I’ve explained several times in the course of media comments that, when it comes to the sea level rise that you experience, it really matters where the water comes from. This point still seems to cause confusion so I’ve written a super fast post on it.
Waves from the Storm Surge that hit Denmark in October 2023 credit: Sebastian Pelt
We very often talk about a metre or two of sea level rise by the end of the century, but in general that refers to global average sea level. And much like a global mean temperature rise doesn’t tell you very much about the kind of temperature changes you will experience in your location due to weather or climate, global mean sea level is also not very informative when talking about preparing your local community for sea level rise. There are other local factors that are important, (see below), but here I’m going to mostly focus on gravity.
Imagine that sea level is more or less stable around the earth (which it was, more or less, before the start of the twentieth century). Just like the moon causes tides because its gravity exerts a pull on the oceans, the ice sheets are large masses and their gravity also attracts ocean water, so the average sea level is higher closer to Greenland and to Antarctica. But there is only a finite volume of water in the oceans, so a higher sea level close to the ice sheets means lower sea levels further away in the tropics for example.
As the ice sheet melts and gets smaller, its gravitational pull becomes smaller so the average height of the sea around Greenland and Antarctica is lower than it was before, but the water gets redistributed around the earth until it is in equilibrium with the gravitational pull of the ice sheets again. The sea level in other places is therefore much higher than it would have been without that gravitational effect.
And in general, the further away from an ice mass you are, the more these gravitational processes affect your local sea level change. In Northern Europe, it often surprises people (also here in Denmark) to learn that while Greenland has a small influence on our local sea level, it’s not very much because we live relatively close to it, however the loss of ice from Antarctica is much more important in affecting our local sea level rise.
Currently, most of the ice contributing to sea level is from the small glaciers around the world, and here too there is an effect. The melt of Alaska and the Andes are more important to our sea level than the Alps or Norwegian glaciers because we are far from the American glaciers but close to the European ones.
This figure below illustrates the processes:
Processes important for local sea level include changes in land height as ice melts but also the redistribution of water as the gravitational attraction of the ice sheets is reduced. The schematic representation is from the Arctic assessment SWIPA report Figure 9.1 from SWIPA 2017
This is partly why the EU funded PROTECT project on cryosphere contributions to sea level rise, which I am currently working on, has an emphasis on the science to policymakers pipeline. We describe the whole project in this Frontiers paper, which includes a graphic explaining what affects your local sea level.
As you can see, it very much depends on what time and spatial scale you’re looking at, with the two ice sheets affecting sea level on the longest time scales.
Figure 1 from Durand et al., 2021 Illustration of the processes that contribute to sea level change with respect to their temporal and spatial scales. These cover local and short term effects like storm surges, waves and tides to global and long-term changes due to the melting of ice sheets.
In the course of the project some of the partners have produced this excellent policy briefing, which should really be compulsory for anyone interested in coastal developments over the next decades to centuries. The most important points are worth highlighting here:
We expect that 2m of global mean sea level rise is more or less baked in, it will be very difficult to avoid this, even with dramatic reductions in greenhouse gas emissions. But the timescale, as in when that figure will be reached, could be anything from the next hundred years to the next thousand.
Figure from PROTECT policy briefing showing how the time when average global sea level reaches 2m is strongly dependend on emissions pathway – but also that different parts of the world will reach 2m of sea level rise at very different times, with the tropics and low latitudes in general getting there first.
What the map shows is that the timing at which any individual place on earth reaches 2 m is strongly dependent on where on earth it is. In general lower latitudes close to the equator will get to 2m before higher latitudes, and while there are ocean circulation and other processes that are important here – to a large extent your local sea level is controlled by how close to the ice sheets you are and how quickly those ice sheets will lose their ice.
There are other processes that are important – especially locally, including how much the land you are on is rising or sinking, as well as changes in ocean and atmosphere circulation. I may write about these a bit more later.
Feel free to comment or ask questions in the comments below or you can catch me on mastodon:
Hands-up who is looking for a new and very cool job in ice sheet and climate modelling and developing new machine learning tools?
REMINDER: 4 days left to apply for this PhD position with me at DMI looking at Antarctic Ice Sheet mass budget processes and developing new Machine Learning models and processes.
UPDATE 2: The PhD position on Antarctica is now live here. Deadline for Applications 18th February!
UPDATE: It’s not technically a PRECISE job, but if you’re a student in Copenhagen and are looking for a part-time study job (Note that this is a specific limited hours job-type for students in higher education in Dnmark) , DMI have got 2 positions open right now, at least one of which will be dedicated to very related work – namely working out how well climate and ice sheet models work when compared with satellite data. It’s part of a European Space Agency funded project that I and my ace colleague Shuting Yang, PI on the new TipESM project, are running. Apply. Apply. Apply…
This is a quick post to announce that our recruitment drive is now open. We’re split across three institutes. We are two in Copenhagen, ourselves at DMI and the Niels Bohr Institute at the University of Copenhagen, and then the University of Northumbria in Newcastle, UK.
The PI at the Niels Bohr Institute is the supremely talented Professor Christine Hvidberg, aided by material scientist and head of the institute, Joachim Mathiesen. I am leading for DMI, and the Northumbria work is led by Professor Hilmar Gudmundsson. We are also very fortunate to have the talents of Aslak Grindsted, Helle Schmidt, Nicolas Rathmann and Nicolaj Hansen already on board.
The project is already very cohesive between institutes, we’ve been working together for some time already and know each other well.
We have a good budget for travel and exchanges between groups, workshops, symposia, summer schools and the like, but perhaps more importantly, all the positions are focused at the very cutting edge (apologies for the cliche) of climate and ice sheet modelling. We are developing not just existing models and new ways to parameterise physical processes, but we also want to focus on machine learning to incorporate new processes, speed-up the production of projections for sea level rise, not forgetting an active interface with the primary stakeholders who will need to use the outcomes of the project to prepare society for the coming changes.
There’s also a healthy fieldwork component (particularly in Greenland, I don’t rule out Antarctica either), and if you’re that way inclined, some ice core isotope work too. So, if you’re looking for a new direction, feel free to give me a shout. I’m happy to talk further.
Links to all the openings, will be updated as they come out, these are currently open and have deadlines at the end of January:
Yesterday, I attended a mini conference on power to X and the potential to generate green synthetic fuels in Greenland.
Power to X became a big thing in Denmark a few years ago and the government is keen to promote it. Danish company Topsoe are currently building a green fuel facility in Herning and they have a nice explainer on their website of the concept.
In Greenland the fuels could be anything from hydrogen to methanol (though I learnt methanol is least likely as it requires a CO2 source that Greenland doesn’t have, ammonia seems the most plausible initially).
It was an interesting meeting, lots of different companies, institutions and the Greenlandic MP Aaja Chemnitz as well as academics were in the room. The emphasis was very much on the social and economic aspects of power to X, but as the title implied: Greenland has the potential to be the “world’s largest energy island.” From a local point of view, Greenland has very high per capita emissions and is heavily dependent on energy imports for transport, though a majority of electricity, at least in the south west, is already hydropower.
Many other smaller and more remote communities however are dependent on diesel generators for heating and power as well as for shipping, fishing and flying between communities.* Transitioning away from these fuels will be challenging but the potential for much larger developments is clear.
Head of development at NunaGreen (the recently rebranded and reoriented NunaOil), Rasmus Wendt, emphasised just how cheap and in theory at least, abundant, Greenland hydropower is. Probably some of the cheapest electricity in the world is generated by Greenlandic dams already operating or planned. And indeed the potential is massive. As the ice sheet melts, enormous amounts of water are produced more or less endlessly in Greenland. It will take at least a thousand years to melt the whole ice sheet, even under a high emissions scenario. We’re not going to run out of water soon.
Figure 2 from Aschwanden et al., 2019. Observed 2008 state and simulations of the Greenland Ice Sheet at year 3000. (A) Observed 2008 ice extent (53). (B to D) Likelihood (percentiles) of ice cover as percentage of the ensemble simulations with nonzero ice thickness. Likelihoods less than the 16th percentile are masked. (E) Multiyear composite of observed surface speeds (61). (F to H) Surface speeds from the control simulation. Basin names shown in (A) in clockwise order are southwest (SW), central-west (CW), northwest (NW), north (NO), northeast (NE), and southeast (SE). RCP 2.6 (B and F), RCP 4.5 (C and G), and RCP 8.5 (D and H). Topography in meters above sea level (m a.s.l.) [(A) to (H)].
Wind energy too is extremely underdeveloped but potentially huge in Greenland. The problem is of course, all that potential energy is a long way from the end users as this screenshot from the global wind atlas, shared by energy scenario planner Brian Vad Mathiessen shows well.
Screenshot from the global wind atlas showing wind energy potential in Greenland and the north Atlantic margin of Europe
By sheer coincidence, this morning I stumbled over this article in the Dutch newspaper NRC on mastodon about the large green hydrogen facility currently under construction by Shell in Rotterdam.
It’s a really interesting read – (if you don’t speak Dutch try DeepL translation) and I was struck by many of the same issues being raised there as in the Greenland meeting: lack of trained staff, uncertain commercial environment, cost and competitiveness with other energy sources. Unlike in Greenland, energy in the Netherlands for producing synthetic fuels is scarce, but the market for using the energy is huge and nearby, and given the EU’s ambitions to produce and, crucially, import large amounts of hydrogen fuel by 2030, it seems like many of the important stars are aligning. Importing ammonia to Rotterdam for cracking back into hydrogen seems like it could actually be a viable future for Greenlandic generated fuels in Greenland he medium to long term.
We at DMI are shortly starting a project within the National Centre for Climate Research framework looking at exactly the potential to generate renewable energy from a climate and weather angle. But what I took away from yesterday’s meeting is that while the physical potential in Greenland really is HUGE, the regulatory environment – and probably the local population – is supportive, the economic certainty is not quite there yet.
It felt a bit like being in a bunch of young seabirds clustered on the edge of the cliff, none quite daring to take the flight, in spite of the undoubted rewards. And indeed, this seems the situation in the Netherlands too. I was especially struck by this quote in the NRC piece:
“Another problem is that many parties are just waiting for each other to take the first step so that they themselves dare to go. Producers, for instance, invest only sparingly because they are not sure whether there will soon be customers, and customers in turn hesitate because they are not sure whether the producers will deliver. The classic chicken-and-egg story.” (Translated with DeepL)
Chris Hensen, NRC, 17thnMay 2023 “De Europese waterstofambities zijn groot, maar bedrijven zijn nog altijd afwachtend”
Perhaps the diving in of Shell, a company that can afford to risk investing a billion Euros in a new facility in Rotterdam, is what the development of Power to X needs?
BP, Air liquide and Uniper already have plans to build follow on plants in Rotterdam. Once one of the birds have taken flight, others will surely follow.
Thanks to Aalborg University,and especially my Danish Arctic Research Forum colleague Carina Ren for an interesting and inspiring meeting.
*(As an aside, I was reflecting while on fieldwork just how difficult removing fossil fuels from scientific work in Greenland will be. We rely on petrol generators to power equipment and oil stoves to warm tents. What if we could develop an easy to operate “tabletop” (or even just room sized) electrolysis system to generate clean fuels from e.g. wind energy, that we could burn instead of paraffin and/petrol? I’d invest in that and it would be a quick win for Greenland science.)
Inside of the tent during fieldwork, note the primus stove, running on petrol, for melting ice for water and food and the paraffin powered oven to keep the inside warm and dry while camping.
In the before times I would usually spend this week walking around a world class city humming an old 80’s hit (- don’t ask me why it was so durable in my head, probably something to do with being an impressionable age at a time when access to pop music meant half an hour on a Thursday evening).
Anyway, it is the time for EGU… Sadly I will not be wandering the streets of the ever beautiful (and most livable) capital of Austria this year. I have to get some actual work done, but I’m following the #EGU23 on mastodon and hoping to catch a few highlights on the sides. I do have a poster, which will be capably presented by PolarRES PI Priscilla Mooney and my DMI Colleague Abraham Torres on Thursday.
The topic is our PolarRES project – an ambitious Horizon 2020 effort to produce a large ensemble of regional climate simulations over both poles. These are state-of-the-art regional climate models run at unprecedented high spatial resolution and all data will be made open access and free via the CORDEX project.
I will also put it here later – feel free to comment here or ask questions on mastodon or get in touch by email if it sounds exciting.
Other posters and talks I’ve contributed to from PolarRES are
Kristiina Verro’s talk on HCLIM_Arome results from the Antarctic peninsula:
Verro, K., van de Berg, W. J., Orr, A., Landgren, O., and van Ulft, B.: New non-hydrostatic polar regional climate model HCLIM-AROME: analysis of the föhn event on 27 January 2011 over the Larsen C Ice Shelf, Antarctic Peninsula, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13864, https://doi.org/10.5194/egusphere-egu23-13864, 2023.
Abraham Torres joined our group last year and is primarily working on PolarRES also. He will show some of our preliminary HCLIM results for both the Arctic and the Antarctic
Torres-Alavez, A., Landgren, O., Boberg, F., Christensen, O. B., Mottram, R., Olesen, M., Van Ulft, B., Verro, K., and Batrak, Y.: Assessing Performance of a new High Resolution polar regional climate model with remote sensing and in-situ observations: HCLIM in the Arctic and Antarctica, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14090, https://doi.org/10.5194/egusphere-egu23-14090, 2023
Quentin Glaude is a collaborator from Liege in the Horizon 2020 PROTECT project on sea level rise contributions from the cryosphere . Baptiste Vandecrux, a former PhD student with me here and now working at GEUS is also presenting some work based on the same models as Quentin, with a comparison to the PROMICE observation statons on the Greealnd ice sheet. It’s very cool application of machine learning and the results are very interesting.
Glaude, Q., Noel, B., Olesen, M., Boberg, F., van den Broeke, M., Mottram, R., and Fettweis, X.: The Divergent Futures of Greenland Surface Mass Balance Estimates from Different Regional Climate Models, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7920, https://doi.org/10.5194/egusphere-egu23-7920, 2023
Vandecrux, B., Fausto, R. S., Box, J. E., Covi, F., Hock, R., Rennermalm, A., Heilig, A., Abermann, J., Van As, D., Løkkegaard, A., Fettweis, X., Smeets, P. C. J. P., Kuipers Munneke, P., Van Den Broeke, M., Brils, M., Langen, P. L., Mottram, R., and Ahlstrøm, A. P.: Historical snow and ice temperature compilation documents the recent warming of the Greenland ice sheet, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9080, https://doi.org/10.5194/egusphere-egu23-9080, 2023.
Nicolaj Hansen (who finished his PhD with me and Sebastian Simonsen at DTU Space last year) has just submitted a beauty of a paper which he will talk about – also partof PROTECT.
Hansen, N., Sørensen, L. S., Spada, G., Melini, D., Forsberg, R., Mottram, R., and Simonsen, S. B.: ICESat-2 Ice Sheet Mass balance: Going below the surface, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12349, https://doi.org/10.5194/egusphere-egu23-12349, 2023
Mathias Larsen is a current Phd student with me and is presenting a poster on the CARRA dataset and an application in surface mass balance modelling. This work falls under the danish National center for klima forskning
Larsen, M., H. Mottram, R., and L. Langen, P.: CARRA-driven simulation of Greenland Ice Sheet surface mass balance at 2.5 km resolution, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-5852, https://doi.org/10.5194/egusphere-egu23-5852, 2023
Last year I co-organised a bootcamp for early career researchers on Arctic processes in the CMIP6 models. It was super fun and would not have been possible without the support offered by Anne Fouilloux, Tina Odaka and colleagues from the Pangeo project. Their poster is super interesting and if you’re interested in optimising the use of big climate data, go and check it out!
Fouilloux, A., Marasco, P. L., Odaka, T., Mottram, R., Zieger, P., Schulz, M., Coca-Castro, A., Iaquinta, J., and Eynard Bontemps, G.: Pangeo framework for training: experience with FOSS4G, the CLIVAR bootcamp and the eScience course, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-8756, https://doi.org/10.5194/egusphere-egu23-8756, 2023.
Excitingly, at least 3 of the projects at the bootcamp will also be presented at EGU this year. So, lots to be getting on with, for now, here’s a link to Ultravox’s finest…
Back in Denmark after 2 weeks in Greenland. Always a bit strange to come back, not just that transition from Arctic cold to European Spring but the sheer abundance of the fertile mid-latitudes, colours, plants, trees, the sheer number of people.
Not to mention that expedition frame of mind, where you are really focused on accomplishing a given set of often quite complex tasks (almost) without distraction. It is the ultimate deep work task, and naturally readjusting to family life, not to mention the tsunami of work tasks left on hold is… difficult.
The town was formerly a summer hunting spot, but after Thule was decided on, the community was moved to Qaanaaq year round. It has an association with the famous Danish explorer Knud Rasmussen, whose old house is a museum (allegedly. I’ve never actually had time to visit it..)
This year we again visited the glaciers at the head of the Inglefield Fjord – expanding a new research programme we piloted last year. We also did a lot of work on the sea ice – not just Steffen Olsen‘s ocean programme, but a new NCKF research programme looking at biological productivity and carbon cycling in the fjord, led by Anna Pedersen, a DMI PhD student also at the University of Southern Denmark. I and another colleagues also did a lot of work on snow processes that is something of a pilot programme for a processes project we’d like to establish next year that will also involve (hopefully) our weather forecasting colleagues and perhaps also the GEUS PROMICE programme.
All of this work involved 6 days of travelling over and camping on the sea ice, plus an additional day trip. We were lucky with the weather, although it was *extremely* cold, around -25 to -28C most days, and dipping well below -30C at night (though being after the equinox it was never truly pitch dark). However, in general there was little wind, no fresh snow (which can really slow the dogs down as they struggle to pull through deep soft snow) and the sun shone every day. This meant we basically managed to achieve the full planned programme – including our extra-optimistic goals – which almost never happens in fieldwork.
I intend to write a whole series of posts based on what we have been doing scientifically and technically as well as some general observations. There have been various hints already in my preferred social network. The whole trip was super inspiring, it’s always valuable to get out and observe the real world when you’re trying to model it, understand it and make projections of sea level rise.
I also promised to make another Lego scientists series and took quite a few photos in between times to do so. However, the research programme was packed, so I had no time at all to make the comic during fieldwork, that will have to wait a few weeks.
Expect my pixelfed account to host gratuitous numbers of dog pictures. And ice pictures. And unexpectedly clear blue skies. For now it’s time to unpack, get the washing machine going and spend some time with my family.
As ever, thanks to my amazing colleagues Steffen Malskær Olsen, Andrea Gierisch and Anna Pedersen for an incredible trip and to DMI station manager in Qaanaaq Aksel Ascanius without whom most of this work would be impossible.
Special thanks to our friends in Qaanaaq, the local hunters, whose unfailing energies and knowledge are absolutely essential to these scientific projects. We literally could not do this without them and of course their dogs.
I must also credit DMI and the Danish Government for funding via the National Center for Klima Forskning and thanks also to Horizon Europe projects PROTECT on sea level rise and PolarRES for additional inspiration and funding and to my colleagues at the Horizon Europe/NERC project OCEAN:ICE for indulging my two weeks away. All three projects will benefit from the insights gained in this fieldwork.
I wrote this series of comics to amuse and inform my kids while I was on fieldwork a few years ago. It turned out to be quite a success and my kids classes both read the Danish versions at their school.
Last year I started https://icemangoeshome.wordpress.com/more-arctic-adventures/ the further adventures of batgirl on the ice with her new friends the Lego scientists and a couple of stowaways.. but last year’s season was extremely busy and I never managed to finish it.
I asked yesterday on mastodon if I should do another this year, and the only feedback I got was I should try to finish the one I started last year. So maybe that’s what I’ll try to do. It’s always challenging fitting around field tasks though so no promises.
This is just a quick post from the airport: you’ve been warned, bat girls and her friends are on their way back with a new season!
Currently, I’m very busy getting ready with colleagues to travel to Greenland next week. We have an extremely full programme of fieldwork activities covering oceanography, biology, sea ice, snow and glacier processes as part of our NCKF work. More on these no doubt in a future post…
Yesterday, one of my ace DMI colleagues (without whom most of the work we plan would definitely not happen) shared the first optical satellite image of the area this year – taken by ESA’s Sentinel 2 (a truly astonishing source of free imagery and everone should know about it). Because the area is very far north, it has been in the Polar night until now so we have been reliant on the ESA Sentinel 1 imagery based on radar.
First Sentinel-2 optical satellite image of the year downloaded from Sentinel Hub’s EO Browser today. Processing with Sentinel Hubs optimised natural colour filter has introduced some artefacts, notable the brigh white patches which probably represent areas of shadow due to the low solar angle. The area is blanketed in thin cloud and only parts of the glaciers, sea ice and icebergs are clearly visibe.
Where biology is clearly showing us earlier springs due to climate change, the date of the first optical image is unlikely to change any time soon due to climate change.
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:
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.
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.
Sea level variation measured by satellite since 1993 from NASA
When we look at tidal gauges,sea level rose about 20cm in the 2oth century
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.
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.
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.
Sterna Paradisaea 
