Horizon 2020 PROTECT project collaborator Ben Marzeion shows something very similar But it’s a nice new result with the latest generation of glacier model and updated with the latest CMIP (IPCC) scenarios and they included some new processes that weren’t very well accounted for in previous work.
My first thought was that these latest estimates were actually a little lower than I expected, but the baseline in the paper is 2015 – we should remember that many of these glaciers have already lost quite a lot of ice (see my two photos of Nigårdsbreen in Norway, taken only 13 years apart) – so the new estimates are basically in line with what I would have expected given earlier work. I’d also expect that they will continue to lose ice beyond 2100 so it’s definitely not an end state that they are giving here. As they state in the article there will be widespread deglaciation of some pretty iconic parts of the world, even under the present planned emissions reductions..
In many ways part of the problem has been the previous studies have not always accounted for all the processes: frontal ablation (melt and calving of vertical ice cliffs, mostly in contact with water), the effect of debris cover and so forth (the latter will likely reduce the rate of loss, the former probably increases it). Given what we know about these processes and how to represent them in models, I still consider this work to be a more realistic estimate. Then we also need to account for the climate models and the scenarios used to force them – there are some important differences between CMIP5 and CMIP6 which might also account for some of this shift. We have actually seen something somewhat similar for the projected changes in the big ice sheets.
It’s probably important to remember though that this study still needs to make simplifications, especially when looking at so many glaciers in so many different regions, so there will always be new updates to come with improved computing power and computational techniques and better representation of processes. Having said that, I do not think the picture will substantially change in future, though I can always be proved wrong, and the glaciers community are now at the stage of refining estimates for rates of mass loss.
Globally the loss of glaciers means sea level rise. Regionally and locally the biggest consequences will be for for water resources and we’re likely to see a local increase in natural hazards like outburst floods and avalanches that will need to be carefully managed. There have been a couple of instances already in the last year or two that probably demonstrate this well (e.g. the Marmolada glacier in Italy last year).
Sea level budget divided into components, from Legeais et al. 2018 ESSD The steric component is the expansion of sea water as it warms.
I include myself in the group who has to get used to the cultural shift. I have worked on glaciers in the Alps and Norway which are really rapidly disappearing. It’s kind of devastating to see, but it’s not actually surprising. We have known it was coming and in many cases (including the authors of this paper), measured the massive losses (last year, 2022 was a disaster for the Alps and both Fabien Maussion and Matthias Huss who are co-authors on the paper are running very comprehensive programmes that show in real time how much of a disaster) and predicted it with some accuracy. But we’re now at the point where it’s really undeniable that these glaciers are going fast.
#Glacier ice melt in 2022 was impressive! See the incredible speed of ice loss at the snout of Rhonegletscher (@VAW_glaciology time lapse by A. Cremona)…
The Rhonegletscher in the timelapse above is a really iconic glacier in the Alps, I have my own favourites, mostly places I’ve worked, like Norway, Iceland and Greenland, which are all to a greater or lesser extent retreating fast now. The glaciers that people consider iconic or at least well-known tend to be accessible and depend very much where you are and they will be the glaciers we mourn over in the next decades. In the French Alps, it’s probably the Mer de Glace, in Switzerland perhaps Rhone glacier or Plaine Morte (both have monitoring programmes), in Canada perhaps the Malaspina or Athabasca glaciers. There are still (just) glaciers on Kilimanjaro and Mount Kenya, the Ruwenzoris are basically gone, as are the Papuan glaciers.
Though they show in the study that ice loss is basically linear with temperature, at some point the glaciers become so small that the remianing melt is highly non-linear. And these won’t grow back under any sensible “overshoot” scenario (never mind that we don’t really have technology to remove carbon from the atmosphere at scale). Once they’re gone, they’re basically gone forever on human timescales Finally, I’d like to add a bit of anlaysis by Ben Marzeion and co-authors , it’s possible to basically put a number on the amount of melted glacier ice each kg of CO₂ leads to.
We find that under present-day climate conditions, every emitted kg of CO2 will eventually be responsible for a glacier mass loss of 15.8 (5.9–20.5) kg. Again, since the global glacier mass is decreasing with increasing temperatures, this number is greater for lower temperatures and smaller for higher temperatures.
I have been meaning to write about my return to field science (after 10 years mostly working on climate models) for the last 2 years, but prompted by this beautifully written piece in the Danish Newspaper information, I decided Christmas Day was the day (it for sure beats the washing up)…
“For at forstå, hvad der er ved at ske ved kloden, rejste vi mod isens ende” “To understand what is happening to the earth, we travelled to the end of the ice”
Martin Bahn og Anders Rye Skjoldjensen (foto) in Information 23rd December 2022
To make one thing very clear straight away, and as the newspaper article also makes very clear, my colleague Steffen Malskær Olsen has established and maintained a very long-running programme of observations in the fjord near Qaanaaq. This town in northern Greenland on the edge of a large fjord, and close to the North Water polynya has a uniquely interesting location to study and understand Arctic processes. The DMI facility there is long established and part of the INTERACT network of Arctic field stations. The 15-year record collected by Steffen is more or less unbroken and uniquely valuable. None of the science I’m planning to do or to work on would be possible without his dedication, hard work, insight and bridge building within the community in Qaanaaq. He and my other DMI colleagues involved in this programme are brilliant scientists and great field companions and I feel privileged to be able to work with them in this incredible place.
In the field: Steffen and team retrieving an oceanographic mooring with instruments on it after a winter out in the fjord in 2021.
Secondly, as the article also makes clear, scientists are not individualistic heroes who beat the odds, it’s a team sport. And it’s especially true in Greenland where the true heroes of this story are probably not scientists but the local hunters and fishers who guide and transport us and whose knowledge and experience is unmatched. I include also on this category our DMI colleague Aksel Ascanius who lives and works in Qaanaaq has been an essential part of the programme since the earliest days, as well as keeping other long-term observations in the network running in this part of the world.
Collaboration with the people who live in the Arctic has been essential for success in Arctic science since since the days of Franklin and Rae (for British readers) or Suersaq, aka Hans Hendrik, (after whom Hans Island is named) for Danes..
Anyway, back to the science of the present-day. DMI has progressively added more and more elements to the field laboratory in Qaanaaq in addition to the longer running observations. A non-exhaustive list would include an infrasound monitoring station that is part of the CTBTO, weather observations (of course), surface emissivity measurements by drone, fjord salinity, temperature and photosynthetically available radiation measurements plus snow and sea ice measurements as well as work with satellites and biology. One glaring omission, up to this year at least, was the glaciology of the region. How does the ice sheet affect the regional climate, how does the ocean affect the glaciers that calve into the fjord? Can we learn about some important but poorly understood processes like calving and melange dynamics using this area as a test bed? What about surface mass budget and snowfall and snow melt?
A lead in the sea ice – these fractures in the ice have sea water (the black) welling up between two thick plates of sea ice. The conditions were perfect for frost flowers to grow on the surface. Sea ice turns out to be a lot more interesting – and complex- than I’d ever imagined…
Now, as a glaciologist, I’ve mostly worked with the interface between atmosphere and ice sheet (at least the last 14 years or so, but I am also still (after my PhD topic on ice fracture and crevasses) interested in calving glaciers and the processes that control how fast icebergs form. And the fjord, Inglefield Bredning has *a lot* of calving glaciers in it. It is a natural laboratory for glaciology and for developing numerical models. Calving is actually a surprisingly difficult thing to model with computer models of glaciers.
Or perhaps it’s not that surprising?
Observations are difficult to get (to put it mildly). There are a number of (possibly wild) theories of “calving laws” that remain poorly constrained by observations as a result. Common parameterizations of ice flow makes it hard to deal with fast flowing glaciers where calving is common. Dealing with grounding lines, where glaciers meet the sea and start to come close to flotation can give notorious numerical errors and retreat requires the remaking of ocean grids in fully coupled climate models.
Satellite image from ESA’s Sentinel-2 satellite showing glaciers calving icebergs into the head of the Ingle field Bredning fjord. The black is open water, icebergs show up as blueish dots, the land is carpeted in snow. Low winter sun (in late September 2022) casts deep shadows.
These are not easy or computationally cheap problems to solve. And where there are at least thousands (maybe even tens of thousands?) of scientists working on atmospheric weather and climate modelling, the community working on ice sheet dynamic models is probably only in the low hundreds.
And of course, we really lack long time series of measurements – essential in a system that changes only s l o w l y, but likely irreversibly and which we are, only now as the system is changing rapidly, starting to understand.
This of course is why the fjord observation record of Steffen is so valuable – these are reliable, repeated measurements of ocean properties that are known to affect the outlet glaciers that meet them. It is indeed a natural laboratory.
What we are now also working on is a field lab to study these calving processes in-situ. I have already found the return to the field scientifically valuable. There is really no replacement for going to observe the earth system you want to understand. (My PhD supervisor used to call it “nurturing your inner glacier”). Observations taken in spring/summer 2022 have already changed how I think about some processes and hopefully the follow-up we have planned in 2023 will confirm our new theoretical framework.
Heading home from the deployment of instruments out near calving glaciers at the head of the fjord.
I am fortunate indeed in that at the same research department, we also have colleagues collecting and analyzing satellite data and developing the numerical models we want to use to understand how ice sheets fit into the earth system. All three of these elements – field, satellite and numerical model- are essential.
In this project we are using the satellite observations to extend the time series of field data and we can use both sets of observations together to develop and test a numerical model of this fjord and the glaciers that calve into it. The numerical model we can then extend to other glaciers in Greenland. Hopefully, we can also use this work to understand how Antarctic glaciers might also respond to a warming ocean. Ultimately, the aim of all this work is to understand the contribution of these glaciers to sea level rise both now and in the future.
This is not a frivolous question. In fact, if large (more than a couple of metres).of sea level rise is expected, it is a question that is basically existential for Denmark.
I will add more on the specifics and science in coming months, this is already long enough. However, I’d like to mention a couple of other points:
Firstly, DMI is by no means alone operating up here. Many of the key articles, particularly on glaciology in this region, have been written by the Japanese group at Hokkaido University and their collaborators at the Meteorological Research Institute, the national institute for polar research and others. We at DMI are also working directly with the Greenland institute of natural resources, Asiaq, GEUS, KU, DTU, AU, SDU, ESA, Eumetsat and many others in this research programme.
Finally, this work is currently being carried out under the auspices of the Danish National Centre for Climate Research (NCKF), funded by the Danish Government though with contributions also from other research projects mostly funded by the EU’s Horizon 2020 and Horizon Europe frameworks as well as ESA’s climate change initiative for the Greenland ice sheet.
UPDATE: The Arctic Sea ice Outlook I mention in the post below has just been published for 2016. We will follow this up in September when the final results will be known, but here are the 30 entries using a rage of different techniques including sophisticated computer models, statistical estimates and what is kindly called “Heuristics” but which may be characterised as an educated guess by people who have been studying this field for a while…
Professor Wadhams has not contributed an estimate this year but it can easily be seen that none of the estimates reach as low as the putative 1 million square kilometres. Nonetheless the view of 27 expert climate scientists put forward by Kay, Bailey and Holland (pdf), not to mention the very sophisticated RASM model (one of the most sophisticated in this area, run by the US Naval Postgraduate school), put the September extent at a very low 3-4 million km2, in the same range as the record low of 2012.
It will be interesting to see how low it does go. The latest results from the polar portal show that Arctic sea ice is currently still on the record low 2012 line but a careful look shows also that the 2012 and 2013 curves diverge around mid to late June. The year 2013 is pretty representative of a “new normal” over the last 4 years or so, it is therefore difficult to tell based on simply extrapolating along the curves which path 2016 is likely to follow.
The area covered by at least 15% sea ice in the Arctic from 1981 to present, the black and red curve shows the year 2016 and is updated daily on the Polar Portal
The Polar Portal has become part of our daily life at DMI where I work in the last few years, it combines detailed observations and models from the Greenland ice sheet, the Arctic sea ice and, soon hopefully, permafrost. I am particularly involved in the Greenland pages where we daily calculate the amount of snowfall and snow melt which gives us a surface mass budget and which we sum up over the year to work out what it means for the health of the Greenland ice sheet. This year has been especially interesting with an extraordinarily early start to melting driven by warm Arctic temperatures. Many records in Greenland have been broken in April, May and June. Spectacularly, last week Nuuk set a new temperature record for June that managed to last only 24 hours, before it was broken again.
Crossing the sea ice in front of Paulabreen, a surge type glacier with a calving front in Svalbard
I trained as a glaciologist originally, but even then I came across sea ice and was first of all unnerved by it, crossing on scooters to visit glaciers in Svalbard, and then fascinated by it. Recently I have been working pretty closely with my colleagues in DMI who are sea ice scientists and I have learnt quite a lot. We even published a paper together in the journal Polarforschung earlier this year. Not only that, I am now part of a big ERC Synergy project known as ice2ice with scientists at four institutions in Bergen and Copenhagen working on the complex connections between sea ice, ocean, atmosphere and ice sheet in the Arctic. More on that another time, but suffice to say it’s fascinating work and I know a hell of a lot more about sea ice than I did even three years ago.
So when this news story crossed my email this evening courtesy a BBC researcher and journalist I knew pretty well straight away what it was about. Basically the scientist Professor Peter Wadhams had made some statements about the extent of Arctic sea ice which might be considered somewhat eyecatching.
Professor Wadhams is a well-known scientist who did some incredibly valuable and indeed ground-breaking early work on sea ice. More recently he has also done some very valuable work reconstructing thickness based on submarine observations during the Cold War (see below on why this is important). I well remember seeing him talk about this as a young graduate student, he is an excellent speaker and gave a very interesting and compelling talk. In the last few years he has made several statements that have been widely reported and perhaps misinterpreted, with regard to the future fortunes of the Arctic sea ice.
Now, I need and want to be clear about this. Most of the global climate models we use are not very good at reproducing the observed historical sea ice extent. They have improved significantly in the last few years but still struggle to reproduce the actual observed decline in sea ice area from satellites. And there are actually very good reasons why this should be. There are some very good stand alone sea ice models which have done a very good job and the key difference between these models is our clue. Sea ice models are generally partly forced with actual observations, or climate reanalyses which assimilate observations, so the atmosphere and the ocean are close to reality. Basically sea ice responds to weather, and if you have a more accurate weather driving your sea ice model you will get a better fit to the observations.
So, is Professor Wadhams correct? Will the sea ice “disappear” this year.
Well, it is pretty clear that given the changes we have already observed in the Arctic, as well as what we know about Arctic amplification and the general direction that anthropogenic emissions are heading in, that unless something changes pretty soon, we will likely see an end to a significant cover of sea ice in the Arctic at some point in the next few decades. But was does that actually mean?
Reading his actual comments in the article he appears to define 1 million km2 as “no sea ice” and that partly reflects how we define sea ice extent. Since most of the data sets use a cut-off figure (typically 15%) to define when a grid square or pixel is or is not a sea ice point. This is known as sea ice concentration and is really something of a hangover from the days when sea ice was observed from ships and an attempt was made to estimate how much sea ice in the area was around the vessel.
There are however lots of things that can affect sea ice extent, including winds and currents and melt ponds. The latter also affects how different algorithms assess the area that is or is not covered by sea ice. As there are a number of different sensors in use and a number of different algorithms processing that data, it is not entirely surprising that there actually a number of different estimates (I will use OSISAF) for how much of the Arctic is covered in sea ice. And this number will vary in years with more winds for example, or stronger ocean currents, sea ice will disperse faster. It is quite likely that much of the variability in sea ice area in recent years is at least partly attributable to different winds, as well as, for example in 2012, big storms that have arrived at just the right moment (or wrong one depending on how you look at it), to break up the sea ice into smaller, more easily transportable pieces.
As an aside, a better measure for how much Arctic sea ice there is actually present is sea ice volume. Unfortunately this is very difficult to measure, especially outside the winter freeze up season, though a research group at the UCL, centre for Polar Observation and Monitoring have developed a way to do so. Here for example is the most recent plot, which as you can see has not been updated since May 2016 due to the presence of melt ponds on the surface of the sea ice which the Cryosat radar cannot penetrate.
So 1 million km2 is probably a reasonable cut off for assuming an “ice-free” Arctic in the sense that it indicates that there will still be some sea ice drifting around (it always forms surprisingly quickly when the winter begins) in summer, even if it is dispersed.
Over the last 40 or so years (we have good observations going back to 1979, it gets patchy after that), in September, when the area covered by sea ice is at it’s lowest, that extent has been between about 7 and 9 million km2, more recently that has dropped and 2012, the lowest on record had an extent of about 4 million km2, which you can see on the latest polarportal sea ice chart below.
I well remember 2012, we had a large melt event over Greenland that year also, but it was still quite a long way from the 1 million km2 quoted by Professor Wadhams. Again, let me be clear, we are pretty sure that at some point on a time scale of a few years to a few decades, the Arctic will become “ice-free” in the summer time. We can predict this, even if we don’t know exactly when, since, as I hope is clear now, sea ice conditions are very dependent on the weather. The weather this year so far, at least this Spring has been very warm and congenial to sea ice melt. The big dive shown on the graph above is no mystery when considering some of the temperature anomalies in the Arctic, as shown also on the Polar Portal.
Nevertheless, the recent plots seem to show that the 2 metre air temperature in the Arctic is returning to close to normal and there is little reason to suppose that will change significantly anytime soon.
Having said that, weather forecasting has improved massively in the last few decades, a true quiet revolution, but we still do not know how the weather will pan out over the whole of this melt season. I am sure that at some point Professor Wadhams will be proved correct, but we do not know when and it is even possible or rather likely that we will have a few years where we switch back and forth between ice free and not ice free conditions. So, the answer to the question I pose above is probably no. But don’t bet on it remaining so for too long.
UPDATE: I recalled this morning on my way in to work that I had somehow failed to mention the Sea Ice Prediction network. This group of people under the auspices of ARCUS, gather predictions on y´the end-of-season sea ice extent ever year. The call for predictions for the 2016 season is now open. Many different research groups as well as one or two enthusiastic amateurs will post their predictions over the next few weeks. It is an interesting exercise, as you can see based on last year’s report (see also figure below), it is not the first time that Profgessor Wadhams has predicted a 1 million km2 extent in September, and his is the lowest (and least accurate) in the rankings.
Endnote: There has been quite an absence of posts from this blog recently. I have been too busy with work, family, travel and more recently the EU Referendum (for which I have been threatening a post for quite some time and may yet get around to before polling day). However, a question about Arctic sea ice has been flickering on the edges of my consciousness for a while now so this was a quick (EDIT: not so quick!) blogpost to try and address it when I should actually be writing something else…
An ultra-quick post today. I have been spending a lot of time lately writing a grant proposal (and occasionally tweeting about it on the #DACEA3 hashtag). Finally it’s in and after a celebratory beer or two at the famous Mikeller last week I have managed to get around to a very brief summary of what it’s all about…
Around 17,000 years ago, Lake Victoria more or less completely dried out. I still find this absolutely staggering. In fact, the lake has dried out and reformed at least 3 times since it first formed about 400,000 years ago.
Lake Victoria is the largest lake in Africa and indeed the tropics, containing 2.75 cubic kilometres of water (though compared to the 2,850,000 cubic kilometres of water in the Greenland ice sheet that seems small, which merely goes to prove how much of our fresh water is locked up in the ice sheets), making it the 9th largest lake by volume in the world.
Gratuitous wildlife shot: A raft of hippos chilling out in the river. Photo credit: Ruth Mottram
Clearly, the disappearance and later reappearance of the lake, and others in the region speaks to monumental shifts in the climate. The East African Rift Valley lakes are largely fed by the East African rains, long and short, delivered by the shifting position of the Intertropical Convergence Zone as the Earth’s seasons change bringing those life-giving rains.
This grant proposal started as idle speculation around the coffee machine (in the grand old scientific tradition) about how this was climatically possible and could it happen again? My colleague (and talented PI on the proposal) Peter Thejll had been reading a book about John Hanning Speke and Richard Burton (not that one) and their famous search for the source of the Nile and has some personal African connections, which prompted the conversation and it seemed obvious to try and find out what happens to the local circulation to allow the lake to dry out. A quick google search revealed an old friend, Dr. Sarah Davies at Aberystwyth University was researching this topic actively and it all fell into place.
Now, I can guess what you’re thinking – this is usually a glaciology or Arctic Climate blog, where on earth has all this Africa stuff come from? Well what happens in the Arctic does not necessarily stay in the Arctic.
There are a number of hypotheses as to the drivers of these changes in African rainfall, among which is the interesting observation that the periods of greater aridity correlate remarkably well with Heinrich events in the North Atlantic.
Heinrich events were first identified as layers of sediment most likely transported into the North Atlantic Ocean by icebergs, known as ice rafted debris – IRD. The southerly position of many of these layers thousands of kilometres from any ice sheets either at the present day or in the past suggests a truly extraordinary amount of icebergs and cold fresh water were discharged over a relatively short period of time, from a large ice sheet. The source of these sediments is most likely the gigantic Laurentide ice sheet of North America, but there is also some evidence of smaller contributions from the British and Fenno- Scandian ice sheets (which may or may not have been joined together across the North Sea depending on how you interpret the evidence). The physics behind this is that as the enormous amount of cold fresh water was discharged into the North Atlantic, the temperature and salinity changes were sufficient to push, or keep the ITCZ far to the south, preventing the rains one East Africa.
On the other hand, other research has linked the failure of the rains to El Niño and related phenomena such as the Indian Ocean dipole and the Walker circulation. Still other scientists have noted that these drying periods seem to correlate with orbital changes in the earth which would affect the seasonality, that is the annual cycle of seasons. It is known as orbital forcing as the Earth’s seasons are driven by changes in our orbit around the sun (have a look at the excellent Orbit documentary from the BBC for a very easy to follow and beautifully filmed introduction to the importance of our orbit around the sun if you’re not familiar with Milankovitch cycles etc).
Milankovitch cycles shown from ocean cores and an Antarctic ice core at the bottom compared with the theoretical cycles. Image: By Incredio (Own work) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia CommonsAll of these hypotheses can be supported by correlations with palaeo evidence, but to really disentangle the connections between different regions of the world and how they affect each other’s weather and climate, we need to use a climate model. Luckily, at DMI we have the perfect tool to hand, a global climate model including ice sheets, EC-Earth. Furthermore we also have a high resolution regional climate model, HIRHAM5, my usual tool of choice. Our friends Morten Dahl Larsen and Martin Drews at the Danish Technical University are experts in using hydrology models so the answer is obvious.
We want to use these model tools and an extensive archive of observations, helpfully curated by our project partners Sarah Davies and Henry Lamb at Aberystwyth University to test all these different ideas. As an extra spinoff from the project, the Aberystwyth group have been intensively involved with the collection and analysis of a new lake sediment core from Chew Bahir in Ethiopia, so it’s going to be pretty exciting seeing if we can get the models to replicate these kind of records.
There is of course an extra urgency to this project. It’s not just a somewhat obscure academic question. A recent paper showed that the long rains have significantly reduced over the last decade, and about 300 million* people live in this region and rely on these rains for drinking water, hydroelectric power and agricultural production. During this period we have also seen rapid changes in the Arctic. Of course the two trends may not be connected, or may be linked via a common third factor which is why the physics of climate are so important to understand.
UPDATE 2: I had no time originally in the writing of this to add a little about our other project associate. One of the best things about doing science are the very smart and friendly people you meet along the way. Social media has really helped here to keep in touch as it is a nomadic lifestyle. By sheer chance I noticed a familiar name in a tweet that seemed to have some direct relevance to the proposal as we were writing it.
John Marsham was an old friend from my student days at Edinburgh University who I had slightly lost touch with. Thanks to the efforts of facebook we were soon back in touch and he is one of the Investigators on the HyCRISTAL project, part of the hugely important Future Climates for Africa Project, funded by the Department for International Development (DFiD) and the Natural Environment Research Council (NERC) in the UK. DACIA has some really obvious parallels with this project, though where we would like to concentrate on past climates, they will be focusing on present day and future climates. We hope therefore to send our PhD student to collaborate with the HyCRISTAL and FCFA projects where our insights from palaeomodelling palaeodata can make a real difference to the way future climate change is adapted to in East Africa. It will be very nice to collaborate with John’s group at Leeds as well as the Aberystwyth group, now we just have to hope we get the money to do it..
Or, to put it another way, “bless the rains down in Africa” ** (As an aside, for years I had always heard this as “I miss the rains down in Africa”, assuming it was about someone from Africa who missed being there).
UPDATE 1: Having viewed the original pop video again, I am rather troubled by the casual racism, sexism and naked orientalism on display (yes it was the 70s but still…) so I think I prefer to post instead this particularly witty deconstruction courtesy of @spaceforpootling
*(based on a back of the envelope calculation based on population statistics from Wikipedia if you know the correct number do let me know).
**(Apologies if you now have cheesy 1970’s pop music going round your head all day… 🙂 )
My 2 kids were singing the rain rain go away rhyme during last weekend’s epic rainfall in Copenhagen and it reminded me that I have not yet put up a post about a paper I was a co-author on this summer related to late summer/autumn rainfall and the effects on the Greenland ice sheet, so here goes….
Mostly when we think of precipitation in Greenland we think of snow in the winter, but it does rain quite a lot, as I know from personal experience (see photo taken as the clouds started to clear one September field season in Eastern Greenland…). This paper in Nature Geoscience by Sam Doyle and co-authors including myself shows that when rain falls on the ice sheet at the “wrong” time of year it can have a very far-reaching effect, causing the speed up of a large area across the ice sheet.
Rain clouds over the Stauning Alps of Eastern Greenland after the third day of rain… Exploratory mining camp tents in the foreground.
The important caveat is that rainfall during the main part of the melt season is more or less evacuated away quickly. Glaciers – and the Greenland ice sheet is basically a very big glacier – develop a drainage system more or less analogous to large underground sewers during the melt season. These tend to close down during the colder accumulation season and reopen by the sheer pressure of water running through them when the melt season starts. Rainfall during that crucial late summer/early autumn period when the drainage is closing down and therefore less efficient at evacuating surplus liquid water is therefore not able to move away from the glacier very easily and forces its way through any way it can find.
During this period, most of the snow will have melted off the surface, leaving vast areas of bare ice. By contrast, rain on snow in the early part of the melt season when there is a thick snow pack is more likely to refreeze inside the snow. In late summer however, there will be a relatively short period between rain falling and accumulating in the glacier drainage system.
In practice this means the water makes its way to the bed of the glacier through moulins and englacial channels, where it more or less hydraulically jacks up the glacier over a large region, allowing the ice to flow to the margins faster. There may then also be a knock-on effect with increased calving of icebergs at outlet glaciers. in 2011, the field team were able to measure both the rain fall and the following cascade of processes in a range of different datasets as shown below:
Rainfall (a,b) over the ice sheet runs off the bare ice quickly as shown by discharge stations on a number of rivers in western Greenland (c). This triggers acceleration across a wide area, shown by GPS stations on the ice sheet at 10 different locations (d). Figure taken from the paper
My contribution to the paper was in the form of some HIRHAM5 model runs for Greenland which show the last decade has seen a significant increase in rainfall events in the summertime compared with the previous decade. We chose as a study region the K-transect of weather stations in western Greenland. These are operated by Utrecht University and have a long time-series of data which previous work has shown our model can replicate quite nicely. The model is forced by the ERA-Interim reanalysis, a data set based on weather forecast models with real observations included in it run for the whole world so we are pretty confident the rainfall patterns are realistic. There are actually two interesting points illustrated in the picture below taken from the paper. Firstly that there is more rain falling and secondly that this rain is falling at higher elevations on the ice sheet, potentially causing a much wider area of the ice sheet to be affected by late-summer rainfall events.
The decadal change in rainfall events is partly due to a persistent North Atlantic Oscillation anomaly which has funnelled storms over the western edge of the ice sheet. There is also some evidence that the stratospheric Rossby waves have become more “wavy” over the same period, due to the increasing warming and vanishing sea ice in the Arctic. This hypothesis was articulated in a very nice paper by Francis and Vavrus but it remains a very open area of research as we just don’t have a lot of evidence right now.
We do know that the Arctic is one of the fastest warming regions on the planet and this will certainly have a knock-on effect on the Greenland ice sheet both in terms of melting and, perhaps, in the frequency of storms bringing rain over the ice sheet in the future. I am now preparing a new study to see if we see a signal along these lines in our future simulations of the Greenland domain.
Rainfall events at a weekly timestep over the K-transect in western Greenland for two different decades and the difference between the two. The second decade has many more rainfall events that reach to a much higher elevation than the first decade.
The official end of the hydrological year in Greenland (1st September to 31st August) means I am rather busy writing reports to give an overview of where the ice sheet is this year and what happened. I will try to write a quick blogpost about this in the next week or so (in case you’re curious here’s a quick plot to show the entire annual SMB, see also: http://polarportal.dk/en/groenlands-indlandsis/nbsp/isens-overflade/)
Daily and accumulated surface mass budget of the Greenland ice sheet, 31st August, 2015Anyway, as I find I am constantly switching between Gigatonnes (or indeed Gigatons), cubic kilometres and sea level equivalent, here is a quick and handy guide to converting different units of mass, for my own use as much as anyone else.
1 gigatonne is 1 billion metric tonnes (or 1 milliard if you like the old British style, that is one thousand million).
However, on the Polar Portal we usually reckon everything in water equivalent. This is to save having to distinguish between snow (with a density between ~100 kg/m3 when freshly fallen and ~350 kg/m3 m when settled after a few days), firn (snow that has survived a full annual cycle with a density up to ~800 kg/m3) and glacier ice (anything from ~850 kg/m3 to 900+). Water has a density (at 4C) of 1000 kg/m3
1 gigatonne of ice will still weigh 1 gigatonne when it is melted but the volume will be lower since ice expands when it freezes.
1 metric tonne of water is 1 cubic metre and 1 billion metric tonnes is 1 km3 (a cubic kilometre of water)
A cubic kilometre of ice does not however weight 1 gigatonne but about 10% less because of the density difference.
100 gigatonnes of water is roughly 0.28mm of sea level rise (on average, note there are big regional differences in how sea level smooths itself out).
Finally, 1 mm sea level rise is 360 Gt of ice (roughly the number of days in a year)
EDIT: – thanks to ice sheet modeler Frank Pattyn and ice core specialist Tas van Ommen on Twitter for pointing out I’d missed this last handy conversion. Interestingly and probably entirely coincidentally this is very close to the amount of mass lost by the Greenland ice sheet reported by Helm et al., 2014 for the the period January 2011 – January 2014 (pdf here) of 375 +/-24 km3 per year.
Over the last 10 years or so, Greenland has lost on average around 250 Gigatonnes of ice a year (Shepherd et al., 2012), contributing a bit less than a millimetre to global sea level every year with some big interannual variability. This year looks like it will be a comparable number but we will have to wait for the GRACE satellite results in a couple of months to fill in the dynamic component of the mass budget and come up with our final number.
It’s been a while since I lasted posted anything, not for want of ideas but mainly lack of time. I shall try to catch up over the next few weeks. For now I was inspired to write an ultra-quick post about a very trivial question that came up at work today. I think it really captures how observational meteorology works (or should work).
Today, a colleague, John Cappelen, (also known as Mr. Greenland observational data), happened to mention in passing that on the 15th July this year, the weather station at Summit on the Greenland ice sheet had transmitted back to us in Copenhagen, a temperature observation of 2.5°C. This was during one of the highest melt periods this summer.
The automatic weather station doing it’s thing at Summit, June 2015. Photo: DMI
Bearing in mind that Summit Camp is at roughly 3,216m, this is a pretty high measured temperature. In fact it would be rather noteworthy, especially as it occurred on one of the highest melt days of the summer. Temperatures above 0°C at Summit are not unknown and the record, during the famous summer of 2012 when around 95% of the ice sheet surface experienced melt, the water sweeping away a bridge on the Watson River near Kangerlussuaq, was 3.6°C.
Now, my colleague is a very experienced and careful scientist. He had checked the observations and the temperatures before and after this measurement were well below zero, so, my colleague asked, was there any reason to believe this measurement or can we assume an instrument failure of some kind?
My office mate in the Arctic and Climate Research section and I obligingly had a quick look at our Polar Portal Greenland ice sheet surface plots (see below) and at the melt extent plots that are updated daily on the DMI website. We had to conclude there was no evidence of melt that high on the ice sheet and there was also no reason to believe that a sudden sharp warming had occurred at Summit on this day based on DMI’s own weather forecast. We then turned to check the weather plots, also on the polar portal and based on data from the European Centre for Medium Range Weather Forecasting (the ECMWF – probably the best weather forecast modellers in the world).
Again, the anomaly plots showed rather cold conditions prevailing over the ice sheet during this period, though at the same time very high melt and low surface mass balance from the ice sheet due to the clear skies.
Graphs showing area of the Greenland ice sheet experiencing melt conditions, compared with the average (dark grey line) and range of past summers (1990-2012), for more detail see the DMI website
Temperature record from Summit Camp for the last month.
Fortunately, due to the American Summit Camp we have access to a back-up dataset very close to this location and after a quick web search John Cappelen was able to confirm that indeed this measurement was an error as the nearby station has not seen anything like that during the period in question (see right).
This kind of thing happens all the time and is therefore not at all newsworthy or interesting enough to write a publication about. However, when a recent record high temperature in the UK can lead to 2 critical articles in the Daily Telegraph and a particularly vigorous exchange on twitter for Met Office scientist Mark McCarthy, as well as this corrective piece on the Carbon Brief blog, perhaps we should be more vocal about just how careful and critical we as scientists are about observations, including the ones we decide to discard as well as the ones we keep.
Surface mass balance of the Greenland ice sheet on the 15th July 2015. Intense melting around the margins led to very negative SMB (the red colours) during this period.
Addendum: I was alerted by this tweet from Gareth Jones, also a Met Office scientist, to some slightly strange cherry picking in the blogosphere of climate records from a couple of DMI stations in Greenland.These have apparently been used to claim no climatic warming trend in Greenland over the 20th Century (I’m not going to link to it).
Anyone who is really interested in the observational data could try checking these reports by Mr Greenland observations himself instead, here is a quick summary:
Mean annual temperature in Copenhagen, Torshavn (Faeroes) and selected DMI weather stations in Greenland from 1873 – 2014. Figure from DMI
The climate of Greenland has been changing over the last 20 or so years, especially in the south. In this paper we showed that the amount of melt and liquid water run off from the ice sheet in the south west has increased at the same time as the equilibrium line (roughly analogous to the snow line at the end of summer on the ice sheet) has started to move up the ice sheet. Unlike previous periods when we infer the same thing happened this can be attributed to warmer summers rather than drier winters.
The area we focus on in this study is in SW Greenland close to Nuuk, the capital. White shows glaciers, blue is sea, brown is land not covered by ice.
We focused on the area close to Nuuk, the capital of Greenland, as we had access to a rather useful but unusual (in Greenland) dataset gathered by Asiaq the Greenland survey. They have been measuring the run off from a lake near the margin of the ice sheet for some years and made this available to us in order to test the model predictions. This kind of measurement is particularly useful as it integrates melt and run-off from a wider area than the usual point measurements. As our model is run at 5.5 km resolution, one grid cell has to approximate all the properties of a 5.5 km grid cell. Imagine your house and how much land varies in type, shape and use in a 5.5 km square centred on your house and you begin to appreciate the problems of using a single point observation to assess what is essentially an area simulation! This is even more difficult in mountainous areas close to the sea, like the fjords of Norway or err, around south west Greenland (see below).
The beautiful fjords near Nuuk. Represent this in a 5.5km grid cell…
The HIRHAM5 model is one of very few regional climate models that are run at sufficiently high resolution to start to clearly see the climate influences of mountains, fjords etc in Greenland, which meant we didn’t need to do additional statistical downscaling to see results that matched quite closely the measured discharge from the lake.
Graph comparing modelled versus measured discharge as a daily mean from Lake Tasersuaq near Nuuk, Greenland. The model output was summed over the Tasersuaq drainage basin and smoothed by averaging over the previous 7 days. This is because the model does not have a meltwater routing scheme so we estimated how long it takes for melt and run-off from the ice sheet to reach this point.
We were pretty happy to see that HIRHAM5 manages to reproduce this record well. There’s tons of other interesting stuff in the paper including a nice comparison of the first decade of the simulation with the last decade of the simulation, showing that the two look quite different with much more melt, and a lower surface mass balance (the amount of snowfall minus the amount of melt and run – off) per year in recent years.
Red shows where more snow and ice melts than falls and blue shows where more snow falls than is melted on average each year.
Now, as we work at DMI, we have access to lots of climate records for Greenland. (Actually everyone does, the data is open access and can be downloaded). This means we can compare the measurements in the nearest location, Nuuk, for a bit more than a century. Statistically we can see the last few years have been particularly warm, maybe even warmer than the well known warm spell in the 1920s – 1940s in Greenland.
Graphs comparing and extending the model simulation back in time with Nuuk observations
There is lots more to be said about this paper, we confirm for example the role of increasing incoming solar radiation (largely a consequence of large scale atmospheric flow leading to clearer skies) and we show some nice results which show how the model is able to reproduce observations at the surface, so I urge you to read it (pdf here) but hopefully this summary has given a decent overview of our model simulations and what we can use them for.
Regional Climate Model Data from HIRHAM5 for Greenland
In this post I am linking to a dataset I have made available for the climate of Greenland. In my day job I run a Regional Climate Model (RCM) over Greenland called HIRHAM5 . I will write a simple post soon to explain what that means in less technical terms but for now I just wanted to post a link to a dataset I have prepared based on output from an earlier simulation.
Mean annual 2m temperature over Greenland at 5km resolution (1989 – 2012) from HIRHAM5 forced by ERA-Interim on the boundaries [Yes I know it’s a rainbow scale. Sorry! it’s an old image – will update soon honest…]
This tar file gives the annual means for selected variables at 0.05degrees (5.5km) resolution over the Greenland/Iceland domain.
I am currently running a newly updated version of the model but the old run gave us pretty reasonable and could be used for lots of different purposes. I am very happy for other scientists to use it as they see fit, though do please acknowledge us, and we especially like co-authorships (we also have to justify our existence to funding agencies and governments!).
This is just a sample dataset we have lots of other variables and they are available at 3 hourly, daily, monthly, annual, decadal timescales so send me an email (rum [at] dmi [dot] dk) if you would like more/a subset/different/help with analysis of data. This one is for the period 1989 – 2012. I have now updated it to cover up to the end of 2014. The new run starts in 1979 and will continue to the present and has a significantly updated surface scheme plus different SST/sea ice forcing and a better ice mask.
I have also done some simulations of future climate change in Greenland at the same high resolution of 5km using the EC-Earth GCM at the boundaries for RCP4.5 and RCP8.5 scenarios which could be fun to play with if you are interested in climate change impacts in Greenland, Iceland and Arctic Canada.
Mean annual 2m temperature change between control period (1990 – 2010) and end of the century (2081 – 2100) under RCP45 from HIRHAM5 climate model runs forced by EC-Earth GCM at the boundaries. This plot shows the full domain I have data for in the simulations.
![Milankovitch cycles shown from ocean cores and an Antarctic ice core at the bottom compared with the theoretical cycles. Image: By Incredio (Own work) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons](https://sternaparadisaea.files.wordpress.com/2015/09/ice_sheet_velocity_rain.png)
Sterna Paradisaea 
![Image: By Incredio (Own work) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons](https://commons.wikimedia.org/wiki/File:MilankovitchCyclesOrbitandCores.png){kind=link}