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.

 

 

 

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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
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.

Let it snow…

I have found myself shovelling a lot of snow this winter. As with last winter, it has been cold and snowy across northern Europe so far, which has led to the usual questioning of climate change by the usual suspects. There is some very good work examining this on the real climate blog and Marcus Brigstocke did his usual amusing best on the Now Show towards the end of last year, so I’m not going to write about the difference between weather and climate, or about how regional and global average temperatures differ. Rather, the time spent shovelling snow and wandering around the city streets camera in hand to take photos, really brought home how many of the snow processes that are subjects of active research in remote or mountainous areas are currently on display in our cities.

For instance, today in the local park I noticed that there is preferential melt occurring around the trees. The dark tree trunks absorb and emit more radiation that then melts snow around the trees faster than it melts in the open areas of the lawn. This is an important consideration in the planting of forests in snowy areas, since the presence of vast forests can significantly alter the albedo of the earth’s surface, that is how much radiation is reflected back in to space. Planting trees in the tundra to combat climate change may have the unintended effect of actually enhancing warming through changes of this kind.

Picture of glacier table - a boulder balanced on a thin stack of ice
Glacier table in Switzerland (Glaciers Online)

The process can also be seen to spectacular effect on glaciers, where rocks and boulders shield the ice below them from melting but enhance it around them, leading to the formation of so-called glacier tables, such as this one in Switzerland (from glaciers online).

More seriously, the heavy snow on rooves around the city is currently posing an avalanche hazard rarely encountered outside the mountains. The effect of sunshine on heavy snow, which is resting on a slope of a critical angle, can be extremely dangerous to the unwary. As are the large numbers of icicles which have developed. These are not just a sign of poorly insulated buildings (where the heat leaking out has caused the snow to melt and then quickly refreeze in the low temperatures we’ve had). Icicles falling from buildings show the same mechanics as seracs falling from the steep parts of glaciers known as ice falls. In this case, the ice builds up to such a degree that the sheer weight of it eventually causes fracture when a critical threshold is reached. Pedestrians are learning to walk on the outside of pavements and to look up frequently at the overhanging cornices of snow and ice.

But back to the snow shovelling. I have not done so much digging since fieldwork last winter in Svalbard, where we set up some experiments to study the properties of snow and how this affects the melt, or conversely the growth, of glaciers. Specifically, we were studying the effects of liquid water from snow melt or rain on the snow pack and the glacier surface. Liquid water filters into the snow, or else runs off bare glacier ice if there is no snow and will typically freeze, forming ice lenses in the snow pack, or large areas of what is known as superimposed ice on the glacier surface.   As you can imagine, there was a lot of snow shovelling, especially as the high winds on the glacier kept filling in the trenches we dug to work in.

Now this probably sounds like a fairly esoteric set of experiments, but the purpose is actually quite serious, since we need to know how much melt water refreezes to work out how much the glaciers and large ice sheets of the world are melting and how sea level rise is likely to progress in the future in a warming world.

Identifying the melt area of a glacier or ice sheet is a relatively straightforward task using satellite imagery, but identifying how much of that melt runs off or refreezes is impossible at present, so we generally use a model, based on observations and experiments like these, to make an approximation. We also need to factor in the effect of latent heat, (heat that is released when liquid water becomes solid ice) since this can warm up the snow pack significantly. In Greenland for instance, it is likely that the effects of higher temperatures over the last 20 years or so have been buffered somewhat by the snow pack and refreezing processes. However, as temperatures continue to increase, melt will probably accelerate partly because the saturated snow pack cannot absorb additional melt water but also because it has a higher temperature from the release of latent heat and thus requires less additional energy to melt.

Last winter I tested out some of the techniques we used in Svalbard, in a pile of snow in my back garden. I am also aware of at least one study into permafrost, where patterned ground usually found in Arctic climates was created in a back garden in St Andrews, so it’s even possible to do valid experimental work during the winter time when conditions are right. However, the climate of glaciated regions is generally unlike that of the cities of Europe so there will still be a need to go to places like Svalbard to do experiments quantifying these kind of processes. Nevertheless, I still find this kind of weather inspiring and I’m hoping to get more insights as the winter progresses.