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Geosciences Column: Landslide risk in a changing climate, and what that means for Europe’s roads

Geosciences Column: Landslide risk in a changing climate, and what that means for Europe’s roads

If your morning commute is already frustrating, get ready to buckle up. Our climate is changing, and that may increasingly affect some of central Europe’s major roads and railways, according to new research published in the EGU’s open access journal Natural Hazards and Earth System Sciences. The study found that, in the face of climate change, landslide-inducing rainfall events will increase in frequency over the century, putting central Europe’s transport infrastructure more at risk.  

How do landslides affect us?

Landslides that block off transportation corridors present many direct and indirect issues. Not only can these disruptions cause injuries and heavy delays, but in broader terms, they can negatively affect a region’s economic wellbeing.

One study for instance, published in Procedia Engineering in 2016, examined the economic impact of four landslides on Scotland’s road network and estimated that the direct cost of the hazards was between £400,000 and £1,700,000. Furthermore the study concluded that the consequential cost of the landslides was around £180,000 to £1,400,000.

Such landslides can have a societal impact on European communities as well, as disruptions to road and railway networks can impact access to daily goods, community services, and healthcare, the authors of the EGU study explain.

Modelling climate risk

To analyse climate patterns and how they might affect hazard risk in central Europe, the researchers first ran a set of global climate models, simulations that predict how the climate system will respond to different greenhouse gas emission scenarios. Specifically, the scientists ran climate projections based on the Intergovernmental Panel on Climate Change’s A1B socio-economic pathway, a scenario defined by rapid economic growth, technological advances, reduced cultural and economic inequality, a population peak by 2050, and a balanced reliance on different energy sources.

They then determined how often the conditions in their climate projections would trigger landslide events specifically in central Europe using a climate index that estimates landslide potential from the duration and intensity of rainfall events. The index, established by Fausto Guzzetti of National Research Council of Italy and his colleagues, suggests that landslide activity most likely occurs when a rainfall event satisfies the following three conditions: the event lasts more than three days, total downpour is more than 37.3 mm and at least one day of the rainfall period experiences more than 25.6 mm.

The researchers also incorporated into their models data on central Europe’s road infrastructure as well as the region’s geology, including topography, sensitivity to erosion, soil properties and land cover.

Overview of a particularly risk-prone region along the lowlands of Alsace and the Black Forest mountain range: (a) location of the region in central Europe and median of the increase in landslide-triggering climate events for (b) the near future and (c) the remote future.

The fate of Europe’s roadways

The results of the researchers’ models suggest that the number of landslide-triggering rainfall events will increase from now up until 2100. Their simulations also find while that these hazardous rainfall events slightly increase in frequency between 2021 and 2050, the number of these occurrences will be more significant between 2050 and 2100.  

While the flat, low-altitude areas of central Europe will only experience minor increases in landslide-inducing rainfall activity, regions with high elevation, like uplands and Alpine forests, are most at risk, their findings suggest.

The study found that many locations along the north side of the Alps in France, Germany, Austria and the Czech Republic may face up to seven additional landslide-triggering rainfall events as our climate changes. This includes the Vosges, the Black Forest, the Swabian Jura, the Bergisches Land, the Jura Mountains, the Northern Limestone Alps foothills, the Bohemian Forest, and the Austrian and Bavarian Alpine forestlands.

The researchers go on to explain that much of the Trans-European Transport Networks’ main corridors will be more exposed to landslide-inducing rainfall activity, especially the Rhine-Danube, the Scandinavian-Mediterranean, the Rhine-Alpine, the North Sea-Mediterranean, and the North Sea-Baltic corridors.

The scientists involved with the study hope that their findings will help European policy makers make informed plans and strategies when developing and maintaining the continents’ infrastructure.  

Geosciences Column: How fast are Greenland’s glaciers melting into the sea?

Geosciences Column: How fast are Greenland’s glaciers melting into the sea?

The Greenland ice sheet is undergoing rapid change, and nowhere more so than at its margins, where large outlet glaciers reach sea level. Because these glaciers are fed by very large reservoirs of ice, they don’t just flow to the coast, but can extend many kilometres out into the ocean. Here, the ice – being lighter than water – will float, but remain connected to the ice on the mainland. This phenomenon is called an ice shelf or, if it is confined to a relatively narrow fjord, an ice tongue. Ice shelves currently exist in Antarctica as well as in high Arctic Canada and Greenland.

Ice shelves already float on the ocean so that their melting does not affect sea level, but they are a crucial part of a glacier’s architecture. The mass of an ice shelf, as well as any contact points with fjord walls, mean that it acts as a buttress for the rest of the glacier, slowing down its flow speed and stabilising it. When ice shelves melt, therefore, this can lead to the whole glacier system behind them flowing faster and thus delivering more land-based ice to the ocean.

Ice shelves lose mass as icebergs calve off at their seaward end, and through melting on their surface – but, unlike glaciers on land, they are with the ocean below. This ice-ocean interface is an important source of melting for a number of glaciers in northern Greenland; instead of the large volume of icebergs produced by many glaciers further south, the large ice tongues reaching into the ocean mean that a lot of ice is instead lost through submarine melting.

This ice-ocean interface is an environment that was, until recently, very difficult to accurately observe and study, and accordingly there is relatively little data on the impact of submarine melting on ice shelves. But the changes that take place here, at the ice-ocean interface, can have important implications for the entire glacier system, as well as for the ice sheet as a whole.

Over the last 30 years, a number of Arctic ice shelves and ice tongues have dramatically shrunk or disappeared entirely. In the Canadian Arctic, the Ellesmere ice shelf broke up into a number of smaller shelves over the course of the 20th century, most of which are continuing to shrink. In Greenland, meanwhile, the dramatic retreat of the Jakobshavn Glacier’s ice tongue during the 2000s has been particularly well documented.

The largest remaining ice tongues in Greenland are now all located in the far north of the island. But even here, at nearly 80°N and beyond, ice tongues are changing rapidly. Warming air temperatures probably play a role in this development, but submarine melting is thought to be the key driver of these rapid changes.

Submarine melting of ice tongues thus appears to be an important variable in ice-sheet dynamics. A new study in the EGU’s open access journal The Cryosphere has now used satellite imagery to produce a detailed map of submarine melt under the three largest ice tongues in northern Greenland. They are the ones belonging to Petermann and Ryder Glaciers in far northwestern Greenland and 79N Glacier – named after the latitude of its location – in the northeast of the island. Each of these ice shelves extends dozens of kilometres from where the glacier stops resting on bedrock and begins to float (the so-called grounding line) and is up to several hundred metres thick.

The locations of Petermann (PG), Ryder (RG) and 79N Glaciers in northern Greenland. From Wilson et al. (2017).

Previous attempts to estimate submarine melt rates relied on an assumption of steady state: that the ice shelf is becoming neither thicker nor thinner. Given the recent changes in all these ice shelves and the glaciers above them, this is not a tenable assumption in this case. Petermann and Ryder Glaciers, in particular, have recently experienced large calving events that were probably related to unusual melt patterns under the waterline.

Lead author Nat Wilson, a PhD student at MIT and Woods Hole Oceanographic Institution, and his colleagues used satellite images spanning four years to create a number of digital elevation models of the Petermann, Ryder and 79N ice shelves. A digital elevation model, or DEM, is a three-dimensional representation of a surface created – in this case – from satellite-based elevation data. By comparing DEMs from different points in time to each other, the team could deduct changes in the height – and therefore volume – of the ice shelves. This method also allowed them to track visible features of the glaciers between images from different years, providing estimates of how fast the ice was flowing down into the ocean.

However, using digital elevation models in a marine setting is not always a straightforward matter. Tides can affect the elevation of ice shelves by a significant amount, especially as the distance from the grounding line increases, and their effect needed to be accounted for in the results. Similarly, the team had to account for the changes on the surface of the ice shelf, where snowfall and melting can affect its volume.

What Wilson and his colleagues were left with was a map of melt rates across the ice shelves. In some respects, the findings were unsurprising. Melt rates were greatest near the coast, where the ice shelves were thickest, because at these points they would be in contact with the ocean at depths of several hundred metres. At such depths, fjords around Greenland often contain warm, dense water that flows in from the continental shelf and contributes to rapid ice melt. As the ice shelves thin towards their outer edges, they are in contact with shallower, colder water that doesn’t melt the ice as quickly.

Submarine melt rates at Greenland’s largest ice tongues are shown in colour shading; the arrows show the direction of ice flow. PG – Petermann Glacier; RG -Ryder Glacier. From Wilson et al. (2017).

All three ice shelves lost between 40-60m per year to submarine melting at their thickest points, while this decreased to about 10m per year in thinner sections. This equates to billions of tonnes of ice melting in contact with the ocean. Each of the ice shelves lost at least five times as much ice to melting underwater than to melting on the surface. This highlights what an important contribution submarine melting makes to the mass balance of Greenland’s ice shelves, and that this remote environment is deserving of our interest and study.

The team found that at Ryder Glacier’s ice shelf, mass loss from melting (from both above and below) is not significantly greater than the amount of ice entering the ice shelf from land: the ice shelf appears to be relatively stable for the time being. The situation is similar at Petermann Glacier, although its ice shelf has been in rapid retreat and lost some 250 km in the decade leading up to 2010. With the extra submarine melting from that area, melting would likely have exceeded incoming ice! It remains to be seen whether Petermann Glacier and its ice shelf will stabilise in their new configuration.

Finally, at 79N Glacier, the results indicate the ice shelf is losing mass faster than it is replenished from upstream. The ice tongue loses some 1.3% of its mass to melting each year – and that’s before iceberg calving is included in the equation. This finding is consistent with satellite imagery that suggests that the ice shelf at 79N has been thinning in recent decades.

This new study shows that there is considerable variability in submarine melting of ice shelves, both in space and in time. 79N glacier’s ice shelf – the biggest one remaining in Greenland – exhibited the highest mass deficit in this study, suggesting that we may see major changes in this glacier in future. With this type of melt making up for the bulk of mass loss of northern Greenland’s ice shelves, its accurate prediction plays an important role in understanding how these huge glaciers – and the whole ice sheet itself – will change in coming years.

By Jon Fuhrmann, freelance science writer

References

Wilson, N., Straneo, F., and Heimbach, P.: Satellite-derived submarine melt rates and mass balance (2011–2015) for Greenland’s largest remaining ice tongues, The Cryosphere, 11, 2773-2782, https://doi.org/10.5194/tc-11-2773-2017, 2017.

Hodgson, D. A. First synchronous retreat of ice shelves marks a new phase of polar deglaciation. Proc. Natl. Acad. Sci. U. S. A. 108, 18859-18860, doi:10.1073/pnas.1116515108 (2011).

Münchow, A., L. Padman, P. Washam, and K.W. Nicholls. 2016. The ice shelf of Petermann Gletscher, North Greenland, and its connection to the Arctic and Atlantic OceansOceanography 29(4):84–95, https://doi.org/10.5670/oceanog.2016.101.

Reeh N. (2017) Greenland Ice Shelves and Ice Tongues. In: Copland L., Mueller D. (eds) Arctic Ice Shelves and Ice Islands. Springer Polar Sciences. Springer, Dordrecht. https://doi.org/10.1007/978-94-024-1101-0_4

Truffer, M., and R. J. Motyka, Where glaciers meet water: Subaqueous melt and its relevance to glaciers in various settings, Rev. Geophys., 54, 220– 239. doi:10.1002/2015RG000494,  (2016)

Geosciences Column: The hunt for Antarctica’s oldest time capsule

Geosciences Column: The hunt for Antarctica’s oldest time capsule

The thick packs of ice that pepper high peak of the world’s mountains and stretch far across the poles make an unusual time capsule. As it forms, air bubbles are trapped in the ice, allowing scientists to peer into the composition of the Earth’s atmosphere long ago. Today’s Geosciences Column is brought to you by PhD researcher Ruth Amey, who writes about recently published research which reveals how a team of scientists might have found the oldest ice yet, which has important implications for our understanding of how Earth’s environment has changed over time.

Ice cores give us a slice through the past. By analysing the composition of ice and gas bubbles trapped within it, we can find out information about temperature, atmospheric conditions, deposition and even the magnetic field strength of the past.

This helps us to understand past conditions on the Earth, but currently the longest record is ~800,000 years (800 kyrs) old. One phenomenon scientists hope to understand better is a change in glaciation cycles. During the Mid-Pleistocene Transition, glaciation cycles changed from 40,000 year cycles related to the obliquity periodicity of the Earth’s orbit to longer, stronger 100,000 year cycles. Scientists of the ice-core community have their eyes on finding out why this change happened, and for this they need data from the onset of the change, between 1250 and 700 kyrs ago.

Which means we need much, much older ice.

A new study, published in EGU’s open access journal The Cryosphere has pinned down two locations where they think the base of Antarica’s ice sheet is significantly older. In fact they believe the ice could be as old as 1.5 million years, which would extend the current ice core record by ~700,000 years: nearly doubling it.

A Treasure hunt – using airborne radar and some simple models

The group, led by Frederic Parrenin at University of Grenoble Alpes, France, went on the hunt for the oldest ice East Antarctica could give them. The survival of ice is an interplay between many factors: the ice acts a little bit like a conveyor belt, being fed by accumulation, with the oldest information lost off the end by basal melting. This means areas of thinner ice, where there is less basal heating, often has a higher likelihood of the old, information-rich ice surviving.

Figure 2: A cross-section of ice in East Antarctica, from surface to bedrock, with colour bar showing the modelled ice age. The model identifies two patches of ice older than 1.5 Myr (shown in white): North Patch and Little Dome D Patch. Adapted from Figure 3 of Parrenin et al 2017.

Airborne radar can ‘see’ into the top three-quarters of the East Antarctica ice sheet. By identifying reflections within it, isochrones of ice of the same age can be traced. Parrenin’s group exploited an area in East Antarctica known as ‘Dome C’ with rich record of radar investigations. Using information derived from the radar, they then created a mathematical model, which balanced accumulation rate, heat flow and melting to give a simple 1-D ice flow model. This helps locate areas of accumulation and melting, which gives an indication of where ice might be the oldest, beyond the sight of the airborne radar. A nearby ice-core, EDC, also provided corroboration of their model.

X Marks the Spot

The team located two sites where they believe the ice to be older than 1.5 million years old, named Little Dome C and North Patch. And fortunately these sites are within a few tens of kilometres from the Concordia research facility, meaning drilling them is a real possibility.

This ancient ice could give vital insight into what happened in the Mid-Pleistocene Transition. What caused the new glaciation cycle onset? Was it a change in sea ice extent? A change in atmospheric dust? Decrease in carbon dioxide concentrations? Changes in the Earth’s orbit? The answers may well be locked in the ice.

By Ruth Amey, Postgraduate Researcher at the University of Leeds

 

References and Resources

Parrenin, F., Cavitte, M. G. P., Blankenship, D. D., Chappellaz, J., Fischer, H., Gagliardini, O., Masson-Delmotte, V., Passalacqua, O., Ritz, C., Roberts, J., Siegert, M. J., and Young, D. A.: Is there 1.5-million-year-old ice near Dome C, Antarctica?, The Cryosphere, 11, 2427-2437, https://doi.org/10.5194/tc-11-2427-2017, 2017

Berger, A., Li, X. S., and Loutre, M. F.: Modelling northern hemisphere ice volume over the last 3 Ma, Quaternary Sci. Rev., 18, 1–11, https://doi.org/10.1016/S0277-3791(98)00033-X, 1999

Imbrie, J. Z., Imbrie-Moore, A., and Lisiecki, L. E.: A phase-space model for Pleistocene ice volume, Earth Planet. Sc. Lett., 307, 94–102, https://doi.org/10.1016/j.epsl.2011.04.018, 2011

Jean Jouzel, Valérie Masson-Delmotte, Deep ice cores: the need for going back in time, In Quaternary Science Reviews, Volume 29, Issues 27–28, Pages 3683-3689, ISSN 0277-3791, https://doi.org/10.1016/j.quascirev.2010.10.002, 2010

Martínez-Garcia, A., Rosell-Melé, A., Jaccard, S. L., Geibert, W., Sigman, D. M., and Haug, G. H.: Southern Ocean dust-climate coupling over the past four million years, Nature, 476, 312–315, doi:10.1038/nature10310, 2011

Tziperman, E., and H. Gildor, On the mid-Pleistocene transition to 100-kyr glacial cycles and the asymmetry between glaciation and deglaciation times, Paleoceanography, 18(1), 1001, doi:10.1029/2001PA000627, 2003

Wessel, P. and W. H. F. Smith, Free software helps map and display data, EOS Trans. AGU, 72, 441, 1991

GeoSciences Column: Don’t throw out that diary – medieval journals reveal the secret of lightning

GeoSciences Column: Don’t throw out that diary – medieval journals reveal the secret of lightning

When 17th century Japanese princess Shinanomiya Tsuneko took note of an afternoon storm in her diary one humid Kyoto summer, she could not have imagined her observations would one day help resolve a longstanding scientific conundrum. Statistical analysis of her journals has revealed a link between lightning strikes and the solar wind – proving that your teenage diary could contain good science, as well as bad poetry.

The mystery of lightning

Lightning has amazed and alarmed weather-watchers since time immemorial. So it may come as a surprise that we still have little idea what sets off one of nature’s most thrilling spectacles.

Any school child will tell you lightning is caused by a difference in electrical charge. Up- and downdrafts cause molecules of air and water to bump against each other, exchanging electrons. When the potential difference is big enough, all those separated charges comes rushing back in one big torrent, superheating the air and turning it into glowing plasma – that’s what we call lightning.

So far, so sensible. But there’s a problem. Air is an insulator – and a very good one at that. To get the current flowing, charged particles need some sort of bridge to travel across. And it’s this bridge that has vexed lightning scientists – fulminologists – for decades.

The most prominent theory points the finger at cosmic rays – heavy, fast-moving particles that impact the Earth from space. Packing energy roughly equivalent to a fast-bowled cricket ball into one tiny atom-sized package, a cosmic ray can shred electrons from their nuclei with ease. The spectacular Northern Lights reveal the effect this can have on the atmosphere: columns of ionised air, perfect conductors for charges to travel along.

Most cosmic rays originate in deep space, hurled at close to the speed of light from distant supernovae. The extreme heat of the sun’s surface also sends more than a few our way – the so-called ‘solar wind’ – but because these particles are more sluggish than galactic cosmic rays, researchers at first doubted they could have much effect on the atmosphere. Lightning’s time in the sun was yet to come.

27 days of summer

Anyone who has lived a year in Japan will be familiar with the country’s long, sultry summers – and its famously methodical Met Agency. It’s a good place to go looking for lightning.

Inspired by some tantalising work out of the UK, Hiroko Miyahara and colleagues across Japan went sifting through their own Met data for patterns that might suggest a connection between solar weather and lightning strikes. They had their eye out for one pattern in particular – the 27-day cycle caused by the sun’s rotation. This is just short enough that the solar wind streaming from any given region of the sun is fairly constant, limiting the impact of solar variability on the data. It’s also short enough to fit comfortably within one season, which helped the authors compare apples with apples over long timespans.

Armed with the appropriate controls, and a clever method they developed for counting lightning strikes that smooths over patchy observations, Miyahara and the team got stuck into the data for Japan circa 1989–2015. Early in 2017, in a paper published in Annales Geophysicae, they presented their results. The 27-day signal stood out to four standard deviations: a smoking-gun proof that solar weather and lightning strikes are connected.

But how is the relatively sluggish solar wind able to influence lightning strikes? The key, according to Miyahara, is the effect the solar wind has on the Earth’s magnetic field – sometimes bolstering and sometimes weakening it, allowing the more potent galactic cosmic rays to wreak their mayhem.

A window into the past

Of course, the 27-day cycle is only the shortest of the major solar cycles. It is well known that the intensity of the sun varies on an 11-year cycle, related to convection rates in the solar plasma. Less understood are the much longer centurial and millennial cycles. The sun passed through one such cycle between the late Middle Ages and now. The so-called Little Ice Age, coinciding with a phase of low sunspot activity known as the Maunder Minimum, precipitated agricultural collapse and even wars across the world – and solar physicists believe we may be due for another such minimum in the near future, if it hasn’t begun already.

Understanding these cycles is a matter of no small importance. Unfortunately, pre-modern data is often scattered and unreliable, hampering investigations. A creative approach is called for – one that blends the disciplines of the human historian and the natural historian. And this is exactly what Miyahara and the team attempted next.

Shinanomiya Tsuneko was born in Kyoto 1642 – just before the Maunder Minimum. A daughter of the Emperor, Shinanomiya became a much-respected lady of the Imperial Court, whose goings-on she meticulously recorded in one of the era’s great diaries. Luckily for Miyhara and his colleagues in the present day, Shinanomiya was also a lover of the weather, carefully noting her observations of all things meteorological – especially lightning.

Figure and text from Miyahara et al, 2017b: “a) Group sunspot numbers around the latter half of the Maunder Minimum. b) Solar cycles reconstructed from the carbon-14 content in tree rings. The red and blue shading denotes the periods of solar maxima and minima, respectively, used in the analyses. c) Periodicity of lightning events during the solar maxima shown in panel (b). The red dashed lines denote 2 and 3 SD during the solar maxima, and the red shaded bar indicates the 27–30-day period. d) Same as in panel c) but for solar minima.”

Shinanomiya’s diary is one of five Miyahara and the team consulted to build a continuous database of lightning activity covering an astonishing 100 years of Kyoto summers. Priestly diaries, temple records, and the family annals of the Nijo clan were all cross-referenced to produce the data set, which preserves a fascinating slice of Earth weather during the sun’s last Grand Minimum.
Analysis of this medieval data revealed the same 27-day cycle in lightning activity observed in more recent times – proof of the influence of the solar wind on lightning frequency. The strength of this signal proved to be greatest at the high points of the sun’s 11-year decadal sunspot cycle. And the signal was almost completely absent between 1668 and 1715 – the era of the Maunder Minimum, when sunspot numbers are known to have collapsed.

Put together, the data provide the strongest proof yet that solar weather can enhance – and diminish – the occurrence of lightning.

Lightning strikes twice

Miyahara and the team now hope to expand their dataset beyond the period 1668 – 1767. With a little luck – and a lot of digging around in dusty old archives – it may be possible to build a record of lightning activity around Japan from before the Maunder Minimum all the way up to the present day. A record like this, covering a grand cycle of solar activity from minimum to maximum and, perhaps soon, back to a minimum again, would help us to calibrate the lightning record, providing a powerful new proxy for solar activity past and future. It may even help us to predict the famously unpredictable – lightning strikes injure or kill a mind-boggling 24,000 people a year.

As for the rest of us, the work of Miyahara and his colleagues should prompt us to look up at the sky a little more often – and note down what we see. Who knows? Three hundred years from now, it could be your diary that sets off a climate revolution – though it may be best to edit out the embarrassing details first.

by Rohan S. Byrne, PhD student, University of Melbourne

References

Miyahara, H., Higuchi, C., Terasawa, T., Kataoka, R., Sato, M., and Takahashi, Y.: Solar 27-day rotational period detected in wide-area lightning activity in Japan, Ann. Geophys., 35, 583-588, https://doi.org/10.5194/angeo-35-583-2017, 2017a.

Miyahara, H., Aono, Y., and Kataoka, R.: Searching for the 27-day solar rotational cycle in lightning events recorded in old diaries in Kyoto from the 17th to 18th century, Ann. Geophys., 35, 1195-1200, https://doi.org/10.5194/angeo-35-1195-2017, 2017b.