More Rain Events Speed Melt on Greenland Ice Sheet

July 13, 2015

New paper in Nature Geoscience, Jason Box and Alun Hubbard are co-authors.
Above, I got a quick rundown from Dr. Box, a few days ago, via (sorry) herky-jerky skype from Northern Iceland.

UPDATE: Below, I finally found the clip I was looking for, Jason talking to the camera in August of last year, in the midst of a 30 hour rain event that engulfed our camp in southwest Greenland.

While on the ice for Dark Snow 2014, we experienced a 30 hour precip event that featured high wind and horizontal driving rain.  Afterward, ablation stakes on-site indicated that a very large amount of surface melting had taken place during the previous day and a half.
The new study finds that increased incidences of rain on the Greenland sheet may indeed be a contributing factor to more mass loss, by sending large volumes of warm water deep into the ice,  now and even more so as the arctic continues to warm.

One of the key factors that accelerates Greenland mass loss is the so-called “Zwally effect”, wherein warm melt water “lubricates” the underbelly of the ice, where it meets bedrock, and cause acceleration toward the sea.
Scientists now know that this effect is moderated over time, as the glacial drainage system opens up during the summer melt and becomes more efficient, meaning more water delivered to the sea with less uplift to the overlying ice.
However, in later summer, that drainage system begins to close down as temperatures drop, – making it vulnerable to increasing numbers of late season warm and wet events, which can cause more upheaval at the base of the ice, and could be responsible for substantial increases in late season movement.

Nature Geoscience: Amplified melt and flow of the Greenland ice sheet driven by late-summer cyclonic rainfall

 For eight days during late August and early September 2011, reanalysis data27 indicate that a cyclone (minimum surface pressure of 992hPa) centred on Baffin Bay off the west coast of Greenland advected warm, southwesterly airflow over the GIS, bringing extensive precipitation, which was especially heavy in southeast Greenland.

We find that a concomitant flow response is evident in all available velocity records from these regions, including three major marine-terminating glaciers located up to 370km north of Kangerlussuaq: ice flow increased by 9% and 95% above the preceding week at GPS sites on Store Glacier30 (S11) and Sermeq Avannarleq6 (A20) respectively.

Science Nordic:

The study began after observing exceptionally warm wet weather in late summer 2011, causing huge amounts of melt at the ice surface. At this time of the year, there was no snow on the surface of the ice to absorb and act as a buffer for all this rain and melt water, which then moved very quickly through the ice sheet.

“At first our observations of this late-August intense rainfall and melt event were met with the attitude of “hey big deal, it’s summer, it melts”,” says professor Alun Hubbard from the Center for Arctic Gas Hydrate, Environment and Climate at The Arctic University of Norway, and principle investigator of the project that led to the study.

“But this new data, shows these periods of rapid movement of the ice are in fact tied to a particular type of rainfall event, the kind of storm you would expect to see in the mid-latitudes — UK or Scandinavia — and not so much in Greenland where high pressure systems are more common.”

“We can now reinterpret these big late summer melt events to get a much better understanding of what is going on — what is affecting the ice sheet system and how it is responding” he says.

Imagine a storm drainage system after heavy rain

Hubbard uses the analogy of a storm drainage system, to explain how the rain and melted ice moves through the ice sheet so quickly.

“Imagine a big downpour in a city. You get so much rain so quickly, on to an impermeable concrete surface that the water is immediately shunted into the city’s drainage system — which due to the huge volumes of water — can’t cope. Drains back up and it floods. Basically, the same thing happens on the bare ice sheet surface, which like the city is literally comprised of pipes, conduits and cavities,” he says.

According to him, when these pipes back up the hydraulic pressure lifts the ice sheet up, like a gigantic iceberg. There is less friction at the bed and so it moves faster.

Below, my 2013 interview with Alun Hubbard.

4 Responses to “More Rain Events Speed Melt on Greenland Ice Sheet”

  1. dumboldguy Says:

    S**T! Something else to worry about. Thanks!


  2. I understand about reducing emissions but, is there any way for individuals to put carbon back into the earth?

    How much does planting a tree help? What kind of trees and how many per person? Do crops help and, if so, which ones? Can you plant annual grasses and mow them under each year? Are there other strategies that may help?

    It may seem small but since there are so many of us small may help even if just a little.

  3. Colorado Bob Says:

    What Box says about warm rain also applies to altitude as well –

    The Hindu Kush Before and After the Great Pakistani Floods


    I saw this image from the Swat Valley in August, and I was stunned . Not for what is in the foreground, I was in the Big Thompson Flood in 1976. I know what happens when it rains like hell in the mountains. What struck me are those mountains in the background. That is the Hindu Kush . These two pictures were shot in the last week of July (left), and from the same spot 3 weeks later. Look at all that missing snow.

    Link

  4. John Says:

    Reblogged this on jpratt27.


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