I was recently asked to comment on this interesting new paper by David Rounce and co-authors for AP by Seth Borenstein called “Global glacier change in the 21st century: Every increase in temperature matters”. You can read his resulting summary here . I’m posting here the slightly expanded and lightly edited response I sent to Seth in response to his (very good) questions.
The authors only look at the small glaciers and ice caps in this study, not the big polar ice sheets, though they do also cover small peripheral glaciers in Greenland and Antarctica that are not part of the main ice sheets. Of course, this means that sea level rise from all the other important processes like thermal expansion and ice sheet met also have to be taken into account on top of the numbers given here.
Their main findings were that at 1.5 °C above preindustrial, we can expect total glacial mass loss between 2015 and 2100 would be 26% with 90 mm of sea level rise and 49% of the small glaciers and ice caps lost globally. The paper only deals with these small glaciers and does not count the big ice sheets!
At 4°C, we’re looking at 41% mass loss with ~154 mm of sea level rise and 83% of glaciers lost. At 2.7 °C, where the world is now heading, 32% mass loss, 115 mm of sea level rise and 68% of glaciers lost.
I’m sad to say that the results aren’t exactly a surprise – the community has known for some time that the loss of glaciers is basically linear with temperature, so the title of the paper is really spot on, every tenth of a degree really does matter. This earlier paper by my Horizon 2020 PROTECT project collaborator Ben Marzeion shows something very similar But it’s a nice new result with the latest generation of glacier model and updated with the latest CMIP (IPCC) scenarios and they included some new processes that weren’t very well accounted for in previous work.
My first thought was that these latest estimates were actually a little lower than I expected, but the baseline in the paper is 2015 – we should remember that many of these glaciers have already lost quite a lot of ice (see my two photos of Nigårdsbreen in Norway, taken only 13 years apart) – so the new estimates are basically in line with what I would have expected given earlier work. I’d also expect that they will continue to lose ice beyond 2100 so it’s definitely not an end state that they are giving here. As they state in the article there will be widespread deglaciation of some pretty iconic parts of the world, even under the present planned emissions reductions..
In many ways part of the problem has been the previous studies have not always accounted for all the processes: frontal ablation (melt and calving of vertical ice cliffs, mostly in contact with water), the effect of debris cover and so forth (the latter will likely reduce the rate of loss, the former probably increases it). Given what we know about these processes and how to represent them in models, I still consider this work to be a more realistic estimate. Then we also need to account for the climate models and the scenarios used to force them – there are some important differences between CMIP5 and CMIP6 which might also account for some of this shift. We have actually seen something somewhat similar for the projected changes in the big ice sheets.
It’s probably important to remember though that this study still needs to make simplifications, especially when looking at so many glaciers in so many different regions, so there will always be new updates to come with improved computing power and computational techniques and better representation of processes. Having said that, I do not think the picture will substantially change in future, though I can always be proved wrong, and the glaciers community are now at the stage of refining estimates for rates of mass loss.
Globally the loss of glaciers means sea level rise. Regionally and locally the biggest consequences will be for for water resources and we’re likely to see a local increase in natural hazards like outburst floods and avalanches that will need to be carefully managed. There have been a couple of instances already in the last year or two that probably demonstrate this well (e.g. the Marmolada glacier in Italy last year).
I include myself in the group who has to get used to the cultural shift. I have worked on glaciers in the Alps and Norway which are really rapidly disappearing. It’s kind of devastating to see, but it’s not actually surprising. We have known it was coming and in many cases (including the authors of this paper), measured the massive losses (last year, 2022 was a disaster for the Alps and both Fabien Maussion and Matthias Huss who are co-authors on the paper are running very comprehensive programmes that show in real time how much of a disaster) and predicted it with some accuracy. But we’re now at the point where it’s really undeniable that these glaciers are going fast.
The Rhonegletscher in the timelapse above is a really iconic glacier in the Alps, I have my own favourites, mostly places I’ve worked, like Norway, Iceland and Greenland, which are all to a greater or lesser extent retreating fast now. The glaciers that people consider iconic or at least well-known tend to be accessible and depend very much where you are and they will be the glaciers we mourn over in the next decades. In the French Alps, it’s probably the Mer de Glace, in Switzerland perhaps Rhone glacier or Plaine Morte (both have monitoring programmes), in Canada perhaps the Malaspina or Athabasca glaciers. There are still (just) glaciers on Kilimanjaro and Mount Kenya, the Ruwenzoris are basically gone, as are the Papuan glaciers.
Though they show in the study that ice loss is basically linear with temperature, at some point the glaciers become so small that the remianing melt is highly non-linear. And these won’t grow back under any sensible “overshoot” scenario (never mind that we don’t really have technology to remove carbon from the atmosphere at scale). Once they’re gone, they’re basically gone forever on human timescales Finally, I’d like to add a bit of anlaysis by Ben Marzeion and co-authors , it’s possible to basically put a number on the amount of melted glacier ice each kg of CO₂ leads to.
To make one thing very clear straight away, and as the newspaper article also makes very clear, my colleague Steffen Malskær Olsen has established and maintained a very long-running programme of observations in the fjord near Qaanaaq. This town in northern Greenland on the edge of a large fjord, and close to the North Water polynya has a uniquely interesting location to study and understand Arctic processes. The DMI facility there is long established and part of the INTERACT network of Arctic field stations. The 15-year record collected by Steffen is more or less unbroken and uniquely valuable. None of the science I’m planning to do or to work on would be possible without his dedication, hard work, insight and bridge building within the community in Qaanaaq. He and my other DMI colleagues involved in this programme are brilliant scientists and great field companions and I feel privileged to be able to work with them in this incredible place.
Secondly, as the article also makes clear, scientists are not individualistic heroes who beat the odds, it’s a team sport. And it’s especially true in Greenland where the true heroes of this story are probably not scientists but the local hunters and fishers who guide and transport us and whose knowledge and experience is unmatched. I include also on this category our DMI colleague Aksel Ascanius who lives and works in Qaanaaq has been an essential part of the programme since the earliest days, as well as keeping other long-term observations in the network running in this part of the world.
Collaboration with the people who live in the Arctic has been essential for success in Arctic science since since the days of Franklin and Rae (for British readers) or Suersaq, aka Hans Hendrik, (after whom Hans Island is named) for Danes..
Anyway, back to the science of the present-day. DMI has progressively added more and more elements to the field laboratory in Qaanaaq in addition to the longer running observations. A non-exhaustive list would include an infrasound monitoring station that is part of the CTBTO, weather observations (of course), surface emissivity measurements by drone, fjord salinity, temperature and photosynthetically available radiation measurements plus snow and sea ice measurements as well as work with satellites and biology. One glaring omission, up to this year at least, was the glaciology of the region. How does the ice sheet affect the regional climate, how does the ocean affect the glaciers that calve into the fjord? Can we learn about some important but poorly understood processes like calving and melange dynamics using this area as a test bed? What about surface mass budget and snowfall and snow melt?
Now, as a glaciologist, I’ve mostly worked with the interface between atmosphere and ice sheet (at least the last 14 years or so, but I am also still (after my PhD topic on ice fracture and crevasses) interested in calving glaciers and the processes that control how fast icebergs form. And the fjord, Inglefield Bredning has *a lot* of calving glaciers in it. It is a natural laboratory for glaciology and for developing numerical models. Calving is actually a surprisingly difficult thing to model with computer models of glaciers.
Or perhaps it’s not that surprising?
Observations are difficult to get (to put it mildly). There are a number of (possibly wild) theories of “calving laws” that remain poorly constrained by observations as a result. Common parameterizations of ice flow makes it hard to deal with fast flowing glaciers where calving is common. Dealing with grounding lines, where glaciers meet the sea and start to come close to flotation can give notorious numerical errors and retreat requires the remaking of ocean grids in fully coupled climate models.
These are not easy or computationally cheap problems to solve. And where there are at least thousands (maybe even tens of thousands?) of scientists working on atmospheric weather and climate modelling, the community working on ice sheet dynamic models is probably only in the low hundreds.
And of course, we really lack long time series of measurements – essential in a system that changes only s l o w l y, but likely irreversibly and which we are, only now as the system is changing rapidly, starting to understand.
This of course is why the fjord observation record of Steffen is so valuable – these are reliable, repeated measurements of ocean properties that are known to affect the outlet glaciers that meet them. It is indeed a natural laboratory.
What we are now also working on is a field lab to study these calving processes in-situ. I have already found the return to the field scientifically valuable. There is really no replacement for going to observe the earth system you want to understand. (My PhD supervisor used to call it “nurturing your inner glacier”). Observations taken in spring/summer 2022 have already changed how I think about some processes and hopefully the follow-up we have planned in 2023 will confirm our new theoretical framework.
I am fortunate indeed in that at the same research department, we also have colleagues collecting and analyzing satellite data and developing the numerical models we want to use to understand how ice sheets fit into the earth system. All three of these elements – field, satellite and numerical model- are essential.
In this project we are using the satellite observations to extend the time series of field data and we can use both sets of observations together to develop and test a numerical model of this fjord and the glaciers that calve into it. The numerical model we can then extend to other glaciers in Greenland. Hopefully, we can also use this work to understand how Antarctic glaciers might also respond to a warming ocean. Ultimately, the aim of all this work is to understand the contribution of these glaciers to sea level rise both now and in the future.
This is not a frivolous question. In fact, if large (more than a couple of metres).of sea level rise is expected, it is a question that is basically existential for Denmark.
I will add more on the specifics and science in coming months, this is already long enough. However, I’d like to mention a couple of other points:
Finally, this work is currently being carried out under the auspices of the Danish National Centre for Climate Research (NCKF), funded by the Danish Government though with contributions also from other research projects mostly funded by the EU’s Horizon 2020 and Horizon Europe frameworks as well as ESA’s climate change initiative for the Greenland ice sheet.
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:
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” 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
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.
The official end of the hydrological year in Greenland (1st September to 31st August) means I am rather busy writing reports to give an overview of where the ice sheet is this year and what happened. I will try to write a quick blogpost about this in the next week or so (in case you’re curious here’s a quick plot to show the entire annual SMB, see also: http://polarportal.dk/en/groenlands-indlandsis/nbsp/isens-overflade/)
Anyway, as I find I am constantly switching between Gigatonnes (or indeed Gigatons), cubic kilometres and sea level equivalent, here is a quick and handy guide to converting different units of mass, for my own use as much as anyone else.
1 gigatonne is 1 billion metric tonnes (or 1 milliard if you like the old British style, that is one thousand million).
However, on the Polar Portal we usually reckon everything in water equivalent. This is to save having to distinguish between snow (with a density between ~100 kg/m3 when freshly fallen and ~350 kg/m3 m when settled after a few days), firn (snow that has survived a full annual cycle with a density up to ~800 kg/m3) and glacier ice (anything from ~850 kg/m3 to 900+). Water has a density (at 4C) of 1000 kg/m3
1 gigatonne of ice will still weigh 1 gigatonne when it is melted but the volume will be lower since ice expands when it freezes.
1 metric tonne of water is 1 cubic metre and 1 billion metric tonnes is 1 km3 (a cubic kilometre of water)
A cubic kilometre of ice does not however weight 1 gigatonne but about 10% less because of the density difference.
100 gigatonnes of water is roughly 0.28mm of sea level rise (on average, note there are big regional differences in how sea level smooths itself out).
Finally, 1 mm sea level rise is 360 Gt of ice (roughly the number of days in a year)
EDIT: – thanks to ice sheet modeler Frank Pattyn and ice core specialist Tas van Ommen on Twitter for pointing out I’d missed this last handy conversion. Interestingly and probably entirely coincidentally this is very close to the amount of mass lost by the Greenland ice sheet reported by Helm et al., 2014 for the the period January 2011 – January 2014 (pdf here) of 375 +/-24 km3 per year.
Over the last 10 years or so, Greenland has lost on average around 250 Gigatonnes of ice a year (Shepherd et al., 2012), contributing a bit less than a millimetre to global sea level every year with some big interannual variability. This year looks like it will be a comparable number but we will have to wait for the GRACE satellite results in a couple of months to fill in the dynamic component of the mass budget and come up with our final number.
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.
We focused on the area close to Nuuk, the capital of Greenland, as we had access to a rather useful but unusual (in Greenland) dataset gathered by Asiaq the Greenland survey. They have been measuring the run off from a lake near the margin of the ice sheet for some years and made this available to us in order to test the model predictions. This kind of measurement is particularly useful as it integrates melt and run-off from a wider area than the usual point measurements. As our model is run at 5.5 km resolution, one grid cell has to approximate all the properties of a 5.5 km grid cell. Imagine your house and how much land varies in type, shape and use in a 5.5 km square centred on your house and you begin to appreciate the problems of using a single point observation to assess what is essentially an area simulation! This is even more difficult in mountainous areas close to the sea, like the fjords of Norway or err, around south west Greenland (see below).
The 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.
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.
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.
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 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 beston 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.
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.