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.

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 question of observation?

It’s been a while since I lasted posted anything, not for want of ideas but mainly lack of time. I shall try to catch up over the next few weeks. For now I was inspired to write an ultra-quick post about a very trivial question that came up at work today. I think it really captures how observational meteorology works (or should work).

Today, a colleague, John Cappelen, (also known as Mr. Greenland observational data), happened to mention in passing that on the 15th July this year, the weather station at Summit on the Greenland ice sheet had transmitted back to us in Copenhagen, a temperature observation of 2.5°C. This was during one of the highest melt periods this summer.

Automatic weather station operating at Summit, June 2015 — The automatic weather station doing it’s thing at Summit, June 2015. Photo: DMI

Bearing in mind that Summit Camp is at roughly 3,216m, this is a pretty high measured temperature. In fact it would be rather noteworthy, especially as it occurred on one of the highest melt days of the summer. Temperatures above 0°C at Summit are not unknown and the record, during the famous summer of 2012 when around 95% of the ice sheet surface experienced melt, the water sweeping away a bridge on the Watson River near Kangerlussuaq, was 3.6°C.

Now, my colleague is a very experienced and careful scientist. He had checked the observations and the temperatures before and after this measurement were well below zero, so, my colleague asked, was there any reason to believe this measurement or can we assume an instrument failure of some kind?

My office mate in the Arctic and Climate Research section and I obligingly had a quick look at our Polar Portal Greenland ice sheet surface plots (see below) and at the melt extent plots that are updated daily on the DMI website. We had to conclude there was no evidence of melt that high on the ice sheet and there was also no reason to believe that a sudden sharp warming had occurred at Summit on this day based on DMI’s own weather forecast. We then turned to check the weather plots, also on the polar portal and based on data from the European Centre for Medium Range Weather Forecasting (the ECMWF – probably the best weather forecast modellers in the world).

Again, the anomaly plots showed rather cold conditions prevailing over the ice sheet during this period, though at the same time very high melt and low surface mass balance from the ice sheet due to the clear skies.

Graphs showing area of the Greenland ice sheet experiencing melt conditions, compared with the average (dark grey line) and range of past summers (1990-2012), for more detail see the DMI website

Temperature record from Summit Camp for the last month.

Fortunately, due to the American Summit Camp we have access to a back-up dataset very close to this location and after a quick web search John Cappelen was able to confirm that indeed this measurement was an error as the nearby station has not seen anything like that during the period in question (see right).

This kind of thing happens all the time and is therefore not at all newsworthy or interesting enough to write a publication about. However, when a recent record high temperature in the UK can lead to 2 critical articles in the Daily Telegraph and a particularly vigorous exchange on twitter for Met Office scientist Mark McCarthy, as well as this corrective piece on the Carbon Brief blog, perhaps we should be more vocal about just how careful and critical we as scientists are about observations, including the ones we decide to discard as well as the ones we keep.

Surface mass balance of the Greenland ice sheet on the 15th July 2015. Intense melting around the margins led to very negative SMB (the red colours) during this period.

Addendum: I was alerted by this tweet from Gareth Jones, also a Met Office scientist, to some slightly strange cherry picking in the blogosphere of climate records from a couple of DMI stations in Greenland. These have apparently been used to claim no climatic warming trend in Greenland over the 20th Century (I’m not going to link to it).

Anyone who is really interested in the observational data could try checking these reports by Mr Greenland observations himself instead, here is a quick summary:

Mean annual temperature in Copenhagen, Torshavn (Faeroes) and selected DMI weather stations in Greenland from 1873 - 2014. Figure from DMI — Mean annual temperature in Copenhagen, Torshavn (Faeroes) and selected DMI weather stations in Greenland from 1873 – 2014. Figure from DMI

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….

Science under attack

I had planned another subject for todays blog, but having watched the recent Horizon programme on science under attack on BBC iplayer (still available for those with a British IP address) I thought it tied in rather neatly with why I decided to start this blog.

In the first place the idea came to me to start a blog as a way of practicing my own writing skills. Then secondly I thought I might have something interesting to say. When people find out I’m a climate scientist I often get all sorts of questions about climate change ranging from the basic (is it really happening?) to the more nuanced and complex (how do models work?) to, unfortunately, yet another repetition of the usual climate myths (see below). This blog should be a small window on the world where I write about things that interest me and hopefully are interesting to others.

As I looked in to the world of blogging, and in particular into blogging on climate related themes, a huge number of blogs came up. Unfortunately, many of them are rather weak on science and very overtly political. In fact a quick scan of the google hits brings up rather more blogs and websites by what might (kindly) be called “sceptics” (or otherwise known as “deniers”) than blogs created by scientists. There is some really good material on the web dealing with climate related issues, for example the excellent Realclimate.org blog but in many other places there is a lot of dross and the same empty myths endlessly recycled and repeated (for example, “it’s the little ice age”, “it was warmer in the Medieval period”, “it’s sun spots” etc etc), largely I’m afraid due to lazy and/or politically motivated journalism. All of these common myths have been explained over and over again, usually by people far better qualified, and far more skilled in writing than I, yet somehow they seem to persist.

As the Horizon documentary made clear, this is a source of immense frustration to many in the climate field, including myself, so I feel the time has come to stick my head above the parapet so to speak and start broadcasting my own opinions. At least I hope it will be a small addition to the counterbalancing work done by people like Real Climate and maybe it will help open some minds.

The same documentary blamed scientists for being poor communicators and I would tend to agree with that, it’s hard to talk about uncertainties in models for examples when even the word uncertainty is used very differently in science than in everyday life. On the other hand, this article on communication in the journal Nature by Tim Radford suggests that in fact scientists can be good communicators and he cites such luminaries as Carl Sagan, E.O. Wilson, Stephen Jay Gould and even Richard Dawkins (although I fear the latter has alienated a large part of the audience with his agressive approach to atheism). These are all great examples of great communicators of science, and though I fear I couldn’t possibly get close to their talent, I hope that this blog will help to develop my skills further.

One further point, Ben Goldacre, the Guardian’s excellent bad science columnist is a witty, knowledgeable and hard working advocate of good science who works tirelessly against vested interests, quackery, big pharma and other ‘enemies of reason’. In this post about the Copenhagen climate summit he explores the psychology of climate science and why it is so difficult to communicate. He points out that

‘climate science is difficult. We could discuss everything you needed to know about MMR and autism in an hour: the experimental techniques of epidemiology and other disciplines, how they’ve been misrepresented, the results, strengths, and weaknesses of the key studies. Climate change will take two days of your life, for a relatively superficial understanding: if you’re interested, I’d recommend the IPCC website itself, where they have a series of three executive summaries for policy makers, which are perfectly good pieces of humourless popular science writing.’

This is very true and I am certainly not going to use this blog to explain all issues related to climate change research. In fact, I aim to produce pieces about all sorts of scientific curiosities, natural wonders and society’s response to these. I have imposed two other conditions on myself. Firstly, I should not spend more than an hour on any one post and secondly, I want to post at least twice a week. I’ve broken the latter already, but thanks to my friend Heather I’ve been inspired to try again.

Enjoy.

Forecasting the weather part 1: Differences between forecasts

This is the first part of an occasional series that I intend to write about why it’s so difficult to forecast the weather. In the UK the forecast can be notoriously wrong but it seems to me that most people have no idea how difficult it is to make a good forecast, especially in a maritime climate with air masses coming from all sides. This first piece is based on something I wrote for an online forum when another forumite complained that there were two different forecasts for their area that never seemed to agree.

The divergence between two weather forecasts for the same area over the same period can actually come from a whole range of differences between the different forecasters. In Europe most forecasters use the same observational dataset provided by the European Centre for Medium Range Weather Forecasting (ECMWF). This cuts out one set of problems as weather is famously chaotic and very small changes in starting conditions can lead to big changes in outcome, otherwise known as the butterfly effect. The famous storm of 1987 which destroyed millions of trees in southern England and caused millions of pounds of damage but which was not forecast accurately turns out to have been a super unpredictable event as shown in this talk given at the American Geophysical Union in San Francisco in December 2010. However, chaos theory is fascinating in it’s own right so perhaps I’ll give it a post to itself another time.

In day to day forecasts, the biggest difference is probably in the resolution of the model (if you imagine that an area, say the UK, is divided up into little squares, the computer model solves a whole lot of equations for each square).
If the square is 5km by 5km in size then some processes, and a lot of the topography will be smoothed out, but if the square is 500m by 500m then a lot more will be captured. Imagine a hill of 1000m rising out of a flat plain only 100m high in a particular location. The elevation of the square is the average of the whole elevation. In the 5km by 5km model, the entire hill and an equal area of plain is captured so in the square the average elevation may be 500m, but in the 500m by 500m model it may need 4 squares to accurately cover the hill alone and each square will have a different elevation.

Temperatures typically go down as you go higher, and rain will fall as the air cools, so if the hill isn’t “resolved” in the model the prediction may be unrealistically warm and dry. This is why forecasters like high resolution models, but that resolution comes at a high cost, because you need to increase the vertical resolution (the number of squares in the atmosphere) and reduce the length of time between each calculation as the horizontal resolution increases.

Another source of difference are the actual equations solved in the model. These can be formulated in different ways and with different approximations and are often “tuned” so a model that works really well in Scotland is unlikely to be so successful in the Sahara (where I imagine forecasting is actually pretty easy – it’ll be hot and sunny). That’s not to say the models are “wrong” just that they perform better in some circumstances than others and are designed for different purposes often.

Finally, a further important difference is the updating of the model with real time observations and at the boundaries. Most models are not run for the whole wold, but only a small portion (the whole world can be run at a resolution of about 20km nowadays, but it takes a lot of very expensive computer power). More effective is running a small section (say the UK), and telling the computer what is happening at the edges of the box based on satellite and ground observations. These can also be fed in to the area within the model to nudge it in the right direction. In practice as I mentioned earlier, in Europe most national agencies get this information from a single source, the ECMWF. Also, the models tend to be “better” than the observations (as measurements can go wrong, instruments might be wrongly calibrated etc), so at any given moment a weighting of about 40% is applied to observations and 60% for the model, depending on what in particular you’re looking at.

So the accuracy of any forecast depends on where you live and also how far in the future you need your weather to be reliable. Most forecasts aren’t bad up to 3 days in advance in general terms but the specifics can change quickly. Beyond that to 5 days is more tricky and depends on the large scale situation, for example is there a stable high pressure dominating or a series of storms and which way will a weather system move. Beyond a week to 10 days the forecasters are basically just guessing (at least in a maritime climate like the UK) and this why the met office has recently discontinued seasonal forecasts as they can be very unhelpful.

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North

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