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When the Great Ice Sheets Start Going Down — Approaching the Age of “Storms”
4
June, 2015
The
great ice sheets are melting with increasing velocity. Melt
ponds are forming over Greenland, then pounding heat down through the
ice like the smoldering hammers of ancient Norse fire giants.
Warming mid-depth ocean waters are eating away at the undersides of
Antarctica’s great ice shelves. Pools of fresh water are expanding
outward from the bleeding glaciers, flooding the surface zones of the
world’s oceans. Sea
level rise rates have jumped to 4.4 millimeters per year. And
the North Atlantic Overturning Circulation (AMOC) is slowing down.
(Accelerating
ice mass loss from Antarctica, Greenland and other continental
glaciers and ice caps [GICs]. Image source: Geophysical
Research Letters.)
Keeping
all this in mind, let’s talk a little bit about the ugly transition
to phase 2 climate change. A transition it now appears we’re at the
start of. The — you should have listened to Dr. James Hansen and
read The
Storms of My Grandchildren —
phase of climate change. The awful, long, stormy period in which the
great glaciers really start going down.
*
* * * *
In
an effort to organize how human-caused climate change may proceed, it
helps to break the likely progression of human-caused climate change
down into three basic phases. For this simplification we have phase 1
— polar amplification, phase 2 glacial melt and storms, and phase 3
— runaway hothouse and stratified/Canfield Oceans. For this
article, we’ll focus mostly on phase 1 and 2.
Phase
1 — Polar Amplification
During
the first phase, human greenhouse gas emissions gradually add heat to
the atmosphere. This causes general warming that is most intense at
the polar regions, especially in the Northern Hemisphere. Called
Polar Amplification, this added heating at the poles occurs due to
greenhouse gasses’ ability to increase the atmosphere’s heat
trapping efficiency at night, when the sunlight angle is low, or
during periods of dimmer light (cloudiness etc). In addition, snow
and ice melt cause albedo loss at the poles and greenhouse gasses
sequestered within frozen carbon stores may release during warming as
ice thaws adding another kick to polar amplification (amplifying
feedbacks). Due to lower volumes of continental ice, more low-albedo
land mass, more vulnerable carbon stores, and closer proximity to
human greenhouse gas emissions sources, the Northern Hemisphere polar
zone is most vulnerable to increased rates of warming during phase 1
climate change.
Weather
impacts during phase 1 include a slowing down of the jet stream due
to loss of polar ice, a multiplication of slow moving weather
systems, an increasing prevalence of drought and heavy rainfall
events, and a slow ratcheting of the intensity of powerful storms.
Phase 1 continues until ice sheets begin to become heavily involved
and melt outflows greatly increase. At that point, we begin a
transition to a more unstable period of human-caused climate change —
phase 2.
Phase
2 — An Age of Storms
During
phase 2, ever-increasing volumes of cold, fresh ice and water pulse
out from the world’s glaciers. Due to highest levels of ice
concentration, the regions seeing the greatest impact are areas
adjacent to Greenland and Antarctica. Cold, fresh water and ice
hitting these local ocean zones have numerous influences. The first
is that the local fresh water acts as a lid on ocean-to-atmosphere
heat transfer. As a result, atmospheric temperatures in the region
near large glacial melts will tend to cool. Warm, saltier surface
waters near the glacial outflows are pushed downward by the lighter,
fresh water — heating the ocean bottom zone and cutting off the
meridional ocean circulations in the North Atlantic and in the
Southern Ocean.
Deep
water formation is driven toward the equator. This stops heat
transport toward the poles in a number of regions resulting in
equatorial heat amplification. Meanwhile, the impact of the fresh
water ocean lid results in local atmospheric cooling near the
glaciers — a counter-trend to a larger global warming.
Weather-wise,
we see a reverse of the trends first apparent during phase 1. The
cooling of surface zones near the great glaciers puts a damper of
phase 1 polar amplification. Meanwhile, the southward progression of
fresh surface waters shuts down the oceanic coveyors transporting
heat into the polar zones. As a result we see heat building up
through a kind of ocean heat transport train-wreck in low latitude
regions near the equator. The combined equatorial heating and near
glacier cooling increases temperature gradients and amplifies the
storm track.
(Model
runs showing temperature anomalies under A1B [near RCP 6.0] scenario
warming with 0.6 meter global sea level rise from glacial outflows by
2065 and 1.44 meter global sea level rise by 2080 vs only thermal
expansion based sea level rise [right frame images]. Note that A1B
implies about 550 ppm CO2 — a bad scenario but no-where near the
worst case. Also note that these models do not include carbon store
response feedbacks. Finally, the models were adjusted by adding fresh
water outflows from glaciers, so this is not a prediction of rate of
sea level rise, only a projection of atmospheric impacts under a
given melt and ghg scenario. Image source: Greenland
Melt Exponential?)
In
the Northern Hemisphere, the North Atlantic sees the greatest
counter-trend cooling influence in atmospheric regions due to glacial
melt. Meanwhile, Arctic regions continue to see (somewhat slowed)
warming conditions. The result is a shift of the center of cold air
to an off-set zone more toward Greenland and a screaming storm track
running oblong over the polar zone and centering over a trough in the
North Atlantic. Amazing temperature differentials between the
continents, the Polar zone, Greenland, the North Atlantic, the
equatorial Atlantic and Africa result in the potential for
continent-sized storms packing the strength of hurricanes according
to a
recent study by Hansen.
The
storms would spin up as the unstable cold air over Greenland ravels
and unravels in great frontal wings of cold air encountering the hot
air roiling at the equator and building in sections of the Arctic and
over the continents. Tropical storms forming adjacent to cold core
storms would increase the potential for hybrid storm events. And
extreme temperature gradients would provide high octane atmospheric
fuel for baroclinic systems. Finally, the great melt pulses
themselves would supply periods of high global thermal variance. The
pre melt pulse times would see rapid warming, while the post melt
pulse times would see cooling. This up-down would periodically load
and then wring the global atmosphere of moisture, resulting in high
risk for extreme deluge events.
Heating
the Deep Ocean Sets Stage for Phase 3
Meanwhile,
heat at the ocean surface is driven toward the deep ocean by the
fresh water melt pulses issuing from the glaciers. So the melt
outflows and storms of phase 2 climate change act as an amazing
mechanism for atmosphere-to-ocean heat transfer. Which is really bad
news for the health of the world ocean system.
This
phase 2 climate change age of storms lasts so long as large glacial
outflows still issue from Greenland (in the North) and Antarctica (in
the South). Since even under the most rapid pace of human-caused
warming it would take hundreds of years for the great ice sheets to
go down, what we are looking at is a period of possibly centuries.
Avoiding phase 2 climate change, on the other hand, involves avoiding
rapid destablization of Greenland and Antarctica’s ice sheets. An
issue we may have already pushed too hard to prevent at least some of
these storm, ocean, and weather destabilization impacts.
As
for phase 3 climate change — that’s a transition to a runaway
hothouse and a stratified/Canfield Ocean state. And we really don’t
want to see that either. But before we get there, it’s a transition
to an age of glacial melt and tremendously potent storms.
Links:
Hat
Tip to Colorado Bob
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