Warning From Scientists — Halt Fossil Fuel Burning Fast or Age of Superstorms, 3-20 Foot Sea Level Rise is Coming Soon
Robertscribbler,
24
July, 2015
24 July, 2015
First
the good news. James Hansen, one of the world’s most recognized
climate scientists, along with 13 of his well-decorated fellows
believe that there’s a way out of this hothouse mess we’re
brewing for ourselves. It’s a point that’s often missed in media
reports on their most recent paper — Ice
Melt, Sea Level Rise, and Superstorms.
A paper that focuses on just two of the very serious troubles we’ll
be visiting on ourselves in short order if we don’t heed their
advice.
The
way out? Reduce global carbon emissions by 6% each year and manage
the biosphere such that it draws carbon down to 350 ppm levels or
below through the early 22nd Century. To Hansen and colleagues this
involves a scaling carbon fee and dividend or a similarly ramping
carbon tax to rapidly dis-incentivize carbon use on a global scale.
Do that and we might be relatively safe. Safe, at least in the sense
of not setting off a catastrophe never before seen on the face of the
Earth. That’s pretty good news. Pretty good news when we consider
that some of the best climate scientists in the world see an exit
window to a hothouse nightmare we’re already starting to visit upon
ourselves.
The
bad news? According to Hansen and colleagues, even if we just
continue to burn fossil fuels and dump carbon into the atmosphere at
a ‘moderate’ pace some of the terrifically catastrophic impacts
of human caused climate change are not too far off.
A
Moderate Pace of Burning
The
new Hansen paper takes a look into both our geological past and our
climate future in an attempt to give us an idea what may be in store.
In this
scenario, model, and paleoclimate based study,
Hansen and colleagues assume two things about global human
civilization. The first assumption is that we don’t follow the
worst case, business as usual carbon emissions policies that lead to
around 1000 ppm CO2 in the atmosphere by 2100. It is instead assumed
that some effort is given to reducing coal, oil, and gas consumption.
That some renewable energy, increased efficiency and behavior changes
replace a significant portion of future fossil fuel emissions. But
the most effective solution — a complete transition away from
fossil fuel burning over the next few decades — fail.
(A1B
is a ‘moderate’ emissions scenario that, according to model
essays, is likely to see between 2.5 and 3.5 C warming by the end of
this Century and around 700 ppm of CO2 accumulation. That is, without
the kind of major ice sheet response indicated in the new Hansen
study. Image source: Knutti
and Sedlacek.)
As
a result, we end up with around 700 parts per million carbon dioxide
in the atmosphere by 2100. In such a case we’ve followed what the
IPCC community terms as the A1B or ‘moderate’ fossil fuel
emissions scenario.
A
Question of Melt Rate Doubling Time
It
is in this context that the Hansen paper attempts to determine a key
factor that will have wide-ranging impacts on ocean health, the
continued existence and lifespan of coastal cities, and on the
severity of the weather itself. That factor is captured by a single
simple question — if we continue a moderate pace of fossil fuel
burning, then how rapidly will ice sheet and ice shelf melt double?
To
Hansen this is a critical question. One he
has already done quite a bit of work to answer over recent years.
And according to his findings it looks as if land ice melt rates for
both Greenland and West Antarctica could now be doubling every 5-20
years. It’s a doubling rate that may find a historical allegory in
the milder yet still intense glacial outflows of times long past. And
it’s something that, according to Hansen, is being directly driven
by an extreme pace of human-based greenhouse gas accumulation.
The
Eemian — Significant Sea Level Rise and Terrible Storms Under Far
Lower CO2 Forcing
To
this point, Hansen’s new paper takes a dive into the paleoclimate
study of an ice age interglacial that bears some stunning
similarities to our own, human warmed, time period. He looks at
the Eemian,
a warm period that occurred 130,000 to 115,000 years ago. A
period that featured temperatures in the range of 1-2 C above 1880s
values (we’re in the process of hitting 1 C above 1880s values this
year). A period in which CO2 levels were in the range of 285 parts
per million (about 15 parts per million higher than the Holocene
average before humans spiked that level to 400 parts per million
during recent years). And a period that,according
to Hansen’s broad study of past research,
included numerous Heinrich type glacial outburst and melt events.
Back
then, at 285 parts per million CO2 levels, seas were as much as 5-9
meters (16 to 30 feet) higher than they are today. The global
climate, on the other hand, was much stormier. For two Heinrich type
events that Hansen investigated were found to have dramatic impacts
on severe storms in the North Atlantic during the Eemian. Hansen
found large boulders propelled up onto the islands of Bermuda and the
Bahamas by what appear to be powerful storm waves.
Hansen also noted chevron shaped wave channels carved into the
calcified sand beds in the Bahama Island Chain.
(Heinrich
events included major glacial outflows like the one seen here at
Jacobshavn, Greenland. Note the significant ice volume outflow
through the channel at center frame. Also note the white dots in
Baffin Bay indicating ice berg discharge. For reference, bottom edge
of frame is about 100 miles. In past Heinrich Events outflows like
the one seen above hit high gear as glaciers released armadas of ice
bergs into the oceans which generated ocean and atmospheric changes.
As the ice bergs melted, they deposited rocks on the sea bed. These
piles of ice raft debris then became a signature geological feature
of Heinrich events in the ancient past. Image source: LANCE
MODIS.)
It
paints an overall picture of very stormy weather in the North
Atlantic as a result of these Heinrich ice sheet melt episodes
affecting Greenland and West Antarctica. These melt events drove
fresh water out into the North Atlantic and the Southern Ocean at the
rate of about 0.5 to 1 meters of sea level rise per century. The
expanding cold, fresh water along the surface zones in the upper
latitude waters shut off heat exchange between the ocean and the
atmosphere by generating a stratified ocean state. This fresh water
wedge interrupted the plunging of heavier, salt-laden waters in the
North Atlantic and the Southern Ocean. A loss of heat exchange that
resulted in the cooling of airs directly over the fresh water outflow
pools.
Meanwhile,
since heavy, saltier waters were no long diving to the ocean bottom
in these regions — broader ocean circulation was interrupted. As a
result, heat from the equator was no longer traveling poleward. The
equator warmed. The cold, fresh water outflow regions cooled. And
this high temperature gradient subsequently became a powerful storm
generator — providing extreme baroclinic potential energies for the
storms that likely reshaped the ocean bottom and deposited massive
boulders upon islands throughout the North Atlantic.
It’s worth noting that the 5-9 meter sea level rise during the Eemian occurred in the context of global temperatures that are now similar to our own (1-2 C above 1880s values). But it’s also worth considering that the underlying CO2 and greenhouse gas conditions for the current age are far, far worse. Peak global CO2 during the Eemian never hit higher that 285 parts per million. For the Anthropocene age we are now leaving the 400 parts per million CO2 level in the dust. Meanwhile, the pace at which we are warming is also more than 10 times faster than the pace of warming to peak Eemian heat values. And it’s these two factors — an extreme greenhouse gas overburden combined with a very rapid pace of warming that has Hansen and colleagues very concerned about our climate situation over the next 10-80 years.
Land
Ice Below Sea Level — Amplifying Feedback For Melt
Turning
to the current day, there’s a growing number of reasons why we
should be concerned that rapid land ice melt, large fresh water
outflow to oceans, and resulting superstorms could be in our future.
First, we’ve learned that the topography of Greenland and
Antarctica include numerous channels that tunnel deep into its great
glaciers at depths well below sea level. When oceans warm, and
they’re warming as you read this, the submerged, sea-facing slopes
of glaciers are confronted with more and more heat gnawing away at
their under-bellies. Just
a 0.1 C increase in water temperature can melt away a meter of ice
over the course of a year.
Multiply that by glaciers with faces that are submerged hundreds of
feet deep whose sea fronting cliffs extend for many miles and you can
end up with quite a lot of melt due to very little warming. As more
of the undersides of glaciers melt, more of the water tunnels inland
and large masses of ice are rafted away from the central ice exposing
still more of the land anchored ice to a warming ocean flood.
(Image
from Hansen Paper shows how land ice melt generates ocean
stratification which is an amplifying feedback that enables ocean
bottom warming and more land ice melt. Note — AABW stands for
Antarctic bottom water, NADW — North Atlantic down welling. Image
source: Ice
Melt, Sea Level Rise, and Superstorms)
As
bad as this dynamic may sound, the process includes one more wrinkle
that makes it even worse. As the undersides of ice shelves erode and
more fresh water laden ice bergs are pulled out into the ocean, these
ice bergs begin to melt en mass. This massive ice melt develops into
an enormous and expanding pool of fresh water at the surface. And its
this troublesome demon that traps heat in the deeper ocean levels.
So, in other words, as the ice from the land glaciers floats away and
melts it traps and focuses more heat at the base of these great
glaciers. It’s an amplifying feedback. A very serious kind that
doesn’t even require the human forced kick to create severe
trouble. One that during the Eemian really wrecked the weather and
caused massive surges in ocean height.
It’s
a process that Hansen and his colleagues believe make both Greenland
and West Antarctica very vulnerable. A process that could, when
combined with the high velocity human heat forcing, produce melt
rates that double every 20, 10 or even every 5 years. But of the two
— Greenland or Antarctica — which is worst off?
(Topographic
map of Greenland sans its great ice sheet. Most of central
Greenland’s mass is now below sea level. It’s a basin that now
holds a miles high ice mountain. Various channels allow ocean water
access to the central ice mass should the channel openings melt due
to warming oceans. Such an invasion could set off a rapid sea level
rise driven by Greenland melt. Image source: Livescience.)
Greenland,
for its part, is little more than a great Archipelago held together
by its stunning ice mass. Remove the ice and the interior of
Greenland would flood, leaving a ring of islands as a final remnant.
Though deep, most of these channels run up slope. And this
feature,according
to the Hansen study,
may be one saving grace for potential Greenland ice melt pace. Up
slope channels limit the impact of basal melt by serving to check
rates of catastrophic destabilization. So though Greenland is
certainly vulnerable to ice melt due to the fact that many channels
cut hundreds of feet below sea level and into the island’s glacial
heart, it is not as vulnerable as West Antarctica.
There,
many channels cut deeper beneath the Antarctic ice mass. But not only
are they below sea level by hundreds of feet as with Greenland, they
slope down. They slope down and not for just a little ways under the
ice sheet — some of these ocean heat skids extend in down-sloping
fashion for hundreds of miles beneath the Antarctic ice. The result
is a kind of skid, that once unlocked by initial melt, can continue
to expose larger and large chunks of bottom ice to the warming ocean.
Allowing, ultimately, the creation of new warming seas underneath the
ice and floating it away in very rapid fashion.
In
West Antarctica, ice shelves facing the Weddell and Ross seas both
feature these dangerous retrograde slopes. In East Antarctica, the
Totten Glacier is likewise vulnerable as are many other glaciers
surrounding the vast periphery of Antarctica.
(Retrograde
slopes behind ice sheet grounding lines are just one reason why
Antarctic land ice is so unstable. Image source: Ice
Sheet Mass Balance and Climate Change.)
Finally,
in addition to being surrounded by the warming, deeper waters of the
Southern Ocean, in addition to featuring dangerous retrograde slopes
that channel warming sea water further and further inland and beneath
the ice sheets, West Antarctica itself sits on a geological hot bed.
Though not mentioned in the Hansen study, recent
work also highlighted that West Antarctica rests atop a geologically
active zone that had formed numerous sub-glacial lakes warmed by
geological activity.
This added geological heat makes West Antarctica that much less
stable — an instability that when given the shove of human heated
oceans is
leading the Larsen B Ice Shelf to completely collapse by 2020.
It makes Antarctic land ice that much more vulnerable to the added
heat human beings are forcing into the oceans and opens up the
ominous possibility that melt rate doubling times for West Antarctica
could become quite extreme indeed.
Modeling
Land Ice Melt’s Impact in the 21st Century — Facing A Coming Age
of Superstorms
So
what does all this mean? In the worst case (5-10 year melt rate
doubling times), it’s possibly 3 meters of sea level rise by mid
Century, perhaps 7 meters by end Century under business as usual
fossil fuel emissions. Even in the more moderate cases (10-20 year
melt rate doubling times), 1 meter of sea level rise by mid Century
and 3 meters or more of sea level rise by end Century is not entirely
out of the question, according
to Hansen’s new research.
These potentials are markedly different than the more conservative
rates outlined by IPCC
which is still calling for a less than 1 meter sea level rise under
even the worst case human carbon emissions scenarios (1000 parts per
million CO2, in the range of 1200 ppm CO2e).
So
much fresh water hitting the oceans would cause a rapid
stratification. A rapid loss of ocean to atmosphere heat exchange in
the regions impacted. A train wreck of heat backing up at the
equator. Such a train wreck would result in temperature extremes and
gradient differences that would make the Eemian Heinrich events
(mentioned above) seem moderate and slow by comparison.
Hansen
has been working on global atmospheric models for tracking these
events for a number of years now. And this new study is an
improvement on his earlier, model-driven “Storms of My
Grandchildren” work. Hansen’s new model runs are imperfect
simulations of what may happen given large melt pulses from Greenland
and Antarctica. The
models, according to Hansen, mix the ocean water too much, reducing
the overall impacts of stratification through the mechanism of the
fresh water wedge.
However, even with this imperfection, the temperature gradients
displayed by these models are absolutely stunning. A clear warning to
anyone who still wants to keep burning fossil fuels that they’re
really grabbing the dragon by the tail.
(A
mid range simulation including 10-20 year melt rate doubling times
and 6 feet of sea level rise by 2080 — half Greenland, half
Antarctica — shows enormous weather impacts in the form of a
severe, superstorm generating, temperature gradient. Image
source: Ice
Melt, Sea Level Rise, Superstorms.)
In
the above image we can see just one of these model runs. The model
assumes a 10-20 year doubling time for rate of land ice melt. It
contributes equal portions of melt from Greenland in the north and
Antarctica in the south. Greenhouse gas accumulation is considered to
be along the moderate case A1B track. By 2080 we have about six feet
of sea level rise globally and about 600 parts per million CO2 in the
atmosphere. The more rapid rate of melt has put a temporary damper on
the rate of global atmospheric warming which has dipped to 1.11 C
above 1880s values (just slightly higher than today). But much of
this cooling is localized to the Southern Ocean and to an extreme
cold pool in the North Atlantic between Northwestern Europe and
Greenland.
There
a massive outflow of fresh water has shut down the ocean’s ability
to exchange heat with the atmosphere. AMOC has been vastly weakened.
The Gulf Stream is backed up along the US East Coast and into the
Gulf of Mexico. Heat is building in the Arctic opposite Greenland and
all along the Equator. Temperature anomalies in the range of 17
degrees Celsius below average occur over the ocean fresh water pool.
This drop is enough to generate year round winter like conditions in
the cold pool region even as other sections of the atmosphere around
it continue to warm or retain severe excess heat.
Energy
imbalance at the top of the atmosphere rockets to between 2 and 4
Watts per meter squared. What this means is that, in failing to ventilate heat to the
atmosphere in the North Atlantic and Southern Ocean, the world ocean
system has continued to accumulate a massive amount of heat. Heat
that is now going to work warming the ocean bottom and hitting the
bases of the already rapidly melting land ice.
(More
superstorms in our future. If Hansen’s new research is correct
storms like Sandy will grow both more powerful and more common as
Greenland dumps ever increasing volumes of fresh water into the North
Atlantic. Image Source: NASA.)
For
the North Atlantic, it is the greatest of understatements to say that
an area of perpetual winter surrounded by warming airs and sitting
atop a warming deep ocean is a major storm generator. Summer time
temperature deltas between the center of the cold pool will range
from near zero C to 20s, 30s and 40s C over nearby ocean and
continental land masses. It’s like taking the High Arctic and
shifting it to Scotland while all the adjacent airs warm. Temperature
gradient and baroclinic (pressure gradient) energy for storm
generation will be on the order of something that modern humans have
never experienced. The potential for superstorms in this model
simulation will, notably be quite high.
Final
Notes — Superstorm Conditions Could Emerge Sooner than Models
Indicate
The
point to consider here is that large scale land ice melt sets in
place forces that result in a weather wip-lash of epic proportion.
It’s been the heart of Hansen’s work for many decades and it’s
an issue that we really need to consider as time goes forward. A
dwindling time for response that may well be much shorter than even
Hansen’s models indicate. First, ice sheet vulnerability may well
be higher than IPCC officials imagine and we could well be on a slope
of melt rate doublings in the range of 5-20 years now.
(Global
sea level rise keeps hitting a steeper and steeper slope. Image
source: Dr.
James Hansen, Columbia University)
Second,
Hansen’s models likely capture the atmospheric impact of such
large-scale land ice melt later than would happen in the real world.
This later capture is due to the fact that his
low resolution models mix the ocean heat more with the atmosphere
than would occur under the kinds of ocean stratification events that
we are likely to see due to these doubling times.
Third, and finally we return again to the paleoclimate time of the
Eemian where there is ample evidence that a mere 0.5 to 1 meter per
century rate of sea level rise due to melting Greenland and West
Antarctic ice during that time set in place conditions to generate
superstorms with high enough peak intensity to deposit massive
boulders upon islands in the Atlantic and to carve the impression of
gigantic, long-period waves into the sea bed.
Anyone
reading this
work and
considering the notion that some of the
greatest scientific minds this age has birthed could
be right is immediately confronted with the realization that the
gargantuan forces we are playing with are not to be trifled with. And
yet, the trifling continues despite the
wise and well considered scientific warning to relent.
Links:
Here
is a comment from Robertscribbler to Paul Beckwith’s video:
A
point to consider is that SLR is more likely to pulse than be
exponential. The exponential studies give us an idea where things
might be headed. But it’s more likely to progress through a process
of destabilization, exponential increase, massive melt pulse, then
pause before hitting another similar ramp.
I
didn’t include this commentary as I thought we’d let the Hansen
Paper stand on its own merits.
Good
points by Paul here, though. If we hit a pure exponential or if the
size of the destabilization is large enough then, yeah. The
potentials can hit pretty high. My opinion is still in the range of
6-9 feet by end century. Could certainly be worse, though.
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