Dear Dr Marcott,
I am fascinated by your research on the Heinrich events [1]. It was a
hot topic at the EGU meeting in Vienna, when I was presenting a paper on
the role of Arctic sea ice in regulating the temperature of the planet.
I had focussed on the warming period of past 20 kyrs (i.e. post LGM) and
how the discharge of meltwater into the North Atlantic had served as a
negative feedback on polar amplification by Arctic sea ice ('albedo
flip' effect) of a Milankovitch warming signal carried by the Gulf
Stream (becoming North Atlantic current) into the Arctic Ocean. However
I was a bit flummoxed by the previous period of glaciation with the
Heinrich events 1-6. At the meeting, I heard of the idea of warming
under the ice shelves that hold back Canadian ice sheet movement. Your
paper makes a very good case for this explanation of the Heinrich events.
I am copying this email to Stefan Rahmstorf, who I met at the EGU
meeting, and has contributed to the discourse on Heinrich events. I
would be interested in his comment on your paper.
Your research raises concerns about the Antarctic role in positive
feedback to sudden sea level rise [2]. Since there are signs of the
Pine Island glacier already being past a tipping point [3], we could see
an accelerating discharge with a positive feedback to the Greenland ice
sheet discharge.
The disharges both from Greenland and Antarctica show ice mass loss rate
greater than previously thought [4]. And Hansen has recently estimated
that discharge rate from Greenland is doubling each decade [5]. He is
now suggesting that we could have several metres of sea level rise this
century.
In the email below, Albert Kallio mentions a comment about the paper by
Joe Romm yesterday [6]. Romm is concerned that only a small amount of
warming could trigger a large sea level rise.
Along with these observations of ice, we have reports of fresh water
building up in the Arctic [7]. This could give rise to a sudden
reduction of the AMOC (Atlantic Meridional Overturning Circulation), and
warmer water in the northwest Atlantic. There are already signs of
warmer water, presumably from the Gulf Stream, appearing on the west
coast of Greenland, suggesting a weakening of the AMOC is taking place.
So my questions to you are: could we be witnessing the start of a
process akin to that which triggered Heinrich events in the past; and
could this process happen over just a few years, rather than centuries
or millenia?
If the answers are in affirmative, then it raises the possibility that a
massive discharge of ice from Greenland would cool the North Atlantic,
Europe and the Arctic, sufficient to restore the Arctic sea ice to its
previous extent and prevent a methane excursion! On the other hand the
discharge might happen too late - in which case we get abrupt global
warming from methane as well as abrupt sea level rise!
Kind regards,
John (Nissen)
Chiswick, London W4
[1] www.pnas.org/content/early/2011/07/25/1104772108
<http://www.pnas.org/content/early/2011/07/25/1104772108>
[2]
http://oregonstate.edu/ua/ncs/archives/2011/aug/ancient-glacial-melting-similar-concerns-about-antarctica
[3]
http://www.newscientist.com/article/dn18383-major-antarctic-glacier-is-past-its-tipping-point.html
[4]
http://www.ncnguyana.com/ncngy/index.php/world/world-news1561100476/antarctica/391-antarctic-glaciers-melting-faster-than-previously-thought
[5]
http://www.columbia.edu/~jeh1/mailings/2011/20110118_MilankovicPaper.pdf
[6]
http://thinkprogress.org/romm/2011/08/02/285696/glacial-melting-subsurface-warming-trigger-rapid-collapse-of-ice-shelves/
[7] http://www.sciencedaily.com/releases/2011/03/110325111901.htm
---
On 03/08/2011 09:19, Veli Albert Kallio wrote:
------------------------------------------------------------------------
Date: Tue, 2 Aug 2011 23:34:36 +0100
Subject: [geo] Heinrich event PNAS paper
From: andrew.lock...@gmail.com
To: geoengineering@googlegroups.com
Sudden rapid collapse of ice suggests a need for vigilance and
possible early geoengineering start imo
Romms interpretation, perhaps going too far?
thinkprogress.org/romm/2011/08/02/285696/glacial-melting-subsurface-warming-trigger-rapid-collapse-of-ice-shelves/?utm_medium=twitter&utm_source=twitterfeed
<http://thinkprogress.org/romm/2011/08/02/285696/glacial-melting-subsurface-warming-trigger-rapid-collapse-of-ice-shelves/?utm_medium=twitter&utm_source=twitterfeed>
Paper: www.pnas.org/content/early/2011/07/25/1104772108
<http://www.pnas.org/content/early/2011/07/25/1104772108>
A
Ice-shelf collapse from
subsurface warming as a
trigger for Heinrich events
Episodic iceberg- discharge events from the
Hudson Strait Ice Stream (HSIS ) of the
Laurentide Ice Sheet, referred to as Heinrich
events, are commonly attributed to internal ice -
sheet instabilities, but their systematic
occurrence at the culmination of a large
reduction in the Atlantic meridional overturning
circulation (AMOC) indicates a climate control.
We report Mg /Ca data on benthic foraminifera
from an intermediate-depth site in the
northwest Atlantic and results from a climate-
model simulation that reveal basin- wide
subsurface warming at the same time as large
reductions in the AMOC, with temperature
increasing by approximately 2 ° C over a 1–
2 kyr interval prior to a Heinrich event. In
simulations with an ocean model coupled to a
thermodynamically active ice shelf, the increase
in subsurface temperature increases basal melt
rate under an ice shelf fronting the HSIS by a
factor of approximately 6. By analogy with
recent observations in Antarctica, the resulting
ice- shelf loss and attendant HSIS acceleration
would produce a Heinrich event.
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