Of Icebergs and Climate Change

(Guest blog by Vikram Goel, an Antarctic Glaciologist. He has been studying Antarctica while living in The Arctic for the past 3 years.)

 

Recently, a very big chunk of ice broke off from an ice shelf in the Antarctic Peninsula. This iceberg (named A68) is 5,800 sq. km in area and weighs more than 1 trillion tonnes [1]. This event was widely reported across the news media. But there seem to be some differences in the story from many news reports and the scientific community [2], especially regarding the relation of this event to climate change. In this text, we discuss this event and its implications through a Q&A format.

Iceberg_Vikram-2

Ice shelves, ice sheets, ice bergs… I´m confused!

Antarctica is a gigantic ‘sheet of ice’ more than 4 km thick at its thickest regions and holds 90% of all the ice in the world! It gains mass through snowfall which compresses over time to form ice. This ice travels towards the Antarctic coast under the force of gravity through giant glaciers. At the coast when the ice reaches the ocean, it starts to float and form flat slabs (like a shelf) of floating ice known as ‘ice shelves’. At the edges of these ice shelves, ice is constantly breaking into smaller pieces, releasing icebergs into the sea.

How much does this trillion tonne iceberg contribute to the sea level rise?

Zero. Since the ice shelf was already floating in the sea, there is no extra increase in the sea level after it broke off.

Is the iceberg a sign of recent climate change?

Icebergs break all the time from Antarctica. It is the prime mechanism through which Antarctica loses its ice and is a very common process. Most of the icebergs are small, but there have been icebergs as large as the A68. As it is such a common process it is hard to say if climate change has a direct role in this calving event.

Phew, so nothing to worry here?

Ermmmm, not so quick. Although the iceberg calving is a natural process, losing such a large piece of an ice shelf can have adverse effects on the stability of the remaining ice shelf, making it more vulnerable to climate change.

Well, the ice shelf is floating anyways, why do we care about it?

Ice shelves are like taps regulating the loss of ice from Antarctica, by slowing down the glaciers feeding into it. If the ice shelf is lost, it would result in loss of this resistance to the glacier flow, leading to increased ice flow and eventually sea level rise.

VG_Larsen-B-Collapse_Dates

Larsen B Ice Shelf Collapse. Image credits: NASA

Has an ice shelf been lost before?

Yes, a few [3]. The most recent and major one was the disintegration of Larsen B ice shelf in 2002. Scientists recorded up to 3 times increase in the ice loss [4] from glaciers feeding into this ice shelf.

What does climate change have to do with ice shelf stability?

Recent changes in climate have increased the access of warm water below the ice shelves. These warmer waters can melt the underbelly of an ice shelf and make it thinner and retreat. Also, warm air temperature can lead to melting on the ice shelf surface. Water being denser than ice cuts through the ice all the way and leads to the formation of large cracks. This process was critical behind the disintegration of Larsen B ice shelf.

 

Effects of global warming on stability of an ice shelf. Source: Reinhard Drews

Pinning points (green) can help stabilize an ice shelf by providing support (buttressing), whereas they are also subject to melting (red) from the underneath from warmer ocean waters. 

Source: Reinhard Drews

 

Map of Larsen C, overlaid with NASA MODIS thermal image from July 12 2017, showing the iceberg has calved. Source - Project Midas

Map of Larsen C, overlaid with NASA MODIS thermal image from July 12 2017, showing the iceberg has calved. Source – Project Midas

Oh no! Are we going to lose Larsen C soon?

Hard to say! Stability of an ice shelf depends upon several other factors. For example, if there is a high in the ocean bed, ice shelf can get ‘pinned’ at such a point. Such pinning point can provide extra support (buttressing) to an ice shelf and help stabilize it. Larsen C has two such pinning points supporting the ice shelf. But since the loss of A68, another rift has started to propagate the ice shelf and is currently extending towards one of the pinning points (Bawden ice rise). Although unlikely, if this crack goes past this pinning point, the ice shelf will lose the support from this ice rise, making a large part of the ice shelf very vulnerable.

I feel bad for the penguins living there, but sea level rise doesn’t affect me?

Like most global problems, the effect of climate change won’t be spread evenly, with some people affected more than others. But as we live in a global interconnected system, these effects will reach everyone eventually.

Let us take the the Bengal region (West Bengal + Bangladesh) as an example. It is one of the most densely populated regions in the world with a population equivalent to  Germany, France, Spain, and Italy combined. This region is also one most exposed to sea level rise, with its rather flat and low elevation. This region is expected to lose 11% of its territory  by 2050 from a sea level rise of only 1 meter, a level that is not a particularly extreme prediction. [5]

One short term increase in sea level rise, increases the penetration power of a cyclone hitting this region. With the stronger storms getting more intense [6] this is a bad combination.

The long term effect is displacement of these millions of mostly poor people which will create a climate refugee problem for India for the decades to come.  Even if you don’t  live in this region, displacement/influx of people in such numbers will affect everyone in form of economic and social policies. And this is just one small part of the story.

What about the glaciers in the Himalayas, are they affected as well?

Yes. Glaciers in the Himalayas are melting and retreating quite fast [7].

Again, there are long term and short term consequences. These glaciers usually have a wall of rubble in front of them, which they have eroded while extending. When these glaciers retreat, these walls of rubble trap the meltwater from the glacier forming huge lakes over time.

But at some point, these natural dams break draining the lake and flooding the villages and towns downstream. The potential of losses to such glacial lake outburst floods has been increasing steadily [8], and is one of the short term hazards of climate change in the Himalayas . Whereas on the longer term, the shrinking glaciers raise difficult questions on the water security of one sixth of the human population.

About the author:

I’m an Antarctic glaciologist and currently investigating ice rises (pinning points in ice shelves) in East Antarctica. I´ve been fortunate enough to visit Antarctica and investigate these features first hand. I’ve also lived in Arctic (one of the fastest warming regions in the world) where I got the opportunity to work with some of the best climate scientists around. In addition to conducting research, I wish to also communicate it to the general public. This article is one such attempt. For more related content, you can follow the NPI Glaciology group on Twitter, Facebook & Instagram.

Questions:

If you have any questions for Vikram, please leave them in the comments below or send your questions to [email protected] with subject ‘Of Icebergs and Climate Change’. 

This article is part of a series where we simplify larger environmental and climatic changes, and explain how they apply in the Indian context. Think you’re an expert and there’s something you want to simplify for others? Write to us at [email protected] with subject ‘ELI5 – Veditum’.

References:

  1. O’Leary, M., Luckman, A. & MIDAS, P. Larsen C calves trillion ton iceberg. Project MIDAS Available at: http://www.projectmidas.org/blog/calving/. (Accessed: 17th August 2017)
  2. Fricker, H. A. Melting and cracking – is Antarctica falling apart? The Guardian (2017).
  3. Davies, B. Ice shelf collapse. AntarcticGlaciers.org Available at: http://www.antarcticglaciers.org/glaciers-and-climate/shrinking-ice-shelves/ice-shelves/. (Accessed: 17th August 2017)
  4. Wuite, J. et al. Evolution of surface velocities and ice discharge of Larsen B outlet glaciers from 1995 to 2013. The Cryosphere 9, 957–969 (2015).
  5. Bay of Bengal: a hotspot for climate insecurity | Sustainable Security. Available at: https://sustainablesecurity.org/2013/08/10/bay-of-bengal-a-hotspot-for-climate-insecurity/. (Accessed: 1st September 2017)
  6. Knutson, T. R. et al. Tropical cyclones and climate change. Nature Geoscience 3, 157–163 (2010).
  7. Contrasting patterns of early twenty-first-century glacier mass change in the Himalayas : Nature : Nature Research. Available at: http://www.nature.com/nature/journal/v488/n7412/full/nature11324.html?foxtrotcallback=true. (Accessed: 2nd September 2017)
  8. Formation of Glacial Lakes in the Hindu Kush-Himalayas and GLOF Risk Assessment – HIMALDOC. Available at: http://lib.icimod.org/record/8047. (Accessed: 2nd September 2017)

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