Category Archives: Cryosphere

Study of Antarctic Ice Balance

The ice is melting everywhere.

In Antarctica, the ice shelves extending over the ocean have been thinning at a rapid pace, likely due to warmer ocean waters undercutting them.  This could lead to ice from the interior flowing faster to the sea, resulting in thinning of the whole ice cap. But this relationship has not be established, nor is it clear how much of overall ice changes might be due to such effects.  In addition, it has not been known how rapidly any effect propagate inland, i.e., how fast the rest of the ice responds to the loss of sea ice.

This winter, researchers from California and Northumbria report a new study of the whole of Antarctica uses improved measurements of ice thickness and movement from IceSat-2 and earlier satellites [1].  They developed a model of the complex processes that occur at the grounding lines of glaciers, which are the product of “an intricate interplay between several opposing processes”.

The model agrees with the observed distribution of ice losses around Antarctica.  Furthermore, the model suggests that the effects are essentially instantaneous, i.e., thinning sea ice causes increased flow upstream with little delay.  This model only includes the effects of thinning at grounding lines, but this seems to be a major contributor to the overall mass loss.  These changes at grounding lines are due to warming ocean waters.

“We find that the magnitude and spatial variability of modelled changes are in good agreement with observations, suggesting that thinning ice shelves have driven a substantial portion of the recent ice-loss of the Antarctic ice sheet”

Both the data and the models have limitations, so this finding will need to be confirmed with further study and better data. The data is still pretty sparse, and there are plenty of other factors that may be involved (such as wind, cloud cover, and precipitation patterns).

But if these findings stand up, we can expect to see further rapid ice loss across all of Antarctica, with much faster losses in places where warm ocean waters are thinning the sea ice.


  1. G. Hilmar Gudmundsson, Fernando S. Paolo, Susheel Adusumilli, and Helen A. Fricker, Instantaneous Antarctic ice-sheet mass loss driven by thinning ice shelves. Geophysical Research Letters, n/a (n/a) 2019/11/20 2019. https://doi.org/10.1029/2019GL085027

The Permafrost Is Outgassing

As the ice melts everywhere, the permafrost (permanently frozen soil) is also melting.  When this frozen muck thaws, it releases swamp gas—lots of CO2 and methane, for example—into the atmosphere.

Depending on the amount of freezing, thawing, and accumulation of seasonal debris (dead plants), the permafrost alternatively sucks in and puts out Carbon.

Since the last ice age, permafrost has generally remained frozen except for relatively shallow surface areas.  This has encapsulated the organic materials frozen there.  During the short summer, plants grow and absorb Carbon from the atmosphere, and the winter cold refrigerates the dead foliage, preventing decay back into the atmosphere.  So, up to now, permafrost has been a Carbon sink, soaking up Carbon out of the atmosphere .

As global air temperatures have risen, and polar surface areas even more rapidly warm, permafrost has begun to perma-melt.  Ultimately, this will tip the balance, so that the soil no longer retains additional Carbon.  Worse, the Carbon frozen underground over centuries will be released into the atmosphere [1].  This, like reduced albedo, is a potential positive feedback, speeding up warming.

However, data from these cold, remote regions is sparse, so it hasn’t been clear how much Carbon these regions absorb (in the summer) and emit (in the winter).  There are vast areas of permafrost in the Northern hemisphere, with a variety of vegetation, microbes, and seasonal patterns.

This winter, an international team reports on a comprehensive collection of measured CO2 emissions from northern permafrost.  They combine these measures with satellite observations of vegetation and conditions, and built a model of the physics.  This study indicates that CO2 emissions may already exceed uptake [2].

Source: NASA Earth Science News [3]
Extrapolating the model with different scenarios for global temperatures, the CO2 emissions could increase 17-41% by year 2100.  This would place it somewhere in the 1-2 billion tons or Carbon per year (compared to 30+ billion tons per year released due to human activities).  It looks like human generated warming has an additional side effect, causing tons of Carbon to be released from permafrost, which will only increase warming further.

Of course, these estimates are extrapolations from relatively sparse data points, and are aggregated over huge spaces and time periods.  (E.g., they estimate emissions for 25×25 km areas for a month.)  The study also neglects the “shoulder seasons” (spring and fall), and other gasses including methane.  Nevertheless, these results seem to be in line with data and theory, so they are plausible, as are the projections into the future.

The upshot is that the arctic is flipping from a Carbon sink to a Carbon source—pretty much the opposite of what we should want to see.

The warmer it gets, the more carbon will be released into the atmosphere from the permafrost region, which will add to further warming,” said co-author and WHRC scientist Brendan Rogers. “It’s concerning that our study, which used many more observations than ever before, indicates a much stronger Arctic carbon source in the winter. We may be witnessing a transition from an annual Arctic carbon sink to a carbon source, which is not good news.” (From [3])


  1. John L. Campbell, Arctic loses carbon as winters wane. Nature Climate Change, 9 (11):806-807, 2019/11/01 2019. https://doi.org/10.1038/s41558-019-0604-8
  2. Susan M. Natali, Jennifer D. Watts, Brendan M. Rogers, Stefano Potter, Sarah M. Ludwig, Anne-Katrin Selbmann, Patrick F. Sullivan, Benjamin W. Abbott, Kyle A. Arndt, Leah Birch, Mats P. Björkman, A. Anthony Bloom, Gerardo Celis, Torben R. Christensen, Casper T. Christiansen, Roisin Commane, Elisabeth J. Cooper, Patrick Crill, Claudia Czimczik, Sergey Davydov, Jinyang Du, Jocelyn E. Egan, Bo Elberling, Eugenie S. Euskirchen, Thomas Friborg, Hélène Genet, Mathias Göckede, Jordan P. Goodrich, Paul Grogan, Manuel Helbig, Elchin E. Jafarov, Julie D. Jastrow, Aram A. M. Kalhori, Yongwon Kim, John S. Kimball, Lars Kutzbach, Mark J. Lara, Klaus S. Larsen, Bang-Yong Lee, Zhihua Liu, Michael M. Loranty, Magnus Lund, Massimo Lupascu, Nima Madani, Avni Malhotra, Roser Matamala, Jack McFarland, A. David McGuire, Anders Michelsen, Christina Minions, Walter C. Oechel, David Olefeldt, Frans-Jan W. Parmentier, Norbert Pirk, Ben Poulter, William Quinton, Fereidoun Rezanezhad, David Risk, Torsten Sachs, Kevin Schaefer, Niels M. Schmidt, Edward A. G. Schuur, Philipp R. Semenchuk, Gaius Shaver, Oliver Sonnentag, Gregory Starr, Claire C. Treat, Mark P. Waldrop, Yihui Wang, Jeffrey Welker, Christian Wille, Xiaofeng Xu, Zhen Zhang, Qianlai Zhuang, and Donatella Zona, Large loss of CO2 in winter observed across the northern permafrost region. Nature Climate Change, 9 (11):852-857, 2019/11/01 2019. https://doi.org/10.1038/s41558-019-0592-8
  3. Samson Reiny and Miles Grant, Permafrost Becoming a Carbon Source Instead of a Sink, in NASA Earth Science News. 2019. https://earthobservatory.nasa.gov/images/145880/permafrost-becoming-a-carbon-source-instead-of-a-sink

Modeling Arctic Albedo

One of the worrying aspects of the great melt is that the melting ice uncovers land and sea that are a lot less reflective than ice.  The decreased albedo of the non-ice absorbs more sunlight, warming the surface and further increasing the melting, and so on, with a positive feedback.  In the worst case, this might lead to a runaway speed up, causing a rapid crash in the ice and snow covers and even higher air and water temperatures.

That’s the theory.  How much is this happening, and how large are the effects?

Observational records show that the albedo in arctic areas has steadily decreased in the last few decades. Climate records for the same times show that arctic areas are warming faster than the global average.  Is this additional warming due to decreased albedo over this period?  If so, what exactly is happening?

As usual, there are a lot of variables contributing to the overall albedo and its effects. Soot and other pollution might be decreasing the albedo of the snow cover itself (i.e, dirty snow isn’t a reflective). While ice and snow have been thinning and retreating in many places, there is also increased precipitation in other places. In addition, snow and ice cover insulates the surface, so thinning snow can increase the flow of heat between the land, sea, and air, as well as change the albedo.  Changes in winds can change the distribution of snow and sea ice, even if the amounts are similar.

And so on.

This winter researchers from US Pacific Northwest National Laboratory report investigations of arctic albedo since 1980 [2].  They ground the model in Earth observations from NASA satellite data, and also in reanalysis of old satellite data.  These data all show a clear trend of decreasing albedo, albeit with considerable spread that reflects (no pun intended) uncertainty.  (Estimating albedo over vast areas of natural surface is not a trivial thing to do. E.g., this.)

The heart of the study is to use the detailed model to “attribute” the albedo changes to various factors.

They find that 70% of the albedo reduction is due to decrease in snow cover, and 30% to the retreat of sea ice.  Of the snow cover, about half is over land, and half over sea.  The latter is snow on top of sea ice, which insulates and increases the albedo.  I.e., loss of snow cover exposes the ice which is darker and melts easier.

The analyses indicate that the important changes in snow cover is driven primarily by increased atmospheric temperature. They also find that effects from soot have decreased, which is in line with decreased emissions.

In short, warmer air and concomitant decreased snowfall have decreased snow cover which has decreased the albedo of the land and of sea ice.  In addition, retreating sea ice exposes lower albedo open water.  These factors have resulted in a decrease of more than 1% per decade in the albedo of arctic regions.

This work certainly makes sense in the overall picture, and perhaps contributes to confidence in the validity of the albedo estimates.  Measuring snow and ice cover is tricky, and deriving albedo is uncertain.

However uncertain the measurements and models may be, the ice is definitely melting, one way or another.  And this study shows a pretty straightforward link between warming air, melting snow and ice, and increased albedo.

So, there’s that.


  1. Mark Kinver, Ice loss causing Arctic to reflect less heat, in BBC News – Science & Environment. 2019. https://www.bbc.com/news/science-environment-50381328
  2. Rudong Zhang, Hailong Wang, Qiang Fu, Philip J. Rasch, and Xuanji Wang, Unraveling driving forces explaining significant reduction in satellite-inferred Arctic surface albedo since the 1980s. Proceedings of the National Academy of Sciences:201915258, 2019. http://www.pnas.org/content/early/2019/11/05/1915258116.abstract

 

PS.  This article suggested a bunch of great names for bands:

Arctic Albedo
Mean Surface Albedo
Arctic Amplification
Amplified Arctic Warming
Surface Air Temperature
Snow Cover Fraction

 

New Baby Iceberg, D28

And another big berg calves in Antarctica!

Ice berg D28 has split from the Amery Ice Shelf [1].  At 1600 sq km, it’s only a third the size of the mighty A68.  But still, it’s a big one, so watch out!

The EU’s Sentinel-1 satellite system captured these before and after images (Image Credit COPERNICUS DATA/SENTINEL-1/@StefLhermitt) (From [1])
(Oooh!  Such a big girl! Who’s a good baby iceberg?  You’re a good baby iceberg.  Isn’t she cute?? )

As far as I can tell, this ice sheet is ‘in balance’, i.e., shedding bergs at a rate to balanced with the inflowing glaciers.  So this part of the ice isn’t going away, at least not at the ice sheet.  (I dunno if the glaciers might be thinning or growing inland.)


  1. Jonathan Amos, 315 billion-tonne iceberg breaks off Antarctica, in BBC News – Science & Environment. 2019. https://www.bbc.com/news/science-environment-49885450

 

Arctic Sea Ice Minimum for 2019

The ice is melting everywhere.

One of the most dramatic melts is the North polar icecap, which is shrinking rapidly.  The US National Snow and Ice Data Center reports this fall on the “minimum” for 2019, based on measurements from several satellites [1].  On September 17, the area covered by ice was 4.15 million square kilometers, which is the second smallestarea  ever recorded (these records go back to 1979).

The NSIDC reminds us that there still could be a late season heat wave or storm that pushes the ice back even farther.  The lowest recorded minimum in 2012 was partly due to a powerful cyclone that smashed into the ice [2].

Changing winds or late-season melt could still reduce the Arctic ice extent, as happened in 2005 and 2010.  (from [1])

It seems clear that the ice is disappearing at the North pole, as it is everywhere.

These particular data are a bit tricky to define for a number of reasons.  For one thing, “sea ice cover” is a bit, well, slushy.  There can be a lot of ice in the water that is still mostly water, and a lot of chunks with water in between, and also ice under the surface.  The NSIDC has heuristics for estimating these, and for defining areas “covered” with sea ice, so these annual estimates should at least be comparable to each other.

In addition to uncertainties in the data, there is no data at all before 1979, a mere 40 years ago.  So, we can’t really say much about long term trends in the past.  And while this year is the second lowest on record, over the last dozen years the data are basically going up and down in a small range.  We are in a relatively low ice period, but things aren’t changing fast.

Still, I’d bet the ice will continue to shrink, just as all the models predict.  This will have, and probably already is having, a positive feedback effect on ocean temperatures.  Exposed sea water is darker and absorbs sunlight faster than ice, increasing the warming in the summer, and generating warmer water that contributes to the overall warming of the oceans.

One thing that the melting ice cap does not do is increase sea levels, at least in any direct sense.  Going from ice to liquid reduces the volume of the water.


  1. National Snow and Ice Data Center, Arctic sea ice reaches second lowest minimum in satellite record, in Arctic Sea Ice & Anaysis. 2019. https://nsidc.org/arcticseaicenews/2019/09/arctic-sea-ice-reaches-second-lowest-minimum-in-satellite-record/
  2. Maria-José Viñas, 2019 Arctic Sea Ice Minimum Is Second Lowest, in NASA Earth Observatory. 2019. https://earthobservatory.nasa.gov/images/145641/2019-arctic-sea-ice-minimum-is-second-lowest

Iceberg A68 on the move

We’ve all been tracking A68 (nee Larsen C), the Manhattan sized iceberg that was born in 2017 and is slowly heading North into the Atlantic ocean.  She’s a big girl, and she moves at a stately pace.

She’s two years old now, and finally on the move.  Cryophile Adrian Luckman assembled a nice sequence from satellite imagery.

(Images from [2])

This gif shows A68 has been caught in the Weddell Gyre, a giant ocean eddy that has pulled her 250 km north.  Cruising at a sustained 1/3 km per hour, trillion tonne A68 or her children will likely reach the South Atlantic eventually, there to menace shipping as she melts.

You go, girl!!


  1. Jonathan Amos, A68: World’s biggest iceberg is on the move, in BBC News – Science & Environment. 2019. https://www.bbc.com/news/science-environment-48920168
  2. Adrian Luckman, Happy second birthday, Iceberg A68, in Ade’s glacier gallery. 2019. https://adrianluckman.wordpress.com/2019/07/11/happy-second-birthday-iceberg-a68/

 

PS.  Wouldn’t  “The Weddell Gyre” be a good name for a band?

The Himalayas are Melting, too

The ice is melting everywhere.

We have detailed measurements in many places, including Greenland and places with a lot of scientists, such as Europe and North America.  Uninhabited (and uninhabitable) Antarctica has been the target of intense investigation, especially with satellites and other remote sensing instruments.

We don’t necessarily have good records from other places, so there has still been room for doubt? hope? whatever that some the melting isn’t ubiquitous.  One of the biggest question marks is the Himalayas and Tibet.  The area is remote and sparsely populated, and politically disputed for more than a century, so there isn’t a lot of data.

This summer a team from Columbia U. report on a study using declassified reconnaissance imagery from 1975 forward [1].  The research constructed a dataset extracted from digitized  KH-9 imagery (1975-2000) and NASA/MITI ASTER images (2000-2016), to give a 40 year record of the extent of the glaciers.  The KH-9 images were used to compute digital elevation models, which indicate the height of the ice.  The data covers about a third of the glaciers across the region.

This data shows that the glaciers in the studied sample have been retreating over the 40 years, and losing ice faster in the twenty first century than the earlier period.  These results are similar to findings from many parts of the world.  The consistent region wide loss of ice suggests that the cause is likely due to atmospheric warming.

This dataset is particularly important because models of these glaciers have high uncertainty.  The complex monsoon weather patterns mean that some glaciers grow from winter snows, and others grow from monsoon precipitation.  In addition, the area has received considerable deposits of soot and dust from the human activities in the area, which decrease the albedo and potentially increase melting.  This dataset helps constrain the modelling, and may help parse out the role of different factors.  (And, as noted, the models must account for the consistent, region wide losses.)

It’s pretty neat to use these old reconnaissance images for this study.  I’ll note that spy satellite data was not intended to measure climate conditions, and simply doesn’t have information comparable to purpose built scientific satellites.  However, the images can be used to create DEMs, and it does record snow and ice cover, as this study shows.

I’ll  note that combining data like this takes a lot of care. The imagery has to be patched together from many passes, and different satellites have different instruments and outputs. The combined dataset must be carefully constructed to account for “variable spatial resolutions, distinct void-filling methods, heterogeneous spatial and temporal coverages, and different definitions of glacier boundaries” ([1], p. 7)

For this reason, it will be important to carefully validate these results with both additional data and with careful modelling.

However, the broad picture is consistent with what we see everywhere, and there is no reason to think that this region would not be following global trends.  So the results are quite plausible.

And the implications are serious.  These glaciers feed rivers that are critical water supplies for many millions of people.  Reduction in the flow will be big trouble for everybody downstream.

“In the short-term, the huge increase in meltwater could cause flooding.

“In the longer term, millions of people in the region who depend on glacier meltwater during drought years could experience very real difficulties.” (From [2])


  1. J. M. Maurer, J. M. Schaefer, S. Rupper, and A. Corley, Acceleration of ice loss across the Himalayas over the past 40 years. Science Advances, 5 (6):eaav7266, 2019. http://advances.sciencemag.org/content/5/6/eaav7266.abstract
  2. Rebecca Morelle, Spy satellites reveal extent of Himalayan glacier loss, in BBC News – Science & Environment. 2019. https://www.bbc.com/news/science-environment-48696023