Sea Level Rise: How far, how fast?

A paper appeared in Science this week about sea level rise in the last interglacial (about 129-116,000 years ago). It has sparked the usual predictable headlines as it points out that during that period, sea level rose by about 6-9 metres but that that the ocean temperature as far as it can be reconstructed, is about what we see now, that is about 0.5C warmer than the preindustrial.

sealevelguardian — Guardian reports on latest study

In a sense this isn’t that “new” – we’ve known about higher sea levels during the last interglacial for ages and that the global mean temperature was roughly 2C above the pre-industrial global mean. This is in fact one of the reasons for the Paris target (though some scientists speculate that it’s also pretty much already out of reach).

However, the sea surface temperature stuff makes it extra interesting as the ocean is a pretty big source of uncertainty in global climate models and mot models do not manage to reproduce modern day ocean temperatures all that well.

It should also be said that the last interglacial is only a good analogue for 2C world up to a point – it was warm because of enhanced solar input, not because of greenhouse gases as this plot from an Antarctic ice core, edited by the awesome Bethan Davies at the Antarctic Glaciers blog shows:

vostok_420ky_4curves_insolation_to_2004 — Carbon dioxide (CO2), Methane (CH4) with reconstructed temperature from the Vostok Ice Core, taken in Eastern Antarctica. Enhanced with modern methane, CO2 and temperature measurements by Bethan Davies. Note that the “modern” value of CO2 here is from 2004. In 2017 it is currently measuring 403 ppm.

It’s also interesting to speculate where the water came from – the Greenland ice sheet was much smaller than today but it was still there and now “only” contains 7m of sea level rise today. So the complete disappearance of Greenland cannot explain the rise in global sea level. The small glaciers and ice caps of the world can’t contribute more than half a metre or so either. Therefore it has to be Antarctica contributing the most – East or West is the question and it really is a very very longstanding question.

The progress in the international polar year (IPY) in mapping the bedrock of Antarctic in the BEDMAP2 brought quite a few surprises, including the discovery of several very deep marine basins in the East that could potentially contribute a lot of water to sea level.

More recently, channels under the floating ice shelves of west Antartica, along with various modelling studies have proposed that the west could be much more unstable than thought. Actually this has been a very very longstanding problem in Antarctic science since at least the late 1970s when John Mercer first proposed the marine ice sheet instability hypothesis.

In any case, events in both Denmark and the UK have brought this problem home more sharply.

stillstormflod — The silent storm surge – coastal flooding in Copenhagen on the 5th January – the water in the harbour is not normally this high! Source: Brian Dehli, shared by DR

The “silent storm surge” in January 2017 around the coast of Denmark was a hundred year event in many places, but as Aslak Grinsted points out, sea level rise makes a hundred year event a 20 year event with only a small rise.

Sea level will not rise equally everywhere, the fingerprint of Greenland ice sheet loss is felt largely in the Pacific, Antarctic ice melt will be felt in Europe. It matters where the water comes from. A point not generally appreciated.

So this new paper is also important, but it only underlines that we need to be able to make much much better estimates of how fast and how far the ice sheets will retreat, which is the justification for much of my own scientific research.

Finally, I think it’s probably necessary to point out that sea level is already rising. This was asked by a listener to Inside science, one of my favourite BBC radio 4 programmes/podcasts. I was a little surprised that an apparently scientifically literate and interested member of the public was not aware that we can measure sea level rise pretty well – in fact to an extent, the global warming signal is more easily detected in the ocean than in the global temperature record. This is because the ocean expands as it warms and there is ocean pretty much everywhere, whereas temperature observations are patchy and mostly on land. Clearly, scientists like myself are *still* not doing a very good job of communicating our science more widely. So here is the global mean sea level record to date, it’s updated pretty regularly here and on average, sea level is rising at about 3mm per year or 3cm per decade.

When we look at tidal gauges,sea level rose about 20cm in the 2oth century

20crsealevel — Sea level rise in the 20th century measured by tide gauges, plot by NASA, data from CSIRO

The big uncertainties we have on whether or not this will accelerate in years to come is largely down to missing processes in ice sheet models that we don’t yet understand or model well – mostly calving by glaciers and ice shelves. I promised Steve Bloom a blog post on that at some point – I have a paper to finish and new simulations to run, but hopefully I’ll get round to that next.

UPDATE: I was made aware this morning of a new report from the European Environment Agency about climate change impacts and adaptation in Europe. In the report they state (correctly) that while the IPCC 5th Assessment Report suggested that in the 21st century the likely sea level rise will be on the order of half a metre, some national and expert assessments (I took part in a couple of these) had suggested an upper bound of 1.5 – 2m this century, for high emissions scenarios.

This is a big difference and would be pretty challenging to adapt to in low-lying countries like the Netherlands and Denmark, not to mention big coastal cities like London or Hamburg. It’s laso important to emphasise that it doesn’t jsut stop at the end of the century, in fact our simulations of the retreat of Greenland ice sheet suggest it’s only just getting going at the end of this century and the next century the rate of ice loss will really start to accelerate.

All of which is to say, there’s really a very good reason to act now to reduce our emissions. The EEA has also produced this very nice map of observed sea level rise in Europe over the last two decades based on Copernicus environmental data.

Check out how much the sea level is rising where you live… Source: European Environment Agency, data from Copernicus Marine Environment Monitoring Service

With the prospect of American federal funding for environmental observations being reduced or strongly constrained in the future, it’s really important we start to identify and support the European datasets which are the only other sources of environmental monitoring out there right now.

The Unicorn and The Lamprey

On the 16th may 1619 two ships, the Unicorn and the Lamprey, set sail from Copenhagen searching for the fabled North West Passage. On board there were 65 men, led by their captain, the Danish explorer Jens Munk. A year and a half later, the Lamprey limped back into Bergen (Norway) with just 3 men, including Munk, on board.

Almost all of the other crew members had died of scurvy in Hudson Bay .

The story of this terrible voyage, their sailing round Iceland, Greenland, Baffin Bay and into Hudson Bay is outlined in this wonderful atmospheric podcast from DR.

jens_munk_map_1624 — A Map, hand-drawn by Jens Munk in 1624 of the area between Cape Farewell and Hudson Bay, seen from the north; (Source: Tromsø University library)

The UK has similarly many tales of Arctic and Antarctic suffering, listening to the podcast I was put in mind of Coleridge’s famous “Rime of the Ancient Mariner”, but we rarely hear of the similar stories from other nations, a clear benefit of learning other languages is being able to access these archives and stories*.

The podcast contains a wonderful description by a Greenland pilot of the sea ice and how tricky navigating it can be along with interviews and inputs from many others. If you are at all familiar with Danish – I really recommend the series.

However, the description by a nutritionist of the terrible effects of scurvy had me wondering. I learn (via Dutch family and confirmed by the OED) that the name of the disease, caused of course by a lack of vitamin C in the diet, is probably from the Dutch Scheurbuik – rip belly – an eloquent description of one of the notable later stages of the disease.

Rip here is less a description of enhanced musculature and much more a description of what it feels like when your internal organs start to bleed and your muscles and bones are weak from lack of nutrition.

asm-30-325-g002 — Photo of chest cage with pectus excavatum and scorbutic rosaries – from this paper

Upon looking it up (Thankyou Wikipedia), I learn that the causes of scurvy had been repeatedly identified, forgotten and mistaken since at least the middle Ages. There is an estimate that around 2 million sailors died as a result of scurvy between 1500 and 1800.

2 Million almost entirely preventable deaths and 2 million men who died in appalling agony.

And this happened in spite of what appears to be the first recorded medical trial by James Lind in the 1750s, it still took the Royal Navy 40 years to start giving out fresh citrus fruits as a standard on their ships. Vitamin C itself was only finally recognised and extracted in 1932.

This story is an outrage in many ways, but a clear example also of how science and medicine, properly conducted, can help to improve and save lives. It is also a clear warning to conduct thoughtful experiments with care and to listen to those warnings when they have been issued.

It might also be a recommendation that learning foreign languages is not only fun and useful but can be it’s own reward.

*I should also mention here that the rather awesome Danish Arctic Institute are currently producing a very well written series on Danish exploration in the Arctic in English, based on their own very comprehensive podcast series. These are published online in the Arctic Journal. Both the series of historical accounts and the newspaper in general are absolute top recommends for those interested in the subject of the Arctic environmentally , socially and politically.

The lure of the poles (Svalbard in Spring, the coldest time of year)

Extract from “Rime of the Ancient Mariner” by Samuel Taylor Coleridge

…With sloping masts and dipping prow,

As who pursued with yell and blow

Still treads the shadow of his foe,

And forward bends his head,

The ship drove fast, loud roared the blast,

And southward aye we fled.

And now there came both mist and snow,

And it grew wondrous cold:

And ice, mast-high, came floating by,

As green as emerald.

And through the drifts the snowy clifts

Did send a dismal sheen:

Nor shapes of men nor beasts we ken—

The ice was all between.

The ice was here, the ice was there,

The ice was all around:

It cracked and growled, and roared and howled,

Like noises in a swound! …”

A Sea-Ice Free Arctic in 2016?

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 current weather plots on the Polar Portal (based on weather forecasts produced by the European Centre for medium Range Weather Forecasting, probably the best numerical weather model in the world) show no unusual temperatures in the Arctic Ocean right now, though parts of Arctic Canada and Siberia certainly look warm.

We’ll have to wait and see until September…

Original post below from June, 14th, 2016.

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.

This is the new reality in the Arctic. And it is also having an effect on sea ice. The Arctic sea ice extent has long been used as a bellwether of climate change with much effort exerted by both activists and sceptics in trying to prove or dismiss claims about climate and its effects on sea ice.

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.

figure_5 — Downloaded from the ARCUS SIPN website

So keep an eye out on this and if you think you can do better, consider submitting a prediction yourself…

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…

How pristine is the Arctic?

“The Arctic is one of the last great pristine ecosystems, a safe haven for endangered species and home to Indigenous Peoples whose lifestyle has survived in harmony with nature for thousands of years.”

This quote in the wake of COP21, extracted from a celebrity I’ve never heard of (sorry, I’m just not that interested in actors) raised my hackles as it repeated yet again the idea that the Arctic is “pristine”.

Even without contemplating climate change, it is most certainly not, as the polar portal season report I was vaguely involved in compiling this year made clear.

The “pristine” wilderness of Von Postbreen, Svalbard

There is a whole literature in the humanities on Orientalism and “othering”, about how we define other people and places partly to define what we are not. I’m not sure if there is a term for this narrative of a “pristine wilderness”, let us call it “pristinism ” for want of a better term. But before I list the ways in which the Arctic is not pristine, let me make very clear, I am well aware I also suffer from pristinism, to some extent. What my boss teasingly refers to as “the white disease”, the fascination with snow and ice that makes me want to leave the comforts of house and home and go and live somewhere deeply uncomfortable, and indeed dangerous in order to plumb the mysteries. I have been visiting the Arctic for well over 12 years now, though as most of my work is on computer, I don’t get the option so often anymore. Maybe that’s a good thing, perhaps the last thing the Arctic needs is more people flying to it.

The ecosystem has been significantly degraded by the loss (hopefully now in reverse) of most of the large cetacean species by commercial whalers. Similarly, walrus and polar bears in Svalbard were almost rendered extinct before hunting was banned. It also appears there were walrus in Iceland when the vikings arrived that, like any polar bear at the present day arriving on Icelandic shores, were quickly dispatched. The Greenland vikings were certainly rich from walrus ivory as their main source of income. Not content with exterminating the walrus the early settlers sent their sheep out and very successfully deforested the 25-40% of Iceland that had been forested, leading to dust storms, soil erosion and the unfortunate inability to build boats to get anywhere else very far away. Deforestation has only recently begun to be reversed. In much the same way Musk Oxen were virtually eliminated from Eastern Greenland by hunting, but then rather too successfully introduced to the west where there has been a population explosion.

Fish stocks have at least been largely preserved in Iceland (sensible given how important fishing is to the economy), but there have been several notorious crashes in different fish species in the North Atlantic and around Greenland. Although, to be fair these latter seem to be at least partly caused by changing ocean temperatures rather than purely overfishing. Then there are the invasive species, largely limited so far to the (admittedly delicious) King crab , an omnivore that will eat everything in it’s path much to the fear of some local ecologists around the Arctic coast of Norway.

And then there are the birds. Different bird species face declining populations due both to loss of habitat outside the Arctic as well as hunting in the Arctic region. I was somewhat surprised, though in retrospect I should not have been, at the very few bird numbers that I saw while on a kayaking trip within an easy boat ride of Nuuk.

I would have seen many more in the Scottish islands, but if a subsistence species is within easy reach of a large town (which in themselves would have been impossible prior to colonisation), it is an inevitable tragedy of the commons waiting to happen. Similarly, seals are incredibly wary and remain as far from people as possible in Greenland, a big contrast to the rather trusting and curious creatures I have been able to paddle very close to around the British Isles. And Heaven help any polar bear that strays too close to any Greenlandic settlements, legal protection or not…

Part of the problem are the difficulties birds have in reproducing. This is at least partly down to the toxic mix of chemicals stored in their fat, which comes out in a rush when these animals and birds have to live on their body fat supplies – as they do each summer when incubating eggs. These eggs also appear to contain high levels of mercury, cadmium, PCBs, organochlorines, dieldrin to mention just a few, with an effect on the developing bird embryos inside and of course anything that eats either bird or eggs.

A report compiled by the WWF in 2006 (pdf) from the peer-reviewed literature lists dozens of such studies like this one. There are also suggestions that environmental pollution is having a significant effect on cetaceans as well as in seal species.

And this of course is because that “pristine” Arctic has an extremely high concentration of industrial chemicals, heavy metals and other by-products of our manufacturing society. Albeit a long way from most sources of production. I was once fascinated to discover that all sorts of historic events such as the Greek and Roman production of silver (and it’s leaden by-product) could be identified in the Greenland ice cores, as could the introduction of leaded petrol and it’s later phasing out. The atmosphere acts as a kind of distillation column, concentrating these poisons at the top (and bottom) of the world, not to mention the local sources. There are coal mines in Svalbard, aluminium smelters in Iceland and Greenland, the oil + gas fields of Alaska, Newfoundland, Norway and Russia. Not to mention god only knows what hazardous (radioactive?) waste is leaching away from forgotten islands in the Russian sector of the Arctic.

Three polar bears take over an abandoned dog shed for a sleep in the shade, Svea coal mine, Svalbard

In the food chain, the little animals get eaten by the bigger ones, which get eaten by the bigger ones, concentrating and accumulating toxic chemicals all the way to the top of the food chain.

To us.

Because humans are, in the Arctic at least, the top predator.

It is by now well known that with a diet that is high in meat, much of it derived from marine mammals and fish, Inuit peoples in the Arctic have very high levels of toxic chemicals in their bodies, and in their breast milk. Greenlandic women are in fact advised to reduce their traditional foods in pregnancy (pdf) and eat something imported instead. Then some recent research suggested the high rates of Parkinson’s disease in the Faroes may be down to a whale meat rich diet.

Yet at the same time we in the crowded, populated mid-latitudes project our fantasies of a pristine fairy-tale at the top of the world.

Sorry.

The Arctic is very very far from pristine, and if what happens in the Arctic doesn’t stay in the Arctic, the reverse is also true, the Arctic is part of this world for good or ill. There is however, no doubt that it exerts a powerful pull on our imaginations.

There is a reason poor old Ursus maritimus has become the poster children of climate change. Perhaps it’s all the bright white snow and ice, even if the Arctic Report card shows us the browning of the Arctic as snow lies for ever shorter periods at the same time as sea ice cover at the end of summer is similarly declining…

From the Arctic report card 2015: "Northern Hemisphere (NH) June snow cover extent and September Arctic sea ice extent. Sea ice extent data for 1979-2014 are derived from the NASA Team algorithm (Cavalieri et al., 1996); ice extent estimates for 2015 are produced from real time data (Maslanik and Stroeve 1999). Bold red and blue lines are 5-year running means of the original snow and sea ice extent records, respectively." — From the Arctic report card 2015: “Northern Hemisphere (NH) June snow cover extent and September Arctic sea ice extent. Sea ice extent data for 1979-2014 are derived from the NASA Team algorithm (Cavalieri et al., 1996); ice extent estimates for 2015 are produced from real time data (Maslanik and Stroeve 1999). Bold red and blue lines are 5-year running means of the original snow and sea ice extent records, respectively.”

I am optimistic but cautious about the Paris agreement at COP21. I hope it will come in time to preserve some remnant of the Arctic wilderness, but even if it does we still have some big challenges to face. Sweeping these under the carpet for the sake of a convenient narrative about a pristine wilderness is not helpful. I have a great affection for the Arctic, the people and the wildlife that lives there. I started this post originally some time ago but failed to finish it as it made me rather depressed to think about, but then I was put in mind of this poem from Seamus Heaney and decided it was worth finishing after all with this piece.

Clearly, the myth of “The North” and “the Arctic” has been with us for some time, but surely we owe it to the Arctic and the peoples who live there to try and see through the “pristinism” and start to fix some of these challenges?

North

BY SEAMUS HEANEY

I returned to a long strand,

the hammered curve of a bay,

and found only the secular

powers of the Atlantic thundering.

I faced the unmagical

invitations of Iceland,

the pathetic colonies

of Greenland, and suddenly

those fabulous raiders,

those lying in Orkney and Dublin

measured against

their long swords rusting,

those in the solid

belly of stone ships,

those hacked and glinting

in the gravel of thawed streams

warning me, lifted again

in violence and epiphany.

The longship’s swimming tongue

was buoyant with hindsight—

it said Thor’s hammer swung

to geography and trade,

thick-witted couplings and revenges,

the hatreds and behind-backs

of the althing, lies and women,

exhaustions nominated peace,

memory incubating the spilled blood.

It said, ‘Lie down

in the word-hoard, burrow

the coil and gleam

of your furrowed brain.

Compose in darkness.

Expect aurora borealis

in the long foray

but no cascade of light.

Keep your eye clear

as the bleb of the icicle,

trust the feel of what nubbed treasure

your hands have known.’

were ocean-deafened voices

A brief introduction to crevasses

As an impressionable seven year old I learnt what a crevasse was; namely a large split in a glacier of great hazard to glacier travellers. This knowledge was imparted by a venture scout in my parents group who, on a climbing trip to the Alps, managed to end up in one, breaking several bones in the process. Years later this did not discourage me from my own forays into alpine mountaineering, so it was probably inevitable that I would have my own brush with mortality in a crevasse while researching them as part of my PhD work (see photo).

Some injuries, 3 days after falling into a crevasse (thankfully to be rescued by quick-thinking field assistants). Not recommended — Some injuries, 3 days after falling into a crevasse (thankfully to be rescued by quick-thinking field assistants).
Not a recommended “experience”.

The research was interesting and made more so by being carried out in such a spectacular environment. Breiðamerkurjökull is a southern outlet glacier of the Vatnajökull ice cap in Iceland. It’s actually one of the more popular tourist destinations in Iceland thanks to the boats that run on the lagoon in front of the glacier, getting people up close and personal with icebergs. The icebergs are one of the reasons we chose to work there, as the rationale of my Phd project was can a crevasse depth relation be used as a parameterisation for calving in ice sheet models?

I was moved to revisit this work recently when a friend (and ace glacier/climate blogger) Liam Colgan posted about crevasse factoids.

Crevasses on Breidamerkurjokull, note figure for scale

Crevasses are extremely beautiful features to observe and they are interesting scientifically since they indicate all sorts of information about what is going on in a glacier. As they are aligned more or less with the principal stresses in a particular location we can see where a glacier is accelerating or decelerating, that is stretching or compressing respectively, based on the shape and alignment. They can also be used as a feature to track glacier velocity between two successive images taken from aircraft or satellites. Crevasses are also significant in other ways, since they are a plane of weakness that can be exploited by meltwater, channelling it away from the surface of the glacier to the bed changing the velocity of the glacier. And as proved in the case of my Phd work, when they extend deep enough in the right place, they cause large chunks of ice, namely icebergs, to fall off the front of glaciers.

Given all these interesting habits it is probably surprising to learn that the large computer models of ice sheets and glaciers don’t usually include crevasses in them, though there are some more recent honourable exceptions, mostly working with single outlets or small glaciers such as Sue Cook’s work with the Elmer model. This is because an individual crevasse is not only too small for the resolution of a model, it’s also a discontinuity, and the approximations of the physics of ice sheets do not easily allow discontinuities. To put it another way, when we model glaciers we usually assume they are really large and thick fluid bodies, and as everyone knows, fluids don’t crack. This is just another bizarre property of water, and if I get chance I’ll discuss that again in further detail in another entry. But back to crevasses.

Now I mostly work with a climate model, HIRHAM5, using it to calculate surface mass balance, that is accumulation of snow and the melt and run-off from the surface of glaciers and ice sheet. However, I am finally (loosely) involved in a project that sets out to finish in some way the work I started as a young PhD student.

At DMI we run the PISM ice sheet model, fully coupled with a global climate model EC-Earth as I wrote about in this post. We will also soon be running HIRHAM5 coupled to PISM in order to study feedbacks between ice sheet dynamics and surface climate forcing (mainly in terms of how topography and elevation of the ice sheet affects the surface mass balance). We also intend to participate in the ISMIP6 model comparison project which will compare the results of several different global climate models that also include ice sheets in a realistic fashion.

One of the key challenges in getting these running is how to deal with the ocean interface with the ice sheet, both in terms of submarine melt of outlet glaciers (likely a far more important process than earlier recognised) and in terms of calving icebergs. One of our main (and in my opinion most interesting) projects right now, ice2ice has allowed us to employ a PhD student to work on this specific issue. She will be using a similar idea to Faezeh Nick’s model of outlet glacier calving, which in turn was based on a long ago work (pdf) I was part of as a lowly PhD student.

By comparing the measured crevasse depths with numerical models I was able to show that simple models can be used as approximations of crevasse depth. That study is still one of the very very few where actual empirical measurements of crevasse depth, strain rate, spacing and other variables were made and compared with model output.

In my current incarnation as modeller I will be keeping very carefully away from all sharp fractures in the ice and concentrating instead on the model part. Expect updates here…

Changes in SW Greenland ice sheet melt

A paper my colleague Peter Langen wrote together with myself and various other collaborators and colleagues has just come out in the Journal of Climate. I notice that the Climate Lab Book regularly present summaries of their papers so here I try to give a quick overview of ours. The model output used in this run is available now for download.

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.

Map showing area around Nuuk — 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).

Represent this in a 5.5km grid cell, include glacier, sea and mountain... Godthåbsfjord near Nuuk in August — 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 fromt he ice sheet to reach this point. — 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.

I may get to the future projections next time…

The Present Day and Future Climate of Greenland

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 (1989 - 2012) from HIRHAM5 forced by ERA-Interim on the boundaries — 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 — 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.

This run should be referenced with this paper:

Quantifying energy and mass fluxes controlling Godthåbsfjord freshwater input in a 5 km simulation (1991-2012), Langen, P. L., Mottram, R. H., Christensen, J. H., Boberg, F., Rodehacke, C. B., Stendel, M., van As, D., Ahlstrøm, A. P., Mortensen, J., Rysgaard, S., Petersen, D., Svendsen, K. H., Aðalgeirsdóttir, G.,Cappelen, J., Journal of Climate (2015)

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00271.1

PDF here

Finally I should acknowledge that this work has been funded by a lot of different projects:

Climate and ice sheet modelling at DMI

I was very honoured to be asked to give a short talk last week to some students at the Danish Technical University. The subject was ice sheet modelling and climate at DMI where I work in the Research department, climate and Arctic section.
I thought this could be interesting for others to look at too, so I have uploaded the powerpoint presentation on my academia.edu page.

In the presentation I try to explain why we are interested in climate and ice sheets and then give a brief overview of our model systems and the projects we are currently working on. We are mainly interested in the Greenland ice sheet from the perspective of sea level rise. If we are to climate change we need to know how fast and how much of Greenland will melt and how this will change local and regional sea level. There are also studies showing that increased run-off from the ice sheet may change ocean circulation patterns and sea ice. There is lots more stuff to look at so feel free to download it.

I end up with a very brief overview of our biggest project at the moment, ice2ice. This is a large ERC funded project with the Niels Bohr Institute and partners in Bergen at the Bjerknes Climate Research Centre. I may write a brief post on ice2ice soon if I get chance. It’s a really interesting piece of work being focused on past glacial-interglacial climate change rather than present day or the future and I think we have potential to do some great science with it.

At the risk of seeming like I’m blowing the DMI trumpet (something rarely done or even really seen as socially acceptable in Denmark!), I think we at DMI have a lot to be proud of. We are a small group from a small country with limited resources but my colleagues have pioneered high resolution regional climate modelling of the Greenland ice sheet and the development of coupled climate and ice sheet models at both regional and global scales. I was brought in as a glaciologist to work on the interface between ice sheet and atmosphere, needless to say I have learnt a hell of lot here. It’s been an exhilarating few years.

If you have any questions, I will enable comments for this thread (but with moderation so it may take a while for you to see it).

Finally, here is a little movie of calving icebergs

shot by Jason Amundson, University of Alaska Fairbanks at Jakobshavn Isbrae in West Greenland.

A Svalbard Field Journal, part 1.

This is a piece about field work I did in Svalbard in 2010. I’m not sure it really belongs here, but I hope it is interesting to read about what Arctic fieldwork is really like. I have been tremendously lucky to have had several opportunities to work in the Arctic, but as I hope this makes clear, it’s quite often a big slog with uncertain outcomes.

The sun rises early in March in Svalbard but it is not yet hitting the town, we are before the Solfest in Longyearbyen, and I am lying in bed alternately wishing I could sleep longer and being hugely excited at the prospect of getting out in the field again. With the light comes the cold, it is -26C outside with a fresh wind and some light snow falling, not brilliant weather for fieldwork. I am 12 weeks pregnant and the nausea comes early and remains all day but I hope the cold dry air on the glacier will help. In spite of that, I know my fieldwork opportunities will likely significantly reduce when the baby arrives so I’m determined to do one last big trip.

Down at UNIS (the university centre on Svalbard), our boxes are already packed with equipment, we just need to get them on the sledges, pick up our snowscooters and go. This is prime fieldwork and study time and the logistics centre is bustling with students, excited to be out on their first trip, and the long-termers getting ready to set up experiments. I’ve already got my scooter gear sorted out, huge padded suit, enormous padded boots, crash helmet, thin woollen undergloves, leather gauntlets, neoprene face mask. It feels a bit ridiculous inside but I know I’ll need it later on the scooter and the glacier.

Packing a sledge is an artform, one which, over the course of the week, I will gradually start to master, but for now I’m pretty useless and just try and hold stuff when asked and keep out the way while my colleague C gets on with showing me how it’s done.

Finally, we’re off, later, as usual, than we’d wanted, but all the kit is with us and we’re making good time. Our route intially lies up Adventdalen (named for the old whaler Adventure which explored this area). In summer this is a more-or less impassable morass of braided streams, gravel, mud and silt, glacially scoured rocks brought down by an ever shifting river. When the cold comes, and the river and the soil freeze, and then the snow falls, this is the main highway out of town.

We follow a long straight line of multiple overlaid scooter trails; riding a scooter is like riding a motorbike, fast, loud and exciting. I get up to 80km/h on the straight, in spite of towing a trailer, and wonder vaguely if the foetus can feel the vibrations. I thank UNIS silently for having such good kit, the heated handlebars of the scooter are essential, and in spite of the boots my feet are already getting chilly, I remember to wiggle my toes to keep them warm and, as we peel away from the main trails and slowly motor up ever narrower valleys and gullies, I lift my goggles momentarily to allow the frozen condensation on the inside to clear.

We are heading to Tellbreen (breen meaning the glacier in Norwegian, the “tell” in question being, I suspect, William Tell), a small and rather unimportant glacier about an hour and a half from Longyearbyen. A number of small and unrelated projects are going on there this year and there is a weather station lower down that we will be using. We will be working very high up on the glacier near the col at the top where the glacier divides in two. It falls fairly steeply down from this point and I struggle to get the scooter with the trailer up. I realise too late I haven’t given it enough power and there is a slow inevitable deceleration as the scooter digs itself into the soft snow. Fresh soft snow on a slope is the hardest for a scooter to deal with and I have just made the classic mistake. I determine not to make it worse and wait for my colleague C to return with the spade. You don’t drive anywhere in Svalbard without a spade. It’s not a bad dig-in and within half an hour we’re finally at the top of the glacier.

C and a student came out in late Autumn and put two tarpaulins on the glacier surface. These will be the baselines for our experiments. Their positions marked with 2m long bamboo canes. Very little of the canes are showing through the snow and it takes us a while to locate them. The wind is getting fresher and blowing snow through the pass, we are in an incredibly exposed position and I am even more thankful for UNIS equipment. Our first task is to dig a work trench. This will give us protection from the wind but will also be where we stick our temperature sensors into the snow. We will be placing two large water canisters in the snow pack and letting the water, with a dye added, drip through the snow and refreeze. At the second site the canister will be directly on the glacier surface. The temperature sensors will record the effect the water has on the snow temperature at different depths. At the end of the experiments we will dig through the snow to find the ice, record how far it has run and how thick it is. The dye will tell us on which day the water ran through.

It sounds like a simple and very esoteric set of experiments, but it is actually intended to help us shed light on a very difficult problem. Most of the glaciers in the Arctic melt, at least partly, in summer, but the water does not run off, it refreezes in the snow or on the surface of the glacier, forming superimposed ice. It is almost impossible to distinguish superimposed ice from normal glacier ice remotely so while we can measure melt directly by satellite, we have little idea how much of it remains on the glacier and how much is lost to the ocean. The GRACE and GOCE missions give us another way to measure mass loss over large regions but for climate models like the one I run in Denmark, where we make future projections of glaciated regions, we still need to factor this in. The work C and I are engaged in is aimed at developing an approximation we can put into the model to take this into account. In Antarctica the problem doesn’t occur as most of the glaciers there don’t melt.

We have brought a snow blower with us to plough the snow away and it is making short work of the trench, there is still a lot of digging to do though, and I reflect that whenever I am in the Arctic I seem to find myself doing a lot of digging either for latrine pits, to examine glacier sediments or to clear snow. At the Greenland ice core sites high up on the ice sheet, famously the first thing you’re given when you arrive is a spade.

I try and cut some blocks of snow to use as a wall against the wind but the snow is too soft and my efforts are only partly successful. Thankfully though, C had thought to bring some wide boards and we use these to cover the trench so we can work sheltered from the howling wind. It has taken us almost all day to dig the trench and the hole for the first water canister. Now it’s starting to get dark and we really need to leave before driving down the glacier gets too hazardous. We hurriedly stick the sensors in the snow pack, I’ll have to measure the spacings accurately tomorrow, fill the canister with dye and warm(ish) water and open the tap to a dripping position. As the wind gets even stronger we cover over the trench as far as we can, gather our stuff, shouting at each other to be heard over the wind and get out of there.

By the time we’re off the glacier it’s almost completely dark and I am grateful for the strong headlights on the scooter, even so it’s a much slower trip back as we carefully try to avoid the rocks and hard ice chunks that litter the track. I am exhausted with the work and the fatigue of early pregnancy, but high as a kite with the successful completion of the work we’ve managed today – I wasn’t sure we’d manage as much as we did. Tomorrow we do the second experiment, but for now it’s time for a beer (for C) and an orange juice a big plate of chips and a hamburger in the pub for me. I had barely managed to eat anything all day, it’s too cold and I simply wasn’t hungry enough to attempt it. I am extremely thirsty, the work was physical and sweaty, but in the cold you don’t feel the thirst, and I always forget to drink.

I fall into bed at 10pm, ready to do it all over again tomorrow.

To be continued….

The life expectancy of the glaciologist

Willi Dansgaard died recently. He gave his name to one half of the Dansgaard-Oeschger events, a sequence of rapid (relatively speaking) climate fluctuations that occurred during the last glacial period where rapid warming (of up to 8C over a matter of a few decades) is followed by a long slow cooling over a few hundreds of years. These events are mostly known from the Greenland ice cores, but there is evidence that they are in fact a worldwide phenomenon.

Willi Dansgaard with ice core (taken from the obituary published by DMI)

Willi Dansgaard will probably be mostly celebrated as the “founder” of ice core science, though of course many people helped to develop the ideas and techniques, some of them are still working in Copenhagen today. Remarkably for a scientist you’ve probably never heard of, a full obituary is given in the LA Times

In the last year or two several eminent glaciologists have passed away, almost all of them well into their 80s and 90s, while some of the founders of the modern discipline, including John Nye and John Glen (who together formulated “Glen’s Flow Law” for ice that describes how glaciers move), are still active in attending meetings and producing papers.

For a profession that specialises in the study of cold, dangerous places (more on my own encounter with mortality on a glacier in a later post) glaciologists seem in general to reach a respectable, and healthy old age. I wonder if this is due to the fact that science teaches a healthy inquisitive attitude to life that keeps people young? Or perhaps those attracted to field based research are naturally likely to be more interested in outdoor activities that help keeping active and fit? On the other hand perhaps it just reflects the fact that people are living longer and healthier lives in general?

Either way, I hope I manage to have as long a productive and healthy life as some of the guiding lights of my profession, even if I can’t hope to replicate their genius.

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