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Cryospheric Sciences

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Image of the week – Learning from our past!

Image of the week – Learning from our past!

Understanding the climate evolution of our planet is not an easy task, but it is essential to understand the past if we are to predict the future! Historic climate cycles provide us with a glimpse into a period of time when the Earth was warmer than it was today. Our image of the week looks at these warmer periods of time to see what they can tell us about the future! For example, during the Pliocene, the global mean sea level was greater than 6 m higher than it is today… so what can these historic records tell us about the future of the ice sheets and their contribution to sea-level rise?


We will work forward in time from 3 million years ago to present-day and examine the evidence we have about the past climate of Earth. In this time period there have been cycles of warm and cool climate (glacials and interglacials – see our previous post). Here we will examine those interglacial periods where the climate was warmer than the preindustrial period (before 1750).

The Pliocene ~ 3 million years ago

Approximately 3 million years ago during the mid-Pliocene period, the earth experienced climate cycles every 41,000 years, and the atmospheric CO2 ranged from 350 to 450 ppm compared to around 400 ppm today and 250 ppm preindustrial. During the Pliocene period, peak global mean temperatures were on average 1.9ºC to 3.6ºC warmer than preindustrial temperatures. Ice sheet modelers have used these changes in climatic conditions to estimate the retreat of the Antarctic and Greenland ice sheets, which predicted the global mean sea level to rise ~6 and ~7 m, respectively (see our Image of the Week). Others have used geochemical methods to reconstruct historic sea level, which suggest that the global mean sea-level rise was 21 ± 10 m! While these studies provide great reason to be alarmed, they are unfortunately plagued with uncertainty that makes it challenging to provide any robust estimates of future sea-level rise based on the Pliocene period. Fortunately, more data is available from time periods closer to the present.

Marine Isotope Stage 11 (MIS 11) ~ 400 thousand years ago

Approximately 400,000 years ago, the earth experienced an unusually long period of warming, where the global mean temperature was estimated to be 1-2ºC warmer than preindustrial levels (see our Image of the Week). This period is known as MIS 11. Historic records such as pollen records, biomolecules, and ice-rafted debris suggest that the Greenland ice sheet severely retreated to the extent that forests developed on Southern Greenland! Ice sheet modelers estimate that this retreat in Greenland could have contributed 4.5 – 6 m to the global mean sea level rise. Paleoshoreline reconstruction at sites across the globe suggests that that the global mean sea level rise was ~6 – 13 m, which supports the large retreat experienced by the Greenland ice sheet and suggests that the Antarctic ice sheet likely experienced significant retreat as well if those higher estimates of sea level rise (~13 m) occurred.

Marine Isotope Stage 5 (MIS 5e) ~ 125 thousand years ago

Approximately 125,000 years ago, the earth experienced a period of warming approximately 1ºC warmer than preindustrial levels, known as MIS 5e. This warmer period has significantly more data available compared to the other time periods. It is often the case that more recent times have more abundant data and in this caseshorelines that developed during MIS 5e provide an excellent record of global mean sea level being an estimated 6 – 9 m higher than present.

Modeling studies suggest that at this time 0.6 – 3.5 m of sea level rise can be attributed to the retreat of the Greenland ice sheet and ~1 m can be attributed to thermal expansion and the melt of mountain glaciers (see Figure 2). Therefore, despite a lack of mass loss records of the Antarctic ice sheet at this time , it is likely that it underwent considerable retreat to enable contributing to the additional sea level rise.

Figure 2: Compilation of MIS 5e reconstructions for peak GMSL, the Greenland ice sheet contribution, and bets estimate of the total sea level budget [Credit: Dutton et al. (2015)].

What does this all mean for our future…

The further back in time, the larger the sources of uncertainty. Hence, there is fairly limited data regarding the Pliocene that may be used to help predict future conditions. Additionally, it’s important to remember that the climatic cycles in the Earth’s history resulted largely from changes in the Earth’s orbit. This is why the CO2 level associated with MIS 5e and 11 are similar to preindustrial levels, and yet these periods experienced significant increases in global mean temperature accompanied by rises in the global mean sea-level.

what we do know from the past is that both ice sheets experienced significant mass loss during these warm periods that directly impacted sea-level rise.

Today, the CO2 concentrations are around 407 ppm and the peak global mean temperature is approximately 1ºC warmer than preindustrial times (see the Image of the Week). For reference, the Paris Climate Accord is trying to bring our world leaders together to keep the peak global mean temperatures lower than 2ºC above pre-industrial levels. While the cause of the warming periods might be different, what we do know from the past is that both ice sheets experienced significant mass loss during these warm periods that directly impacted sea-level rise. Therefore, it’s very important to monitor and improve our future projections of mass loss from these ice sheets in order to better understand how sea-level rise will affect us.

Further Reading

  • Read the paper this article is based on here

Edited by Emma Smith 

Image of the week – Getting glaciers noticed!

Image of the week – Getting glaciers noticed!

Public engagement and outreach in science is a big deal right now. In cryospheric science the need to inform the public about our research is vital to enable more people to understand how climate change is affecting water resources and sea level rise globally. There is also no better way to enthuse people about science than to involve them in it. However, bringing the cryosphere to the public is a little more difficult when compared to other fields of science. Whilst volcanologists can cause mini explosions, seismologists can simulate earthquakes (such as Explosive Earth at last year’s Royal Society science fair) and realistic rivers can be simulated using interactive stream tables, combining ice and glacier dynamics in a public engagement setting can a little more challenging!


Despite the challenges involved in bringing the cryosphere to the public, a huge variety of great outreach projects concerned with glaciers exist, which deal with different aspects of the cryosphere; from using glacier goo to display how glaciers flow, recreating hydrology of a glacier with ice blocks, dressing up school children in fieldwork kit, or passing wires through ice to show regelation at work. But what should you keep in mind when planning your next cryospheric themed outreach activity?

Figure 2: The Vanishing Glacier of Everest stand at the Manchester Science festival [Credit: Owen King].

Keep it simple. By nature, academics are good at complexity. However, the most effective project I have been involved in was very simple – one where an ice block simply sat and melted (see our Image of the week). The team involved with this project came up with a vast array of complex ideas when planning the stand, but settled on the simple, effective idea of an ice block – which has been a great hit. The stand has now been to numerous science festivals, and people are constantly surprised by the ice being real! Once past the initial shock we have a great base from which to start conversations on the basics of how ice melts to the impact of climate change on glaciers around the world.

Keep it broad. Academics are also very good at forgetting just how specific their area of research is. You may want to link your outreach work to a particular project, but if you try to attempt something very specific you will spend a great deal of time talking to public about the basics before you get to the detail. To ensure everyone can get something out of your outreach work the best way is to provide a platform on which the basics can be taught but, if a conversation takes you there, you have the resources to explain your research in greater detail. At ‘Vanishing Glaciers of Everest’ we have the ice block for introductory discussions, but if someone gets really interested in the details we have figures and photos on the stand behind that can be used to introduce more complex areas of our research (Fig. 1 and Fig. 2).

Figure 2: Glacier goo at science and engineering week, Aberystwyth University [Credit: Morgan Gibson]

Make it interactive. Generally, people don’t want to be talked at. Instead, most people want to discuss what they know with you, so make it easy for them to do so. Give people something to do (e.g. glacier goo – Fig. 3) as soon as they reach the stand that they can explore on their own. You can then join them and ask exploratory questions, which starts a discussion rather than presenting to them. You are then likely to engage the person you are talking to much more effectively, and may well find out something yourself!

Consider all ages. Outreach work is often focused on children. However, adults are also a key demographic on which to focus. Engaging teachers and parents is vital to really bring home the importance of science to children in school and at home; I have found that almost all children have an interest in what you are saying, but without enthusiasm and interest from the supervising adult your hard work at engaging the children will not be encouraged once they leave. Consider how you will show how your aspect of science is fun, but also relevant to peoples’ everyday lives – that way you can appeal to both demographics.

Be innovative. Hanging an ice block from a wire to show regelation is cool, as is glacier goo. However, increasingly I am finding people have seen these experiments before, and are finding it all a little boring as a result. By repeating the same experiments again and again we are in danger of suggesting our research is static, which is obviously not the case! So be inventive when you are coming up with ideas and don’t forget all the new technology you could include!

Figure 4: “Icy bear” – a Twitter-based public engagement ‘project’ that documents research on microbes on ice, and fieldwork, across the world [Credit: Arwyn Edwards]

Be prepared for anything. I’ve had people talk to me, at length, about how the best way for us adapt to sea level rise is for all of us live in high rise blocks on hill tops. I’ve also spent a great deal of time explaining how we know anthropogenic climate change is real. You will get some strange questions and bold statements, but they are part of the experience. Keep an open mind and be positive; you meet amazing, interesting people at these events, and I have had conversations that have led to new research ideas, or to me rewriting paragraphs of a paper due to discussions at such events.

Be reflective. Spend some time considering the effectiveness of your outreach once you have finished (and recovered) from an event. What worked well and what didn’t? Do aspects of your stand or event need adapting for different audiences? Can you expand what you are doing to enable more flexibility on the overall message for your work? Being reflective will only lead to more effective public engagement, more interesting discussions, and you feeling satisfied that you have enthused and engaged public on your research, so it is worth doing!

 

 

Public engagement, done right, is incredibly rewarding. You not only spread your enthusiasm for research and get to discuss your work with a huge range of people, but it also enables you to show people that like science is relevant to everyone.

If you want to see some public outreach in action for yourself, the upcoming International APECS Polar Week (September 18-24, 2017) is a great chance to get involved in some outreach activities. For example, the #PolarWorld Frostbytes competition, to design a short audio or video recording used as a tool to help researchers easily share their latest findings with a broad audience!

Edited by Emma Smith


Morgan Gibson is a PhD student at Aberystwyth University, UK, and is researching the role of supraglacial debris in ablation of Himalaya-Karakoram debris-covered glaciers. Morgan’s work focuses on: the extent to which supraglacial debris properties vary spatially; how glacier dynamics control supraglacial debris distribution; and the importance of spatial and temporal variations in debris properties on ablation of Himalaya-Karakoram debris-covered glaciers. Morgan tweets at @morgan_gibson, contact email address: mog2@aber.ac.uk.

Image of the Week – Fifty shades of snow

Image of the Week – Fifty shades of snow

When I think of snow, I tend to either think about the bright white ski slopes in the mountains or the large white areas in the Arctic. However, natural phenomena can lead to colorful snow. Our Image of the Week shows snow can be green! Snow can also turn orange, pinkish, grey and even yellow… But where do these different shades of snow come from?


White

The most common color of snow is white (see Fig. 2). Snow generally appears white when it is pure snow, which means that it is only an aggregate of ice and snow crystals. When sunlight meets the snow surface, all frequencies of the sunlight are reflected several times in different directions by the crystals, leading to a white color of the snowpack.

 

Fig. 2: Fresh powder snow, snow crystals [Credit: Introvert, Wikimedia Commons]

 

 

If other particles or organisms are present in the snow though, they can alter the color of the snow’s surface…

Green

Snow can obtain a green color if it is host to an algal bloom (see our Image of the Week). Depending on the wetness of the snow, sunlight conditions and nutrient availability, unicellular snow algae can develop and thrive on the snow. Although it is not clear exactly how fast snow algae grow, algae populations from temperate regions have been found to grow sixteen-fold in one day! As the algae population increases, the snow turns green as the algae reflect the green light back.

 

Red/Pink

The pink-red-colored snow, commonly called “watermelon snow”, can also be caused by snow algae (see Fig. 3). The snow algae responsible for the pink color are similar to the ones responsible for green color. However, these algae use pigments of red color to protect their cells from high sunlight and UV radiation damage during the summer. Just like how we use sunscreen to protect our skin! The red pigments come either from iron tannin compounds or, more commonly, from orange to red-pigmented lipids.

There is also another origin for pink snow: Penguin poo! Indeed, the krill they eat contain a lot of carotenoids that give their poo a red color.

Fig. 3: Watermelon snow streaks [Credit: Wikimedia Commons].

 

Yellow

Yellow snow is the result of a different process (and no, it is not from Penguin pee!). Fig. 4 shows the Sierra Nevada in Spain before and after dust transported from the Sahara settled down on the snow-covered mountain tops. The dust was lifted up from the Sahara desert and blown north before ending its trip in Spain.

Fig. 4: Snow-covered Sierra Nevadas (Spain) before and after a dust deposition event [Credit: modified from NASA’s Earth Observatory]

 

Do these colors have an influence on snow cover?

In all cases of colored snow, the snow surface is darker than before. The darker surface absorbs more sunlight than a white surface, which causes the snow to melt faster… Therefore, although it looks artistic, colored snow is not necessarily healthy for the snow itself…

 

So, if you don’t like winter because everything is boring and white, just think about the variety of snow colors and try to look out for these special types! 🙂

 

Further reading

Edited by David Rounce

Image of the Week – Far-reaching implications of Everest’s thinning glaciers

Fig. 1: Surface lowering on the debris-covered Khumbu Glacier, Nepal derived from differencing two digital elevation models. (a) The debris-covered surface looking down-glacier. (b-d) Surface elevation change 1984−2015. [Credit: Scott Watson and Owen King]

From 1984 to 2015, approximately 71,000 Olympic size swimming pools worth of water were released from the melting Khumbu Glacier in Nepal, which is home to Everest Basecamp. Find out how Himalayan glaciers are changing and the implications for downstream communities in this Image of the Week.


Himalayan glaciers supply freshwater

Himalayan glaciers supply meltwater for ~800 million people, including for agricultural, domestic, and hydropower use (Pritchard, 2017). They also alleviate seasonal variations in water supply by providing meltwater during the dry season. This freshwater resource is rapidly depleting as glaciers thin and glacial lakes begin to form (Bolch et al., 2008; Watson et al., 2016; King et al., 2017). Additionally, outburst floods from these lakes (see those previous posts on the topic) threaten downstream impacts for communities and infrastructure (Rounce et al., 2016).

Debris-covered glaciers thin, rather than retreat

Erosion in the rugged mountain topography leads to high quantities of rocky debris accumulating on the glacier surface, which changes the glacial response to climatic warming. The debris-layer (which can be several metres thick at the lower terminus) insulates the ice beneath, leading to highest melt rates up-glacier of the terminus. Therefore these debris-covered glacier thin, rather than retreat up-valley.

This thinning is actually a complex process of sub-debris melt, and mass loss associated with supraglacial ponds and ice cliffs, which form pits on the glacier surface and are ‘hot-spots’ of mass loss. Since the highest rates of surface lowering are up-glacier from the terminus, the surface slope of the glacier reduces and meltwater increasingly ponds on the surface, which can ultimately form a large glacial lake.

Khumbu Glacier

Fig 2 : Khumbu Icefall viewed from Kala Patthar. [Credit: Scott Watson]

The image of this week (Fig 1) shows surface elevation change on Khumbu Glacier, which flows down from Everest and is home to Everest Base Camp in Nepal. Parts of the glacier surface have thinned by up to 80 m 1984−2015 and over 197,600,000 m³ of ice melted over study period, which is approximately 71,000 Olympic size swimming pools worth of water! The thinning is clearly visible in the vertical offset between the contemporary glacier surface and the Little Ice Age moraines (a) and is highest in the mid-section of the glacier (b).

Mountaineers ascending Mount Everest climb the Khumbu icefall (Fig 2) and camp on the glacier surface. Additionally, popular trekking routes also run alongside and across the glacier, which are used by thousands of tourists every year. The accessibility of both these mountaineering and trekking routes is changing in response to glacier mass loss.

Stagnating glaciers are unhealthy glaciers

Accumulation of snowfall in the highest reaches of the glacier would typically compress to form new ice and replenish mass loss on the lower glacier as the glacier flows downstream. However, trends of reduced precipitation (Salerno et al., 2015) and decreasing glacier surface slopes promote a reduction in glacier velocity. Figure 3 shows glaciers stagnating in their lower reaches, where water is also visibly ponding on the glacier surface. For Khumbu and Ngozumpa glaciers, this contributes to the development of large glacial lakes. If these lakes continue to grow, once fully established they can rapidly increase glacier mass loss as a calving front develops (e.g. at Imja Lake).

Fig. 3: Surface velocity of glaciers in the Everest region derived from feature tracking on ASTER satellite imagery. [Credit: Scott Watson]

Edited by Sophie Berger

References/further reading

  • Bolch, T Buchroithner, MF Peters, J Baessler, M and Bajracharya, S. 2008. Identification of glacier motion and potentially dangerous glacial lakes in the Mt. Everest region/Nepal using spaceborne imagery. Nat. Hazards Earth Syst. Sci. 8: 1329-1340. 10.5194/nhess-8-1329-2008
  • King, O Quincey, DJ Carrivick, JL and Rowan, AV. 2017. Spatial variability in mass loss of glaciers in the Everest region, central Himalayas, between 2000 and 2015. The Cryosphere 11: 407-426. 10.5194/tc-11-407-2017
  • Pritchard, HD. 2017. Asia’s glaciers are a regionally important buffer against drought. Nature 545: 169-174. 10.1038/nature22062
  • Rounce, DR McKinney, DC Lala, JM Byers, AC and Watson, CS. 2016. A new remote hazard and risk assessment framework for glacial lakes in the Nepal Himalaya. Hydrol. Earth Syst. Sci. 20: 3455-3475. 10.5194/hess-20-3455-2016
  • Salerno, F Guyennon, N Thakuri, S Viviano, G Romano, E Vuillermoz, E Cristofanelli, P Stocchi, P Agrillo, G Ma, Y and Tartari, G. 2015. Weak precipitation, warm winters and springs impact glaciers of south slopes of Mt. Everest (central Himalaya) in the last 2 decades (1994–2013). The Cryosphere 9: 1229-1247. 10.5194/tc-9-1229-2015
  • Watson, CS Quincey, DJ Carrivick, JL and Smith, MW. 2016. The dynamics of supraglacial ponds in the Everest region, central Himalaya. Global and Planetary Change 142: 14-27. http://dx.doi.org/10.1016/j.gloplacha.2016.04.008

Scott Watson is a PhD student at the University of Leeds, UK. He studies glaciers in the Everest region and specifically the surface interactions of supraglacial ponds and ice cliffs, which act as positive feedback mechanisms to increase glacier mass loss. He also investigates glacial lake hazards and the implications of glacial lake outburst floods.

Tweets @CScottWatson. Outreach: www.rockyglaciers.co.uk

Image of the Week – The Sound of an Ice Age

Image of the Week – The Sound of an Ice Age

New Year’s Eve is just around the corner and the last “image of the week” of 2016 will get you in the mood for a party. If your celebration needs a soundtrack with a suitably geeky touch then look no further. Here is the music for climate enthusiasts: The sound of the past 60,000 years of climate. Scientist Aslak Grinsted (Centre for Ice and Climate, University of Copenhagen, Denmark) has transformed the δOxygen-18 values from the Greenland NorthGRIP ice core and the Antarctic WAIS ice core into music (you can read more about ice cores in our Ice Cores for Dummies post). Using the Greenlandic data as melody and the Antarctic data as bassline, Aslak has produced some compelling music.

You can listen to his composition and read more about his approach here.

The δOxygen-18 values are a measure of the isotopic composition of the ice, and they are a direct indicator of temperature. The image of the week above shows the isotope values for the past 20,000 years as measured by polar ice cores. On the left-hand side, we are in present-day: an inter-glacial. The δOxygen-18 values are high indicating high temperatures. In contrast, on the right-hand side of the figure we are in the last glacial with lower δOxygen-18 values and lower temperatures. One remarkable thing about these curves is how fast the temperature changes in Greenland (top) compared to Antarctica (bottom). This delayed coupling is called the Bipolar Seesaw.

The clefs are our own addition of course. We have not included the time signature because who knows what the rhythm of the climate might be? (Personally, I think it might be in ¾ like a waltz: An unrestrained movement forward with small underlying variations).

The data from Antarctica is published by WAIS Divide Project Members, 2015. The Greenlandic data can be found on the Centre for Ice and Climate website and in publications by Vinther et al., 2006, Rasmussen et al., 2006, Andersen et al., 2006 and Svensson et al., 2006.

Happy New Year!

 

Image of the Week – Let it snow, let it snow, let it snow…

Image of the Week – Let it snow, let it snow, let it snow…

Christmas is coming to town and in the Northern Hemisphere many of us are still dreaming of a white Christmas, “just like the ones we used to know”. But how likely is it that our dreams will come true?


What is the definition of a White Christmas ?

Usually Christmas can be defined as a “White Christmas” if the ground is covered by snow on either Christmas Eve or Christmas Day depending on local traditions. If you believe Christmas movies, it seems like Christmas was accompanied by snow much more often in the past than today! But is this really the case, or is it just the “Hollywood” version of Christmas? According to the UK Met Office White Christmases were more likely in the past. Due to climate change, average global temperatures are higher, which in many places reduces the chance of a White Christmas. However, the chances of a White Christmas also depend strongly on where you live…

Living in Western or Southern Europe, the Southern US or the Pacific coast of the US? Unlucky you!

Not too surprisingly, most of the inhabitants of Portugal, Southern Spain, and Southern Italy have probably never experienced White Christmas in their hometown. Maybe more counter intuitively the probability of a White Christmas is also low in most of France, the Netherlands, Ireland, and the Southern UK! In the US, the probability of a White Christmas increases from South to North, except on the Pacific Coast, which has a very low probability of a White Christmas.

Probability of a White Christmas in Europe (snow on the ground on 25th of December), inferred from reanalysis data (ERA Interim from 1979-2015). Probability [in %] increases from white to blue [Credit : Clara Burgard, Maciej Miernecki. We thank the ECMWF for making the data available]

What influences the probability of snowfall on Christmas?

The mean air temperature decreases with altitude and latitude, meaning that chances of a white Christmas increase the further North and at the higher you travel. However, coastal regions represent an exception. The air often has traveled over the ocean before reaching land. As the ocean is often warmer than the land surface in winter, the air in coastal regions is often too warm for snow to form. Additionally, in the Northern Hemisphere, ocean currents on the Western coast of the continents tend to carry warm water to high latitudes, while ocean currents on the Eastern coast tend to carry cold water to low latitudes. The probability of snowfall is therefore even lower in Western coastal regions (e.g. Pacific coast of the US, Atlantic coast of Europe).

Don’t despair !

If you want to increase your chances of experiencing a White Christmas, you have three solutions:

    1. You already live in an area with high probability of White Christmas (lucky you!) – Sit tight and do a “snow dance”, here is one suggestion that we have heard works well:

    2. Travel or move to one of these 10 suggested destinations (e.g. St. Moritz, Swizerland)

      Frozen Lake St. Moritz in Winter 2013 [Credit: Wikimedia Commons]

    3. Build your own snow with this simple recipe!

We hope that you find a satisfactory solution that makes you happy this Christmas. Otherwise, remember that snow is not the only thing that defines Christmas. Enjoy the relaxed time with family and friends and prepare yourself for the coming new year! If you find yourself at a loose end, then there is always the back catalogue of EGU Cryosphere Blog posts to read – and we guarantee a healthy dose of snow and ice can be found here.

So, this is it from the EGU Cryosphere blog team for 2016. See you in 2017 – after all, the snow must go on…

Further reading:

      •  MetOffice website with interesting facts around White Christmas!

Edited by Emma Smith

Image of the Week – Sea Ice Floes!

Image of the Week – Sea Ice Floes!

The polar regions are covered by a thin sheet of sea ice – frozen water that forms out of the same ocean water it floats on. Often, portrayals of Earth’s sea ice cover show it as a great, white, sheet. Looking more closely, however reveals the sea ice cover to be a varied and jumbled collection of floating pieces of ice, known as floes. The distribution and size of these floes is vitally important for understanding how the sea ice will interact with its environment in the future. [Read More]

Image of the Week – The Polar Hole!

Image of the Week – The Polar Hole!

Have you ever stumbled upon a satellite picture showing observations of the Arctic or Antarctic? You often see a circle where there is no data around the exact location of the geographic pole – as you can see in our Image of the Week. A few days ago, I wanted to explain this to one of my friends and turned to my favourite search engine for help. My search turned up a tremendous amount of stories and “scientific” studies about the Earth being hollow, with access to the centre of our hollow planet through these holes at the pole.

Obviously this is not the case. So here at the EGU Cryosphere blog we thought we’d better to set the record straight and explain the real reason for the “polar hole”.


Why do we need satellites?

Let’s start at the very beginning with how Earth observation data (e.g. temperature, ice cover, cloud cover, etc…) is collected. In the early days, measurements could only be collected pointwise, e.g. at weather stations (see Fig. 2) or by scientists traveling over land and by ship to specific locations. As a consequence, data coverage was very sparse and often clustered in places that were easily accessible, such as North America or Europe (Fig. 2). Additionally, measurements were even more sparse in hostile environments like the polar regions. It was therefore difficult to monitor these areas and study, for example, the evolution of polar ice sheets and sea-ice cover.

Since the 1970s, the use of satellites has greatly improved our ability to make remote observations around the world with a high spatial and temporal resolution, leading to much better monitoring of, for example, global weather and temperature. It has also allowed us to collect a vast amount of data in the difficult to access polar regions.

Figure 2: Map of the land-based long-term monitoring stations included in the Global Historical Climatology Network. Colours indicate the length of the temperature record available at each site. [ Credit : created by Robert A. Rohde from published data and is incorporated into the Global Warming Art project ]

Figure 2: Map of the land-based long-term monitoring stations included in the Global Historical Climatology Network. Colours indicate the length of the temperature record available at each site. [Credit: created by Robert A. Rohde from published data and is incorporated into the Global Warming Art project]

Earth Observation Satellites

Satellites orbiting the Earth allow is to make remote observations and measurements of what is happening in the atmosphere and on the surface of the Earth. Earth observation satellites are divided in two categories according to the way in which they circle (orbit) the planet:

    • Geostationary satellites: orbit around the Earth’s Equator at an altitude of about 36000 km. They orbit in sync with the Earth (taking around 24h to complete a rotation) and therefore are always pointing at the same region (see video below). They provide observations of a given region on a high temporal resolution. However, given their location at the Equator, they do not cover the polar regions well.
    • Polar orbiting satellites: circle the Earth at a lower altitude around 850 km and their orbit is nearly perpendicular to the Equator. They are not in sync with the Earth’s orbit, circling the the Earth around once every 100 minutes. They therefore cross polar regions several times a day. Have a look at the video below to see how this works!

So…we have polar orbiting Satellites – why can can’t we “see” the poles?

The answer: sun-synchronous orbits!

 

 

Sun-synchronous Orbit

To understand the data “hole” at the poles, we need to a little more detail about the path of polar orbiting satellites. To follow the evolution of a given point on Earth, it is useful for polar orbiting satellites to always cross that point at the same time of day – this way the angle of sunlight on the surface of the Earth is as constant as possible, resulting in a consistent series of images and observations over time . This is called a sun-sychronous orbit. To follow a sun-synchronous orbit, the orbit of the satellite has to be tilted at an angle from the geographic poles, thereby preserving the observed solar angle at the Earth’s surface .

Figure 3: These illustrations show 3 consecutive orbits of a sun-synchronous satellite with an equatorial crossing time of 1:30 pm. The satellite’s most recent orbit is indicated by the dark red line, while older orbits are lighter red. [Credit: NASA , illustration by Robert Simmon ]

Figure 3: These illustrations show 3 consecutive orbits of a sun-synchronous satellite with an equatorial crossing time of 1:30 pm. The satellite’s most recent orbit is indicated by the dark red line, while older orbits are lighter red. [Credit: NASA , illustration by Robert Simmon]

If you get a picture of all the trajectories of a sun-synchronous satellite, they will overlap (see video below), providing a seemingly closed picture. The only region that is not covered by the satellite is a circle (the size of the circle depends on the orbit tilt) around the geographic pole. This is the explanation for the data “hole” at the pole.

Sorry to debunk the myth but there is there is no hollow Earth that can be accessed through holes at the poles. The “Polar Hole” is a purely technical matter!

 

 

Further reading:

Edited by Emma Smith

Image of the Week – Yes, you’re looking at one of Peru’s most dangerous glacial lakes!

Image of the Week – Yes, you’re looking at one of Peru’s most dangerous glacial lakes!

As mountain glaciers melt and recede, they often leave behind large glacial lake that are contained by the glaciers’ old terminal moraines. These glacial lakes are found throughout the world and can pose a significant flood hazard to downstream communities and infrastructure.

The image of this week focuses on Lake Palcacocha, a large glacial lake located in Peru’s Cordillera Blanca at an elevation of 4,562 m. It is one of Peru’s most dangerous glacial lakes because it threats to flood the inhabited valley downstream.


More than 75 years of flood hazard

In 1941, an avalanche entered the glacial lake, causing a tsunami-like wave that overtopped and eroded its terminal moraine, and ultimately triggered a glacial lake outburst flood. The flood traveled down the valley and killed an estimated 1,800-6,000 people in the city of Huaraz (see map below). The flood drained the volume of the lake from 10-12 million m³ to just 0.5 million m³.

A map showing the location of Lake Palcacocha and the city of Huaraz below [Credit: fig 1 from Somos-Valenzuela et al., (2016)] LINK: http://www.hydrol-earth-syst-sci.net/20/2519/2016/

A map showing the location of Lake Palcacocha and the city of Huaraz  [Credit: fig 1 from Somos-Valenzuela et al., (2016)]

The 1941 flood drained the volume of the lake from 10-12 million m³ to just 0.5 million m³

In 1974, to prevent this from happening again, a drainage structure was built that lowered the level of the lake by 8 m. However, over the years as the glacier continued to recede, the glacial lake continued to grow. In 2011, siphons were also installed (see our image this week) within the drainage structure to lower the lake by an additional 3-5 m.

Visiting the hazardous lake

Despite these major efforts to reduce the flood hazard, the lake is now over 73 m deep with a volume exceeding 17 million m³. As part of the Foro Internacional de Glaciares y Ecosistemas de Montaña, a weeklong conference bringing together international experts on topics related to the social, ecological, hydrological, and hazard studies associated with mountain ecosystems, INAIGEM (Instituto Nacional de Investigación en Glaciares y Ecosistemas de Montaña) organized a field expedition that brought ~30 participants to visit Lake Palcacocha. The view of the lake, with its two 6,000+ m peaks behind it, was absolutely stunning. Unfortunately, the glaciers on these peaks are the very things that threaten the lake’s safety, as an avalanche entering the lake could cause another glacial lake outburst flood like the 1941 event – a possibility Peru is very well aware of.

Modelling the glacial lake outburst flood

In response to this threat, a team from the University of Texas at Austin (Daene McKinney, Marcelo Somos-Valenzuela, Rachel Chisolm, and Denny Rivas) has been working closely with Peruvian organizations (INAIGEM and the Glaciology Unit) to model the potential flood from Lake Palcacocha. Hydraulic models were used to investigate the downstream impact, produce preliminary hazard maps, and quantify the amount that the lake should be lowered in order to reduce the hazard of the lake to a safe level. The study of Somos-Valenzuela et al. (2016) found that lowering the level of the lake by 30 m would reduce the total affected area by 30% and, more importantly, would reduce the intensity of the flood (a combination of the water depth and velocity) for most of the city from high to low thereby making the lake much safer.

Overview of the avalanche, lake, and terminal moraine (left) and the potential inundation downstream based on the current level of the lake (right) performed by the University of Texas at Austin. [Credit: fig 2 and 10 from Somos-Valenzuela et al., (2016)] LINK: http://www.hydrol-earth-syst-sci.net/20/2519/2016/ .

Overview of the avalanche, lake, and terminal moraine (left) and the potential inundation downstream based on the current level of the lake (right) performed by the University of Texas at Austin. [Credit: fig 2 (left) and 10 (right) from Somos-Valenzuela et al., (2016)]

 

A hopeful future

The good news for Peru is they have extensive experience lowering the level of their lakes and safely reducing the hazards. Since the Government of Peru established a Glaciology Unit in 1951, Peru has successfully lowered the level over 30 glacial lakes that were considered to be hazardous. Additionally, the citizens of Huaraz are well aware of the hazardous lakes situated above their city and want them to be lowered as well. Given Peru’s track record, hopefully their concerns will be alleviated soon.

Further Reading

Edited by Sophie Berger and Emma Smith

Image of the Week – The Journey of a Snowflake

Image of the Week – The Journey of a Snowflake

REMARK: If you’ve enjoyed reading this post, please make sure you’ve voted for it in EGU blog competition (2nd-to last)!

You remember last winter, when everything was white and you had so much fun building a snowman with your friends? What you see on this image above, is what you would see, if you took a tiny tiny piece of your snowman and put it under a low-temperature scanning electron microscope (SEM). The colours are called “pseudo colours”, they are computer generated based on the number of electrons reflected from a particular part of the image when scanned with a focussed beam of electrons. This is a standard technique used with SEM images to help identify patterns and structure in the image.

This week, let us take you on a journey…from the water vapour in a cloud to the snowman in your garden, to find out what leads to the complex structure you can see on our Image of the Week!


To this purpose we need to start at the very beginning, with a seemingly obvious question:

What is snow?

Snow is, very simply, precipitation in the form of ice crystals that originate in clouds. These ice crystals form when water vapour condensates directly to ice, without becoming liquid water.

From water vapour to ice crystals

For its formation, an ice crystal needs the atmosphere to be colder than the freezing point (0°C) and at least slightly humid. Additionally, like water droplets, ice crystals need a condensation nucleus, for example a dust or pollen particle, to start the growing process around – see the clip from Frozen Planet (below). During the transformation from water vapour to ice, an ice crystal always takes the form of a hexagon due to the way hydrogen and oxygen atoms bond to form water. Afterwards, the temperature and humidity of the atmosphere will shape the crystals and determine how fast they grow (see Fig. 2).

 

Between 0 and -60°C, the basic form (also called “habit”) of an ice crystal changes three times (near -3, -8 and -40°C). Between -3 and -8°C as well as below -40°C, the crystals take the form of six-sided plates, while between 0 an -3°C as well as between -8 and -40°C, the crystals form solid columns that are hexagonal in cross section.

Fig2: Ice Crystal Morphology diagram, indicating the basic form of ice crystals as a function of temperature and supersaturation (humidity). For more information see Libbrecht (2005) [Credit: K. Libbrecht]

In drier air, the growth occurs preferentially across flat surfaces, while in moister air, growth occurs preferentially at the tips, edges and corners. Also, the higher the moisture, the more water droplets can be absorbed, enhancing the growth rate and leading to more complex crystals. On the way between cloud and ground, an ice crystal will pass through layers of different temperature and moisture, leading sometimes to melting and refreezing on the way, changing parts of the crystal as well. All these factors together lead to the fact that finding two identical snowflakes is NEXT TO IMPOSSIBLE

 

From ice crystals to snowflakes

When an ice crystal becomes heavier than the surrounding air, it falls down. If it meets other ice crystals on its way to the ground, they will aggregate, forming new structures and the snowflake will grow. When reaching the ground, a snowflake can therefore be an aggregate of hundreds or sometimes even thousands of ice crystals.

From snowflakes to snowmen

Even when the snowflake has reached the ground, the journey is not finished. If the snow does not melt away rapidly, ice crystals will still modify their texture, size, and shape due to changing temperature and moisture conditions, melting and refreezing processes and/or compressing due to subsequent snowfall.

When the snow cover grows due to many subsequent snowfalls (over the winter or in cold areas over several years), a complex layered structure forms, made up of a variety of ice crystals, that reflect both the weather conditions at the time of deposition and the changes within the snow cover over time.

OR… you build a snowman out of it 🙂

Olaf the enchanted snowman from Disney's 2013 animated feature film, Frozen. [Credit : Disney Wikia]

Olaf the enchanted snowman from Disney’s 2013 animated feature film, Frozen. [Credit : Disney Wikia]

Further Reading

Edited by Emma Smith and Sophie Berger

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