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Permafrost Thaw Feedback To Blow Carbon Budget ‘Faster Than We Would Expect’
30
April, 2015
“Permafrost
carbon emissions are likely to be felt over decades to centuries as
northern regions warm, making climate change happen faster than we
would expect based on projected emissions from human activities
alone.” — Climate
Change and the Permafrost Carbon Feedback
*
* * *
(Extent
of Northern Hemisphere 1 meter soil organic carbon store in the now
thawing and burning permafrost. At about 1,000 billion tons, it’s
more than enough to put a hefty strain on the IPCC’s remaining 275
billion ton carbon budget. Image source: Stockholm
University.)
For
a moment, let’s consider some rather difficult to deal with numbers
—
790
billion tons —
that’s the so-called ‘carbon budget’ IPCC estimates we need to
stay within to prevent 2 degrees Celsius of warming in just this
Century. It’s the level IPCC says we need to stay below to prevent
‘bad outcomes.’ A rate of warming that does not including later
temperature increases in following centuries — which would be about
double the 21 Century’s amount if global greenhouse gas levels
managed to plateau and the global carbon stores remained on good
behavior.
515
billion tons —
that’s the amount of carbon humans have already emitted into the
atmosphere. It leaves us with less than 275 billion tons remaining.
About 24
years —
that’s how long it will take for humans to burn enough fossil fuels
and emit enough carbon (at current and projected rates) to use up
that ‘carbon budget.’ A break-neck pace of burning and dumping of
carbon that is now probably about six times faster than at any time
in the geological record. Faster than the atmospheric carbon
accumulation during the last hothouse extinction — the PETM. Faster
than during the worst hothouse mass extinction of all — the
Permian.
Hitting
Carbon Limits
Sound
like we’re up against some hard limits? Well, we are. Because the
above basically implies that human emissions would need to start
falling dramatically now and get to near zero by 2050 to meet IPCC’s
goal. A limit that, by itself, may have built in too much slack and
may not have taken into account other responses from the Earth
climate system.
Now
let’s consider these new numbers from a
recent permafrost study released earlier this month in
the context of IPCC’s ‘carbon budget…’
0.6
degrees Celsius —
that’s the pace at which the Arctic is warming each and every
decade. According to the
new study:
This is causing normally frozen ground to thaw — exposing substantial quantities of organic carbon to decomposition by soil microbes. This permafrost carbon is the remnant of plants and animals accumulated in perennially frozen soil over thousands of years, and the permafrost region contains twice as much carbon as there is currently in the atmosphere.
This
amounts to about 1400 billion tons and around 1,000
billion tons in
the shallow carbon store alone. A massive fireplug of carbon stored
in thawing (and
burning)
land-based permafrost in the Northern Hemisphere at a shallow depth
of zero to 3 meters. The new study expects 50
to 150 billion tons of
this carbon store to release over the next 85 years. A further 120
to 300
billion tons could
hit the atmosphere by 2300 if the ongoing thaw in the north
continues.
(Model
estimates of potential carbon release from permafrost. Note that Pg
carbon is roughly equivalent to gigatons of carbon. Image
source: Climate
Change and the Permafrost Carbon Feedback.)
So
where does that leave our so-called carbon budget?
Averaging
the report’s findings, we can add about 100 gigatons of baked-in
feedback from the shallow permafrost zone alone and end up with 615
billion tons of carbon (human + expected permafrost). This leaves us
with about 15 years before we are locked in to hit the ‘2 C limit’
of around 450 ppm CO2 by end Century (not considering a current 485
ppm CO2e level or end Century CO2e of 530 to 550 ppm when all other
greenhouse gasses are added in).
In
addition, the 120 to 300 billion additional tons from the shallow
permafrost store expected to keep out-gassing through 2300 would
ultimately result in a carbon pool that pushes atmospheric values up
to 480-530 ppm CO2 (560 to 600 CO2e) and turns the ‘2 C limit’
into a 4-6 C long term climate bake.
Carbon
Debt With Compound Interest
Looking
at the report’s numbers leaves us with the all-too-salient
impression that we really don’t have a carbon budget at all. What
we have is carbon bankruptcy. A carbon compounded debt shock enough
to crack the whole of the Earth System carbon piggy bank and bleed
out gigaton-sized carbon pennies for decades and centuries to come.
And the new shallow permafrost carbon feedback estimate does not
include the approximate 400 gigatons of carbon in the deep
permafrost. Nor does it consider ocean carbon stores — which may
provide their own carbon debt spiral. Nor does it include Antarctic
carbon stores or a number of other possible stores that could be
pushed out by heat stress.
Needless
to say, some considered the news in the recent Nature Report
‘good.’ At
least it didn’t identify a 50 gigaton methane release over one
decade from the East Siberian Arctic Shelf as some other recent
articles have considered.
Some news reports even went so far as to call an approximate 92
gigaton release by 2100 (or a little more than 1 gigaton per year)
from permafrost carbon ‘slow.’ The last hothouse extinction, the
PETM, also saw similar ‘slow’ rates of release from the global
carbon system. So, slow when compared to the raging 10 gigaton per
year pace of current human emissions, but fast when compared to about
practically anything else in geological history.
What
the new report really means is that humans can’t afford to emit any
more carbon. And what we need to be looking at now is a way to
swiftly transition to a net carbon negative civilization — fast.
“This
is not a minor feedback,” Kevin Schaefer, a prominent scientist
from the National Snow and Ice Data Center said
in a recent report on the new study’s findings.
“… If you don’t account for it, you’ll overshoot this 2
degree target.”
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