The GlobalArctic MOOC introduces you the dynamics between global changes and changes in the Arctic. This course aims to highlight the effects of climate change in the Polar region. In turn, it will underline the impacts of a warmer Arctic on the planet Earth. For human civilization, the Arctic stands both as a laboratory and a warning for human kind. Besides, this course gives course followers an understanding of the key challenges and pathways to sustainable development in the Arctic region. This course is unique as it gathers several world’s experts for the first time to speak about the Arctic. Their respective inputs from different academic perspectives and disciplines offer a relevant and complete assessment of the Arctic region and its connection to the rest of the planet. At the end of the day, the course intends to offer in full scope the keys to understanding as the Arctic plays as a mirror of the human and geological dynamics.
Global warming, permafrost thawing and its effects on the Arctic
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Global Arctic
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WEEK 1 EARTH SYSTEM DYNAMICS
This first week aims to overlook the different effects of the climate change in the Arctic. And vice-versa, we will introduce and evaluate the effects of a warmer Arctic on the rest of the planet. Besides, lectures will raise consequences on the biodiversity and negative outcomes with pollutants in the Arctic region.
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Matthias FingerProfessor
EPFL, ITPP, MIR, IGLUS Lab
Hi, my name is Benjamin Abbott,
I'm an assistant professor of Ecosystem Ecology in
the Plant Wildlife Sciences Department at Brigham Young University.
I'm excited to talk to you today about effects of
climate change and permafrost thaw on Arctic and boreal ecosystems.
First, we'll talk about climate change in the permafrost zone,
what has changed in the past and what may change in the future.
Then we'll talk about the permafrost climate feedback.
In its simplest terms,
what do we mean when we talk about the permafrost climate feedback.
Then we'll discuss three reasons why
the permafrost climate feedback is not as simple as we might think.
Finally, we'll talk about two different approaches for
constraining the permafrost climate feedback.
High latitudes have warmed two to six times faster than the global average.
So looking at climate records over the past 50 or 100 years,
there has been extreme warming at high latitudes.
This is primarily for two reasons,
they're strong albedo feedbacks.
When you lose snow and ice cover,
that accelerates the warming.
The second reason is, there's atmospheric circulation,
transport of heat from low latitudes to high latitudes.
These two factors have caused extreme warming at high latitudes.
It's important to remember that we're not talking about average annual conditions.
There have been strong differences,
the warming has been primarily during
the winter time and it has been strongest in the continuous permafrost zone.
This is that area farthest to the North,
where most of the land is underlain by permafrost.
Finally, we can't forget that we're not just talking about temperature, either.
These changes in temperature have been accompanied by changes in
precipitation, evapotranspiration, and runoff.
So there's a strong hydrological and also biological component to this climate change.
Changes in surface air temperature and hydrology have affected ground temperature.
You can see a plot by Romanovsky et al.
that shows permafrost temperatures.
These are observed data from boreholes drilled into permafrost.
You can see that in almost every case,
these boreholes in Alaska are showing a strong increase through time of temperature.
You may notice that the most extreme warming is happening at the bottom of the figure,
and the coldest permafrost near the top
as permafrost gets towards the freezing point, zero degree Celsius.
That warming can be delayed by that latent heat of thaw.
Now, let us look into the future if we can.
The top side of this figure,
you can see the projected temperature change for four of the IPCC warming scenarios.
These are called RCPs, representative concentration pathways.
RCP 2.6 represents CO2 concentrations stabilizing and starting to
decrease before the middle of the century and
RCP 8.5 is something of a business as usual scenario.
So on the top part of the figure,
we see that Arctic temperatures are expected to increase substantially through 2100.
The bottom half of the figure is the permafrost extent.
So starting from the current permafrost extent of about 1.6 million square kilometers,
permafrost extent is projected to decrease by 40 to 80 percent by 2100.
Well, one of the reasons why we care about this is,
the permafrost zone contains a huge stock of carbon.
Soils in the permafrost zone contained between 1,300 and
1,600 petagrams of organic carbon.
Petagram is one billion tons.
For reference, all living things contain about 600 petagrams of carbon and
the atmosphere contains between 600 and 800 petagrams
of carbon depending on the time of year.
So you can see, this area has a giant carbon pool.
If that carbon pool becomes active,
if it moves into the atmosphere and surface
ecosystems then it could affect the way the climate system works,
not just in the Arctic but around the world.
So when we talk about the permafrost climate feedback or the permafrost carbon feedback,
this consists of four simple steps.
There's warming of surface temperature,
in this case primarily due to anthropogenic greenhouse gases and land use change,
that thaws permafrost exposing organic matter
that was previously locked in permafrost to microbial degradation.
That microbial activity produces carbon dioxide,
CO2 and methane, CH4.
Two important greenhouse gases which then reinforce warming,
accelerating this whole process.
The permafrost carbon feedback is considered to be
the largest and most likely terrestrial feedback to climate change because of the size,
that giant size of the permafrost carbon pool.
However, it is not incorporated or considered in current climate negotiations.
That means that if countries agree to a certain level of emissions,
they haven't considered the permafrost climate feedback,
they could go past those emissions.
The projections of the size of this feedback by
2200 range from negative 100 to positive 650 petagrams of carbon.
Now, you may be asking yourself,
how could this be negative?
These protections aren't even agreeing in sign,
let alone in magnitude.
That brings us to our first permafrost carbon complexity.
When you're trying to understand what's going on with a pool of carbon,
you can't just think about what's leaving the pool,
you also need to think about what's going into the pool.
This is what we call net ecosystem carbon balance.
It's the sum of all of the inputs and outputs into and out of the ecosystem.
So if we look on the left-hand side of this figure,
there's about 1,400 petagrams carbon stored in permafrost and the overlying soil.
Some of this can be released.
As warming occurs, the permafrost can degrade,
there's a longer decomposition season,
there can be hydrologic release.
So lateral flushing of carbon into rivers and streams, lakes and estuaries.
Finally, there can be ecosystem disturbances like wildfire.
All of these factors accelerate loss from the soil to the atmosphere.
On the other side of the equation,
there can be uptake by increased plant growth.
Currently Arctic and boreal plants contain about 111 petagrams of carbon.
So carbon pool which is much smaller,
an order of magnitude smaller.
However, nutrient release from decomposition of that organic matter,
CO2 fertilization from higher levels of CO2 in
the atmosphere and a longer growing season can stimulate plant growth.
Currently, models project that the release from
warming could be between 160-650 approximately petagrams by 2,200,
whereas the uptake by plants could be between 8-200 petagrams of carbon.
However, we might throw into question some of those higher estimates from the models.
Just because they're so much larger than the current pool of biomass,
it's hard to imagine what kind of vegetation community could contain that much carbon.
This brings us to the second part,
the second permafrost complexity.
There are different pathways of permafrost degradation.
In that simplified cartoon,
we just showed the permafrost table degrading from the
top-down and if you go into the field and look at the surface it may seem simple.
However, if you look underneath the surface,
much of permafrost is underlain by massive ground ice,
chunks of ice which are frozen in the soil.
When that ice melts due to permafrost degradation,
the soil surface can collapse in a process known as thermokarst.
This abrupt permafrost collapse may affect 10-40 percent of the total area of permafrost.
Now this is really important because it abruptly
exposes the whole soil profile to decomposition.
Rather than a gradual top-down thaw,
the whole soil profile can immediately be attacked by microbes.
This also disrupts plant growth.
So it's going to reduce the inputs into the ecosystem at least
initially and it affects the oxygen conditions,
the redox conditions in the soil during decomposition.
Thermokarst tends to form on coastlines,
riverbanks and the sides of lakes,
so that carbon can be washed into aquatic and marine ecosystems where it may
experience very different physical and biological conditions during decomposition.
This brings us to the third complexity.
What are the conditions following thaw?
Redox conditions influence the rate of decomposition of
soil organic matter and also the type of greenhouse gas produced.
So, this figure by show it all.
From a few years ago,
conceptually shows how the wetness or dryness of the soil organic matter
after thaw can affect what kind of effects it has on the permafrost climate feedback.
If they're primarily oxic conditions.
So, if permafrost degradation is accompanied by drawing of the soil,
this results in faster decomposition of
the soil organic matter but the greenhouse gas produced is primarily CO2.
In anoxic conditions, they're slower decomposition because oxygen is not available.
However, methane can be produced and methane is a much more powerful greenhouse gas.
Also the nutrient availability will
control plant growth so that's that gross primary productivity,
the carbon going back into the ecosystem.
It could also trigger non-carbon greenhouse gases such as nitrous oxide,
N2O, which is over 100 times more powerful greenhouse gas than CO2.
So considering these permafrost complexities is
critical to properly estimating the magnitude,
timing and type of greenhouse gases released from the permafrost zone.
If we look back over these complexities, many of them,
these ones highlighted in red are not currently included in
these large earth system models that are trying to
predict the magnitude of the permafrost climate feedback.
So, if models can't currently constrain the permafrost feedback,
do we have any other options?
We performed a study a few years ago that used expert assessment methods where we simply
asked over 200 permafrost experts for
quantitative estimates of how much carbon would come out of the permafrost zone.
Here is the summary figure from that study where on the top,
you see the amount of carbon released from soil organic matter for RCP 2.6,
that's the tan wedge,
and then the green wedge which you can't see very much is the amount
of that carbon that's offset by new plant growth, changes in biomass.
So the two take-home messages from this study were
biomass offsets little to none of carbon released from permafrost regions soils,
that biomass just can't keep up with the amount of carbon being lost from the soils.
The second point is there's a four-fold difference in net emissions
between RCP 2.6 and RCP 8.5.
So, this could be interpreted to mean that three quarters of
the permafrost climate feedback could still be
avoided if human emissions are actively reduced.
Another way of constraining the permafrost climate feedback is to look in the past.
It can often pass ecosystem behavior can inform what may happen in the future.
Permafrost has thought before.
Fifty five million years ago there was
abrupt climate change at the Paleocene-Eocene Thermal Maximum.
There was a doubling of atmospheric CO2,
global temperature increased by five degrees Celsius.
Following that abrupt increase,
nearly all permafrost was degraded
and that soil organic matter was returned to the atmosphere.
This resulted in cycles of warming and cooling unstable climate for almost 200,000 years.
More recently in the early Holocene between five and 9000 years ago,
there was more limited warming of 1-2 degrees Celsius.
This resulted in some permafrost degradation but there was
limited carbon release and after this warm period, permafrost re-accumulated.
So this could suggest that there may be some kind of tipping point
between one and two and five degrees Celsius.
Though this is pretty speculative.
We need to recognize that there are many uncertainties associated
or concerning the response of the permafrost zone to climate change.
So in conclusion, climate ecosystem interactions will determine the magnitude,
timing and type of greenhouse gas release.
You can't just consider changes in temperature,
you need to consider how those changes in surface temperature,
hydrology, precipitation, et cetera,
are propagated into the soil profile and what are the effects after permafrost thaw.
Second, biomass is unlikely to offset greenhouse gas release.
Third, disturbance such as drought, fire,
and thermokarst are important uncertainties
that should be incorporated into models in the future.
Finally, the four-fold difference in net emissions between scenarios
suggests that three-quarters of permafrost carbon release may potentially be avoided,
though this is highly speculative.
Thank you very much for your time.
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